Review
Quaternary Alkylammonium Conjugates of Steroids: Synthesis, Molecular Structure, and Biological Studies Bogumił Brycki *, Hanna Koenig and Tomasz Pospieszny Received: 23 October 2015 ; Accepted: 17 November 2015 ; Published: 23 November 2015 Academic Editor: Roman Dembinski Laboratory of Microbiocides Chemistry, Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89b, 61-614 Poznan, ´ Poland;
[email protected] (H.K.);
[email protected] (T.P.) * Correspondence:
[email protected]; Tel.: +48-61-829-1694
Abstract: The methods of synthesis as well as physical, spectroscopic (1 H-NMR, 13 C-NMR, and FT-IR, ESI-MS), and biological properties of quaternary and dimeric quaternary alkylammonium conjugates of steroids are presented. The results were contrasted with theoretical calculations (PM5 methods) and potential pharmacological properties (PASS). Alkylammonium sterols exhibit a broad spectrum of antimicrobial activity comparable to squalamine. Keywords: squalamine; bile acids; sterols; quaternary alkylammonium salt; conjugates; prediction of activity spectra for substances (PASS); PM5 calculations
1. Introduction Steroids are an enormous group of very important natural products. The most significant compounds of this group are sterols (cholesterol, ergosterol, stigmasterol), bile acids (lithocholic, deoxycholic, cholic), and hormones (testosterone, estrogens, progesterone) [1–5]. Sterols are crucial constituents of the cell membrane of eukaryotes. Bile acids are amphipathic molecules with large, curved and rigid skeletons; chirality as well as the specific orientation of their chemically different polar hydroxy groups play an important role in metabolic processes. In turn, hormones determine the characteristics of sex and regulate pregnancy in animals, while plant hormones (brassinosteroids) cause elongation of stems and stimulate cell division (e.g., brassinolide) [6]. Another class of compounds that are involved in many biological processes are polyamines (spermidine, spermine, putrescine, cadaverine) [7–10]. Some of these are very important plant hormones and coenzymes. The connection of steroids and biogenic amines give the new conjugates unusual biological properties. The best-known compound of this type is squalamine (3β-spermidine-7α-hydroxy-5αcholestan-24R-yl sulphate) (1) (Figure 1). The steroid–polyamine conjugate was isolated from the liver tissues of the dogfish shark (Squalus acanthias) [11–14]. This aminosterol is a novel broad-spectrum antibiotic and exhibits a biocidal activity against Gram-positive and Gram-negative bacteria, fungi, protozoa, and viruses [15–23]. The antimicrobial activity of the squalamine has inspired work to design and synthesize new derivatives of steroidal–polyamine conjugates [24–32].
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(a)
(a)
(b) Figure 1. (a) The stereochemistry and numbering of squalamine and (b) a molecular model calculated
Figure 1. (a) The stereochemistry and numbering of squalamine and (b) a molecular model calculated by the PM5 method. (b) by the PM5 method. Figure 1. (a) The stereochemistry and numbering of squalamine and (b) a molecular model calculated 2. Quaternary Alkylammonium Conjugates of Steroids by the PM5 method. 2. Quaternary Alkylammonium Conjugates of Steroids
The basic criteria for the synthesis of biologically active conjugates of steroids and polyamines have been given by Salunke al. [11]. Firstly, the must have a rigid extensive hydrophobic part The basic criteria for the etsynthesis of biologically active conjugates of steroids and polyamines 2. Quaternary Alkylammonium Conjugates ofstructure Steroids and a flexible hydrophilic chain with a polar head group attached to a hydrophobic part. Secondly, the have been given by Salunke et al. [11]. Firstly, the structure must have a rigid extensive hydrophobic The basic can criteria for the synthesis of biologically active conjugatesgroup. of steroids andthe polyamines sulfate groups be removed or replaced by a hydroxyl or carboxylate In turn, structure part and a flexible hydrophilic chain with a polar head group attached to a hydrophobic part. have given by et al. [11]. Firstly, structurecan must a rigidinextensive hydrophobic part of thebeen polyamine is Salunke not important, and partsthe of steroids behave modified various ways. Secondly, the sulfate groups can bewith removed or replaced by a hydroxyl or carboxylate group. In turn, and aOn flexible hydrophilic chain a polar head group to aanalogue hydrophobic Secondly, the this basis, Kim et al. described the synthesis of a attached squalamine frompart. bisnoralcohol (2) the structure of the polyamine is not important, and parts of steroids can be modified in various ways. sulfate groups be structure removed of or the replaced by awas hydroxyl or carboxylate group. In turn,DEPT, the structure 13C-NMR, (Scheme 1) [16].can The product confirmed by 1H-NMR, COSY, On this basis, Kim et al. described the synthesis of a squalamine analogue from bisnoralcohol of the polyamine is not important, and parts of steroids can be modified in various ways. HETCOR, and FT-IR, as well as low- and high-resolution mass spectra. Additionally, the biological (2) 13 C-NMR, On[16]. this basis, Kim et al. described the of a squalamine analogue from bisnoralcohol (2) (Scheme 1) The of the product was confirmed by 1shows H-NMR, COSY, activity of (4) hasstructure been determined. Thesynthesis squalamine analogue biocidal activityDEPT, against 1 13 (Scheme 1) [16]. The structure of the product was confirmed by H-NMR, C-NMR, DEPT, COSY, HETCOR, and FT-IR, as well as lowand high-resolution mass spectra. Additionally, the biological M. luteus 9341, S. aureus 6538P, K. pneumoniae 10031, S. equi 6580C, and B. subtilis 6633. However, HETCOR, and FT-IR, as well as lowandsqualamine high-resolution mass spectra. Additionally, the biological activity of 25922, (4) has determined. The analogue shows biocidal activity against E. coli P. been aeruginosa 27853, P. mirabilis 25933, S. marcescens 27117, and S. typhimurium 14028 are M. activity of (4) has been determined. The squalamine analogue shows biocidal activity against sensitive to (4).6538P, In general, the antimicrobial compound (4)subtilis is weaker in comparison toE. coli luteusnot 9341, S. aureus K. pneumoniae 10031,activity S. equiof 6580C, and B. 6633. However, M. luteus 9341, S. aureusof6538P, K. pneumoniae 10031, S. equi 6580C, and B. subtilis 6633. However, squalamine. 25922,theP.antibacterial aeruginosa activity 27853, P. mirabilis 25933, S. marcescens 27117, and S. typhimurium 14028 are not E. coli 25922, P. aeruginosa 27853, P. mirabilis 25933, S. marcescens 27117, and S. typhimurium 14028 are sensitive to (4). In general, the antimicrobial activity of compound (4) is weaker in comparison to the not sensitive to (4). In general, the antimicrobial activity of compound (4) is weaker in comparison to antibacterial activityactivity of squalamine. the antibacterial of squalamine.
Scheme 1. Synthesis of analogue of squalamine (4) from bisnoralcohol (2).
2 Scheme 1. Synthesis of analogue of squalamine (4) from bisnoralcohol (2). Scheme 1. Synthesis of analogue of squalamine (4) from bisnoralcohol (2). 2
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Other analogs analogs (6–15) (6–15) of of MSI-1436 MSI-1436 (5) (5) have have been been synthesized synthesized from from stigmasterol stigmasterol by by Shu Shu et et al. al. Other Other analogs (6–15) of MSI-1436 (5) have been synthesized from stigmasterol by Shu et al. (Figure 2) [33]. The multistep reactions gave final products with very good yields. All analogs exhibit (Figure 2) [33]. The multistep reactions gave final products with very good yields. All analogs exhibit (Figure 2) [33]. The multistep reactions gave final products with very good yields. All analogs exhibit broad spectrum spectrum of of antimicrobial antimicrobial activity, activity, which which strongly strongly depend depend on on the the stereochemistry stereochemistry of of C(7) C(7) and and aa broad a broad spectrum of antimicrobial activity, which strongly depend on the stereochemistry of C(7) C(3). By contrast, the stereochemistry at the C(24) has a negligible effect on the antibacterial activity. C(3). By contrast, the stereochemistry at the C(24) has a negligible effect on the antibacterial activity.and C(3). By contrast, the stereochemistry at the C(24) has a negligible effect on the antibacterial activity. R2 R2
OSO3H OSO3H
HN HN
N H N H
R1 R1
OH OH
H H
H N H N (5) (5)
NH2 NH2
H H
C(24) mixed isomers C(24) mixed isomers (6) R1 = α−spermine, R2= NH2, R3 = H 1 2 3 (7) α−spermine,RR2==NH NH22, ,RR3==HH (6) RR1==β−spermine, 1 2 3 (8) (7) RR1==α−spermine, β−spermine, RR2== OH, NH2R , R3==HH 1 2 3 (9) α−spermine,RR2==OH, OH,RR3==HH (8) RR1==β−spermine, 1 2 3 (10) β−spermine, RR2== OH, OH, RR3 == OH H (9) RR1==α−spermine, 1 2 3 (11) (10)RR1==β−spermine, α−spermine,RR2==OH, OH,RR3==OH OH (11) R1 = β−spermine, R2= OH, R3 = OH
R3 R3
C(24) single stereoisomer C(24) single stereoisomer (12) R1 = α−spermine, R2= (R)OH, R3 = OH 1 2 3 (13) (12) RR1==β−spermine, α−spermine,RR2== (R)OH, (R)OH, R R3 == OH OH 1 2 3 (14) H,3 R = OH (13) RR1==α−spermine, β−spermine, RR2== (R)OSO (R)OH,3R = OH 1 2 3 (15) (14) RR1==β−spermine, α−spermine,RR2== (R)OSO (R)OSO33H, H, R R3 == OH OH (15) R1 = β−spermine, R2= (R)OSO3H, R3 = OH
Figure Figure 2. 2. The The structure structure of of MSI-1436 MSI-1436 (5) (5) and and its its synthesized synthesized analogs analogs (6–15). (6–15). Figure 2. The structure of MSI-1436 (5) and its synthesized analogs (6–15).
Similarly, Kim and co-workers focused on the effect of stereochemistry at the C(3) and C(5) atoms Similarly, Kim and andco-workers co-workers focused on effect of stereochemistry the and C(3)C(5) andatoms C(5) Similarly, Kim thethe effect of stereochemistry theatC(3) of steroids’ skeleton, as well as the focused types ofon polyamine attached to C(3) onatactivity against various atoms of steroids’ skeleton, as well as the types of polyamine attached to C(3) on activity against of steroids’ skeleton, as well as the types of polyamine attached to C(3) on activity various human pathogens (Figure 3) [34–37]. The results showed that the stereochemistry of theagainst C(3) and C(5) various human pathogens (Figure 3)The [34–37]. The results showed that the stereochemistry of C(5) the human pathogens (Figure 3) [34–37]. results showed that the stereochemistry of the C(3) and carbon atoms has a significant influence on the antimicrobial activity. For example, 3α-spermidineC(3) and C(5) carbon atoms has a significant influence on the antimicrobial activity. For example, carbon atoms has a significant influence antimicrobial For example, 3α-spermidine23,24-bisnor-5α-cholane (16) was found toon bethe more active thanactivity. other spermidine analogues (16–19). 3α-spermidine-23,24-bisnor-5α-cholane (16) was found tothan be more active than analogues other spermidine 23,24-bisnor-5α-cholane (16) was found to be more active other spermidine However 3β-spermine-23,24-bisnor-5β-cholane (23) exhibits the highest biological activity (16–19). among analogues (16–19). However 3β-spermine-23,24-bisnor-5β-cholane (23) exhibits the highest biological However 3β-spermine-23,24-bisnor-5β-cholane (23) exhibits thetohighest activity among all the compounds (16–23). The conjugate (17), which is similar (24–26) biological with the exception of the activity among all the compounds (16–23). The conjugate (17), which is similar to (24–26) with the all the compounds (16–23). The conjugate (17), which is similar to (24–26) with the exception the functional group at position C(7), has comparable antimicrobial activity to (25). Both compoundsof were exception of the functional group at position C(7), has comparable antimicrobial activity to (25). Both functional group at position C(7), has comparable antimicrobial activity to (25). Both compounds were much more active than the compounds (24) and (26). All synthesized conjugates (16–26) exhibited very compounds were much more active than (24) and (26). All synthesized conjugates muchactivity more active than the compounds (24)the andcompounds (26). All synthesized conjugates (16–26) exhibited very good against Gram-positive bacteria. (16–26) exhibited very good activity against Gram-positive bacteria. good activity against Gram-positive bacteria.
Figure 3. The structures of steroid–polyamine conjugates (16–26). Figure 3. 3. The The structures structures of of steroid–polyamine steroid–polyamine conjugates conjugates (16–26). (16–26). Figure
The synthesis of a series of 7-fluoro-3-aminosteroids (36–42) is shown in Scheme 2 [37]. These The synthesis of a series of 7-fluoro-3-aminosteroids (36–42) is shown inStaphylococcus Scheme 2 [37].aureus, These compounds demonstrate a high activity, especially The synthesis of a series ofantimicrobial 7-fluoro-3-aminosteroids (36–42) against is shown in Scheme 2 [37]. compounds demonstrate a high antimicrobial activity, especially against Staphylococcus aureus, Pseudomonas aeruginosa, Streptococcus pyogenes, and Escherichia coli (Tableagainst 1). These compounds demonstrate a high antimicrobial activity, especially Staphylococcus aureus, Pseudomonas aeruginosa, Streptococcus pyogenes, and Escherichia coli (Table 1). Pseudomonas aeruginosa, Streptococcus pyogenes, and Escherichia coli (Table 1).
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OR
OH i
O
H
F
ii HN
OH
H
F H N
N HN
F
H
Boc
H2N
OR
i O
OR
OR
3Cl-
ii Boc
F
H
F
H
N H2
H2N
F
H
NH3
-
3Cl R = H (36) 3α,7α-F, (37) 3α,7β-F, R = H N 3β,7β-F, R = NH (38) H 3 H23α,7α-F, R = SO H (39) 3 (40) 3β,7α-F, R = SO3H (41) 3α,7β-F, R = SO3H (36)3β,7β-F, 3α,7α-F,RR==SO H H (42) (37) 3α,7β-F, R = H 3 (38) 3β,7β-F, R = H (39) 3α,7α-F, R = SO3H (40) 3β,7α-F, R = SO3H (41) 3α,7β-F, R = SO3H (42) 3β,7β-F, R = SO3H
(27)
(28) 3α,7α-F, R =HH (29) 3β,7α-F, R =NH N 3α,7β-F, R = H Boc (30) (31) Boc3β,7β-F, R = H (32) 3α,7α-F, R = SO3H (33) 3β,7α-F, R = SO3H (27) (28)3α,7β-F, 3α,7α-F,RR==SO H H (34) (29)3β,7β-F, 3β,7α-F,RR==SO H 3H (35) (30) 3α,7β-F, R = H 3 (31) 3β,7β-F, R = H (32) 3α,7α-F, R = SO3H MeOH, CH i) Boc-spermidine, NaBH3CN, THF/MeOH; ii) SOCl 2 3H (33)2,3β,7α-F, R =2Cl SO (34) 3α,7β-F, R = SO3H (35) 3β,7β-F, R = SO3H
Scheme 2. Synthesis of 7-fluoro-3-aminosterols (36–42).
Scheme 2. Synthesis of 7-fluoro-3-aminosterols (36–42). i) Boc-spermidine, NaBH3CN, THF/MeOH; ii) SOCl2, MeOH, CH2Cl2
Table 1. Minimum inhibitory concentrations (MIC, μg/mL) of 7-fluoro-3-aminosterols [37].
Table 1. Minimum inhibitory (MIC, µg/mL) of 7-fluoro-3-aminosterols [37]. Scheme 2.concentrations Synthesis of 7-fluoro-3-aminosterols (36–42). Conjugate/MIC (μg/mL) Microorganisms 25concentrations 36 37 38 40 41 42[37]. Conjugate/MIC (µg/mL) Table 1. Minimum inhibitory (MIC, μg/mL) of39 7-fluoro-3-aminosterols Microorganisms S. pyogenes 308A 25 6.3 3625.0 37 12.5 12.5 12.5 50.0 38 39 40 25.0 4150.0 42 Conjugate/MIC (μg/mL) S. pyogenes 77A 6.3 12.5 6.3 12.5 12.5 50.0 12.5 50.0 Microorganisms S. pyogenes 308A 6.3 25 25.0 36 12.537 12.5 12.5 50.0 4125.0 42 50.0 38 39 40 S. ureus 503 6.3 12.5 6.3 6.3 12.5 25.0 S. pyogenes 77A 6.3 12.5 6.3 12.5 12.5 50.0 6.312.550.0 50.0 S. E. pyogenes 308A 6.3 25.0 12.5 12.5 12.5 12.5 25.0 12.5 50.0 50.0 25.0 25.0 25.0 50.0 coli DC2 6.3 50.0 S. ureus 503 6.3 12.5 6.3 6.3 12.5 25.0 6.3 50.0 S. pyogenes 77A 6.3 12.5 6.3 12.5 12.5 50.0 12.5 P. aeruginosa 9027 6.3 50.0 12.5 12.5 25.0 12.5 50.0 50.0 E. coli DC2 6.3 50.0 12.5 12.5 25.0 50.0 25.050.0 25.0 S. ureus 6.3 50.0 12.5 12.5 6.3 12.5 6.3 12.5 25.0 25.0 6.350.050.0 50.0 50.0 P. aeruginosa 1771M6.3 3.1 100.0 25.0 6.3 50.0 P. aeruginosa 9027503 25.0 12.5 50.0 E. 1771M coli DC2 3.1 100.0 6.3100.0 50.0 25.0 12.5 100.0 12.5 100.0 25.0 100.0 50.0 25.0 25.0 50.0 P. aeruginosa 6.3 50.0 25.0 50.0 50.050.0 S. typhimurium 100.0 50.0 P. 9027 6.3100.0 50.0 50.0 12.5 100.0 12.5 100.0 25.0 100.0 12.5 50.0 50.0 50.0 S. typhimurium 100.0100.0 100.0 100.0 50.0 50.050.0 E.aeruginosa cloacae 1321E 100.0 100.0 100.0 E. cloacae 1321E 1771M 100.0 3.1100.0 100.0 100.0 50.0 50.050.0 50.0 P. aeruginosa 100.0100.0 25.0 100.0 6.3 50.0 25.0 S. typhimurium 100.0 50.0 100.0 100.0 Okumura 100.0 50.0et al. 50.0 Great efforts have also been made100.0 to synthesize squalamine. synthesized E. cloacae 1321E of desmosterol 100.0 100.0via100.0 100.0of the 100.0 squalamine from a derivative 12 steps100.0 with 7.4% total50.0 yield50.0 [38]. Moriarty
Great efforts have also been made to synthesize squalamine. Okumura et al. synthesized
and co-workers synthesized (1) from 3β-acetoxy-5-cholenic acid by 17 steps [39,40]. Jones et al. squalamine from a derivative of been desmosterol 12 stepssqualamine. with 7.4% of the totaletyield [38]. Moriarty Great have also made tovia synthesize al.An synthesized described a efforts practical synthesis of squalamine from stigmasterol in 15Okumura steps [41,42]. excellent and review co-workers synthesized (1) from 3β-acetoxy-5-cholenic acid by 17 steps [39,40]. Jones et al. squalamine from a for derivative of desmosterol via and 12 steps with 7.4% of the total yield [38]. Moriarty of methods the synthesis of spermine spermidine analogues of squalamine is made described a practical synthesis of They squalamine from stigmasterol in 15 steps [41,42]. An etand excellent andBrunel co-workers synthesized (1) from reviewed 3β-acetoxy-5-cholenic acid by 17 steps [39,40]. Jones al. by and Letourneux [43]. the synthesis of squalamine from cholestane described a practical synthesis of from inanalogues 15 steps [41,42]. An excellent review of methods forand the synthesis of spermine andstigmasterol spermidine of squalamine is made dinorcholenic acid described itssqualamine biological activity and clinical perspectives. review of methods the[43]. synthesis ofreviewed spermine and spermidine of squalamine is made and by Brunel Letourneux They synthesis ofanalogues squalamine from cholestane In and turn, Rao andfor co-workers isolated six otherthe aminosterols (43–48) from the liver of the dogfish by Brunel and Letourneux [43]. They reviewed the synthesis of squalamine from cholestane and shark (Figure 4) [15]. The authors presented a very accurate spectral analysis based on 2D NMR dinorcholenic acid and described its biological activity and clinical perspectives. dinorcholenic acid and described its biological activity and clinical perspectives. (COSY, as well as low-six andother high-resolution mass spectrafrom (FAB,the ESI,liver MALDI). In turn,HETCOR, Rao and HMBC) co-workers isolated aminosterols (43–48) of theThe dogfish In turn, Rao and of co-workers isolated six and othersqualamine aminosterols from theinliver of 2. the dogfish (43–48) (1) (43–48) is summarized sharkantimicrobial (Figure 4) activity [15]. Theaminosterols authors presented a very accurate spectral analysisTable based on 2D NMR shark (Figure 4) [15]. The authors presented a very accurate spectral analysis based on 2D NMR (COSY, HETCOR, HMBC) as as well as low- and high-resolutionmass massspectra spectra (FAB, ESI, MALDI). The 2 Rwell R3 as low- and high-resolution (COSY, HETCOR, HMBC) (FAB, ESI, OMALDI). The O R1 antimicrobial activity of aminosterols (43–48) and squalamine (1) is summarized in Table antimicrobial activity of aminosterols (43–48) and squalamine (1) is summarized in Table 2. 2. HN
HN
H
N H
R1 OH
NH2 H
R4 R2 R3
R O HN
H
R4
OH
(43) R1 = H, R2 = OH, R3 = H, R4 = OSO3H (44) R1 = OH, R2 = OSO3H, R3 = R4 = H N 2 NH (45) R1 = H H, R = OSO3H, R23 = CH2OH, R4 = H
HN
N H
NH2
O HN
OH
R
OH
H (46) R = SCH2CH(NH2)CO2H (47) R = OSO3H N NH2 H
isolated (43) R1Figure = H, R2 = 4. OH,The R3 = structures H, R4 = OSO3H of aminosterols (46) R = SCH(43–48) 2CH(NH2)CO2H (44) R1 = OH, R2 = OSO3H, R3 = R4 = H (47) R = OSO3H 1 2 3 4 (45) R = H, R = OSO3H, R = CH2OH, R = H
HN
H
N H
NH2 H (48)
N H
OH
OH
NH2
from the dogfish shark. (48)
Figure 4. The structures aminosterols (43–48) isolated thethe dogfish shark. 4 (43–48) Figure 4. The structures ofofaminosterols isolatedfrom from dogfish shark.
4
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Table 2. Minimum inhibitory concentrations (MIC) of 3β-aminosterols [15]. Molecules 2015, 20, page–page Table 2. Minimum inhibitory concentrations (MIC) of 3β-aminosterols [15]. Conjugates/MIC (µg/mL)
Microorganisms
1 43 Microorganisms S. aureus (29213) 1 4–8 1 E. coli (25922) S. aureus4(29213) 128 1 P. aeruginosa (27853)E. coli (25922) 16 32 4 C. albicans (90028) 16 16 P. aeruginosa (27853) 16 C. albicans (90028) 16
44 45 46 Conjugates/MIC (μg/mL) 2 438–16 44 45 46 8–16 47 4–816 8–16 28 8–16 2568 16 12816 16 8 256 256 128 32 32 128 32 16 16 256 128 16 32 32 128 32
48 2 16 16 2
47
48
8 128 128 32
2 16 16 2
Synthesis of 6β-hydroxy-3-α-(or β-)aminosterols (53–58) from hyodeoxycholic acid (49) has been β-)aminosterols (53–58) hyodeoxycholic acid (49) has been presentedSynthesis by Jonesof et 6β-hydroxy-3-α-(or al. (Scheme 3) [44]. The modification offrom hyodeoxycholic acid was carried out by presented by Jones et al. (Scheme 3) [44]. The modification of hyodeoxycholic acid was carried out by the esterification of the carboxyl group and oxidation of both hydroxyl groups to ketones, followed by the esterification of the carboxyl group and oxidation of both hydroxyl groups to ketones, followed by a conversion of the A/B ring system from cis to trans by acid-catalyzed isomerization. Then various a conversion of the A/B ring system from cis to trans by acid-catalyzed isomerization. Then various polyamines werewere added andand thethe corresponding wereobtained. obtained. polyamines added correspondingstereoconjugates stereoconjugates were
CO2Me
CO2H i-iii
CO2Me
iv-v O
HO
H
O OH
H
O
O
(49)
H
OH
(50)
(51) vi
R
H
CO2H
CO2Me
viii
vii R
OH
(57) R = β-ethylene diamine (58) R = β-spermine
H
CO2Me
O OH
(53) R = α-ethylene diamine (54) R = β-ethylene diamine (55) R = α-spermine (56) R = β-spermine
H
OH (52)
i) MeOH, H+; ii) PCC, CH2Cl2; iii) HCl, MeOH; iv) ethylene glycol, TsOH, PhH; v) NaBH4, MeOH; vi) H+, acetone; vii) NaBH3CN, ethylene diamine or spermine, THF, MeOH; viii) NaOH, THF.
Scheme 3. Synthesis of analoguesofofsqualamine squalamine (53–58) acidacid (49).(49). Scheme 3. Synthesis of analogues (53–58)from fromhyodeoxycholic hyodeoxycholic
The synthesized aminosterol conjugates (53–58) exhibit a broad spectrum of antimicrobial
The synthesized aminosterol conjugates activity, similar to other aminosterols (Table 3).(53–58) exhibit a broad spectrum of antimicrobial activity, similar to other aminosterols (Table 3). Table 3. Minimum inhibitory concentrations (MIC, μg/mL) of 3α (or 3β)-aminosterols [44].
Table 3. Minimum inhibitory concentrations (MIC, µg/mL) of 3α (or 3β)-aminosterols [44]. (μg/mL) Conjugates/MIC Microorganisms 1 53 54 55 56 57 58 Conjugates/MIC (µg/mL) 0.5–1 16 1 2–4 2 >256 16 Microorganisms S. aureus 1 53 54 55 56 57 58 E. coli 2–4 32–64 8–16 32 32 >256 16 S. aureus 0.5–1 16 16 P. aeruginosa 16 128 1 64 2–4 128 32 2128 8>256 E. coli 2–4 32–64 8–16 32 32 >256 16 C. albicans 8 8 2–4 4 2 >256 4 P. aeruginosa 16 128 64 128 32 128 8 C. albicans 8 8 2–4 4 2 >256 4 The presented data show that the β-analogs (54, 56) are slightly more active against microorganisms than the α-analogs (53, 55). Moreover, the biocidal efficacy against S. aureus is higher for methyl esters (54, 56) show in comparison to free acids (57, 58). of themore polyamine hasagainst no The presented data that the β-analogs (54,The 56)chain arelength slightly active significant effect on biocidal activity. However, for acid derivatives, a conjugate with spermine chain microorganisms than the α-analogs (53, 55). Moreover, the biocidal efficacy against S. aureus is higher (58) was much more active than a conjugate with an ethylene diamine chain (57).
for methyl esters (54, 56) in comparison to free acids (57, 58). The chain length of the polyamine has no significant effect on biocidal activity. However, for acid derivatives, a conjugate with spermine chain (58) was much more active than a conjugate 5with an ethylene diamine chain (57).
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Maitra et al.et used their own theside sidechain chainofof bile acids [45,46]. synthesis Maitra al. used their ownmethod methodto to modify modify the bile acids [45,46]. The The synthesis Molecules 2015, 20, page–page of quaternary alkylammonium conjugates of bile acids (63–75) is shown in Scheme 4. of quaternary alkylammonium conjugates of bile acids (63–75) is shown in Scheme 4. Maitra et al. used their own method to modify the side chain of bile acids [45,46]. The synthesis R2 R2 R2 Q + II of quaternary alkylammoniumCOconjugates of bile acids (63–75) is shown in Scheme 4. H 2
iv
i-iii
2
R2
R HO
HO
1
R
H
CO2H
(59) R1 = H, R2 = OH (60) R1 = R2 = OH R1 H 1
HO
H
R
HO iv
(61) R1 = H, R2 = OH (62) R1 = R2 = OH R1 H
i-iii HO
R2
I
1
(59) R = H, R = OH (60) R1 = R2 = OH
Q + I-
R1 = H, R2 = OH (63) Q = N,N,N',N'-tetramethylethylenediamine (64) HO Q = DABCO R1 H (65) Q = quinuclidine 2 (66) R1 =QH,=Rpyridine = OH (67) (63) Q Q= = 4,4'-bipyridyl N,N,N',N'-tetramethylethylenediamine (68) (64) Q Q= = N-methylpyrrolidine DABCO (69) (65) Q Q= = N-methyldiethanolamine quinuclidine (70) (66) Q Q= = 4-methylmorpholine pyridine (71) Q = N-methylpiperidine (67) Q = 4,4'-bipyridyl (72) (68) Q Q= = N,N-diethylmethylamine N-methylpyrrolidine (73) (69) Q Q= = N,N,N-triethylamine N-methyldiethanolamine (74) Q = N,N-dimethylhydrazine (70) Q = 4-methylmorpholine
(61) R1 = H, R2 = OH (62) R1 = R2 = OH
2
R1
H
(71) Q = N-methylpiperidine 1 R R2==N,N-diethylmethylamine OH (72)= Q (75) (73) Q Q= = DABCO N,N,N-triethylamine (74) Q = N,N-dimethylhydrazine i) HCO2H, 50oC; ii) I2, Pb(OAc)4, CCl4, hv; iii) MeOH, K2CO3, THF; iv) CH3CN, reflux, amine R1 = R2 = OH (75) Q = DABCOof bile acids. Scheme 4. Synthesis of cationic bile salts from iodo derivatives
Scheme o4. Synthesis of cationic bile salts from iodo derivatives of bile acids. i) HCO2H, 50 C; ii) I2, Pb(OAc)4, CCl4, hv; iii) MeOH, K2CO3, THF; iv) CH3CN, reflux, amine
Bile acids (59, 60) were transformed to the 24-nor-23-iodo (61, 62) derivatives by a Hunsdiecker Scheme 4. Synthesis of cationic bile salts from iodo derivatives of bile acids. reaction followed bywere a reaction with secondary tertiary amines,(61, respectively. All conjugates (63–75) Bile acids (59, 60) transformed to the or 24-nor-23-iodo 62) derivatives by a Hunsdiecker 1H-NMR, 13C-NMR, and FT-IR, were obtained with good yields 65%–75% and were characterized by reaction followed reaction with secondary tertiary amines, (63–75) Bile acidsby (59,a 60) were transformed to theor24-nor-23-iodo (61, respectively. 62) derivativesAll by conjugates a Hunsdiecker well as mass quaternary ammonium conjugates found to13be good gelators. 1 H-NMR, wereas obtained withspectrometry. good yieldsThese 65%–75% and were characterized bywere C-NMR, and FT-IR, reaction followed by a reaction with secondary or tertiary amines, respectively. All conjugates (63–75) Some of the quaternary ammonium bile salts gelled water and many of them13gelled aqueous salt C-NMR, andto FT-IR, were with good yieldsThese 65%–75% and were ammonium characterized conjugates by 1H-NMR, were as well asobtained mass spectrometry. quaternary found be good solutions even in the presence of organic solvents such as alcohol (methanol, ethanol) as well as as well as mass spectrometry. These quaternary ammonium conjugates were found to be good gelators. gelators. Some of the quaternary ammonium bile salts gelled water and many of them gelled aqueous DMF or DMSO. These gels form fibrous networks [46]. Some of the quaternary ammonium bile salts gelled water and many of them gelled aqueousassalt salt solutions even in the of organic solvents such to asprepare alcohol (methanol, ethanol) well as Lopushanskii andpresence Udovitskaya described the method cholesteryl 3β-bromoacetate solutions even in the presence of organic solvents such as alcohol (methanol, ethanol) as well as DMFand or DMSO. These gels formwere fibrous networks [46]. of quaternary ammonium derivatives of 3β-chloroacetate, which used in the synthesis DMF or DMSO. These gels form fibrous networks [46]. Lopushanskii and Udovitskayaderivatives described(81–91) the method cholesteryl 3β-bromoacetate cholesterol and its 5α,6β-dibromo (Schemeto5) prepare [47]. Lopushanskii and Udovitskaya described the method to prepare cholesteryl 3β-bromoacetate and 3β-chloroacetate, which were used in the synthesis of quaternary ammonium derivatives of and 3β-chloroacetate, which were used in the synthesis of quaternary ammonium derivatives of cholesterol andand its 5α,6β-dibromo (Scheme5)5)[47]. [47]. cholesterol its 5α,6β-dibromoderivatives derivatives (81–91) (81–91) (Scheme X
HO (76)
ii
O
i
ii
(77)OX = Br X (78) X = Cl O
i
HO
O X
O
(79)OX = Br (80) X = Cl X O
(77) Xiii= Br (78) X = Cl
(76)
R
N
Br
Br
Br
Br
(79) Xiii= Br (80) X = Cl
iii
O X
O
iii O
O
X
R
N
O
Br
Br
O O (81) R = (CH2)2N(CH3)2, X = Cl (89) R = (CH2)2N(CH3)2, X = Br N N (90)X R =R(CH2)2N+(CH (82) R = (CH2)2XN(CHR O 3)2CH2CO2-5α,6β-cholestenyl-3β, X = 2Cl 3)2, X = Br O Br 2-5α,6β-cholestenyl-3β, X = 2Cl (91) R = (CH2)2N+(CH3)6CH2CO (83) R = (CH2)6N(CH3)2, X = Cl Br (84) R = (CH2)2N+(CH3)2CH2CO2-Δ5-cholestenyl-3β, X = 2Cl + 5 (85) R = (CH2)6N (CH3)2CH2CO2-Δ -cholestenyl-3β, X = 2Cl (81) R = (CH2)2N(CH3)2, X = Cl (89) R = (CH2)2N(CH3)2, X = Br (86) R = (CH2)6N+(CH3)2CH2CO2-Δ5-cholestenyl-3β, X = 2Br (90) R = (CH2)2N+(CH3)2CH2CO2-5α,6β-cholestenyl-3β, X = 2Cl (82) R = (CH2)2N(CH3)2, X = Br (87) R = (CH2)7N+(CH3)2CH2CO2-Δ5-cholestenyl-3β, X = 2Cl (91) R = (CH ) N+(CH ) CH CO -5α,6β-cholestenyl-3β, X = 2Cl (83) R = (CH2)6N(CH 2 2 3 6 2 2 + 3)2, X = Cl 5 (88) R = (CH2)10N+ (CH3)2CH2CO2-Δ5 -cholestenyl-3β, X = 2Cl (84) R = (CH2)2N (CH3)2CH2CO2-Δ -cholestenyl-3β, X = 2Cl (85) R = (CH2)6N+(CH3)2CH2CO2-Δ5-cholestenyl-3β, X = 2Cl (86) R = (CH2)6N+(CH3)2CH2CO2-Δ5-cholestenyl-3β, X = 2Br +(or BrCH2COBr), CHCl 5 ClCH 2COBr 3 (or PhH), KX 2CO 3; ii) Br2, AcOH, Et2O; iii) tertiary or ditertiary amines, PhH = 2Cl (87)i) R = (CH 2)7N (CH3)2CH 2CO2-Δ -cholestenyl-3β, (88) R = (CH2)10N+(CH3)2CH2CO2-Δ5-cholestenyl-3β, X = 2Cl
Scheme 5. Synthesis of monoquaternary (81–83, 89) and symmetrical bisquaternary salt (84–88, 90, 91) derivativesi)of cholesterol. ClCH 2COBr (or BrCH2COBr), CHCl3 (or PhH), K2CO3; ii) Br2, AcOH, Et2O; iii) tertiary or ditertiary amines, PhH Scheme 5. Synthesis of monoquaternary (81–83, 89) and symmetrical bisquaternary salt (84–88, 90, 91)
Scheme 5. Synthesis of monoquaternary (81–83, 689) and symmetrical bisquaternary salt (84–88, 90, derivatives of cholesterol. 91) derivatives of cholesterol.
6
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Molecules 2015, 20, page–page
In addition to monoquaternary salts (81–83) and (89), as well as symmetrical bisquaternary salts In addition topage–page monoquaternary salts (81–83) and (89), as well as symmetrical bisquaternary salts Molecules 2015, 20, the (84–88) and (90, 91), authors obtained and described unsymmetrical bisquaternary salts (92–105) (84–88) and (90, 91), the authors obtained and described unsymmetrical bisquaternary salts (92–105) (Figure 5). The unsymmetrical bisquaternary ammonium salts (92–101) demonstrate a bacteriostatic (Figure The unsymmetrical bisquaternary ammonium (92–101) demonstrate a bacteriostatic In 5). addition to monoquaternary salts (81–83) and (89),salts as well as symmetrical bisquaternary salts activity that that depends on on thethe alkyl activity depends alkylchain chainlength. length. (84–88) and (90, 91), the authors obtained and described unsymmetrical bisquaternary salts (92–105) (Figure 5). The unsymmetrical bisquaternary ammonium salts (92–101) demonstrate a bacteriostatic activity that depends on the alkyl chain length. 2Cl O RO
RO
N
2Cl
N
O
O
O
N (92) R = CH3 O (99) R = i-C5H11 (93) R = C2H5 (100) R = C7H13 (94) R = n-C3H7 O (101) R = C8H17 (95) R = i-C3H7 (102) R = C9H19 (92) R = CH (99) R = i-C H (96) R = n-C43H9 (103) R = C105H11 21 (93) R = C H (100) R = C7H13 (97) R = i-C24H59 (104) R = Ph-CH (94) R = n-C3H7 (101) R = C8H172 (98) R = n-C5H11 (105) R = CH -Ph-C (95) R = i-C3H7 (102) R = C93H19 3H7 (96) R = n-C4H9 (103) R = C10H21 Figure 5. The structures of unsymmetrical bisquaternary saltR(92–105) (97) R = i-C4H (104) = Ph-CH2derivatives of cholesterol. 9 Figure 5. The structures of unsymmetrical bisquaternary salt of cholesterol. (98) R = n-C5H11 (105) R =(92–105) CH3-Ph-Cderivatives 3H7 N
Brycki and co-workers the series of quaternary alkylammonium conjugates of Figure 5. The structures ofobtained unsymmetrical bisquaternary salt (92–105) derivatives of cholesterol. ergosterol, cholesterol, and cholestanol [48]. The conjugates were synthesized by two-step reactions. Brycki and co-workers obtained the series of quaternary alkylammonium conjugates of In the first step ergosterol, cholesterol, and cholestanol were reacted with bromoacetic acid bromide ergosterol,Brycki cholesterol, and cholestanol [48]. conjugates were synthesized by two-step reactions. and co-workers obtained theThe series of quaternary alkylammonium conjugates of calcium and hydride (or sodium hydride) in anhydrous toluene give 3β-bromoacetates ergosterol, cholesterol, cholestanol [48]. The conjugates synthesized by two-step reactions. In thewith firstTEBA stepand ergosterol, cholesterol, and cholestanol werewere reacted withtobromoacetic acid bromide of sterols [49]. Inergosterol, the second step, 3β-bromoacetates have been treated with tertiary acid alkylamines In the first step cholesterol, and cholestanol were reacted with bromoacetic bromide with TEBA and calcium hydride (or sodium hydride) in anhydrous toluene to give 3β-bromoacetates (CH 2)n–N(CH 3)2, n hydride = 8–14) under SN2hydride) reaction inconditions to give conjugates of ergosterol with3–(CH TEBA calcium sodium anhydrous give tertiary 3β-bromoacetates of sterols [49]. and In the second step,(or3β-bromoacetates have been toluene treatedtowith alkylamines (106–109), and cholestanol (114–117) (Figure of sterols cholesterol [49]. In the(110–113), second step, 3β-bromoacetates have been 6). treated with tertiary alkylamines
(CH3 –(CH2 )n –N(CH3 )2 , n = 7, 9, 11, 13) under SN 2 reaction conditions to give conjugates of ergosterol (CH3–(CH2)n–N(CH3)2, n = 8–14) under SN2 reaction conditions to give conjugates of ergosterol (106–109), cholesterol (110–113), and cholestanol (114–117) (Figure 6). (106–109), cholesterol (110–113), and cholestanol (114–117) (Figure 6). Br
Br O N
n
O N
O
n
O (110) n = 6 (111) n = 8 (112) n = 10 (113) n = 12
(106) n = 6 (107) n = 8 (108) n = 10 (109) n = 12
Br O N n
O
H
(114) n = 6 (115) n = 8 (116) n = 10 (117) n = 12
Figure 6. The quaternary alkylammonium conjugates of sterols (106–117).
The authors also obtained a series of N,N-dimethyl-3-phthalimidopropylammonium conjugates of sterols (ergosterol, cholesterol, cholestanol) (118–120) and bile acids (lithocholic, deoxycholic, Figure 6. The quaternary alkylammonium ofofsterols (106–117). cholic) (121–123) (Figure 7) [50]. Thealkylammonium synthesis and conjugates physicochemical properties of quaternary Figure 6. The quaternary conjugates sterols (106–117). N,N-dimethyl-3-phthalimidopropylammonium conjugates of ergosteryl 3β-bromoacetate, cholesteryl The authors also a series of N,N-dimethyl-3-phthalimidopropylammonium conjugates 3β-bromoacetate, andobtained dihydrocholesteryl 3β-bromoacetate, as well as methyl litocholate The authors also obtained a series of N,N-dimethyl-3-phthalimidopropylammonium conjugates of sterols (ergosterol, cholesterol, cholestanol) (118–120) and bile acids (lithocholic, deoxycholic, 3α-bromoacetate, methyl deoxycholate 3α-bromoacetate, and methyl cholate 3α-bromoacetate with of sterols (ergosterol, cholesterol, cholestanol) (118–120) and bile acids (lithocholic, deoxycholic, cholic) (121–123) (Figure 7) [50]. The synthesis and physicochemical properties of quaternary N,N-dimethyl-3-phthalimidopropylamine in acetonitrile were investigated and described. N,N-dimethyl-3-phthalimidopropylammonium conjugates of ergosteryl 3β-bromoacetate, cholesteryl cholic) (121–123) (Figure 7) [50]. The synthesis and physicochemical properties of quaternary 3β-bromoacetate, and dihydrocholesteryl 3β-bromoacetate, as well as methyl litocholate N,N-dimethyl-3-phthalimidopropylammonium conjugates of ergosteryl 3β-bromoacetate, cholesteryl 3α-bromoacetate, methyl deoxycholate 3α-bromoacetate, and methyl with 3β-bromoacetate, and dihydrocholesteryl 3β-bromoacetate, as cholate well 3α-bromoacetate as methyl litocholate 7 N,N-dimethyl-3-phthalimidopropylamine in acetonitrile were investigated and described.
3α-bromoacetate, methyl deoxycholate 3α-bromoacetate, and methyl cholate 3α-bromoacetate with N,N-dimethyl-3-phthalimidopropylamine in acetonitrile were investigated and described. 7
20893
Molecules 2015, 20, 20887–20900
Molecules 2015, 20, page–page Molecules 2015, 20, page–page Br
Br O N
R
Br
O O (118)
O R
N
N
R
Br
O (119)
O
O
R
N
O
(118)
(119) R2 Br
Br O Br
R
N O
R
N
R2
O O
Br R
H
N
O
O
O R=
R
N
(121) R1 = R2 = 1H R2 1 (122) H R = H, R = OH (123) R1 = R2 = OH
O
N CH2 CH2 CH2
(120)
(121) R1 = R2 = H (122) R1 = H, R2 = OH (123) R1 = R2 = OH
O O R=
CO2CH3 R1
H
O (120) H
CO2CH3
N CH2 CH2 CH2
Figure 7. N,N-dimethyl-3-phthalimidopropylammonium conjugates of sterols (118–120) and bile
O Figure 7. N,N-dimethyl-3-phthalimidopropylammonium conjugates of sterols (118–120) and bile acids (121–123). acidsFigure (121–123). 7. N,N-dimethyl-3-phthalimidopropylammonium conjugates of sterols (118–120) and bile
acids (121–123). The symmetrical dimeric quaternary alkylammonium conjugates of sterols (124–132) prepared
The symmetrical dimeric quaternary alkylammonium conjugates of sterols (124–132) prepared by two-step reactions of ergosterol, cholesterol, or cholestanol with bromoacetic acid bromide, The symmetrical dimeric quaternary alkylammonium conjugates of sterols (124–132) prepared followed reactions by bimolecular nucleophilic substitutionor with N,N,N',N'-tetramethyl-1,3-propanediamine, by two-step of ergosterol, cholesterol, cholestanol with bromoacetic acid bromide, by two-step reactions nucleophilic of ergosterol,substitution cholesterol, cholestanol with bromoacetic acid bromide, N,N,N',N'',N''-pentamethyldiethylenetriamine, andor 3,3′-iminobis-(N,N-dimethylpropylamine) have followed by bimolecular with N,N,N',N'-tetramethyl-1,3-propanediamine, followed by bimolecular nucleophilic substitution with N,N,N',N'-tetramethyl-1,3-propanediamine, 1 been also described by Brycki et al. (Figure 8) [51]. The final reactions were carried out in acetonitrile N,N,N',N'',N''-pentamethyldiethylenetriamine, and 3,3 -iminobis-(N,N-dimethylpropylamine) have N,N,N',N'',N''-pentamethyldiethylenetriamine, and 3,3′-iminobis-(N,N-dimethylpropylamine) have favor bimolecular nucleophilic substitution and The optimize reactionwere yields. been to also described by Brycki et al. (Figure 8) [51]. finalthe reactions carried out in acetonitrile been also described by Brycki et al. (Figure 8) [51]. The final reactions were carried out in acetonitrile to favor bimolecular nucleophilic optimizethe thereaction reaction yields. to favor bimolecular nucleophilicsubstitution substitution and and optimize yields. Br
Br O
O Br
O
N
SPACER
N
Br
SPACER N N (124) -CH 2-CH2-CH2SPACER O (125) -CH2-CH2-N(CH3)-CH2-CH2(126) -CH2-CH2-CH2-NH-CH2-CH2-CH2SPACER (124) -CH2-CH2-CH2(125) -CH2-CH2-N(CH3)-CH2-CH2Br (126) -CH2-CH2-CH2-NH-CHBr 2-CH2-CH2-
O
O
O Br
O
N
SPACER
N
Br
SPACER N (127) -CH2-CH2-CH2- N SPACER O (128) -CH2-CH2-N(CH3)-CH2-CH2(129) -CH2-CH2-CH2-NH-CH2-CH2-CH2SPACER (127) -CH2-CH2-CH2(128) -CH2-CH2-N(CH3)-CH2-CH2Br (129) -CH2-CH2-CH2-NH-CHBr 2-CH2-CH2-
O
O
O
H
Br
O
N
SPACER
N
Br
O O
O O
O O
O
H
O O
O
SPACER N (130) -CH2-CH2-CH2- N SPACER O (131) -CH 2-CH2-N(CH3)-CH2-CH2(132) -CH2-CH2-CH2-NH-CH2-CH2-CH2SPACER (130) -CH2-CH2-CH2(131) -CH2-CH2-N(CH3)-CH2-CH2(132) -CH2-CH2-CH2-NH-CH2-CH2-CH2-
H
H
Figure 8. The symmetrical bisquaternary alkylammonium conjugates of sterols (124–132). 13C-NMR, Figure 8. The bisquaternary alkylammonium conjugates of sterols (124–132).and FT-IR) All structures of symmetrical the conjugates were confirmed by spectral (1H-NMR, Figure 8. The symmetrical bisquaternary alkylammonium conjugates of sterols (124–132). analysis and mass spectrometry as well as theoretical semiempirical methods (PM5). PM5 semiempirical 1H-NMR, 13C-NMR, and FT-IR) All structures of the conjugates were confirmed2003 by spectral calculations were performed using the WinMopac program( [52–54]. In all13cases, the heat of All structures ofspectrometry the conjugates were confirmed by spectral (1 H-NMR, C-NMR, and FT-IR) analysis and mass as well as theoretical semiempirical methods (PM5). PM5 semiempirical formation (HOF) was consistent with the expected values. The lowest values of HOF for sterols were analysis and mass spectrometry as well as theoretical semiempirical methods (PM5). calculations were performed using the WinMopac 2003 program [52–54]. In all cases, the heat observed for conjugates of cholestanol (114–117, 120, 130–132) where there were no double bondsof to PM5 semiempirical calculations were performed using the WinMopac 2003 program [52–54]. In all formation (HOF) was consistent with the expected values. The lowest values of HOF for sterols were stabilize the molecule and hinder its reactivity. This was in contrast to conjugates of ergosterolcases, observed for conjugates of cholestanol (114–117, 120, 130–132) where there were double bondsof to HOF the heat of formation (HOF) was consistent with the expected values. The no lowest values stabilize the molecule and hinder its reactivity. This was in contrast to conjugates of ergosterol 8 for sterols were observed for conjugates of cholestanol (114–117, 120, 130–132) where there were no
double bonds to stabilize the molecule and hinder its reactivity. This was in contrast to conjugates 8 of ergosterol (106–109, 118, 124–126) and cholesterol (110–113, 114, 127–129), where the double bonds 20894
Molecules 2015, 20, page–page Molecules 2015, 20, 20887–20900
(106–109, 118, 124–126) and cholesterol (110–113, 114, 127–129), where the double bonds increase the reactivity of the molecule, thereby increasing values of HOFvalues (Figure In turn, the9). HOF of conjugates increase the reactivity of the molecule, thereby increasing of 9). HOF (Figure In turn, the HOF of esters bile acids can (121–123) be explained in aexplained similar manner. For these compounds of methyl conjugates of of methyl esters(121–123) of bile acids can be in a similar manner. For these the number of hydroxyl in thegroups steroidinskeleton lowers the value of HOF. compounds the number groups of hydroxyl the steroid skeleton lowers the value of HOF.
(113)
(118)
(123)
(132) Figure 9. The representative quaternary alkylammonium conjugates of sterols calculated by the Figure 9. The representative quaternary alkylammonium conjugates of sterols calculated by the PM5 PM5method. method.
The potential pharmacological activities of the synthesized compounds have been studied potential pharmacological activities of thewith synthesized compounds been studied using usingThe a computer-aided drug discovery approach the in silico Predictionhave of Activity Spectra for a computer-aided drug discovery approach withanalysis the in of silico Prediction of Activity Spectrainfor Substances (PASSs) program. It is based on a robust the structure–activity relationships a Substances (PASSs) program. It is based on a robust analysis the structure–activity relationships in heterogeneous training set currently including about 60,000of biologically active compounds from a heterogeneous setabout currently about 60,000 biologically active compounds from different chemical training series with 4500 including types of biological activities. Since only the structural formula different chemical series with about 4500 typesa of biological activities. Since only theused structural of the chemical compound is necessary to obtain PASS prediction, this approach can be at the formula of the chemical compound is necessary to obtain a PASS prediction, this approach can be earliest stages of investigation. There are many examples of the successful use of the PASS approach used at the earliest stages of investigation. There are many examples successful usestudy of theofPASS leading to new pharmacological agents [55–59]. The PASS softwareofisthe useful for the the approach leading to new pharmacological agents [55–59]. The PASS software is useful for study biological activity of secondary metabolites. The types of activities that were predicted for a the potential of the biological activity of secondary metabolites. The types activities that If were predicted for a compound with the highest probability (focal activities) haveofbeen selected. predicted activity potential compound with the highest (focal activities) been selected. predicted (PA) > 70, the substance is very likely toprobability exhibit experimental activityhave and the chance of theIf substance activity (PA) > 70, the substance is very likely to exhibit experimental activity and the chance of the being the analogue of a known pharmaceutical agent is also high. If 50 < PA < 70, the substance is substance being the analogue of a known pharmaceutical agent is also high. If 50 < PA < 70, the unlikely to exhibit the activity in experiment, the probability is less, and the substance is unlike any substance is unlikely toagent. exhibitAthe activity in experiment, the selected probability less, of and the substance is known pharmaceutical research group led by Brycki theistypes activity that were unlike any known pharmaceutical agent. A research group led by Brycki selected the types of activity predicted for a potential compound with the highest probability (Table 4). that were predicted for a potential compound with the highest probability (Table 4). 9 20895
Molecules 2015, 20, 20887–20900
Table 4. Probability “to be Active” (PA) values for predicted biological activity of compounds (106–132). Focal Predicted Activity (PA > 80) Cholesterol antagonist Antihypercholesterolemic Glyceryl-ether monooxygenase inhibitor Acylcarnitine hydrolase inhibitor Alcohol O-acetyltransferase inhibitor Oxidoreductase inhibitor Prostaglandin-E2 9-reductase inhibitor Alkylacetylglycerophosphatase inhibitor Alkenylglycerophosphocholine hydrolase inhibitor
106–109
110–113
88 91 89 – 91 81 – – –
90 87 92 87 – – 86 – –
114–117 87 – 95 97 – – – 92 90
118
Conjugates 119 120 121 122 123 124 125 126 127 128 129 130 131 132
– – 87 – – – – – –
– – 91 – – – – – –
20896
– – 93 81 – – – 84 –
– – 93 83 – – – 82 –
– – 94 91 – – – 90 80
– – 95 94 – – – 86 –
81 88 89 – 91 87 – – –
85 83 89 – 90 86 – – –
– 86 88 – 90 85 – – –
87 85 92 85 – – – – –
89 80 92 80 – – – – –
82 83 91 – – – – – –
82 – 95 96 – – – 90 88
86 94 95 – – – – 87 82
– – 94 93 – – – 83 80
Molecules 2015, 20, 20887–20900
3. Conclusions The design and preparation of new steroid conjugates allow us to develop the fields of supramolecular chemistry, material chemistry, and nanotechnology. In this paper we described the synthesis and physicochemical properties of quaternary alkylammonium conjugates of steroids. Most of the described compounds are characterized by high biological activity with a broad spectrum of antimicrobial and antifungal activity. Moreover, these compounds can actively participate in transport across biological membranes, which offers tremendous possibilities in biochemistry, pharmacology, and medicine. The spectroscopic data, semiempirical calculations, and potential pharmacological properties (PASS) obtained in this work significantly extend the library of new steroid conjugates. Acknowledgments: of Chemistry.
This work was supported by funds from Adam Mickiewicz University, Faculty
Author Contributions: All authors contributed to the reported research and writing of the paper. All authors read and approved the final manuscript. Conflicts of Interest: The authors declare no conflict of interest.
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Sample Availability: Samples of the compounds 106–132 are available from the authors. © 2015 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons by Attribution (CC-BY) license (http://creativecommons.org/licenses/by/4.0/).
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