NPC
Natural Product Communications
Insecticidal Properties of Annonaceous Acetogenins and Their Analogues. Interaction with Lipid Membranes
2012 Vol. 7 No. 0 1-2
Lilian Di Toto Blessing a, Juan Ramos d, Sonia Diaz b, Aída Ben Altabef b, c, Alicia Bardón a, c, Margarita Brovetto d, Gustavo Seoane d and Adriana Neske *a a
Instituto de Química Orgánica, and bInstituto de Química Física, Facultad de Bioquímica, Química y Farmacia, Universidad Nacional de Tucumán, Ayacucho 471, Tucumán 4000, Argentina c INQUINOA-CONICET, Tucumán, Argentina d Dpto de Química Orgánica, Fac de Química, UdelaR, Montevideo, Uruguay.
[email protected] Received: May 15th, 2012; Accepted: XX, 2012
The interactions were studied by FTIR and DSC of the terminal lactone of annonaceous acetogenins (ACGs) and synthetic analogues, such as THF, with POPC bilayers, as well as the toxic effect produced by these compounds on Spodoptera frugiperda larvae. The aim of this work was to find a relationship between ACG insecticidal properties and the specific sites of interaction with lipid membranes. ACGs interact to different extents with the phosphate of lipid membranes and differences in the antisymmetric stretching of the phosphate groups were found in the presence of water that indicate water loss and further hydrogen bonding.The ACG tested produced more than 70% larval mortality. Rolliniastatin-1 (3) proved to have the most toxic effects (100%) on early larval instars when incorporated in the larval diet at a dose of 100 μg per g of diet. Additionally, it produced a significant decrease in growth rate (GR) and consumption index (CI), and reduced the efficiency with which larvae converted ingested food into biomass (ECI). The destabilization that occurs in the membrane due to dehydration around the phosphate groups caused by interaction with ACGs and their synthetic analogues would account for ACGs’ insecticidal action. Keywords:Annonaceous acetogenins, POPC, FTIR, DSC, Toxicity.
Annonaceous acetogenins (ACGs) are secondary metabolites isolated from species of Annonaceae, known in traditional and folk medicine and for their economic potential. ACGs are characterized by a common skeleton usually formed by 35 to 37 carbon atoms, that have a long alkyl chain that usually exhibits a terminal α,βunsaturated-methyl--lactone. In the hydrocarbon chain attached to the lactone at position 2, there are usually one, two, or, more rarely, three-ring tetrahydrofuran (THF) units and it can also have oxygenated functions and double bonds.The most important effects of ACGs have been described on cancer cell lines, particularly those resistant to chemotherapy. Their cytotoxicity is due to the fact that they inhibit ATP synthesis at the mitochondrial complex I [1a,b]. In addition, toxic effects of annonaceous acetogenins have been reported for several species of insects, including Spodoptera littoralis, Leptinotarsa decemlineata, Mizus persicae [2], S. frugiperda, Oncopeltus fasciatus, and Ceratitis capitata [3a-c]. The insecticidal properties of acetogenins against several key crop pests in different parts of the world have repeatedly been described. In recent years a series of studies have been carried out that postulate the way the ACGs interact with the CRM complex I and the requirements for obtaining the highest activity were established. Previous reports of Shimada et al. determined that the THF rings of the ACGs, annonacin and sylvaticin, must interact strongly with the polar ends of the liposomal membrane phospholipids and suggested that these rings act as a THF hydrophilic membrane anchor to optimally position the conformation of ACG functional groups with the lactone terminal, together with part of the spacer domain, the portion of the molecule that would interact directly with the active site of the enzyme in complex I [4a,b]. While studies by NOE have shown how the ACG is located in the membrane, nothing has been said about the effects that occur in the membrane structure due to the presence of ACGs. We have recently analyzed the
intermolecular interactions between the lipid headgroups (glycerol and phosphate) of POPC and the THF/flanking hydroxyls of ACG. To understand the molecular details of these interactions we performed MD simulations in which ACGs interact with POPC in the fully hydrated state of the lipid. Our results revealed intermolecular interactions between the headgroups of POPC (specifically phosphate groups) and the hydroxylated-THF of the ACGs annonacin and rolliniastatin-1. These interactions indicated that the phosphate groups of the lipid membrane form stronger hydrogen bonds with hydroxylated-THF rings of ACG than with water molecules. This suggests that there is a strong dehydration in its environment. These results reveal that the OH groups of ACG might preferably interact with the phosphate groups of membranes in the liquid crystalline state [5]. In biological membranes, the hydrophobic core is “fluid” because of the liquid-crystalline state of the bilayer. The degree of hydration and the structural dynamics of water molecules at the cellular envelope polar interphase are known to play very important roles in the structural stabilization of a lipid membrane and in the definition of its biological activity [6a-c]. The membrane environment determines and limits the conformations and the location of lipophilic compounds acting at a membrane receptor in the lipid bilayer [4a,b]. Therefore, to determine the location and conformation of ACG in those membranes, it is necessary to understand their role as potent toxic compounds. The toxicity of the ACG would seem to be strongly related to the membrane conformation [4b]. Previous results have indicated that the effects caused by certain compounds on the hydration patterns surrounding the phospholipid phosphate and carbonyl groups can be studied by FTIR spectroscopy [6c-7a,b], using multilamellar vesicles (MLVs) made from POPC.
2Natural Product Communications Vol. 7 (0) 2012
O
O
OH
HO
vibrational band assigned to the PO2−antisymmetric stretching mode (ν PO2− as) is centered at 1229.5 cm−1, while the band assigned to the PO2− symmetric stretching mode (ν PO2− s) is centered at 1085.0 cm−1. It is widely accepted that the frequency of the vibration (ν PO2− as) is very sensitive to lipid hydration, mainly because of direct H binding to charged phosphate oxygens [15a-e].
OH O
(CH2)12
Author A et al.
O
(CH2)9 CH3 1
O
O
OH
OH
OH O
(CH2)12
O
(CH2)5CH3 2
O
O OH
OH
Dehydration of a biological membrane usually results in such massive upheavals that its structure and functions are irreversibly damaged. Phospholipid polar head groups normally are hydrated tosome extent, and are separated from each other by these water molecules. Thus, when phospholipids are dehydrated, the packing density of the head groups would be expected to increase, thereby increasing opportunities for van der Waals interactions among the hydrocarbon chains.
OH O
(CH2)10
O
(CH2)9 CH3 3
O
O OH
OH
OH O
(CH2)10
O
(CH2)9 CH3 4
O
O OH
OH
OH (CH2)5
O OH
O
Table 2: Frequency shifts of PO2−antisymmetric and symmetric stretching modes as a function of ACG/lipid molar ratio of POPC bilayer (liquid-crystalline state, 25°C).
(CH2)11 CH3 5
Compounds
O OH
OH
OH (CH2)5
O
POPC (CH2)11 CH3
O
1/POPC
6
Figure 1: ACG mono and bis THF tested 2/POPC I
H
O
H OH
HO H
O
H OH
I
H
COOMe
COOMe 7
O
I
H OAc
H
COOMe
8
9
AcO
O
H OH COOMe
3/POPC
10
4/POPC O O
O
H N
CH3 O
O
H N
(CH2)10 CH3 O
11
5/POPC 12
Figure 2: ACG synthetic analogues tested
6/POPC
Table 1: Transition properties of anhydrous liposomes of pure POPC and ACG1/POPC (molar ratio 0.6:1). Lyophilized liposomes POPC ACG1/POPC
ONSET Tm (ºC) 32,67 118,08
PEAK Tm (ºC) 36,08 120,75
H(J/g) 47,72 7,65
In this work, we first carried out the isolation of the mono and bis THF ACGs, laherradurin (1) [8], squamocin (2) [9], rolliniastatin-1 (3) [10], asimicin (4) [11], annonacin (5) [12] and cis-annonacin-10one (6) [13] (Figure 1). ACG synthetic analogues, compounds 7-10 were synthesized (Figure 2) and characterized by spectroscopic techniques [14].The compounds 11 and 12 were purchased from Sigma Aldrich. Out of all the compounds tested by FTIR spectroscopy, we selected 3, 5, 8 and 11 for the evaluation of their toxic effects on larvae of the lepidopteran pest Spodoptera frugiperda. The DSC of lyophilized liposomes of pure POPC and ACG1/POPC (molar ratio 0.6:1) were studied. The endotherms showed that the Tm maximum was shifted to a higher temperature and there was a decrease in enthalpy of transition. That would indicate loss of structured water in the polar lipid head. The transition properties of anhydrous liposomes of ACG1/POPC, shown in Table 1, could be due to the relative specificity of ACG 1 interactions with phospholipids of the membrane. DSC has been used to measure the strength of ACG-phospholipid interactions and showed that the ACG strongly interact at the hydrocarbon core/water interface of POPC [8]. Such effects could, therefore, be an important factor in the ability of this molecule to remove water around the head group of phospholipids and thereby destabilize it. In FTIR measurements in fully hydrated phosphatidylcholine in the liquid-crystalline state, the characteristic phosphate group
Molar ratio ACG/POPC 0:1 0.6:1 1.2:1 2.4:1 0.6:1 1.2:1 2.4:1 0.6:1 1.2:1 2.4:1 0.6:1 1.2:1 2.4:1 0.6:1 1.3:1 2.6:1 0.6:1 1.3:1 2.6:1
Ṽp / cm-1 PO2- st antisym 1230.4 ± 1.3 1225.4 ± 0.1 1227.4 ± 0.6 1228.4 ± 0.3 1229.2 ± 0.8 1227.7 ± 1.2 1228.6 ± 0.1 1238.7 ± 0.6 1238.8 ± 0.2 1239.0 ± 0.7 1236.2 ± 0.4 1239.1 ± 0.3 1239.2 ± 0.8 1222.1 ± 0.8 1223.7 ± 0.5 1225.8 ± 0.9 1226.4 ± 0.6 1226.1 ± 0.6 1226.0 ± 0.1
ΔṼ cm-1 0.0 -5.0 -3.0 -2.0 -1.2 -2.7 -1.8 8.3 8.4 8.6 5.8 8.7 8.8 -8.3 -6.7 -4.6 -4.0 -4.3 -4.4
Ṽp / cm-1 PO2- st sym 1087.6 ± 0.3 1088.5 ± 0.9 1089.3 ± 0.2 1088.8 ± 0.9 1087.6 ± 0.4 1088.5 ± 0.3 1088.2 ± 1.0 1087.7 ± 1.0 1087.8 ± 0.8 1087.8 ± 0.1 1089.3 ± 0.8 1088.9 ± 0.4 1089.2 ± 1.0 1086.4 ± 0.7 1086.0 ± 0.2 1086.3 ± 0.4 1086.7 ± 0.6 1086.2 ± 1.0 1086.3 ± 0.4
ΔṼ cm-1 0.0 0.8 1.6 1.1 0.0 0.9 0.6 0.1 0.2 0.2 1.7 1.2 1.6 -1.2 -1.6 -1.3 -0.9 -1.4 -1.3
Compounds 1-12 were evaluated for their interaction with POPC bilayers. The bis THF ACGs 1 and 2, included in artificial lipid membranes, have small negative changes in the frequency wavenumbers of the phosphate group of the lipid membrane with respect to the pure lipid. This suggests that, in addition to water loss, there is a weak H-bond formation with phosphates. The most effective interaction between ACG1/POPC corresponds to the ratio 0.6:1 (Table 2). The bis THF ACGs 3 and 4, included in different molar ratios in artificial lipid membranes, produced significant positive changes in the frequency wavenumbers of the phosphate group of the membrane with respect to the pure lipid in all molar ratios assayed (Table 2). This occurs when the first layer of hydration of the phosphate group is modified, indicating the displacement of water molecules around its polar head. The mono THF ACGs 5 and 6, included in different molar ratios in artificial lipid membranes, have negative changes in the frequency wavenumbers of the phosphate group of the lipid membrane with respect to pure lipid, suggesting that mono THF ACG would replace the hydration water of the same environment. The most effective interaction between ACG5/POPC corresponds to the ratio 0.6:1 (Table 2). Moreover, the results corresponding to the semisynthetic compound 7 shows small displacements to higher wavenumbers compared to the environment of the carbonyl group more hydrated (P2) in pure lipid (3.8; 3.2; 2.6 cm-1 for the different molar ratios), indicating water loss. Otherwise, the semisynthetic compounds 7 and 8, exhibit shifts to lower wavenumber antisymmetric stretching frequencies of the phosphate group, indicating displacement of water molecules with subsequent formation of hydrogen bonds in the same environment in all molar ratios assayed (Table 3).
Running title here
Natural Product Communications Vol. 7 (0) 20123
Table 3: Frequency shifts of PO2−antisymmetric and symmetric stretching modes as a function of compounds/lipid molar ratio of POPC bilayer (liquid-crystalline state, 25°C). Compounds POPC 7/POPC 8/POPC 9/POPC 110/POPC 11/POPC 12/POPC
Molar ratio ACG/POPC 0:1 0.2:1 0.4:1 0.8:1 0.1:1 0.3:1 0.5:1 0.2:1 0.5:1 0.9:1 0.2:1 0.5:1 0.9:1 1.8:1 3.6:1 7.3:1 1.1:1 2.2:1 4.4:1
Ṽp / cm-1 PO2- st antisym 1230.4 ± 1.3 1225.6 ± 1.1 1225.2 ± 1.6 1224.0 ± 1.4 1225.8 ± 0.3 1225.0 ± 0.4 1224.4 ± 0.7 1230.9 ± 1.7 1231.5 ± 1.2 1230.8 ± 2.0 1234.1 ± 0.1 1235.6 ± 0.5 1236.7 ± 0.1 1225.9 ± 1.3 1226.6 ± 0.4 1224.3 ± 1.3 1226.2 ± 0.9 1225.3 ± 0.4 1224.8 ± 0.2
ΔṼ cm-1 0.0 -4.8 -5.2 -6.4 -4.6 -5.4 -6.0 0.5 1.1 0.4 3.7 5.2 6.3 -4.5 -3.8 -6.1 -4.2 -5.1 -5.6
Ṽp / cm-1 PO2- st sym 1087.6 ± 0.3 1088.3 ± 0.5 1088.1 ± 0.8 1088.2 ± 0.5 1086.6 ± 1.2 1086.8 ± 1.0 1086.6 ± 0.9 1089.3 ± 0.5 1088.4 ± 0.3 1088.7 ± 1.3 1086.7 ± 0.4 1085.0 ± 0.5 1084.0 ± 0.7 1088.2 ± 0.7 1089.2 ± 0.6 1088.3 ± 1.3 1087.7 ± 0.3 1088.4 ± 1.5 1087.9 ± 0.7
ΔṼ cm-1 0.0 0.7 0.5 0.6 -1.0 -0.8 -1.0 1.7 0.8 1. -1.0 -2.7 -3.6 0.6 1.6 0.7 0.1 0.8 0.3
Compound 9 (without OH) has no wavenumber differences in the phosphate group with the pure lipid in all molar ratios assayed (Table 3); compound 10 (OAc in the THF ring), has wavenumber differences only in the phosphate group, producing dehydration in the lipid bilayer in all molar ratios assayed. Hence, the THF rings behave differently with specific groups of the phospholipid polar heads according to whether or not they have linked OH groups. Compounds 11 and 12 (lactone terminal) have negative changes in the wavenumbers of the phosphate frequencies indicating the displacement of water molecules around the polar head group of the lipid membrane (Table 3). The frequencies of carbonyl groups and the CH2 and CH3 symmetric and antisymmetric stretching modes of vibration of the lipid acyl chains were not affected by mono or bis THF and acetogenin synthetic analogues at the temperatures and conditions assayed. Solute H bonding is possible with the PO2- and C=O groups of diacyl lipids and has been investigated in detail for a membrane-bound disaccharide [7a, 16]. It is rather natural that the hydrogen-bonding around the phosphate group is enriched in the presence of the hydroxylated mono and bis THF ring analogues because they are hydrogen-bond donors and/or acceptors. In the present study, we could identify ACG mono and bis THF specific areas of interaction with PO2- groups in the lipid interphase, but there was no evidence of interactions of the investigated solutes with the C=O group. This indicates that ACG and analogues do not penetrate this deeply into the membrane. A toxicity test at 100 ppm of treatment with 3, 5, 8 and 11 to the larval diet produced more than 70% larval mortality at early larval stages, as shown in Table 4. The most important toxic action was observed on larvae. Compounds 3 and 11 produced a delayed mortality of the whole population, and, therefore no adult emergency occurred. The bis THF acetogenin rolliniastatin-1 (3), produced a stronger activity than the mono THF, annonacin (5), indicating that the number of THF groups had a differential incidence on the activity [17]. In fact, all compounds tested produced larval mortality. In order to assess how the treatment induced mortality, we analyzed the nutritional effects produced by the addition of the above mentioned compounds to the larval diet of S. frugiperda. The addition of ACG to the larval diet caused significant changes to the nutritional indices in connection with larvae fed the control diet.The nutritional index values obtained for larvae fed with the compounds tested would reveal the presence of toxic compounds when compared with control. The differences observed became much
Table 4: Toxic effects and nutritional indices of annonaceous acetogenins and their analogues on S. frugiperda Compounds 3 5 8 11
(%) Larval mortality 100 70 80 100
Emergency adults (%) 30 20 -
CIT/CIC (%) 48.3 83.3 106.7 123.4
GR T/GRC (%) 10.2 68.2 150.1 176.4
ECIT/ECIC (%) 21.4 68.1 135.8 144.4
CIT/CIC (Consumption Index); GR T/GRC (Growth Rate); ECIT/ECIC (Efficiency in the Consumption Index).For comparison purposes, rates of Nutritional Indices are expressed as a relationship between treatment and control.
more significant when the diet contained the bis THF ACG rolliniastatin-1 (3) and the mono THF, annonacin (5). This resulted in an important larval growth decrease and subsequent 100 and 70% larval mortality at very early stages in their life cycle, respectively (Table 4). The remaining compounds, 8 and 11, had no effect on the nutritional index values, despite causing a high mortality. Our results suggest that another reason why the ACG produced an insecticidal action would be that the destabilization that occurs in the membrane due to dehydration around the phosphate groups is caused by interaction with ACG and their synthetic analogues. Experimental Compounds: Laherradurin (1), squamocin (2), rolliniastatin-1 (3), asimicin (4), annonacin (5), and cis-annonacin-10-one (6) were exhaustively purified by RP-HPLC. ACG synthetic analogues, compounds 7, 8, 9, and 10 were prepared by iodoetherification of chiral 4-alkenols obtained in four steps from 3-bromo-3,5cyclohexadiene-1,2-diol. This chiral starting material was obtained by microbial dihydroxylation of bromobenzene [18]. Lipid sample preparation: POPC was purchased from Avanti Polar Lipids, Inc. (Birmingham, AL) and used without further purification. The lipid and samples at different molar ratios of ACG/POPC in chloroform solution were dried to form a film under a nitrogen stream. Lipids were rehydrated in deuterated water, heating above the phase transition temperature (Tm= -4ºC), and gently shaking for 15 min to produce multilamellar vesicles (MLVs). The final lipid concentration was 40 mg/mL. MLV samples with and without acetogenins were left at room temperature for 1 h before the measurements. DSC and FTIR measurements: DSC was carried out on a PerkinElmer DSC 6 with a nitrogen gas purge. Heating rates of 10°C/min were used. FTIR measurements were carried out in a Perkin Elmer GX1 spectrophotometer, provided with a DTGS detector. The resolution of the equipment employed was 1 cm-1. Acetogenin interaction with the phospholipid dispersed in D2O was studied employing a cell with AgCl windows assembled in a SPECAC variable temperature cell controlled by a EUROTHERM automatic temperature controller. The spectra were taken for POPC and different molar ratios of ACG/POPC bilayers in the liquid crystalline state (25°C). After a total of 1024 scans, the spectra were analyzed using the mathematical software provided by Perkin Elmer for FTIR equipment. The mean values of the main bands were obtained from a total of 3 different batches of samples. The standard deviation of the frequency shift calculated from a data pool was about ±1.5 in all the conditions assayed. D2O was used as a solvent to disperse the lipids in order to visualize the carbonyl region. The spectra of pure D2O were subtracted in all analyzed samples to avoid solvent interference with the phosphate group. In the subtracted spectra, D2O bands were absent and those corresponding to the antisymmetric stretching of the phosphate groups were centered in the region observed in solid POPC [7b, 15a, 19a,b]. The contours of C=O stretching bands were obtained by Fourier Self
4Natural Product Communications Vol. 7 (0) 2012
Deconvolution using band width parameters between 18 and 20 cm−1 and a band narrowing factor of 2, as defined by the GRAMS/32 Spectral Notebase mathematical software. Deconvolution was used to obtain the peak frequencies of the component bands reported for the 2 populations of carbonyls: the nonhydrated (centered at 1742.5 cm−1) and hydrated (centered at 1724.0 cm−1) populations in the gel state, and the non-hydrated (1737.0 cm−1) and hydrated (1722.0 cm−1) populations in the fluid state [7b, 15a, 19a,b]. The shifts of these 2 populations were studied as a function of acetogenin/lipid ratio of POPC in the liquid crystalline state. Test insects: S. frugiperda larvae were obtained from our laboratory population and maintained with an artificial diet. Toxicity tests were recorded for treatments with all compounds (100 ppm) and control
Author A et al.
experiments [20]. Determination of Consumption (CI), Growth (GR), and Efficiency in the Consumption Index (ECI) were carried out. Indices were calculated for the experiment and control treatments. For comparison purposes, rates are expressed as a relationship between treatment and control; the latter are considered 100%. Values are expressed as (GRT/GRC) 100%, (CIT/CIC) 100% and (ECIT /ECIC) 100% in the tables [20]. Acknowledgements – This work was supported by grants from the Agencia Nacional de Promoción Científica y Tecnológica (ANPCyT), Consejo de Investigaciones de la Universidad Nacional de Tucumán (CIUNT) and Concejo Nacional de Investigaciones Científicas y Técnicas (CONICET), República Argentina.
References [1]
[2] [3]
[4]
[5] [6]
[7]
[8] [9] [10] [11] [12] [13] [14] [15]
[16] [17] [18]
(a) Barrachina I, Neske A, Granell S, Bermejo A, Chahaboune N, El Aouad N, Álvarez Colom O, Bardón A, Zafra-Polo MC. (2004) Tucumanin, a β-hydroxy-γ-lactone bistetrahydrofuranic acetogenin from Annona cherimolia, potent inhibitor of mitochondrial complex I. Planta Medica,70, 866868; (b) Álvarez Colom O, Neske A, Chahaboune N, Zafra-Polo MC, Bardón A. (2009) Tucupentol, a novel mono-tetrahydrofuranic acetogenin from Annona montana, as a potent inhibitor of mitochondrial complex I. Chemistry & Biodiversity,6, 335-340. Guadaño A, Gutiérrez C, De la Peña E, Cortes D, González-Coloma A. (2000) Insecticidal and mutagenic evaluation of two annonaceous acetogenins. Journal of Natural Products,63, 773-776. (a) Álvarez Colom O, Neske A, Barrachina I, Ayala Mingol I, Moya Sanz P, Bardón A. (2008) Toxic effects of annonaceous acetogenins on Oncopeltus fasciatus. Journal of Pest Science,81, 85-89; (b) Álvarez Colom O, Salvatore A, Willink E, Ordóñez R, Isla MI, Neske A, Bardón A. (2010) Insecticidal, mutagenic and genotoxic evaluation of annonaceous acetogenins. Natural Product Communications,5, 391-394; (c) Di Toto Blessing L, Álvarez Colom O, Popich S, Neske A, Bardón A.(2010) Antifeedant and toxic effects of acetogenins from Annona montana on Spodoptera frugiperda. Journal of Pest Science,83, 307-310. (a) Shimada H, Kozlowski JF, McLaughlin JL. (1998) The localisations in liposomal membranes of the tetrahydrofuran ring moieties of the annonaceous acetogenins, annonacin and sylvaticin, as determined by 1HNMR spectroscopy. Pharmacological Research,37, 357-363; (b) Shimada H, Grutzner JB, Kozlowski JF, McLaughlin JL. (1998) Membrane conformation and their relation to cytotoxicity of asimicin and its analogues. Biochemistry,37, 854-866. Bombasaro JA, Di Toto Blessing L, Díaz S, Neske A, Suvire FD, Enriz RD, Rodríguez AM. (2011) Theoretical and experimental study of the interactions of annonaceous acetogenins with artificial lipid bilayers. Journal of Molecular Structure,1003, 87-91. (a) Rand RP, Parsegian VA. (1989) Hydration forces between phospholipid bilayers. Biochimica et Biophysica Acta,988, 351-376; (b) Disalvo EA, Lairion F, Martini F, Almaleck H, Díaz SB, Gordillo GJ. (2004) Water at biological interfaces: does it play a functional role? Journal Argentine Chemical Society,92, 1-22; (c) Volkov VV, Palmer, DJ, Righini R. (2007) Distinct water species confined at the interface of a phospholipid membrane. Physical Review Letters,99, 078302. (a) Díaz SB, Amalfa F, López de Biondi AC, Disalvo EA. (1999) Effect of water polarized at the carbonyl groups of phosphatidylcholines on the dipole potential of lipid bilayers. Langmuir,15, 5179-5182; (b) Hübner W, Blume A. (1998) Interactions at the lipid-water interface. Chemistry and Physics of Lipids,96, 99-123. Cortes D, Myint SH, Leboeuf M, Cave A. (1991) A new type of cytotoxic acetogenins: The tetrahydrofuranic β-hydroxy methyl γ-lactones. Tetrahedron Letters,32, 6133-6134. Fujimoto Y, Eguchi T, Kakinuma K, Ikekawa N, Sahai M, Gupta YK. (1988) Squamocin, a new cytotoxic bis-tetrahydrofuran containing acetogenin from Annona squamosa. Chemical and pharmaceutical bulletin,36, 4802-4806. Pettit GR, Cragg GM, Polonsky J.(1987) Isolation and structure of rolliniastatin-1 from the South American tree Rollinia mucosa. Canadian Journal of Chemistry,65, 1433-1435. Rupprecht JK, Chang CJ, Cassady JM, McLaughlin JL, Mikolajczak KL, Weisleder D, (1986) Asimicin, a new cytotoxic and pesticidal acetogenin from the pawpaw, Asimina triloba (Annonaceae). Heterocycles,24, 1197-1201. McCloud TG, Smith DL, Chang CJ, Cassady JM. (1987) Annonacin, a novel, biologically active polyketide from Annona densicoma. Experientia,43, 947-949. Rieser MJ, Gu Z, Fang XP, Zeng L, Word KV, McLaughlin JL. (1996) Five novel mono-tetrahydrofuran ring acetogenins from the seeds of Annona muricata. Journal of Natural Products,59, 100-108. Ramos JC, Bracco P, Mazzini M, Gamenara D, Brovetto M, Seoane G. (2010) XIV Semana Científica Antonio González. Universidad de la Laguna, Tenerife, España. (a) Pohle W, Selle C. (1996) Fourier-transform infrared spectroscopic evidence for a novel lyotropic phase transition occurring in dioleoylphosphatidylethanolamine. Chemistry and Physics of Lipids,82, 191-198; (b) Arrondo JLR, Goni FM, Macarulla JM. (1984). Infrared spectroscopy of phosphatidylcholines in aqueous suspension: a study of the phosphate group vibrations. Biochimica et Biophysica Acta,794, 165168; (c) Jendrasiak GL, Smith RL. (2001) The effect of the choline head group on phospholipid hydration. Chemistry and Physics of Lipids,113, 55-66; (d) Lewis RNAH, McElhaney RN. (1998) The structure and organization of phospholipid bilayers as revealed by infrared spectroscopy. Chemistry and Physics of Lipids,96, 9-21; (e) Luzardo MC, Amalfa F, Núñez A, Díaz SB, Biondi de Lopez AC, Disalvo EA. (2000) Effect of trehalose and sucrose on the hydration and dipole potential of lipid bilayers. Biophysical Journal,78, 2452-2458. Popova AV, Hincha DK. (2003) Intermolecular interactions in dry and rehydrated pure and mixed bilayers of phosphatidylcholine and digalactosyldiacylglycerol: a Fourier-transform infrared spectroscopy study. Biophysical Journal,85, 1682-1690. Álvarez Colom O, Neske A, Popich S, Bardón A. (2007) Toxic effects of annonaceous acetogenins from Annona cherimolia (Magnoliales: Annonaceae) on Spodoptera frugiperda. Journal of Pest Science,80, 63-67. Brovetto M, Schapiro V, Cavalli G, Padilla P, Sierra A, Seoane G, Suescum L, Mariezcurrena R. (1999) Osmylation of chiral ciscyclohexadienediols. New Journal of Chemistry,23, 549-556.
Running title here
[19]
[20]
Natural Product Communications Vol. 7 (0) 20125
(a) Díaz SB. (2001) Acción de lisoderivados sobre membranas lipídicas en presencia de azúcares absorbidos en la interfaz. Ph.D. Thesis, Universidad Nacional de Tucumán, Argentina; (b) Mantsch HH, McElhaney RN. (1991) Phospholipids phase transitions in model and biological membranes as studied by infrared spectroscopy. Chemistry and Physics of Lipids,57, 213-226. Villafañe E, Tolosa D, Bardón A, Neske A. (2011) Toxic effects of Citrus aurantium and C. lemon essential oils on Spodoptera frugiperda (Lepidoptera: Noctuidae). Natural Product Communications,6, 1389-1392.
