Dihydropyridine Derivatives as Bioprotectors - Teknoscienze

Gunars Duburs

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Medicinal chemistry

GUNARS DUBURS BRIGITA VIGANTE AIVA PLOTNIECE AIVARS KRAUZE ARKADIJS SOBOLEVS JANINA BRIEDE VIJA KLUSA ASTRIDA VELENA

Dihydropyridine derivatives as bioprotectors ABSTRACT Depending on the chemical structure peculiarities 1,4dihydropyridines possess electron/hydrogen donor, peptide type and lipid-like characteristics and many regulatory activities: neuro- and radio- protection, anti-mutagenic, antidiabetic, anti-inflammatory, anti-ischaemic/anti-anginal and anti-hypertensive actions, as well as growth stimulating and gene transfection properties. These effects appear mostly in low concentrations/doses and show a long-term manifestation. Green chemistry approaches and chemoenzymatic transformations have been used for synthesis of novel bioprotective compounds. This mini-review comprises mainly the data obtained at the Latvian Institute of Organic Synthesis. INTRODUCTION 1,4-Dihydropyridines (1,4-DHPs) 1 can be attributed to specific types of compounds both from a chemical and a pharmacological (medicinal) point of view. Appropriately decorated with substituents, 1,4-DHPs can be regarded as biomimetics, they may possess bioprotective activities. They can undergo conversion to heteroaromatic forms 2 by splitting off electrons and hydrogen, thus interfering with free radical processes. β-Carbonyl-1,4-DHPs mimic redox coenzymes; β- (or γ-)-carbonyl-1,4-DHPs comprise structural elements of amino acids (they can be regarded as cyclic unsaturated amino acids); 1,4-DHPs can also serve as templates for construction of lipid-type compounds. ANTI-OXIDANT, ANTI-MUTAGENIC, RADIOPROTECTIVE, AND GROWTH STIMULANT PROPERTIES 1,4-DHPs are regarded as model compounds of redoxcoenzymes NAD(P)H and analogues of 1,4-dihydronicotinamide. Depending on their structure, 1,4-DHPs possess anti-oxidant, radical scavenging properties, and they quench reactive oxygen species (1-3). In case of 3,5-dialkoxycarbonyl derivatives of 1,4-DHP (compound 1, X,Y=OAlk) 4-unsubstituted derivatives have the highest anti-oxidant activities (AOA). In case of less effective electron withdrawing substituents (3,5-dicarbamoyl) also substituted in position 4 1,4-DHPs have AOA (4, 5). Accordingly, several 1,4-DHP derivatives are modifiers of free radical processes, protectors and stabilizers of model membranes, such as phosphatidylcholine (lecithin) liposomes (4), biological membranes (5-8). 2,6-Dimethyl-3,5-diethoxycarbonyl-1,4-dihydropyridine reveals synergism with a-tocopherol and some amino acids and peptides (9).

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Several compounds of the 1,4-DHP series have been shown to reduce spontaneous, alkylation- and radiation-induced mutation rates in animal test systems (10, 11). A derivative of 1,4-dihydroisonicotinic acid, AV-153 (sodium 2,6-dimethyl3,5-diethoxycarbonyl-1,4-dihydropyridine-4-carboxylate 1, R=CO2Na, R’=R’’=Me, X=Y=OEt) has dual bioprotective properties: at higher concentrations it has anti-oxidant properties (12), at lower concentrations (even at 0.01 nM) it has anti-mutagenic properties (13). Alkaline single-cell gel electrophoresis (Comet) assays shows that the 1,4dihydroisonicotinic acid derivative reduces the number of DNA breaks in untreated cells and also in cells exposed to gamma-radiation, ethyl methanesulfonate (EMS), or H2O2. Comparison of the kinetics of DNA strand-break rejoining in the presence and absence of the compound reveals a considerable influence on the rate of repair. 2,6-Dimethyl-3,5-diethoxycarbonyl-1,4-DHP (Hantzsch ester) 1 (R=H, R’=R’’=Me, X=Y=Et) possesses anti-oxidant and antimutagenic activities, radioprotector and skin protector properties (14). It has extremely low toxicity (LD50 > 30 000 mg/kg p/o for mice). It stimulates growth, reproduction and productivity of pigs, cows, chicken, turkeys, minks, fish, turtles, etc. (15-17), prolongs mean life span of Drosophila melanogaster and mice (18). PEPTIDE TYPE ACTIVITIES: NEUROPROTECTIVE, ANTI-INFLAMMATORY, ANTI-DIABETIC Discovery of anti-hypertensive and anti-anginal activities, calcium antagonists and agonist properties of 4-aryl-1,4DHPs stimulated search, elaboration, development and marketing of several well-known cardiovascular drugs (19, 20). Further extensive synthesis, studies of mechanism, elaboration of the second and the third generations of calcium antagonists, broadening of pharmacological studies resulted in discovery of novel biological properties of substances, connected or not connected with calcium ion transport (e.g., effect on T-, Ncalcium channels, potassium channels, adenozine and adrenoreceptors, NO synthesis, COX activity etc.) (19-24). In line with above mentioned, studies of several 4-aryl-1,4DHPs (e.g., compound 3) and of a novel group of compounds (N-(1,4-dihydroisonicotinoyl)amino acid derivatives 4) have

chimica oggi • Chemistry Today • vol 26 n 2 / March-April 2008

Compound 3 induced a long-term activation of memory processes in CAR (conditioned avoidance response) test at a dose range of 0.005 – 0.5 mg/kg even on the 20th day of extinction period. Compound 3 prevented alterations in CNS function observed in various neurodeficit models: it normalized offspring developmental disturbances at paternal and maternal alcoholization (27, 28). In 1-methyl-4-phenylpyridinium (MPP+) neurotoxicity model in cerebellar granule cells, compound 3 showed neuroprotective properties by complete prevention of cell death, free radical production and drop in mitochondrial membrane potential, indicating the compound’s ability of targeting the mitochondrial complex (29). It showed also significant psychogeritropic activity in different aging models: in normally aged mice; in mice accelerated aging model induced by 5-month exposure to ethanol overdosage; in rats exposed for 3 months to food enriched with cholesterol (30). The action of compound 3 resembles that of neuropeptides capable of normalizing disregulated states: in the stress model it demonstrated anti-stress effects (31); in the convulsion models – anti-convulsant effect (32); in the depression model – anti-depressant activity (33); in disbalanced feeding – anorexic effect (34). Compound 3 administered prior to occlusion of both common carotid arteries completely prevented a fall in the ATP content in brain (35), produced a regular α-rhythm during ischemia and prevented cerebral bioelectric activity from significant changes. It was recently revealed that some 1,4-DHP derivatives such as cardiovascular drugs amlodipine (36), benidipine (37), felodipine (38) and compound 3 (39, 40) showed antiinflammatory properties. Amlodipine inhibited IL-1α release (36), compound 3 showed an anti-inflammatory effect by reducing inflammation in the rat paw edema model, and inhibiting secretion of neurotoxic cytokines interleukines IL1β and IL-6 in human monocyte (THP-1) cell line (39). Therefore the neuroprotective ability of compound 3 can be attributed to a great extent to its anti-inflammatory effects.

Benidipine (37) inhibited expression of iNOS and NO production, felodipine (38) diminished superoxide expression evoked by cytokines and high glucose and nifedipine decreased factor NF-κB activity (41). Immunomodulatory mechanisms of different 1,4-DHP derivatives may be beneficial for insulin-dependent diabetes mellitus (IDDM) and non-insulin-dependent diabetes mellitus (NIDDM) patients. IDDM is an autoimmune disease characterised by selective destruction of insulin-secreting pancreatic islets βcells. The formation of cytokines (IL-1β, IL-6, TNF-α, etc.) leads to extensive morphological damage of β-cells, DNA fragmentation, formation of anti-bodies against insulin and its receptors etc. Diabetes mellitus is accompanied by hyperglycaemia and hyperlipidaemia, arising from cardiovascular complications. Compound 3 protects the immune system in STZ-induced diabetic rats from STZ toxicity, preventing thymus and lymph node mass loss (40), as well as pancreatic beta cells damage (42). Compound 3 stimulates the process of rat spleen lymphocyte proliferation and DNA synthesis in the presence of ConA, IL-2, insulin and promotes formation of insulin and IL-2 receptors on their membrane surface. Compound 3 protects the organism against the overproduction of insulin and its receptor anti-bodies, which could play an important role in the treatment of diabetes mellitus (43). Compound 3 has long-lasting effects (up to 2 weeks) on glucose metabolism in STZ-induced diabetic rats. It decreases significantly plasma glucose levels and the insulin level in plasma is maintained until the 21st diabetic day (42). Compound 3 promotes glucose uptake in brain, transport of glucose in isolated human erythrocytes (44), as well as enhances glucose uptake in isolated rat hearts and significantly increases production of ATP in the myocardium (45). The compound normalizes the plasma lipid profile and inhibits release of 3 H-arachidonic acid from platelet plasma membrane phospholipids (46). Compound 3 acts through both pancreatic (prevention of STZ toxicity and evoked mobilization of insulin from pancreatic beta cells) and extrapancreatic mechanisms. The mentioned compound administered prior to occlusion of both common carotid arteries completely prevents a fall in the ATP content in brain, produces a regular alpha rhythm during ischaemia and prevents cerebral bioelectric activity from significant changes (33). By immunomodulating, hypoglycaemic and hypolipidaemic actions, on the one hand, and cardioprotective activity by protecting heart and brain from ischaemic damage, on the other hand, the compound may be useful for the treatment of diabetes. Changes of mitochondrial bioenergetics induced by compound 3 (e.g., alterations on membrane lipid organization, inhibition of the inner mitochondrial anion channel, prevention of the Ca2+induced opening of the mitochondrial membrane permeability transition pore and permeabilization of the mitochondrial inner membrane to Cl– in association with H+) can be considered as beneficial for the treatment of several mitochondrial diseases, such as neurodegeneration and diabetes (26). N-(Dihydroisonicotinoyl)amino acid derivatives 4 comprise two amino acid moieties. They are isosteric to appropriate dipeptides and possess several peptidomimetic properties. They demonstrate neuroprotection in oxygen-glucose deprivation (ischemia) and glutamate models. Compounds 3 and 4d showed neurotrophic activity, since they stimulated neurite outgrowth in immature cerebellar granule cells (47). Compound 4c (possessing dipeptide mimicking structure) revealed intensification of intracellular processes and long-lasting enhancing of brain functions (47). The DHP molecule is capable of exerting peptide-like regulatory activity resulting in longlasting improvement of CNS function. Compounds 3, 4b demonstrated common anti-neurodeficiency activities in in vivo models (48). Compound 4b was capable of protecting


Medicinal chemistry

been performed. They possess significant and broad spectrum of protective properties (neuroprotective, memory enhancing, anti-ischemic, cardioprotective, anti-diabetic, anti-inflammatory), and peptide-like long-lasting activities at low concentrations and doses. 2-Propoxyethyl ester of 4-(2-difluoromethoxyphenyl)-2,6dimethyl-1,4-dihydropyridine-3,5-dicarboxylic acid (compound 3, cerebrocrast) differs from the typical calcium antagonistic drugs of the 1,4-DHP series. It has no calcium antagonistic properties in neuronal tissues (25). It has high lipophilicity and membranotropic properties that may favour its broad spectrum of pharmacological activities. In its structure, the so-called “crypto” amino acid moieties (β-alanine, NMDA), included in the cyclic unsaturated system, and the dihydronicotinamide residue, which forms the DHP skeleton, are considered substantial for defining this molecule as a peptidomimetic one. Possibly, these structural peculiarities have an important impact in providing the neuropeptidelike properties of compound 3, such as neuromodulatory, neuroregulatory action, that manifest at low doses (25, 26).

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REFERENCES AND NOTES 1. 2. 3. 4. 5.

The same types of compounds (1,4-DHPs) were used as templates to obtain amphiphilic cations (5 and 6) possessing liposome-forming properties. DHP derivatives comprising suitable alkyl chains and pyridinium cations possess gene transfection activity. 1,4-DHP moiety is an active linker in this case. The impressive increase of the DHP cycle N-H acidity (up to pKa ~7-8) is the basis for its buffering activity in these novel types of gene transfection agents. In like manner another putative approach to bioprotection (e.g., cardioprotection, neuroprotection) could be realized (53).

6. 7.

8. 9. 10. 11. 12. 13. 14. 15. 16.

Synthesis of DHP derivatives has been performed by means of a green chemistry approach – low toxicity starting compounds and solvents were used, separation of lacrimators was avoided. Such approach is in line with the same principles of bioprotection – very careful attention to environment (54). Green chemistry is based on a number of principles (54) that ensure that both processes and end products are clean and safe. It aims to conserve both energy and raw materials and make chemical processes cheaper than by applying conventional methods. One of the basic ideas of green chemistry is to prevent the production of hazardous and polluting materials rather than producing them and then cleaning up. Another key idea of green chemistry is atom economy. This considers how much of the reactants in a chemical reaction end up in the final useful products. Efficient cyclocondensations carried out as one-pot four component synthesis under mild reaction conditions for preparation of biologically active 2-carbamoylmethylthio1,4-dihydropyridines 7 have been achieved. They were designed by making use of the principles of green chemistry: some unpleasant toxic intermediates – 2-arylmethylene-1,3dicarbonylderivatives were prepared in situ; the economy of solvent, time and energy was reached; piperidine as catalyst was substituted with ammonium hydroxide, iodoacetamide with much cheaper chloroacetamide, and alcohols with water, which resulted in environmentally friendly reaction by-product – ammonium chloride and more than 22 percent atom economy (55). Above-mentioned approach is characteristic for contemporary chemistry (56, 57). These data support the opinion that 1,4-DHPs are privileged structures (58), since they have an ability of demonstrating broad spectrum of activities characteristic for biomimetics and bioprotectors. It is increasingly clear that the 1,4dihydropyridine structure is a pharmacophoric template or “privileged structure” that, when appropriately substituted, can exert potent and selective actions at a diverse set of membrane structures, including ion channels, G-protein

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17. 18. 19. 20. 21. 22. 23. 24. 25. 26.

27. 28. 29. 30.

Readers interested in having a list complete of references are kindly invited to write to the author at [email protected]

GUNARS DUBURS1*, BRIGITA VIGANTE1, AIVA PLOTNIECE1, AIVARS KRAUZE1, ARKADIJS SOBOLEVS1, JANINA BRIEDE1, VIJA KLUSA2, ASTRIDA VELENA1 ˆ

GENE TRANSFECTION AGENTS AND ELABORATION OF GREEN CHEMISTRY PROBLEMS ON THE BASIS OF 1,4-DHPS

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Medicinal chemistry

coupled receptors and enzymes. Thus these compounds could be joined to the multifactorial and polyvalent acting pleyotropic agents.

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the oxygen-glucose deprivation induced cell damage in cerebellar granule cell culture, and of protecting against cell death in the glutamate-toxicity model. Compound 4b was highly active in the protection of glutamate-induced free radical production (48, 49). Radical scavenging, inhibition of lipid peroxidation have been observed also in case of amlodipine, nisoldipine, BAYK 8644 a.o. DHP derivatives (50-52).

*Corresponding author 1. Latvian Institute of Organic Synthesis Aizkraukles 21 Riga LV 1006, Latvia 2. University of Latvia 1A Sarlotes Str. Riga LV-1001, Latvia
