Edith Tot

CoMFA, CoMSIA and GRID/GOLPE studies on calcium entry blocking 1,4-dihydropyridines

Three different 3D QSAR methods have been applied for a common pharmacophore model of 45 calcium antagonistically active 1,4-dihydropyridines (DHP) in order to find best correlation of interaction fields and biological activity. Analysis for the entire data set yielded r2/q values in a range starting from 0.821/0.620 (GRID/GOLPE) over 0.872/0.600 (CoMFA) to 0.908/0.744 (CoMSIA). The robustness of these models was tested not only via leave-one-out but also by leave-9-out crossvalidations. Furthermore, models were constructed using a subset of 37 DHPs (training set) allowing the prediction of activity for the residual 8 DHPs (test set). The training set yielded r2/q values starting from 0.826/0.672 (GRID/GOLPE) over 0.872/0.540 (CoMFA) to 0.899/0.662 (CoMSIA). For the test set r values from 0.677 (GRID/GOLPE) over 0.639 (CoMFA) to 0.470 (CoMSIA) were calculated. Besides the statistics, each 3D QSAR model yields further information by analysis of the generated contour maps. Consideration of the CoMFA and CoMSIA fields indicates unfavourable steric interactions for bulky moieties in 4′-position. On the other hand, sterical demanding 2′- and 3′-substituents are favourable and the biological activity of DHPs is further increased if these moieties produce a negative electrostatic potential. In contrast, high π-electron density on top of and parallel to the 4-phenyl ring beside the 2′-position is associated with decreasing activity. This could point to repulsive electronic interactions with binding site residues or to the potential of electron-deficient 4-aryl moieties to behave as electron acceptors in a charge transfer (CT) mechanism.

Pharmacophore modelling of structurally unusual diltiazem mimics at L-type calcium channels.

The purpose of this theoretical study was to investigate the molecular features of some structurally unusual calcium antagonists with experimentally proved affinity to the diltiazem-binding site at L-type calcium channels. Therefore, sterical and electronic characteristics of cis-/trans-diclofurime, the verapamil-like derivatives McN-5691 and McN-6186 as well as the natural products papaverine, laudanosine, antioquine and tetrandrine were compared with the pharmacophoric requirements detected for classical diltiazem-like derivatives. This yielded a common pharmacophore model for all of these compounds. Based on this model, one single negative molecular electrostatic potential induced by the free electron pairs of the oxime oxygen of trans-diclofurime was detected that might be responsible for the stronger effects compared to the cis isomer. Furthermore, the dual diltiazem- and verapamil-like features of McN-5691 (and McN-6186) as well as the distinct pharmacophoric assignment of the laudanosine enantiomers may be interpreted on a molecular level. Finally, the crucial partial structure of the bis-benzylisoquinoline derivatives antioquine and tetrandrine being responsible for the calcium antagonistic effects could be revealed by superposition on the most active benzothiazepinone derivative 8-methoxydiltiazem. The results obtained for these unusual diltiazem mimics are discussed taking into consideration earlier findings for classical diltiazem-like derivatives.

Reaktionen vinyloger Hydrazide mit Carbiminium-Verbindungen / Reactions of Vinylogous Hydrazides with Carbiminium Compounds

Vinylogous hydrazides of type 1 react with methyleniminium salts only in 2-position to form aminomethylated compounds 2·HX. The oxidation of 1 with Hg(II)-EDTA results in a twofold dehydrogenation to the lactams 3, which may be aminomethylated in 2-position. The methylpiperidine derivatives 4 and 5 with Hg(II)-EDTA yield in a monodehydrogenation cyclic iminium compounds. These are isolated as 6 · ClO4 and 7 · ClO4 respectively, and show an enolimine structure, which is not accessible to intramolecular aminoalkylation. With the 2-methylsubstituted enhydrazinones 11 methyleniminium salts cause an attack at 4-position, vinylogous to the carbonyl function, and produce the aminomethylated derivatives 13. Oxidation of 11 gives rise to the lactams 12, which are inert to Mannich reagents. The Mannich bases 2 undergo an amine elimination to form the pyrazolinium betaines 15. The aminomethylated lactams 20 show, in addition to amine eliminations, retro Mannich reactions and from the cleavage products methylenebis(lactam-enhydrazinones) 21 result. Formaldehyde and primary amines generate with 1 and 3 the tetrahydropyrimidine derivatives 24/25 and 22/23, respectively. Hexahydroacridinediones 27 are obtained from the reaction of 21 with formaldehyde and acetic acid.

Darstellung von 2,3,8-substituierten Perhydrooxazolo[3,2-a]pyridinen und die Kristallstruktur von (E)-3-(2-Fluorbenzyliden)-1-[1,2-bis(2-fluorphenyl)- 2-hydroxyethyl]-3,4,5,6-tetrahydropyridiniumchlorid

2-Fluorobenzaldehyde (1) and pipecolic acid (7) react in dimethyl sulfoxide with potassium carbonate to form benzylidene-oxaindolizidines 4. These diastereomers yield with acids uniform salts, so from 4 with hydrogen chloride results (E)-3-(2-fluorobenzylidene)-1-[1,2-bis(2-fluorophenyl)-2- hydroxyethyl]-3,4,5,6-tetrahydropyridinium chloride (6·Cl), elucidated by X-ray structural analysis. Treatment of 6·Cl with alkali hydroxide regenerates 4. Similarly proline (13), when treated with two equivalents of 1, gives rise to oxapyrrolizidines 14. From 14 in presence of 1 the perchlorate of the benzylidene derivative 15·ClO4 can be obtained which is transformed to benzylideneoxapyrrolizidines 15 by bases.