[The study of biologically active conformation of cholecystokinin-4 dipeptide analog GB-115].

The conformational analysis with 1H NMR spectroscopy method in solution and the structure-activity relationship study of a series sterically restricted analogs allowed to detect the possible biologically active conformation of N-(6-phenylhexanoyl)glycyl-tryptophan amide (GB-115), a highly active dipeptide cholecystokinin-4 analog with anxiolytic activity. The structure-activity relationship study of GB-115 and the series of its' glycine- and proline-containing analogs with different C-terminal substitute detected the anxiolytic activity of compounds with beta-turn like conformation and inactivity of compounds with gamma-turn like conformation. So, the GB-115 biologically active conformation is beta-turn. The results of nuclear Overhauser effect study permitted to qualify the betaII-turn conformation as GB-115 biologically active conformation. The following synthesis of sterically restricted GB-115 analogs (2S)-2-{(3R)-3-[(6-phenylhexanoyl)amino]-2-oxopyrrolidin-1-yl}-3-(1H-indol-3-yl)propionic acid ethyl ester, N-(6-phenylhexanoyl)glycyl-N(alpha)(methyl)-tryptophan ethyl ester, (2S)-2-[10,11-dihydro-5H-dibenzo[b,f] azepin-5-carbonyl)-amino]-3-(1H-indol-3-yl)propionic acid methyl ester and (2S)-2-[({3-[(ethoxycarbonyl)amino]-10,11-dihydro-5H-dibenzo[b,f]azepin-5-yl}carbonyl)amino]-3-(1H-indol-3-yl)propionic acid methyl ester confirmed the estimated type of GB-115 biologically active conformation.

[Synthesis of cyclic analogues of the nerve growth factor loop 4].

Cyclic peptides cyclo(-Gly-Asp-Glu-Lys-), cyclo(-Gly-Gly-Asp-Glu-Lys-) and cyclo(-Gly-Gly-Gly-Asp-Glu-Lys-) were synthesized as models of the beta-turn of nerve growth factor loop 4. The corresponding protected linear precursors were obtained in 52-83% yields by the solid-phase method with the use of the Fmoc/Bu(t) strategy and a chlorotrityl anchor group. The cyclization was carried out with benzotriazolyloxy-tris(dimethylamino)phosphonium (BOP) hexafluorophosphate, N-[(1H-benzotriazole-1-yl)-(dimethylamino)methylene]-N-methylmetanaminium-N-oxide (HBTU) hexafluorophosphate, and diphenylphosphorylazide (DPPA) at a dilution of 10(-3) M. The distribution of reaction products was studied for each cyclopeptide in dependence on the type of the coupling agent. The use of DPPA was shown to completely inhibit the formation of cyclodimers in the synthesis of five- and six-membered cyclopeptides; however, in the case of a four-membered peptide, an additional tenfold dilution of the reaction mixture was necessary to achieve the effect. The identification of several byproducts during the synthesis showed that the elongation of the polypeptide chain using the BOP reagent can be complicated by substantial racemization and the cleavage of the chlorotrityl anchor group by 0.5% TFA in dichloromethane proceeds with insufficient selectivity and is accompanied by the premature Boc deblocking of the lysine side function.