Studies on amino acids and peptides XII1: Synthesis of thiated analogues of Boc-S-Ala-Aib-S-Ala-OMe and Ac-S-Ala-Aib-S-Ala-OMe

Add time:09/08/2019    Source:sciencedirect.com

The two model peptides Boc-S-Ala-Aib-S-Ala-OMe (1a) and Ac-S-Ala-Aib-S-Ala-OMe (1b) and their monothiated analogues Boc-S(R)-AlaΨ(CSNH)-Aib-S-Ala-OMe (3a), Boc-S-Ala-AibΨ(CSNH)-S-Ala-OMe (4a), AcΨ(CSNH)-S-Ala-Aib-S-Ala-OMe (2b), Ac-S-Ala-AibΨ(CSNH)-S-Ala-OMe (4b),and the dithiated Boc-S-AlaΨ(CSNH)-AibΨ(CSNH)-S-Ala-OMe (5a) are synthesized. Peptide 3a was obtained from the coupling of HCl·H-S-Ala-OMe to 5-2-(1-(tert-butoxycarbonyl-amino) ethyl-4,4-dimethyl-1,3-thiazol-5(4H)-one (11). The thioamide analogues 4a (together with 5a) and 2b were obtained by regioselective thiation of the respective model peptides 1a and 1b using 2,4-bis(4-methylphenyl)-1,3,2,4-dithiadiphosphetane 2,4-disulfide, Lawesson's Reagent (LR). Deprotection of the Boc group of 4a followed by acetylation of the product, afforded 4b. The magnetic nonequivalence of the gem-methyl groups of Aib is discussed.

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