Syntheses of racemic and non-racemic silicon- and germanium-containing α-amino acids of the formula type H2NCH(CH2ElR3)COOH (El=Si, Ge; R=organyl) and incorporation of d-H2NCH(CH2SiMe3)COOH and d-H2NCH(CH2GeMe3)COOH into biologically active decapeptides: a study on C/Si/Ge bioisosterism
摘要:
Two novel efficient methods for the synthesis of racemic silicon- and germanium-containing a-amino acids of the formula type rac-H2NCH(CH2EIR3)COOH (El = Si, Ge; R = organyl), starting from 3,6-diethoxy-2,5-dihydropyrazine, have been developed. Racemic cc-amino acids synthesized: rac-H2NCH(CH2SiMe3)COOH (rac-2), rac-H2NCH(CH2GeMe3)COOH (rac-3), rac-H2NCH(CH2SiMe2Ph)COOH (rac-4), rac-H2NCH(CH2GeMe2Ph)COOH (rac-5), and rac-H2NCH(CH2SiMe2CH=CH2)COOH (rac-6). Preparative liquid-chromatographic resolution of rac-2 and rac-3 [CHIROBIOTIC T (glycopeptide Teicoplanin covalently linked to spherical silica gel) as the stationary phase] yielded the alpha -amino acids (R)-2, (S)-2, (R)-3, and (S)-3. The (R)- and (S)-enantiomers of beta-(trimethylsilyl)alanine [(R)- and (S)-2] and beta-(trimethylgermyl)alanine I(R)- and (S)-3] are sila-analogs and germa-analogs, respectively, of the antipodes of the non-proteinogenic alpha -amino acid beta -tert-butylalanine [(S)- and (R)-H2NCH(CH2CMe3)COOH; (S)- and (R)-1]. Starting from the N-Fmoc-protected C/Si/Ge-analogous (D-configurated) alpha -amino acids (R)-1, (S)-2, and (S)-3, the C/Si/Ge-analogous decapeptides 7-9 [Ac-D-Nal(1)-4-Cl-D-Phe(2)-D-Pal(3)-Ser(4)-N-Me-Tyr(5)-D-Hci(6)- Nle(7)-Arg(8)-Pro(9)-D-Me(3)El-Ala(10)-NH2 (7, El = C; 8, El = Si; 9, El = Ge)] were prepared by sequential solid-phase synthesis. The decapeptides 7-9 were studied in vitro in a functional assay using a recombinant cell line expressing the human GnRH receptor (agonist Triptorelin). Compounds 7-9 behaved as medium-potent GnRH antagonists, the antagonistic potencies of these three C/Si/Ge analogs being very similar. (C) 2001 Elsevier Science B.V. All rights reserved.
of β-silyl α-amino acids is reported via the application of visible-light-mediated hydrosilylation. The reaction utilizes readily accessible and structurally diverse hydrosilanes to provide radicals for conjugate addition to dehydroalanine ester and analogues. Notably, the use of chiral methyleneoxazolidinone as the substrate and chiral inducer enabled the highly stereoselective synthesis. Furthermore