Stereoselective Synthesis of [l-Arg-l/d-3-(2-naphthyl)alanine]-Type (E)-Alkene Dipeptide Isosteres and Its Application to the Synthesis and Biological Evaluation of Pseudopeptide Analogues of the CXCR4 Antagonist FC131

Abstract

L,L-Type and L,D-type (E)-alkene dipeptide isosteres (EADIs) that have unnatural side chains at the alpha-position were synthesized by the combination of stereoselective aziridinyl ring-opening reactions and organozinc-copper-mediated anti-S(N)2' reactions toward a single substrate of gamma,delta-cis-gamma,delta-epimino (E)-alpha,beta-enoate. The utility of this methodology was demonstrated by the stereoselective synthesis of a set of diastereomeric EADIs of L-Arg-L/D-3-(2-naphthyl)alanine (Nal) that is contained in a small CXCR4 antagonist FC131 [cyclo(-D-Tyr-Arg-Arg-Nal-Gly-)]. Furthermore, a (Nal-Gly)-type EADI was synthesized by samarium diiodide (SmI(2))-induced reduction of a gamma-acetoxy-alpha,beta-enoate. Several FC131 analogues, in which these EADIs were inserted for reduction of their peptide character, were synthesized with analogues containing reduced amide-type dipeptide isosteres to investigate the importance of these amide bonds for anti-HIV and CXCR4-antagonistic activity.