A PHOTOCHEMICAL ROUTE TO VINYLGLYCINE AND A VINYLGLYCINE DIPEPTIDE

Enantiomerically pure vinylglycine (4b) can be prepared from natural ( ''chiral pool'') amino acids by photoelimination of gamma-functionaliz ed N-phthaloyl amino acid esters. Two routes have been developed: (a) a three-step synthesis of substrate 3b [PhtN-Met(SO)OMe] from (S)-meth ionine and subsequent photolysis, (b) the use of N-phthaloyl activated methyl 2-amino-4-chloro- or -4-bromobutanoates 3d, e which are availa ble from (S)-methionine (four-step synthesis) or from (S)-homoserine ( two-step synthesis). The photoelimination (of HOSMe from 3b and of HX from 3d, e) proceeds quantitatively and leads to N,C-protected vinylgl ycine 4a in high yields. This strategy could also be applied to peptid e-bound substrates as was shown for the protected Met-Gly (5b) which w as transformed into the N-protected vinylglycine-glycine dipeptide 6 i n three steps.