Syntheses of monofunctional porphyrinyl peptides containing glycine and leucine

Abstract

4,6,8-Triethyl-2-(2-methoxycarbonylethyl)-1,3,5,7-tetramethylporphyrin is synthesised using the a,c-biladiene route. Activated derivatives of the corresponding porphyrin free carboxylic acid were coupled with glycine ethyl ester, and the resulting porphyrinyl-glycine ester was hydrolysed and coupled with L-leucine methyl ester to give a porphyrinyl dipeptide; an isomer of this dipeptide was prepared by direct coupling of the activated porphyrin with L-leucyl-glycine methyl ester. A porphyrinyl tripeptide was also prepared in low yield by coupling the porphyrinyl-glycine with L-leucyl-glycine methyl ester. Attempts to synthesise porphyrinyl peptides containing unprotected histidine (which would have yielded haem protein models) were largely unsuccessful. Mass-spectral fragmentation patterns for the synthetic porphyrinyl peptides are reported.