CONVERSION OF BACTERIOCHLOROPHYLL-A TO BACTERIOPURPURIN-18:A USEFUL SYNTHON FOR THE CONSTRUCTION OF BIOACTIVE AGENTS FOR PHOTODYNAMIC THERAPY (PDT)

摘要

Bacteriochlorophyll-a 5 present in Rb.sphaeroides was converted into bacteriopurpurin-18 methyl ester 10 by following three different approaches and was used as a substrate for the preparation of a series of stable bacteriochlorins with long wavelength absorptions ranging from 760 to 824 nm.Bacteriopurpurin p6 17,obtained by the base hydrolysis of 10,on reacting with L-aspartyl-di-tert-butyl ester in presence of EDCI and DMAP afforded the corresponding N-aspartyl-bacteriopurpurinimide 21 in high yield,possibly by the base-catalyzed intramolecular cyclization via the isoimide intermediate(s) 19 and 20.A possible mechanism for the formation of 10 and bacteriochlorin 15-glyoxilic acid trimethyl ester 8 from 5 via hydroxylactone 11 is also discussed.Among the compounds synthesized,the bacteriochlorin 21 containing a fused cyclic imide ring system was found to be the most stable in various solvents at room temperature and exhibited the longest wavelength absorption at 824 nm in dichloromethane.