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Paper | Regular issue | Vol 71, No. 9, 2007, pp.1929-1949
Published online, 8th June, 2007
DOI: 10.3987/COM-07-11077
Conversion of Bacteriochlorophyll-A to Bacteriopurpurin-18: A Useful Synthon for the Construction of Bioactive Agents for Photodynamic Therapy (PDT)

Lalit N. Goswami, Yihui Chen, Joseph Missert, Guolin Li, Alex Pallenberg, and Ravindra K. Pandey*

*Medicinal Chemistry Division, Photodynamic Therapy Center, Roswell Park Cancer Institute, Buffalo, NY 14263, USA

Abstract

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.