PREPARATION OF INTERMEDIATES FOR COPROPORPHYRIN SYNTHESIS

The synthesis of dipyrrylmethanes necessary for the synthesis of coproporphyrins I-IV (1-4) is described. The synthesis of the former was designed so as to avoid isomeric mixtures to obtain pure samples of the latter. The asymmetric dibenzyl-3,4''-bis(.beta.-ethoxycarbonylethyl)-4,3''-dimethyl-5,5''-dipyrrylmethane and the symmetric dibenzyl 3,3''-dimethyl-4,4''-bis(.beta.-ethoxycarbonylethyl)-5,5''-dipyrrylmethanedicarboxylate were obtained. Hydrogenolysis of the dibenzyloxycarbonyl groups and condensation of the 5,5''-dicarboxydipyrrylmethanes with a 5,5''-diformyldipyrrylmethane gave coproporphyrins III and IV. Conversion of tert-butyl 3,4''-dimethyl-4,3''-bis(.beta.-ethoxycarbonylethyl)-5''-(benzyloxycarbonyl)-5-dipyrrylmethanecarboxylate into a (tert-butyloxycarbonyl)-5''-formyldipyrrylmethane was followed by treatment of the latter with HBr. By a self-condensation of the resulting product, coproporphyrin I was obtained in good yield.