| Popis: |
2-Ethyl-2-devinylprotoporphyrin-IX dimethyl ester has been synthesised by the a-oxobilane route, the 4-vinyl group being introduced by a new method, viz. transformation of a β-acetoxyethyl side-chain present in one of the intermediate pyrroles. Protoporphyrin-IX dimethyl ester has also been prepared by both the a- and b-oxobilane routes, again with β-acetoxyethyl groups as precursors of the two vinyl groups in the porphyrin. The use of a pentachlorophenyl pyrromethane ester in the a-oxobilane synthesis and of a t-butyl pyrromethane ester in the b-oxobilane route enables these syntheses to be carried out in an entirely rational fashion without involving symmetrical intermediates, because the nuclear pentachlorophenyl ester can be selectivety cleaved by mild alkaline hydrolysis, and the nuclear t-butyl ester by trifluoroacetic acid in the presence of nuclear benzyl esters. The intermediate oxophlorin formed in the b-oxobilane route undergoes exchange with tritium at the meso-position opposite the oxo-group, and thus the oxo-function facilitates the synthesis of δ-meso-tritiated protoporphyrin-IX required for biosynthetic experiments in the chlorophyll field. Attempts to prepare the 2,4-divinyl-β-oxophlorin were frustrated by preferential formation of a cyclic ether from the 4-substituent and the β-oxygen atom. |
