A significant deactivating metabolic transformation of natural prostaglandins is enzymatic oxidation of the C-15 hydroxyl to the corresponding ketone. This is prevented, with retention of activity, by methylation to give the C-15 tertiary carbinol series. ). This molecular feature is readily introduced at the stage of the Corey lactone (
1) by reaction with methyl
Grignard reagent or
trimethylaluminium. The resulting mixture of tertiary carbinols (
2) is transformed to oxytocic carboprost (
3) by standard transformations, including separation of diastereomers, so that the final product is the C-15 analogue. This diastereomer is reputably freeer of prostaglandin side effects than the C-15 (S) isomer. == References ==