Characterisation of novel 3-carboxyalkyl-steranes occurring in geological samples
摘要:
Three novel series of 3-carboxyalkyl-steranes have been identified by synthesis in sediments from an evaporitic basin. These compounds may derive from precursor steroids bearing a polyfunctionalised side-chain at C-3, yet unknown in living organisms. Geochemical data suggest a microalgal or a bacterial origin.
The epimeric 4,5-epoxides derived from 4-methylcholest-4-en-3-one and 3α- and 3β-acetoxy-4-methylcholest-4-enes have been rearranged with boron trifluoride. Each of the six epoxides exhibits its own distinctive pattern of behaviour.
4β,5β-Epoxy-4α-methylcholestane undergoes rearrangement with boron trifluoride to give mainly 5-methyl-5α-cholestan-4-one. Under similar conditions the 4α,5α-epoxide gives the 5β-methyl-A-nor-B-homo-6-ketone (VI), which rearranges on prolonged treatment with boron trifluoride to give 5-methyl-5β-cholestan-4-one.