Ratio of products formed on photo-oxidation of the neem triterpenoids nimbin and salannin

Abstract

Two isomeric products containing a hydroxybutenolide, formed from the furan ring, are produced by the photo-oxidation of the neem triterpenoid nimbin, an analogous pair of isomers are similarly formed by oxidation of salannin. The relative amounts of these products can be varied by the addition of a hindered base either during or after the oxidation. Addition of DABCO after the oxidation can increase appreciably the proportion of the minor isomer, the biologically more valuable products, from both reactions.