On the reported transformation of β-amyrin into oleanolic acid
Abstract
Reduction of 3β-acetoxy-12α,13α-epoxyoleanan-3β-yl acetate (β-amyrin acetate epoxide)(5) with lithium–ethylamine affords β-amyrin (17%), oleanane-3β,12α-diol (3; R1= R2= H)(50%) and 13α-oleanane-3β,12α-diol(6; R1= R2= H)(27%). On photolysis 3β-acetoxyoleanan-12α-yl nitrite (3; R1= Ac, R2= NO) affords the 27-oxime (10), which has been further transformed into the aldehyde (9; R1= H, R2= OH) and the corresponding lactone (11; R1R2= O). The latter had previously been identified erroneously as oleanolic lactone acetate (12; R1= Ac, R2R3= O).