Berberidic acid

Berberidic acid (2), obtained by nitric acid oxidation of berberine (1), can be esterified to diester 3, or to monoesters 4 and 5. Sodium borohydride reduction of 4 provides γ-lactone 6 which can be oxidized with iodine to pyridinium salt 7. In like fashion, monoester 5 leads to γ-lactone 8 which is oxidized by mercuric acetate to salt 9. Berberidic acid dimethyl ester (3) is hydrogenated to allo hexahydro diester 10 from which normal diester 11 can be derived by base isomerization. Hydrogenation of lactone 6 produces allo lactone 14 whose further reduction with lithium aluminum hydride gives diol 15. This same diol can also be obtained from the lithium aluminum hydride reduction of hexahydro diester 10. Alternatively, lithium aluminum hydride reduction of diester 11 gives rise to diol 16, diastereomeric with 15. Catalytic hydrogenation of lactone 8 provides normal lactone 18 which is transformed to diol 6 by lithium aluminum hydride.