“…The stereochemistries of the protons at C(15) and C(17) of nimbin were assigned by considering all the possible configurations at these points and the effects of their possible coupling patterns on the C(16) protons and then comparing these values with those actually observed (Narayanan & Pachapurkar, 1965). Structures of related natural products, such as deacetylnimbin (Narayanan & Iyer, 1967), nimbolide (Ekong, 1967), vepinin (Narayanan, Pachapurkar, • Sawant & Wadia, 1969), salanin (Henderson, die, Malera & Overton, 1968), vilasinin (Pachapurkar, (12) Kornule & Narayanan, 1974) and azadirachtin (12) (Zanno, Muira, Nakanishi & Elder, 1975), which have (10) (9) many features in common with nimbin, were elucidated (10) largely by PMR spectral analysis and by considering (9) (9) their evident relationship to nimbin. Hence it was con- (8) sidered desirable to perform an X-ray structure deter- (9) mination of a derivative of the parent compound (10) (9) nimbin, so that the structures of all these compounds (10) would stand on a firmer basis.…”