Abstract
Abstract The stereochemically-complete molecular structure of demycarosyl leucomycin A3, C30H49-NO11, has been determined by means of an X-ray crystal analysis of its hydrobromide. The crystals of the hydrobromide are orthorhombic with four chemical units in a unit cell with the dimensions of a=19.52±0.03, b=20.63±0.03, and c=9.28±0.03 Å. The space group is P212121. As a result of the present study, it has been found that the crystals contain about 0.6 mole of ethanol per mole of the hydrobromide as alcohol of crystallization. The intensity data were obtained from equi-inclination integrating Weissenberg photographs taken with CuKα radiation around the b and c axes. The structure was elucidated by means of the minimum function, least-squares, and Fourier methods. The atomic coordinates obtained were refined by the block-diagonal least-squares method, anisotropic thermal motion being assumed for only the bromine atom. The final R factor is 14.6%. The molecular structure thus obtained corresponds exactly to that proposed in 1967 by Hata et al. on the chemical evidence, considering the allylic rearrangement in the hydrolysis of leucomycin A3 with dilute hydrochloric acid. The conjugated diene system in the macro ring has the trans-trans configuration. The sugar component, mycaminose, forms a β-glycosidic linkage with the lactone ring.
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