Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
Hydrogenation of the ketone group in di-O-benzylderivative (8) of the known macrocyclic lactone zeralenone (7) using a novel chiral borane complex 3. BH3, prepared in situ, proceeded at lower temperatures with moderate diastereoselectivity (∼40%, d. e. at -60°). Unsaturated diastereomers 9 and 10 were separated, and 9 converted into zeranol (11), a known anabolic agent. Restricted conformational mobility at lower temperatures is assumed for the intermediate 8 on the basis of the temperature-dependent CD spectra of its acetyl congeners 18 and 19. X-Ray structure analysis of 7-O-acetylderivative (13) of 11 revealed the (R)-configuration at C(7). Two crystallographically independent H2O molecules are involved in the H-bonds, one of them (O(21)) rises the helices of the molecules of 13 along b. Small positive torsional angle [C(16)-]C(161)-C(1) [=O] (+19.3°), transoid(E) conformation of the lactone group, and nearly achiral arrangement of the C(11)-C(12) bond (torsional angle [C(11)-]C(12)-C(121)[C(161)] is -93°) are the main conformational features that differentiate the macrocylic RAL (resorcinic-acid lactone) derivatives from the 6-membered lactone derivative 20, studied earlier by CD. Consequently, the rules developed for the CD effects within conjugation band (around 270 nm), and n→π* band (around 255 nm) of the latter compound, cannot be applied the macrocyclic lactones.
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