Alkaloids: Chemistry and Pharmacology, Volume 12 by R.H.F Manske, H.L. Holmes

By R.H.F Manske, H.L. Holmes

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Additional resources for Alkaloids: Chemistry and Pharmacology, Volume 12

Sample text

A recent report (70) describes the isolation of a new alkaloid, 14-dehydrobrowniine (CXX), along with browniine from the aerial portions of D . cardinale Hook, a large species native to southern and Baja California. Sodium borohydride reduction of 14-dehydrobrowniine proceeded stereospecifically to give browniine as the only product. Also, oxidation of browniine with sodium dichromate in acetic acid gave low yields of a basic ketonic material from which 14-dehydrooxobrowniine was separated and found to be identical with the naturally occurring alkaloid.

It is perhaps significant t o note that the secondary hydroxyl a t C- 15was never observed t o undergo oxidation even though models show the hydrogen of C- 15 is quite exposed. A possible explanation lies in the steric inhibition of the chromate ester formation. This same hydroxyl is also impervious t o mesylation, even though the tertiary C-13 hydroxyl undergoes this reaction smoothly (90).

THE C 1 9 - ALKALOIDS ~ ~ ~ ~ ~ ~1 1 ~ structure for lycoctonine (11) followed unambiguously (5). Shortly before publication of the previous review, however, a further study of the X-ray crystallographic data ( 6 ) showed that the absolute configuration of des(oxymethy1ene)lycoctonine hydroiodide monohydrate was the mirror image of I. Thus, the correct representation of lycoctonine is I11 and it should be borne in mind that the structures of all of these compounds mentioned in the previous review are in reality the mirror images of those shown.

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