By R.H.F Manske, H.L. Holmes
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Additional resources for Alkaloids: Chemistry and Pharmacology, Volume 14
This was dehydrated to the dienone 43 and hydrogenated fl CHO RO H 38 39 H R = H R = CH,CO 40 41 12 J. TOMKO AND z. VOTICKY to give a mixture of saturated (44) and unsaturated (45) ketones. Introduction of a methyl group a t C-13 in compound 44 led to 46 which after acetylation was shown to be identical with 3/3-acetoxy-14(13 ---f 12aH)-abeo-androstan-17-one(47) obtained earlier from hecogenine (74) (43, 44). Reintroduction of the C-12-C-13 olefinic linkage yielded the reaction product 48. This, when coupled with 2-ethyl-5- fl f l o H H HO HO H H 43 42 @ H O& H H H RO HO H H 44 45 46 47 48 126-H 412"3, R = H R = CH,CO R = CH3C0, 4'2"3' methylpyridine (49) and acetylated, afforded a mixture of epimers from which the desired isomer 50 was isolated.
The methine proton of the )CHOH grouping appearing as a septet showed the same splitting pattern as 1. STEROID ALKALOIDS 37 C- 1 6 /3-protons of other Buxus alkaloids. Attempted N-methylation of 148 to 150 according to the Eschweiler-Clarke method resulted in the cleavage of the cyclopropane ring and in production of an amorphous mixture; therefore the N-methylation had to be carried out with methyl iodide. On the other hand, the dihydroderivative (149) can be readily methylated by the Eschweiler-Clarke method.
N-Chlorination of 111 with N-chlorosuccinimide led to the N-chloro derivative (116). The negative molecular rotation difference between 116 and 111 established the 22S-configuration. Alkaline-catalyzed elimination of hydrogen chloride in 116 afforded the cyclic azomethine 117. The latter compound did not cyclize to the corresponding spiroaminoketal, thus demonstrating the trans orientation of the C-16 hydroxy group to the heterocyclic side-chain moiety at C-17. The weak negative Cotton effect of the azomethine 117 proved the 25s-configuration (73) of veralkamine and its derivatives.