Indole alkaloid biosynthesis

13C‐NMR. Spectroscopy of Naturally Occuring Substances. XLII. Conformational analysis of quebrachamine‐like indole alkaloids and related substances

“…(3 b), lG/3-hydroxymethylcleavamine (3 c ) , 1Ga-methoxycleavamine (3 d), 16p-carbomethoxycleavamine (Elsa-carbomethoxycleavamine [6]) (3 e ) , 16/3-methoxycleavamine (3 f)-and eight dihydrocleavamine-like substances-l5,20~.-dihydrocleavamine (~4/3-dihydrocleavamine [GI) (4a), 16~-hydroxymetliyl-l5,20a-dihydrocleavamine (4b), 16~-carbomethoxy-15,20u-dihydrocleavamine (=_lSj3-carbomethoxy-4/3-dihydrocleavamine [GI), (4 c) , 15,20/3-dihydrocleavamine (~4a-dihydrocleavamine [GI) (4 d) , 16 u-carbomethoxy-15,20~-dihydrocleavamine (~18/3-carbomethoxy-4 a-dihydrocleavamine [6]) (4e), 16~-carbomethoxy-15,20~-dihydrocleavamine ( 4 8 oc-carbomethoxy-4u-dihydrocleavamine [6]) (4f), velbanamine (4 9) [ Qo Et R' R *: .…”

“…Reduction of the latter by sodium borohydride in acetic acid has been reported to yield 16u-carbomethoxycleavamine (3b) [6], but repetition of this reaction has shown it to be more complex. Both borohydride and cyanoborohydride reductions yielded 3 b accompanied by 16/3-carbomethoxycleavamine (3 e) , its 15,20/3-dihydro derivative (4f) and pseudocatharanthine3).…”

“…Lithium aluminum hydride reduction of the two epimeric esters led to the carbinols 3c and 39. Cleavamine (3a) was prepared by the reported procedure of hydrolysis and decarboxylation of 16%-carbomethoxycleavamine (3 b) [6]. Methanolysis of the /3-chloroindolenine 6, derived from treatment of cleavamine (3a) with t-butyl hypochlorite [14], yielded two methyl ethers, 3d and 3f, in analogy with previous experience in the 15,20cr-dihydroc1eavamine (4 a) series [14].…”

“…No systematic study of the spatial configuration of the medium-sized heterocycle has been reported, although the ring conformation in vincaminorine and vincaminoreine [5] as well as in carbomethoxydihydrocleavamines derived from catharanthine [6] has been determined by the 1H-NMR. analysis of a key, centrally located hydrogen atom and X-ray analyses of salts have shown the ring orientation in cleavamine (3a) [7], vincristine [3] and related, synthetic 'dimers' [S] in the solid state.…”

“…study of a select group of such substances in view of the high sensitivity of this spectral method of analysis to configuration and in order to evaluate the factors inducing conformational change. The compounds chosen for the study consisted of five quebrachamine-like alkaloids-( +)-quebrachamine (1 a), 16cc-carbomethoxy-(+)-quebrachamine (r(+)-epivincadine [9]) (1 b), 16&car-bomethoxy-(+)-quebrachamine (r(+)-vincadine [9]) (1 c), 16cc-carbomethoxy-14,15-dehydro-(+)-quebrachamine (=(+)-6,7-dehydroepivincadine [9]) (2 a) and 16P-carbomethoxy-14,15-dehydro-(+ ) quebrachamine (= (+) -6,7-dehydrovincadine [9]) (2 b)-16fl-hydroxymethyl-( +)-quebrachamine (1 d), six cleavamine-like compounds-cleavamine (3 a) [6], 16~-carbomethoxycleavamine (-lS@-carbomethoxycleavamine [6])…”