3-Yohimbine structure

Heteroyohimbine alkaloids. A group of indole alkaloids with the yohimbine structure but with an oxygen function in ring E (see formula under yohimbine) H. occur mainly in the Apocynaceae. Typical examples are ajmalicine (raubasine), 19-epi-ajmalicine, tetrahydroalstonine, rauniticine (all with the 3o-con-figuration), as well as serpentine and alstonine with an aromatic ring C. 

The first indication of the nature of the nuclear structure of yohimbine was seciu-ed by Barger and Field,(1915) who, by distilling the alkaloid with soda-lime, obtained a base, (m.p. 56° picrate, m.p. 157°),... 

The chemistry of yohimbine is also under active discussion and new papers have appeared, or are promised, dealing with the structure and synthesis of ketoyobyrine. ... 

Cleavage of the hetero ring in a number of extended tetrahydro-j8-carboline systems was observed in the course of structural elucidation of tetrahydro-jS-carboline alkaloids. A few examples only will be given. The indole derivative 287 was isolated as one of the products of the selenium dehydrogenation of yohimbine (358 R = and... 

During the past two decades a great number of papers have been published on the isolation, structure elucidation, synthesis and transformation, biogenesis, chemotaxonomy, and pharmacology of indole alkaloids. In this chapter we summarize the new results that appeared from 1968 to mid 1984 for the cory-nantheine-yohimbine group of monoterpene indole alkaloids with greater emphasis on their chemistry, excluding the related oxindoles and heteroyohimbines. 

Two important books on the biogenesis of indole alkaloids have been published (5, 6), therefore we do not intend to cover the literature of the biogenesis of corynantheine- and yohimbine-type alkaloids. Our chapter begins with the structure elucidation of the alkaloids isolated during the past two decades and proceeds with the synthesis, transformation, as well as spectroscopy of the alkaloids in question. 

This compound, the active constituent of Tabernanthe iboga, a plant used for its psychic effects by African natives, has recently been synthesized. However, there seems to be nothing in the trip it produces to justify the arduous synthesis (likewise for the structurally similar yohimbine). 

Vinblastine is also transformed by Streptomycespunipalus A36120 to give lO -hydroxyvinblastine (48) in 9% yield (55). Hydroxylation of indole alkaloids at C-10 had been observed previously with yohimbine and related compounds (81, 82). The structure of 48 was deduced from spectral analysis of the phenol and of the methoxyl derivative 49 produced by treatment of 48 with diazomethane (55). The appearance of signals at 5 6.91 (singlet, C-9 hydrogen) and 6.71/6.95 ppm (AB quartet, C-l 1 and C-12 hydrogens) in the PMR spectrum of 48 were particularly characteristic of the presence of the C-10 hydroxyl function. 

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