Yohimbine alkaloids structures

Deoxytubulosine has been extracted from the seeds of Alangium lamarckii.41 In connection with structure elucidation in this area, the compilations of rH n.m.r. data for geissoschizine, ajmalicine, 19-ep/-ajmalicine, tetrahydroalstonine, and rauniticine480 and of 13C n.m.r. data for diploceline19c should prove useful. The effect of stereoisomerism on the mass-spectrometric behaviour of some corynantheine and yohimbine alkaloids has also been studied.486... 

The main alkaloid of this plant material was isolated in 1896 by Spiegel [1] and named yohimbine.The alkaloid was the same as one obtained previously from Aspidosperma quebracho-bianco (Apocynaceae) [2]. Isoyohimbine and allo-yohimbine, possessing structures similar to that of yohimbine, were also isolated from P. yohimba [3,4]. Isoyohimbine, based on the studies of Warnat [3], is known as a-yohimbine. 

As can be seen by reviewing the chemistry outlined above, a variety of cleverly devised strategies have been employed for the synthesis of the structurally complex yohimbine alkaloids. One elusive problem in many of these approaches has been the proper adjustment of the C(3) stereochemistry, particularly in approaches to reserpine (2) and deserpidine (3). It is well-known that epimerization at C(3) of the yohimbine skeleton 1 can occur under acidic conditions presumably via a mechanism involving cleavage of either the C(2)-C(3) or C(3)-N(4) bond to afford the respective iminium cation 532 or a-indolylcarbinyl cation 533. In this section, we will review investigations which focus on this epimerization process. 

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°),... 

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. 

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. 

Monoterpenoid Alkaloids.—Corynantheine-Heteroyohimbine- Yohimbine Group, and Related Oxindoles. The leaves of Strychnos decussata (Pappe) Gil. contain a new glycosidic alkaloid for which the gross structure (78) has been proposed 52 so far, nothing is known about its stereochemistry. Nevertheless it seems distinctly possible that this alkaloid is a close biosynthetic relative of vallesiachotamine. 

With the structure of quinamine firmly established, its other reactions can now be considered (Chart II), all of which proceed via VIII. When the alkaloid was refluxed with acetic anhydride or acetyl chloride, acetyl-apoquinamine (O-acetyl-d3- 14-cinchonamine, XII), picrate, mp 143° was obtained. The change may be formulated, quinamine VIII-XII, with the last step being a special case of a general reaction of hydroxy-indolenines (20). The analogous transformation can be realized very easily when 7-hydroxy-7/f-yohimbine methiodide (X) is boiled in methanol (21). 

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