Alkaloids, continued

Alkaloids continue to provide mankind with a plethora of medicines, poisons, and tonics. As many precious drugs result from such natural compounds, there is much interest in their transformation to provide new compounds or intermediates for the synthesis of new or improved drugs [1]. 

Alkaloids containing the acridine moiety, such as the tricyclic (19) and tetracyclic (20) acridone alkaloids, continue to be isolated from a variety of sources and are periodically reviewed (B-77MI20900). 

Figure 8. Biologically active Amaryllidaceae alkaloids (continued next page).

During the last decade, as the number of bisbenzylisoquinoline alkaloids continued to increase rapidly, a systematic classification system became highly desirable, and no doubt many workers were using informal systems. In 1976, a formal line notation was developed that designates the skeleton and location of substituents (337) it is suitable for computer retrieval and has found use in review articles (see Section IX). A more extended system that allows specification of substituents and is adaptable to unusual structural types [e.g., repanduline (Section H,B,7)] has also been described (338). The chirality of asymmetric centers may also be designated (160). 

Thus, although the yields in the oxidative cyclizations of diphenolic substances and their derivatives may sometimes be lower than might be desired, this biomimetic approach constitutes a rapid and concise entry to the crinine family of alkaloids. Continued research in this area should lead to the development of improved synthetic methodology and tactics for effecting this important conversion, resulting thereby in highly useful syntheses of members of this class of naturally occurring bases. 

For the first time, the chemistry of Nuphar alkaloids has been characterized in greater detail. The ring systems present in this group of alkaloids continue to... 

The stmctural complexity and diversity of bromopyrrole alkaloids continue to challenge organic chemists, as indicated by the high number of contributions appearing since 2000. 

Numerous new alkaloids continue to be isolated from Buxus spp. for details see, inter al., Voticky et al.. Coll. 

The bioactivity of castanospermine and related alkaloids continues to inspire chemists to devise new synthetic routes to the alkaloid, as well as to iimumerable structural, stereochemical and other analogs. The ensuing discussion deals only with reported syntheses of the four natural products 239-242. For syntheses of other reported stereoisomers of the indolizidine-l,6,7,8-tetraols (Fig. 4), the following references should be consulted (-)-l-epicastanosp>ermine (243) (194), ( )-7-epicastanospermine (195) and (15,6S, 75, 87f,8a7 )-7-epicastanospermine (244) (196),... 

The degradation of the Senecio alkaloids continues to be effected by saponification or hydrogenolysis. The use of alkali in the hydrolysis does not alter the necine moiety but it may cause a change in the geometrical configuration about an a,j8-oarbon-carbon double bond in the necic acid. Hydrogenolysis provides important information as to the location of the esterified hydroxyl on the necine, and subsequent conversions permit a decision as to which end of a dicarboxylic necic acid (in the cyclic diesters) is attached to the allylic or primary hydroxyl of the necine. 

Active interest in the toxic nature of the Senecio alkaloids continues to be taken by R. Sohoental and her collaborators in Britain and by... 

This sub-group of alkaloids continues to be a popular area for synthesis, and several notable contributions have been published... 

Indole and isoquinoline alkaloids continue to play a dominant role. The apor-phinoids, comprising proaporphines, aporphines and related dimers, are treated separately, partly in order to reduce the burden on contributors aristolactams and aristolochic acids, which have not been reviewed since 1961, also are discussed in this chapter. This year the quinolizidine alkaloids, including the sesquiterpenoid Nuphar bases and the appropriate Lythraceae alkaloids, as well as azaphenalenes of plant and insect origin are reviewed together. Amaryllidaceae, Erythrina, imidazole, purine and peptide alkaloids are omitted from this volume, but it is expected that the chemistry of these groups covering the period 1974—1976 will be surveyed in Volume 7. 

Synthetic work on morphine and morphinandienone alkaloids continues unabated. Amurine " and O-methylflavinantine have been obtained by the benzyne reaction of appropriate benzyl isoquinoline precursors. A review concerning new synthetic derivatives of dihydrocodeinone is not readily available.Codeine has been prepared in 98% yield from morphine using... 

This group of alkaloids continues to attract some attention, and the contributions published during the period under review range in emphasis from the purely pharmacological to the purely mechanistic aspects of organic chemistry. As well as reports on the isolation of new alkaloids, attempts to find new pharmaceuticals, and improved methods of assay, the recent publications include studies in which tropane derivatives have been used as a convenient vehicle for conformational and mechanistic studies. 

New investigation of bisbenzylisoquinoline biosynthesis is welcome (see ref. 32 also this Report, p. 16). Although aporphine alkaloids are the simplest developments of the benzylisoquinoline skeleton, their biosynthesis need not, as several examples show, be simple. It has, however, been found that the biosynthesis of boldine and isocorydine is straightforward. Further detail has been repor-ted on the biosynthesis of Erythrina alkaloids, which were established to be modified benzylisoquinolines some time ago. Further detail on the biosynthesis of morphine (23) and related alkaloids continues to be published. Of particular R. B. Herbert, in ref. 9, p. 11. 

Study of the biosynthesis of ergot and steroidal alkaloids continues. The biosynthesis of the necic acid components of the pyrrolizidine alkaloids has been elucidated,and attention has turned to the biosynthesis of the pyrrolizidine nucleus, which is largely unknown (see this Report, p. 13). 

Much of the new work on the larger ring peptide alkaloids continues to emanate from Tschesche and his collaborators. From the Rhamnaceae family, the bark of Scutia buxifolia has been found to contain scutianines A, B, C, D, and F (19) as... 

Bursera morelensis (Buseraceae). ° In addition the known deoxypodo-phyllotoxin was isolated again from Jmiperus bermudiana (Pinaceae)/ Among the nitrogen-containing plant biosynthetic products, the indole alkaloids continue to receive major emphasis. The previously known tubotaiwine A-oxide was found to be the cytotoxic component of Tabernae-montana holstii K. Schum. (Apocynaceae). The same plant has been... 

The rich stmctural diversity of Veratrum and Solanum alkaloids continues to attract the interest of isolation chemists, synthesis-oriented groups. 

Table 4.3 Ipomoea species apparently devoid of ergobne alkaloids (continued)... 

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