Alkaloids classes

Unger, M., Stockigt, D., Beider, D., and Stockigt, J. (1997). General approach for the analysis of various alkaloid classes using capillary electrophoresis and capillary electrophoresis mass spectrometry. /. Chromatogr. A 767, 263—276. 

This overall biosynthetic scheme is summarized in Scheme 7, and it is well to remember that C. roseus is almost alone as a plant in which this whole pathway can be viewed in its entirety, for most indole alkaloid-containing plants produce only one or two of the major alkaloid classes, and not all four. In addition, C. roseus is without doubt the most economically important of the indole alkaloid-containing plants, and thus studies were, and continue to be, driven by the goal of increasing the availability of the commercially significant alkaloids ajmalicine (39), vinblastine (1), and vincristine (2). 

The reaction of many compounds of biological interest with ammonium bicarbonate on thin-layer plates permits detection of 10-100-ng amounts of these compounds [141]. Many compounds in the lipid, steroid, sugar, amino acid, purine, pyrimidine and alkaloid classes can be analyzed in this way (Table 4.26). 

Sophisticated physical techniques have had a major impact on alkaloid research, particularly on the determination of novel structures. Progress in this area will be reviewed periodically, and the chapter on Elucidation of Structural Formula, Configuration, and Conformation of Alkaloids by X-Ray Diffraction is the first of a series of such reviews. Attention is given to chemical methodology, found to be most valuable in alkaloid synthesis, presented here in the chapter on Application of Enamide Photocyclization in Alkaloid Synthesis. Of a more traditional nature is the presentation of alkaloid classes, which have not been reviewed for many years and where considerable new material has accumulated. Hence, two chapters, namely, The Imidazole Alkaloids, last reviewed in Vol. Ill (1953) and Ipecac Alkaloids and (3-Carboline Congeners, reviewed in Vol. XIII (1971), are included. 

A total selectivity has been observed in the cyclization6 of l-benzyloxycarbonyl-2-(1-methylethenyl)pyrrolidine (13), a useful intermediate in the synthesis of the pumiliotoxin A alkaloid class. Thus, A -bromosuccinimide in dimethyl sulfoxide/water or iodine in acetonitrile was utilized as electrophile. 

Homopavinane (57) and homoisopavinane (58) ring systems represent examples of the phenethylisoquinoline alkaloid class. A synthesis of racemic... 

Because benzylisoquinolines have been available synthetically (in racemic form) for decades, there is quite a bit of chemistry known regarding their use as key intermediates in the synthesis of a number of more complex isoquinoline alkaloids. The asymmetric synthesis of benzylisoquinolines has been used to complete total synthesis of representative members of several of these alkaloid classes. As shown in Figure 6, the protoberberine alkaloid norcoralydine, the aporphine alkaloid ocoteine, the isopavine alkaloid reframoline and the morphinan 0-methylflavinantine have been made available in optically active form for the first time (except by isolation or resolution) using this approach. 

Nummularine-F (60) and zizyphine-G (61), elaborated by Z. nummularia and Z. oenoplia respectively, represent the only new additions to the 14-membered-ring alkaloid class which exhibit the p-hydroxystyrylamine and 3-hydroxyproline units as characteristic features. The known cyclopeptide mauritine-A, together with minor amounts of amphibines-A, -E, and -F, and mauritine-C have been isolated from Z. spinachristi of Nigerian origin. ... 

The benzyne reaction of the bromoisoquinoline 140 was examined by using sodium methylsulfinylmethanide, and dibenz[6,g]azecine 141 was obtained (80,81). An attractive modification appeared to be the expansion of the central ring of ( )-homoargemonine (143), since it seemed possible that 143 could be a representative of a new, as yet undiscovered alkaloid class originating from a 1-phenethyltetrahydroisoquinoline precursor. The synthesis of 143 was accomplished by reaction of the 1,2-dihydroisoquinoline 142 and formic acid-phosphoric acid (82). 

The chiral allylic carbamate (249) reacts with NBS in DMSO-HjO with high 1,2-relative asymmetric induction, via carbonyl participation, to give the chiral 3-oxo-l,l-disubstituted per-hydropyrrolo[l,2-c]oxazole (250) in a particular case of halolactonization used in the synthesis of the pumiliotoxin A alkaloids class <82TL4887, 84JA4192>. Similar reactions of halonium-initiated cyclization using brominium dicollidine perchlorate have been studied <83JA654>. 

Of the three major indole alkaloid classes (i) the iboga system appears to have the narrowest distribution (d). 

The Aspidosperma alkaloids are a group of more than 100 monomeric and dimeric monoterpene indole alkaloids with aspidospermidine (228) representing a key member of the class and sometimes considered to be the parent [68]. Numerous total syntheses of this pentacyclic compound have been reported. Our own contributions in the area were prompted by the discovery of a new method for preparing indoles via a palladium-catalysed Ullmann cross-coupling reaction that proceeds especially efficiently at close to room temperature [69] and which we felt could serve as the centrepiece in developing a new synthesis of compound 228 and, in the longer term, syntheses of dimeric members of the indole alkaloid class such as the clinically significant alkaloids vinblastine and vincristine. 

Number of Unique Structures in Major Alkaloids Classes in NAPRALERT Database"... 

Preakuammicine (19) serves as an efficient precursor of akuammicine (20) (a class 1 Strychnos alkaloid) and vindoline (9) (an Aspidosperma alkaloid). When labeled stemmadenine (21) (a Strychnos alkaloid) (class 1) was fed to Catharanthus roseus plants, labeled tabersonine (24) (class 1), vindoline (9) (class 3), and catharanthine (10) (class 5) were produced. Thus, preakuammacine (19) and stemmadenine (21) serve as key intermediates of both class 3 and 5 alkaloids. It has been proposed that incorporation of stemmadenine (21) into vindoline (9) and catharanthine (10) proceeds via dehydrosecodine (25). A Diels-Alder reaction could lead to the formation of tabersonine (24) and catharanthine (10), respectively (Fig. 34.5). 

These feeding experiments seem to suggest that As-pidosperma-Hunteria alkaloids (classes 3 and 5) arise by prior formation of Corynanthe and then Strychnos alkaloids (class I) (Atta-ur-Rahman and Basha, 1983). 

A number of miscellaneous types of alkaloids not easily assignable to other alkaloid classes, but that are of interest because of their medical, drug, systematic, biosynthetic, or other properties, are surveyed in this chapter. Many of these are of limited distribution, whereas others, such as caffeine (a xanthine base), are widely and sporadically distributed. 

Solanidine and demissidine can be separated on a silver nitrate-impregnated silica gel layer. Schbeibeb et al. [207 b] have used TLC also for preparative separation of Solanum alkaloids. Using 8 solvents on silica gel G layers, Paqijin and Lepage [158] have separated the three principal alkaloids from Solanum tuberosum, i. e., solanine, chaconine and solanidine. Antimony(III) chloride reagent was used for visualisation. P bez-Medina et al. [164] have investigated many Solanum species in the search for a raw material source of solasodine. They used TLC on silica gel 6 with n-butanol-methanol-diethylamine (85 + 5 + 10) as solvent and antimony(III) chloride (Rgt. No. 16) for visualisation. The TLC of this alkaloid class is described in other publications [2, 25, 183, 208]. 

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