Alkaloid Precursors

The biogenetic approach, which is a linear approach, is based on the stepwise disconnection of 18 into a series of biogenetically related alkaloid precursors. The precursors are usually built up in the actual synthesis with the C10 indole chromophore attached from the beginning and with stepwise modification of the alicyclic portion of the molecule later on. An example of this kind of approach is illustrated in Scheme 14 (43). 3(R)-Vobasinediol (58) is... 

The intramolecular version of the Heck reaction has been extremely fruitful, enabling elegant synthesis of many complex molecules [68, 69]. The Mori-Ban indole synthesis (Section 1.10, vide infra) is a good example of such method. In addition, Rawal et al. carried out an intramolecular Heck cyclization of pentacyclic lactam 55 with a pendant vinyl iodide moiety [70]. Employing Jeffery s ligand-free conditions, 55 was converted to a hexacyclic strychnan alkaloid precursor 56 with complete stereochemical control... 

Mevalonate pyrophosphate, role in cholesterol synthesis, 5 142 Mevalonic acid, 2 93 14 132 alkaloid precursor, 2 78 Mexican Molango ore, 15 544 Mexican oregano, 23 169 Mexico... 

Nicotine adenine dinucleotide phosphate (NADP+), 24 147 Nicotinic acid, 9 477-478 26 291 alkaloid precursor, 2 78 Ni-Cr alloys, 23 499. See also Nickel-chromium entries NiCrAlY coatings, 13 508 nido designation boranes, 4 184-186 boron hydrides, 4 170, 172-176 Nidrel, molecular formula and structure, 5 129t... 

Kreuger and Carew (141) examined the effects of a number of alkaloid precursors on alkaloid production in suspension cultures and found that at 100 mg/liter tryptamine hydrochloride enhanced alkaloid production. The alkaloids produced, however, were A-acetyltryptamine and N,N-dimethyltryptamine, rather than the monoterpenoid indole alkaloids. Added geraniol and mevalonic acid had no effect on alkaloid production. 

The precursors of true alkaloids and protoalkaloids are aminoacids (both their precursors and postcursors), while transamination reactions precede pseudoalkaloids (Tables 1 and 10). It is not difficult to see that from all aminoacids only a small part is known as alkaloid precursors (Table 19). Both true and proto alkaloids are synthesized mainly from the aromatic amino acids, phenylalanine, tyrosine (isoquinoline alkaloids) and tryptophan (indole alkaloids). Lysine is the... 

The skeleton nucleus of the alkaloid is the main criterion for alkaloid precursor determination. Many skeletons are produced in the process of alkaloid synthesis. Figure 24 illustrates some nuclei and skeletons supplied in the synthesis. Alkaloid... 

L-lysine furnishes alkaloids with at least four different nuclei. It is a protein amino acid, one of the most important alkaloid precursors. L-lysine-derived... 

Although L-phenylalanine is a protein amino acid, and is known as a protein acid type of alkaloid precursor, its real role in biosynthesis (providing C and N atoms) only relates to carbon atoms. L-phenylalanine is a part of magic 20 (a term deployed by Crick in his discussion of the genetic code) and just for this reason should also be listed as a protein amino acid type of alkaloid precursor, although its duty in alkaloid synthesis is not the same as other protein amino acids. However, in relation to magic 20 it is necessary to observe that only part of these amino acids are well-known alkaloid precursors. They are formed from only two amino acid families Histidine and Aromatic and the Aspartate family . 

Other precursors of alkaloids form intermedia as acids (e.g., capric acid in the coniine pathway, 26-hydroxycholesterol in the solasodine pathway and piperidine in the jervine pathway). Moreover, in the case of purine as an alkaloid precursor, the intermedia is inosine monophosphate (IMP). 

The special treatment of cell cultures for increasing the yield of alkaloids can be linked to improvements in medium composition, the addition of enzymes and alkaloid precursors, the addihon of the so-called elicitors and changes in environmental factors. The medium can be improved by changes in the relahons between its components sucrose and carbon components, nitrogen, phosphorus... 

N-Substituted 2,4-quinazolinediones are often prepared by the reaction of substituted 2-aminobenzamides with triphosgene, as demonstrated by the synthesis of the alkaloid precursor 822 <2004MOL609>. 

Scheme 39. An indole alkaloid precursor via a 5-exo-digl6-endo-trig double radical cyclization...

Under NADPH-regenerating conditions, (99) was converted into geisso-schizine (101), which has been shown not to be a direct alkaloid precursor (for further discussion, see below). 

Schulz S., Francke W., Boppre M., Eisner T. and Meinwald J. (1993) Insect pheromone biosynthesis stereochemical pathway of hydroxydanaidal production from alkaloidal precursors in Creatonotos transiens (Lepidoptera Arctiidae). Proc. Natl. Acad. Sci. USA 90, 6834-6838. 

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