Central precursor

The energy and reducing power necessary (E) for the synthesis of cell substance, i. e., growth and multiplication, can be made available simultaneously with the synthesis of the central precursor. If this assimilatory energy (Ea) is not sufficient (Ea< E) to convert the precursor-carbon completely into biomass, further substrate must be dissimilated. 

Aryl azides constitute central precursors for heterocyclic compound generation (e.g., click chemistry applications) [101]. Interestingly, a safe, convenient and microwave-compatible aryl azidonation process has been dis-... 

Gene regulation represents the most basic level of metabolic control. Although there are few examples in the alkaloid literature, the post-translational regulation of enzymes can also exert considerable influence over the control of metabolic flux. Recent work in our laboratory suggests that enzymatic controls function of the regulation in alkaloid biosynthesis. (5)-Norcoclaurine is accepted as the central precursor to all BAs produced in plants.6,7 However, NCS was first isolated based on its ability to convert dopamine and 3,4-dihydroxyphenylacetaldehyde (3,4-DHPAA) to the tetrahydroxylated alkaloid (S)-norlaudanosoline.129 The ability of NCS to accept either 4-HPAA or 3,4-DHPAA contributed to the incorrect conclusion that (S)-norlaudanosoline is a common pathway intermediate. However, only (5)-norcoclaurine has been detected in plants. 

The stereospecific condensation of dopamine with 4-hydroxyphenylacetaldehyde is catalyzed by NCS to yield S-norcocIaurene, the central precursor of thousands of benzylisoquinoline alkaloids, including morphine. This poorly characterized, but key enzyme in benzylisoquinoline alkaloid biosynthesis has recently been purified to homogeneity, and its kinetic properties have been elucidated.35 NCS occurs as a 28 kDa dimer composed of 15 kDa... 

All naturally occurring benzodiazepines are biosynthesized from anthranilic acid. The benzodiazepine moiety is formed by reacting this central precursor with derivatives of phenylalanine (cyclopenin group), tyrosine (tomaymycin-anthramycin group), glutamine (auranthine), or tryptophan plus another molecule of anthranilic acid (asperlicin). Intensive biosynthetic work has been published for the cyclopenin and tomaymycin-anthramycin groups only. 

Transannulation of the mesylate (33), derived from 4,8-dimethylcycloocta-4-en-l-ol, using sodium carbonate in aqueous dioxane has provided the bicyclo[3.3.0]octanol (34), a central precursor to the monoterpene iridomyrmecin (35 equation 13). In studies of the biomimetic synthesis of the natural tri-quinanes capnellene (37 equation 14) and pentalenene (40 equation IS) Pattenden et al. have shown that both molecules can be produced from appropriate cycloocta-l,S-diene precursors, i.e. (36) and (39) [or indeed their corresponding positional isomers (38) and (41), respectively] by treatment with boron trifluoride. Mehta et al. have described an alternative transannulation approach to the triquinane unit found in pentalenene, i.e. (42) - (43 equation 16), and also to the ring system (44 equation 17) found... 

Fig. (5). Biosynthesis of catharanthine and tabersonine from strictosidine, the central precursor of all terpenoid indole alkaloids. SGD strictosidine p-D-glucosidade.

Morphine and codeine are members of the large and diverse group of benzylisoquinoline alkaloids, of which morphine and sanguinarine share a common biosynthetic pathway, beginning with the condensation of two L-Tyr derivatives to produce the central precursor (S)-norcoclaurine yields (S)-reticuline, the last common intermediate in the biosynthesis of both sanguinarine and morphine. Berberine bridge enzyme (BBE) catalyzes the conversion of (S)-reticuline to (S)-scoulerine, the first committed step in the sanguinarine pathway. Alternatively, (S)-reticuline can be isomerized to its (R)-epimer as the first step in the formation of morphine. Since the pathway from tyrosine to (S)-reticuline is also known at the enzyme level, the conversion of L-tyrosine to macarpine involves a total of 19 enzymes which are now at least partially characterized. 

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