Proposed pathway of biosynthesis

Figure R Proposed pathway of biosynthesis of the aminosugar moieties of polyene macrolide antibiotics.

Scheme 14. Proposed pathways of biosynthesis of chebulinic acid (56) and chebulagic acid (57) from P-penta-o-galloyl-D-glucose (11), 81). Hydrolysis of (56 and 57) to give...

Figure 25-21 Proposed pathways for biosynthesis of thiamin phosphate and pyridoxol phosphate.

Fig. (2). Proposed pathways of SA and 4HBA biosynthesis. Enzymatic steps for which the enzymes have been identified include PAL, CA4H (cinnamic acid 4-hydroxylase), and BA2H (benzoic acid 2-hydroxylase). Taken from Smith-Becker et al., 1998, [55].

Scheme 20.4 Proposed pathway for biosynthesis of the aminopentose in AT2433. N-methylation might alternatively occur after the sugar is transferred to the aglycone.

Fig. 10. Proposed pathways for biosynthesis of archaeol phospholipids and glycolipids in extreme...

Figure 1. (A) Domain organization of the NcsB naphthoic acid synthase and (B) proposed pathway for biosynthesis of the naphthoic acid intermediate (2) from the acyl CoA substrates by NcsB and its subsequent conversion to 3 by NcsB3 and NcsB 1 and incorporation into neocarzinostatin (I) by NcsB2. ACP, acyl carrier protein AT, acyltransferase DH, dehydratase KR, ketoreductase ...

Fig. 2. Proposed pathway for biosynthesis of c/s-vaccenate. ACP, acyl carrier protein.

Figure 3.103 Proposed pathways of deoxysugars biosynthesis and post-PKS modifications in S. bikiniensis showing roles for the various enzymes encoded by genes in the chm cluster.

Figure 4.1 Proposed pathways for biosynthesis of azetidine-2-carboxylic acid 1.

If the pathway of biosynthesis of alio bile acids from cholestanol is similar to that proposed for the 5p bile acids from cholesterol, 7a-hydroxyla-tion should be the next step. The microsomal fraction of rat liver properly fortified with NADPH and oxygen was observed to hydroxylate cholestanol and cholesterol to the respective 7a-hydroxy derivatives at equivalent rates (127). With cholestanol the 7 -hydroxylase was inhibited by the product, or the 7j3-ol or 7-keto sterol. The rate of hydroxylation could be enhanced by prior treatment of the rats with cholestyramine (a bile acid sequestrant) and/or phenobarbital. A C5 double bond was not considered a requirement for enzymatic hydroxylation at C7. 

On the basis of this and the other biosynthetic evidence, Kominek has identified the rate limiting steps in the biosynthesis of novobiocin as the formation of the coumarin (123) and p-hydroxybenzoic acid from (—)-shikimic acid. He proposed a pathway of biosynthesis (Figure 4.19) in which the final step is condensation of the noviosyl coumarin (124) and the p-hydroxy-benzoic acid derivative (125). 

Scheme 1. Proposed pathway of patulin biosynthesis. This figure is modified after the various experimental results obtained from different research groups (Zamir, 1973 Scott et ai, 1973 Light, 1969 Light and Vogel, 1975 Murphy et al., 1974 Scott and Beadling, 1974 Murphy and Lynen, 1975 Forrester and Gaucher, 1972).

Fig. 11. Proposed pathway for the biosynthesis of L-ascorbic acid (with inversion of configuration) in plants using C-l-labeled D-glucose or C-l-labeled...

The proposed pathway for the biosynthesis of the avermectins (Fig. 3) has been described in a review (23). Some of the details are yet to be elucidated, although the steps, in general, are based on firm evidence from four types of studies incorporation of labeled precursors, conversion of putative intermediates by producing strains and blocked mutants, in vitro measurement of biosynthetic enzymes, and studies with enzyme inhibitors. The biosynthesis of the oleandrose units was elucidated from studies using and labeled glucose, which indicated a direct conversion of glucose to... 

Based on the pathways just proposed for the biosynthesis of anandamide and 2-AG, the formation of these endogenous ligands must also be dependent on the composition of the precursor lipids. This dependence is of greater importance for anandamide rather than for 2-AG because... 

The in vivo transformation of [6-14C]strictosidine (19) to gelsemine in Gelsemium sempervirens was claimed with an incorporation of 0.47% (33). This provides another experimental support to the proposal that strictosidine appears to be the original precursor in the biosynthesis of monoterpenoid indole alkaloids, although the detailed pathway of this biosynthetic process still remains obscure. 

Additional hypotheses concerning prostaglandin biosynthesis in P. homomalla resulted from isolation of 11R-HETE (76) from the polar lipid fraction [95]. Apparently, 11R-HETE (76) is also a minor product of incubations of arachidonic acid with acetone powder preparations of P. homomalla [95], In this alternate hypothesis (Scheme 8), an 11-hydroxy or 11-hydroperoxy-8,9-allene oxide intermediate is formed from a sequence of oxidations at C8 and Cll. Opening of the allene oxide to a transient C8 earboeation induces eycli-zation with a consequent addition of water to C15. This proposed pathway leads initially to formation of PGE2 (16 or 38), which following acetylation, elimination of acetic acid from Cl 1-12, and esterification, forms the observed major natural product in the coral, 15-acetoxy methyl PGA2 (36 or 54). Notably, if... 

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