Biosynthetic pathways schemes

Recently it was shown by radiolabeling studies that the formation of the serrulatane skeleton is catalyzed by the pseudopterosin diterpene cyclase, which can be considered as a key enzyme in terpene biosynthetic pathways (Scheme 2). The elisabethatriene cyclase is a monomer with a molecular mass of47kDa [25]. 

E)-l-Hydroxy-2-methyl-but-2-ary 1-4-diphosphate (44) has been prepared in six steps from tetrahydropyranyl ether (42), derived from hydroxyacetone and phosphonium ylide (43), in 35% yield. The compound (44) was shown to be identical with the product of I spG protein, which serves as an intermediate in the non mevalonate terpene biosynthetic pathway (Scheme 7). ... 

Not all fungal tetronic acids are derived by this pathway. The biosynthesis of multicolic acid (6.17), a metabolite of P. multicolor, has been shown by carbon-13 labelling experiments to follow entirely a polyketide pathway. The proposed biosynthetic pathway (Scheme 6.2) involves the intermediacy of a 6-pentylresorcylic acid (6.16) and the cleavage of an aromatic ring. 

The biosynthetic source of the pyridone ring of 87 was investigated [260]. Thymine was found to inhibit uracil catabolism and 87 biosynthesis by Nocardia lactamdurans this inhibition was reversed by uracil catabolites. Both [5,6-3H]-uracil and [4,5-13c]-uracil were incorporated, with both labelled carbons of the latter being incorporated as a unit at C(4) and C(5) of 87. The proposed biosynthetic pathway (Scheme 2) involved catabolism of uracil to p-alanine, which was then incorporated into the pyridone ring of 87 [260]. 

Pyrrolnitrin.—Pyrrolnitrin (52), a metabolite of Pseudomonas aureofaciens, is known to derive from tryptophan and the D-isomer is a more effective precursor than L-tryptophan. The amino-compound (51) has been isolated from Ps. aureofaciens and is efficiently incorporated into pyrrolnitrin. A biosynthetic pathway (Scheme 7) has been proposed. 

Fig. 2.3 Biosynthetic pathway scheme for diterpene resin acids. Di-TPS is diterpene synthase P450 is cytochrome P450 dependent monooxygenase.

The most unexpected feature of the leu S mutants at the time they were first encountered was the effect of the mutation on the enzymes of the isoleucine-valine biosynthetic pathway (Scheme 2). As shown in... 

In general, alkaloids derive from the metabohsm of amino acids such as phenylalanine (Phe), tyrosine (Tyr), tryptophan (Trp), omitine (Om), or lysine (Lys). Quinolizidine alkaloids derived from L-lysine. Its decarboxylation by means of the enzyme lysine decarboxylase gives cadaverine (Cad), the first detectable intermediate of this biosynthetic pathway (Scheme 14.1). 

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