Building blocks enzymatic conversion

In keeping with its biogenetic origin m three molecules of acetic acid mevalonic acid has six carbon atoms The conversion of mevalonate to isopentenyl pyrophosphate involves loss of the extra carbon as carbon dioxide First the alcohol hydroxyl groups of mevalonate are converted to phosphate ester functions—they are enzymatically phosphorylated with introduction of a simple phosphate at the tertiary site and a pyrophosphate at the primary site Decarboxylation m concert with loss of the terti ary phosphate introduces a carbon-carbon double bond and gives isopentenyl pyrophos phate the fundamental building block for formation of isoprenoid natural products... 

The enzymatic conversion of a-(aminomethyl)pyrroles is also used by nature to produce porphyrinogens like uroporphyrinogen III (see introduction, compound 8), which is the key building block in the biosynthesis of all known porphinoid natural products. This biomimetic method is a powerful tool for the synthesis of different porphyrins, e.g. for the preparation of JV,Af, V ,Ar"-tetramethylporphyrin-2,3,7,8,12,13,17,18-octaacetic acid dibromide 12.36... 

The TS mediates the conversion of 2-deoxyuridine monophosphate (dUMP) into deoxythymidine monophosphate (dTMP). This enzymatic methylation reaction is a key step in the synthesis of DNA and involves a ternary complex between the substrate, the enzyme and the co-factor [methylene tetrahydrofolic acid (CH2FAH4)] (Fig. 24) [8,80,81], This transformation represents the sole de novo source of dTMP, a building block for DNA synthesis and repair [82]. 

Microbial or enzymatic preparations of the chiral building blocks useful in organic synthesis are reviewed. Conversions of these chiral building blocks to important bioactive natural products are also illustrated. 

The biosynthesis of cephalosporins is analogous to that of the penicillins. It is derived from the peptide 5-(a-aminoadipoyl)cysteinylvaline (see p 160). First, the P-lactam ring is formed. This is followed by a C-H bond fission, not at the p-position but at the y-position of the valine building-block. However, enzymatic conversion of the penam system into the ceph-3-em system cannot be excluded. 

Biosynthetically, majority of terpenoids are formed via the mevalonic acid, but they may also be formed through methyl-erythritol-4-phosphate (MEP) pathway. The C5 isoprene unit which can be linked together head to tail to form linear chains or cyclized to form rings is considered the building blocks of terpenes. Rather the C5 units exist as isopentenyl pyrophosphate or its isomer dimethylallyl pyrophosphate by enzymatic conversion and phosphorylation from mevalonic acid. The IPP may be considered as the precursor of hemiterpenes. In the biosynthesis of mono- and higher terpenes/terpenoids, the starting molecule is DMAPP, which... 

Well-defined sophorolipid biosurfactant analogs were also prepared via enzymatic synthesis for the evaluation of the bioactivity and as building blocks for the preparation of glycolipid-based polymers [107]. The direct enzymatic ring-opening polymerization of lactone sophorolipids (SLs) was carried out with lipases. The reaction proceeded with the formation of mono-acylated lactone SLs and the subsequent conversion of the intermediates to oligomers and polymers (Scheme 12) [108]. 

Several other materials are also produced in maize and a fairly high amount of solar energy is trapped in unused lignocellulosic stover. Ongoing studies are focused on the development of enzymatic biocatalyst and/or thermochemical processes to utilize lignocellulosic biomass, with improved conversion into energy or into molecular building blocks such as levulinic acid [361]. 

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