Ester enzymic preparation

In another approach, the alcohol moiety, formed by an enzymatic hydrolysis of an ester, can act as a nucleophile. In their synthesis of pityol (8-37a), a pheromone of the elm bark beetle, Faber and coworkers [17] used an enzyme-triggered reaction of the diastereomeric mixture of ( )-epoxy ester 8-35 employing an immobilized enzyme preparation (Novo SP 409) or whole lyophilized cells of Rhodococcus erythro-polis NCIMB 11540 (Scheme 8.9). As an intermediate, the enantiopure alcohol 8-36 is formed via kinetic resolution as a mixture ofdiastereomers, which leads to the diastereomeric THF derivatives pityol (8-37a) and 8-37b as a separable mixture with a... 

Hahlbrock K, Grisebach H (1970) Formation of coenzyme a esters of cinnamic acids with an enzyme preparation from cell suspension cultures of parsley. FEBS Lett ll(l) 62-64... 

CHS carries out a series of sequential decarboxylation and condensation reactions, using 4-courmaroyl-CoA (in most species) and three molecules of malonyl-CoA, to produce a poly-ketide intermediate that then undergoes cyclization and aromatization reactions that form the A-ring and the resultant chalcone structure. The chalcone formed from 4-courmaroyl-CoA is naringenin chalcone. However, enzyme preparations and recombinant CHS proteins from some species have been shown to accept other HCA-CoA esters as substrates, such as cinnamoyl-CoA (see, e.g., Ref. 37). In particular, the Hordeum vulgare (barley) CHS2 cDNA encodes a CHS protein that converts feruloyl-CoA and caffeoyl-CoA at the highest rate, and cinnamoyl-CoA and 4-courmaroyl-CoA at lower rates. 

Guanosine 5 -(a-D-rhamnopyranosyl pyrophosphate) (23) was shown to be a product of enzymic reduction of the mannosyl ester (17) in the presence of a plant extract93 or an enzyme preparation from an unidentified strain of Gram-negative bacteria.94,95 In the latter example, the 6-deoxy-D-talosyl ester, presumably 24, is also produced. 

The pyrophosphorylase procedures have been applied widely for preparation of various naturally occurring a-D-glucopyranosyl esters of nucleoside pyrophosphates. For synthetic purposes, it is common to use crude or partially purified enzyme preparations, which may be a mixture of individual, specific enzymes. The synthesis of adenosine 5 -(a-D-glucopyranosyl pyrophosphate) was achieved with pyrophos-phorylases from Arthrobacter viscosus 216,217 Azotobacter vinelandii,52... 

Enzyme preparations that can convert a-D-mannopyranosyl or 6-deoxy-a-D-Zt/xo-hexopyranosyl-4-ulose esters of guanosine 5 -pyro-phosphate into the /3-L-fucopyranosyl ester were obtained from Aerobacter aerogenes,99 432 Escherichia coli,100 Salmonella strains,433 higher plants,92 and animal tissues.434 Further purification of these enzymes will be necessary for mechanistic studies. 

Enzymic hydrolysis can often provide the means for solving a problem involving the partial hydrolysis of esters. A synthesis145 of 1-O-ab-scisoyl-/3-D-glucopyranose proved difficult at the last step, but the use of a crude enzyme-preparation obtained from ripe seeds of Helianthus annus allowed deacetylation to be achieved at 0-2, 3, 4, and 6 of the D-glucosyl group without rupture of the ester bond to the anomeric center. 

International Specialty Products (ISP) supplies ethyl, isopropyl, and n-butyl half-esters of PMVEMA as 50% solutions in ethanol or 2-propanol. These half-esters do not dissolve in water but are soluble in dilute aqueous alkali and in aqueous alcoholic amine solutions. The main application for the half-esters is in hairsprays where they combine excellent hair-holding properties at lugli humidity without making the hair stiff or harsh. These half-esters are easily removed during shampooing, have a very low order of toxicity, and form tack-free films that exhibit good gloss, luster, and sheen (see Enzyme Preparations). 

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