AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The asymmetric oxidation of some enones (Table 1), selected dienones 3-5, and a trienone 13 is accomplished using poly-L-leucine or poly-D-leucine and urea hydrogen peroxide under non-aqueous conditions. One of the resultant epoxy ketones 6 has been converted into the delta-lactones 19 and 22.

The oxidation of chalcone 1 to optically active epoxide 2 [a precursor of (+)-clausenamide (+)-3] may be effected using a 15-mer or 20-mer of L-leucine bound to a PEG based support; poly-L-leucines of this type may be used as immobilised catalysts in a fixed-bed reactor.

Polyamino acids are easy to prepare by nucleophile-initiated polymerisation of amino acid N-carboxyanhydrides. Polymers such as poly-(l)-leucine act as robust catalysts for the epoxidation of a wide range of electron-poor alkenes, such as γ-substituted α,β-unsaturated ketones. The optically active epoxides so formed may be transformed into heterocyclic compounds, polyhydroxylated materials and biologically active compounds such as diltiazem and taxol side chain.

Poly(L-leucine) catalysed oxidation of dienes 2, 3, 10, 16 and 18 and the triene 17 furnishes the corresponding epoxides 4, 5, 11, 19, 21 and 20 respectively in good to excellent yield and in states of high optical purity. Some regioselective reactions of the saturated epoxy ketones 5 and 11 are described.

The enantioselective hydrolysis of chiral esters using esterases and lipases gives access to key optically active intermediates en route to prostaglandins, coriolic acid, the anti-HIV agent carbovir and mevinic acid type hypocholestemic agents. The hydrolysis of meso-esters using hydrolases is a very efficient strategy in organic synthesis and has been used to prepare the carbocyclic nucleosides neplanocin and risteromycin. Acylases have been used to prepare (-)-carbovir and both enantiomers of a GABA-mimetic from 2-azabicyclo[2.2.1)hept-5-en-3-one. The employment of nitrilases and nitrile hydratases is gaining in popularity; for example, prochiral 2-benzoyloxypropane-1,3-dinitrile is hydrolysed to (S)-3-benzoyloxy-4-cyanobutanoic acid with exquisite selectivity. Lipases in organic solvents can effect esterification, transesterification and interesterification reactions and this popular methodology has been used to prepare key norcarbocyclic nucleotides and carbocyclic oxetanocin A in single enantiomer form. Yeast­ catalysed reductions of ketones afford optically active secondary alcohols, typically employed for the synthesis of pheromones, fragrances and chemotactic agents such as leukotriene-84. Instead of a whole-cell system such as yeast, partially purified dehydrogenases can be employed to synthesise (S)-secondary alcohols, for examplan intermediate to the antifungal agent brefeldin-A. Biohydroxylations are important reactions and are being applied to a wide range of substrates. The oxidation of benzene and derivatives to the corresponding cyclohexadiene diols are classic examples and have provided a route to analogues of cyclophellitol. Similarly, mono-oxygenase catalysed Baeyer-Villiger reactions are now well-documented and have furnished intermediates to carbocyclic-AZT, lipoic acid and azadirachtin. Sulfoxides of high optical purity have been prepared by yeast-catalysed oxidation, while enzymes in the transferase and lyase classes have been used to make carbohydrates and amino acids. In conclusion, the science of biotransformations opens up numerous synthetic routes to a wide variety of target molecules that are not easily accessible by other methods of synthetic organic chemistry.