Mechanochemo-enzymatic synthesis of aromatic aldehyde oxime esters

Abstract

The synthesis of aromatic aldehyde oxime esters (considered fragrances, antifungal and antimicrobial compounds) was achieved by two reactions which combine the advantage of green chemistry and biocatalysis. In the first step, the mechanochemical oxime synthesis by means of grindstone milling of six solid aromatic aldehydes and hydroxylamine hydrochloride in the presence of FlorisilR, as the best support, yielded the aromatic aldehyde oximes 1-6 with high purity and good yields. In the second step the lipase catalyzed acetylation reaction at 40°C for three days of those oximes with vinyl and isopropenyl acetates as acyl donor substrates and ethyl acetate as the solvent, yielded the aromatic aldehyde oxime esters. With Candida antarctica lipase (Novozyme 435), the conversions of oximes 1-6 into their esters were ≥ 99% according to the 1H NMR results and it was the best biocatalyst compared with others such as Candida rugosa (CRL), porcine pancreas lipase and the recombinant lipase LipMatCCR11 from the thermophilic strain Geobacillus thermoleovorans CCR11 cloned and expressed in Escherichia coli BL21 (DE3), all of which showed lower yields.