No abstract

C h e m o e n z y m a t i c P r e p a r a t i o n o f N o v e l S u b s t r a t e s f o r F e r u l o y l E s t e r a s e sAbstract: Four novel active esters of 4-hydroxy-3-methoxycinnamic acid as substrates for feruloyl esterases were prepared in a four-step procedure including chemoselective enzymatic deprotection of acetylated compounds by Lipase PS.Hydroxycinnamic esterases are attracting growing interest as promising biocatalysts in the processing of hemicelluloses 1 and wine 2 as well as in the production of phenolic acids as fine chemicals 3,4 from natural resources. Although not distributed as purified enzymes, they are present in commercial hemicellulases, pectinases and lipases. This fact has generated a demand for new substrates of hydroxycinnamic esterases for use in rapid assays and enzymatic synthesis. Here we report a facile and efficient way to prepare 4-nitrophenyl, 4-methylumbelliferyl, 1-naphthyl and 2,2,2-trifluoroethyl esters of 4-hydroxy-3-methoxycinnamic acid with chemoselective enzymatic alcoholysis of the corresponding 4-O-acetylated ester intermediates as a key deprotection step.The synthesis of active esters 4a-d started from ferulic acid (4-hydroxy-3-methoxy-trans-cinnamic acid, 1). In the first step, acetylation of 1 was necessary to avoid side reactions. 5 Chloride 2 was then prepared by stirring acetylated 1 with SOCl 2 in toluene at 75 °C for 2 hours. Efficient esterification (0.85 equiv Et 3 N-0.25 equiv DMAP in CH 2 Cl 2 ) 6 gave 3a-d in 88-91% yield after crystallization from aqueous acetone (Scheme).There are numerous mild and selective chemical and enzymatic methods described in the literature for deacetylation of aromatic acetates without affecting aliphatic esters. 7-10 Esters 3a-d, however, represent activated aryl and alkyl esters sensitive both to acidic and mildly basic conditions. 11 That is why selective deprotection of the hydroxycinnamate part of the molecule is a delicate problem. Treatment of 3a-d (1 mmol) with the 1.1 equivalent of pyrrolidine 12 (added stepwise during three days) in 100 mL ethanol/CH 2 Cl 2 (1:1) showed very low chemoselectivity and high sensitivity of aryl esters 3a-c to mild basic conditions (Scheme). No hydrolysis of trifluoroethyl ester 4d was observed, 13 but 4-nitrophenyl (4a) and 4-umbelliferyl (4b) esters were completely hydrolyzed (Table). 1-Naphthyl ferulate (4c) was partially cleaved, approximately 10% of ferulic acid was found in the reaction mixture according to TLC. Subsequent purification of 4c was complicated by the presence of liberated 1-naphthol.During our work on feruloyl esterases we found that a commercial preparation of lipase from Burkholderia cepacia 14 (originally classified as Pseudomonas cepacia) possesses no feruloyl esterase or any other contaminating hydrolase activity, 15 thus allowing it to be used for deacetylation of 3a-d without risking concurrent hydrolysis of labile ester bonds. Moreover, the enzyme is stable in chlorinated solvents 16 in which the starting esters 3a-d are soluble. The enzymatic acetyl cleava...

ChemInform 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.