Regioselective acylation of d-ribono-1,4-lactone catalyzed by lipases

Lipases from ten different sources and two mycelium-bound lipases isolated from Amazonian fungi were screened as biocatalysts in the acylation reaction of d-ribono-1,4-lactone with a variety of acyl donors in non-aqueous media. Several reaction parameters were evaluated including the type and amount of enzyme, acyl donor, and organic solvent, as well as the influence of water and the recyclability of the catalyst. When Candida antarctica lipase (CAL-B) was used, the acylation was highly regioselective and the corresponding 5-acyl-d-ribono-1,4-lactones were observed as the sole product. The best conversion (>99%) into 5-acetyl-d-ribono-1,4-lactone was obtained through the combination of vinyl acetate as the acetyl donor and 10 mg (100 U) of CAL-B in dry acetonitrile after 24 h. However, lipases from Burkholderia cepacia (PSL-C and PSL-D), Pseudomonas fluorescens (AK) and Thermomyces langinosus (Lipozyme TL-IM) gave mixtures of mono-, di- and tri-acetylated products in lower conversions. CAL-B maintained its catalytic activity during five cycles of repeated use when decanoic and dodecanoic acids were employed as acyl donors in the acylation of d-ribono-1,4-lactone.