Hyflo Super Cell

In conventional synthetic transformations, enzymes are normally used in aqueous or organic solvent at moderate temperatures to preserve the activity of enzymes. Consequently, some of these reactions require longer reaction times. In view of the newer developments wherein enzymes can be immobilized on solid supports [183], they are amenable to relatively higher temperature reaction with adequate pH control. The application of MW irradiation has been explored with two enzyme systems namely Pseudomonas lipase dispersed in Hyflo Super Cell and commercially available SP 435 Novozym (Candida antarctica lipase grafted on an acrylic resin). 

Celite or hyflo super cell (20 g) was added to the suspension which was then filtered through a pad of hyflo in a wide-sinter funnel the pad was washed with water (100 mL). The filtrate was saturated with sodium chloride and then extracted with ethyl acetate (5 x 500 mL). The combined extracts were dried over magnesium sulfate, filtered and the solvent was removed under reduced pressure to afford a pale viscous oil. 

The fermentation broth is adjusted at pH 8.0 and then filtered using Hyflo super-cell as a filter aid. The mycelium is discarded and the filtrate is extracted with an amount of butanol corresponding to about 0.5 of its volume. The organic phase is separated from the aqueous one, and, after washing with acidic water (pH 4.0) is concentrated to about 1 10 of its original volume and allowed to stand for 10-12 h at a temperature of 3°-6°C. A crude precipitate forms, which is collected on filter, washed with butanol and dried under vacuum at room temperature yield 3.0 g. 

Kellogg, Feringa and co-workers have achieved successful dynamic kinetic resolution reactions using cyclic hemiacetals as substrates[13, 14l The enzyme-catalyzed acetylation of 6-hydroxypyranone shown in Fig. 9-6 has been achieved with reasonable enantioselectivity with essentially complete conversion. The racemisation of the hemiacetal is presumed to proceed via reversible ring-opening of the pyranone1 1. The rate of reaction was found to greatly increase when the enzyme, lipase PS (Pseudomonas sp.) was immobilized on Hyflo Super Cell (HSC). 

PCL on Hyflo Super Cell , vinyl acetate, t-BuOMe, from 85 to 93 % ee... 

Recently, Feringa explored also another variant of this methodology by replacing (5/ )-menthyloxyfuran-2(5//)-one with another chiral butenolide, namely (/ )-5-acetoxyfuran-2(577)-one (113), Scheme (20) [76,77]. The chiral butenolide was obtained in several gram scale by enzymatic esterification of 5-hydroxyfuran-2(577)-one (111) using lipase R immobilized on hyflo super cell. 

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