ORGN 767 |
| Kinetic resolution of racemates is an important method for the production of enantiomerically-pure compounds (eg Scheme 1). If k >> kent both the unchanged alcohol ent-1 and the product acetate 2 can be obtained in high enantiomeric purity (>99%). However, each product is obtained with a maximum yield of 50%. Dynamic kinetic resolution (DKR) is possible when the chiral starting material racemises rapidly (krac >> k >> kent) but when racemisation of the product is very slow (Scheme 2). In this case, it is possible to reach high enantiomeric purity with a theoretical maximum yield of 100%. In general, two catalysts are required for DKR, one of which must be enantioselective (usually an enzyme). However, “it is essential to identify a suitable enzyme to effect the kinetic resolution [...] which is not adversely affected by (or causes adverse effects on) the [...] catalyst". (Caddick, 1996) We are developing an entirely novel protocol, which obviates the need for the enantioselective and racemisation DKR catalysts to tolerate each other. Our proposal rests on the principle of membrane-separation of higher molecular weight species (the catalysts) from lower molecular weight species during the reaction. We will present the comparative results of reactions carried out in normal and membrane-separated systems, with chiral alcohols as substrates and organoruthenium racemisation catalysts and lipase enzymes that would not normally tolerate each other.
|
|
Asymmetric Reactions, Molecular Recognition, Self Assembly, Bioorganic Chemistry, Process R&D
8:00 PM-10:00 PM, Wednesday, 16 March 2005 Convention Center -- Hall D, Poster
Division of Organic Chemistry |
