Fumarase-Catalyzed Synthesis of t-threo-Chloromalic Acid and lts Conversion to 2-Deoxy-D-ribose and D-erythro-Sphingosine

These enzyrnes are indisputably valuable but have certain disadvantages, among which is often imperfect enantioselectivity. The standards in enantioselective synthesis are now very high: for most applications, an enantiomeric excess (ee) in an enantioselective step of less than 90% is essentially useless, and values of ee >99% are very desirable.a It is often difficult to achieve broad substrate selectivity and high enantioselectivity simultaneously. This difficulty poses a strategic question for the synthetic chemist: Is it better to use a structurally "efficient" intermediate with modest enantiomeric purity in a synthetic