50 g of acetic acid 2-[5-(2,2-dimethylpropionylamino)-pyrazin-2-yl]-2-oxo-ethyl ester (178 mmol) was stirred in 150 ml tert-butyl methyl ether (TBME). Subsequently the reaction buffer, 674 mL 20 mM of 2-(4-morpholino)-ethansulfonic acid, and 100.1 g of D-glucose (658 mmol) were added. The temperature was adjusted to 29° C. and the pH to 6.25. The reaction—deacetylation—was started by the addition of 2.01 g lipase AH. Directly afterwards, 40 mg of glucose dehydrogenase GDH 102, 201 mg of ketoreductase KRED 101 and 202 mg of cofactor NADP were added to initiate the asymmetric reduction. The reaction temperature was increased up to 37° C. The stirred suspension was maintained at pH 6.25 (and 37° C.) by the controlled addition (pH-stat) of 1.0 N sodium hydroxide solution. After 11.2 h, after a total consumption of 354.1 mL of 1.0 N sodium hydroxide, and after complete conversion, the reaction mixture was stirred for further 10.5 h. For the product extraction 300 g of sodium chloride were added into the reaction mixture and the pH was adjusted to 7.5. Subsequently, the reaction mixture was extracted 5 times with 1 L of ethyl acetate. The phase separation occurred spontaneously. The combined organic phases were dried over anhydrous sodium sulfate, evaporated and dried on HV over night. 44.76 g (S)—N-[5-(1,2-dihydroxy-ethyl)-pyrazin-yl]-2,2-dimethyl-propionamide (4) (96.4% HPLC purity, [SupelcoSil ABZ+, 250×4.6 mm, eluent 20-90% acetonitrile/water+0.1% TFA over 10 min at 1 mL/min, detection at UV 300 nm, retention time 5.3 min], ee>99.9% [Chiralpak IA, 250×4.6 mm, 5 μm, eluent 50% Heptane 50% Ethanol/Methanol 1:1 over 20 min at 1 mL/min, detection at UV 240 nm, retention time enantiomers 9.3 and 10.9 min]) were isolated as a light orange, highly viscous oil.
