A practical chemoenzymatic synthesis of (R)-isovaline based on the asymmetric hydrolysis of 2-ethyl-2-methyl-malonamide

(R)-Isovaline has potential applications in drug development, and therefore the development of an efficient method for the production of (R)-isovaline is desired. Herein we have investigated the asymmetric hydrolysis of 2-ethyl-2-methyl-malonamide into (S)-2-ethyl-2-methyl-malonamic acid, a useful synthetic intermediate in the production of (R)-isovaline, using CsAM, which is a recombinant amidase originally derived from Cupriavidus sp. KNK-J915. The produced (S)-2-ethyl-2-methyl-malonamic acid (98.6% ee) could be easily converted into (R)-isovaline by the Hofmann rearrangement. Starting from diethyl 2-methylmalonate, we obtained (R)-isovaline (99.1% ee) in 58.6% yield over eight steps, including the CsAM-catalyzed asymmetric hydrolysis of 2-ethyl-2-methyl-malonamide.

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(S)-2-Ethyl-2-methyl-malonamic acidC6H11NO3Ee = 98.6%[α]D25 = +9.0 (c 0.1, MeOH)Absolute configuration: (S)

(R)-IsovalineC5H11NO2Ee = 99.1%[α]D25 = −8.2 (c 1.0, H2O).Absolute configuration: (R)