Abstract An efficient eight-step synthesis of optically pure (2S, 3R, 4S)-4-hydroxyisoleucine (1), a potent insulinotropic α-amino acid found in the seeds of fenugreek (Trigonella foenum- graecum L.), is achieved in 39% overall yield. The method is suitable for large-scale production of the title compound. The key steps involve the biotransformation of ethyl 2- methylacetoacetate to ethyl (2S, 3S)-2-methyl-3-hydroxybutanoate (2) with Geotrichum ...