Crystal structure of a new polymorph of (2S,3S)-2-amino-3-methylpentanoic acid

A new polymorph of (2S,3S)-2-amino-3-methylpentanoic acid, l-isoleucine C6H13NO2, crystallizes in the monoclinic space group P2(1) with four independent molecules in the asymmetric unit. The molecules are zwitterions. In the crystal, N-H center dot center dot center dot O hydrogen bonds link two pairs of independent molecules and their symmetry-related counterparts to form two types of layers stacked in an anti-parallel manner parallel to (001). The hydrophobic aliphatic isopropyl groups protrude from these layers.