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 P21 with four independent molecules in the asymmetric unit. The molecules are zwitterions. In the crystal, N—H...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