- 2 - amino - 7 -- 2 - methylhept - 5 - enoic acid is crystallized as an anhydrous , stoichiometric 1 . 5 hcl salt and a scaleable crystallization method is disclosed . the salt form was characterized and the absolute configuration of the chiral center was confirmed as “ s ”. - 2 - amino - 7 -- 2 - methylhept - 5 - enoic acid was high melting and appears acceptably non - hygroscopic for use in a pharmaceutical composition .