The present disclosure relates to salts and polymorphs of aminoalkylfumagillol carbamates (e.g., fumagill-6-yl N-(trans-4-aminocyclohexyl)carbamate benzenesulfonic acid salt and fumagill-6-yl N-(trans-4-aminocyclohexyl)carbamate hydroxynaphthoic acid salt). The polymorphs are characterized by X-ray powder diffraction, differential scanning calorimetry, and thermogravimetric analysis, among other methods. The polymorphs and salts can be used as intermediates in the production of fumagillol derivatives (e.g., polymer-conjugated fumagillol derivatives) as well as therapeutic agents for the treatment of various diseases and conditions such as cancer.
