Patent ID: 8871972

Claim:
A method for preparing adapalene, or a salt thereof, suitable for pharmaceutical use, comprising the steps of: (a) providing adapalene, or a salt thereof; (b) assessing the purity of said adapalene, or a salt thereof, by using 3,3′-diadamantyl-4,4′-dimethoxybiphenyl as a reference marker to determine the level of 3,3′-diadamantyl-4,4′-dimethoxybiphenyl impurity; and (c) subjecting the adapalene, or a salt thereof, to one or more purification steps until the content of 3,3′-diadamantyl-4,4′-dimethoxybiphenyl in said adapalene is not more than 0.2% with respect to adapalene.