Chemical structures of isolated compounds from mangosteen peel: protocatechuic acid a, cyanidin-3-sophoroside b, cyanidin-3-glucoside c, pelargonidin-3-glucoside d, procyanidin A-2 e, procyanidin B-2 f, (−)-epicatechin g, garcimangosxanthone A h, garcimangosxanthone B i and garcimangosxanthone C j (modified from Yoshikawa et al. 1994; Zhang et al. 2010; Zarena and Udaya Sankar 2012)