A new indole alkaloid, 7-α-hydroxy-7H-mitragynine, from Mitragyna speciosa in Thailand - Ponglux,D.; Wongseripipatana,S.; Takayama,H.; Kikuchi,M.; Kurihara,M.; Kitajima,M.; Aimi,N.; Sakai,S. (Planta Medica, 1994)