A detailed account is given of the chiral synthesis of tri-O-methylimbricatine (3), the tri-O-methyl derivative of the structurally unique benzyltetrahydroisoquinoline alkaloid imbricatine (2) isolated from the starfish Dermasterias imbricata. The route begins with the asymmetric synthesis of the sulfur-containing d-phenylalanine derivative (R)-11a and includes its conversion into the cis-benzyltetrahydroisoquinoline moiety 26a possessing the thiol group and construction of the 5-arylthio-3-methyl-l-histidine portion. The correctness of the structure and absolute configuration proposed for imbricatine has been unequivocally confirmed as a result of the present synthesis.