title: Longiberine and O-methyllongiberine, dimeric protoberberine-benzyl tetrahydroisoquinoline alkaloids from Thalictrum longistylum(1).
abstract: Two benzyltetrahydroisoquinoline-protoberberine dimers, longiberine (1) and O-methyllongiberine (2), were isolated from the roots of Thalictrum longistylum and represent a new class of dimeric alkaloids. The structure of longiberine (1) was established by spectral and chemical methods. Reductive cleavage of O-ethyllongiberine (4) with Na/liquid NH(3) yielded (+)-(S)-N-methylcoclaurine (5), which determined one-half of the dimer, and 1D and 2D NMR studies arranged the substituents on the protoberberine nucleus. Chemical conversion of thalidezine (6) to 1 via the O-acetyl N,N-didemethyl derivative 9, which was methylenated in the Mannich reaction and N-methylated by the Eschweiler-Clarke procedure, established the second asymmetric center as S and confirmed the ring size and the order of the substituents for 1. Methylation of 1 with diazomethane formed the O-methyl derivative 2, identical with the natural product.
authors.affiliation: Division of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, The Ohio State University, Columbus, Ohio 43210-1291, USA.
authors.forename: S S
authors.initials: SS
authors.lastname: Lee
authors.forename: W N
authors.initials: WN
authors.lastname: Wu
authors.forename: J H
authors.initials: JH
authors.lastname: Wilton
authors.forename: J L
authors.initials: JL
authors.lastname: Beal
authors.forename: R W
authors.initials: RW
authors.lastname: Doskotch
mesh_terms: D000470:Alkaloids / Q000737:chemistry / Q000302:isolation & purification*; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry / Q000379:methods; D015394:Molecular Structure; D010944:Plants / Q000737:chemistry*
chemical_list: D000470:Alkaloids; C400583:O-methyllongiberine; C400582:longiberine