PHOTODISCOLORATION OF WESTERN HEMLOCK (TSUGA-HETEROPHYLLA) SAPWOOD .2. STRUCTURES OF CONSTITUENTS CAUSING PHOTODISCOLORATION

The constituents causing photodiscoloration in Tsuga heterophylla (Raf .) Sarg. (Western hemlock, Pinaceae) sapwood were investigated. Five l ignans and one neolignan, the main constituents causing the discolorat ion, were isolated from the ethyl acetate soluble fraction of the meth anol extract of sapwood powders. (+)-Cedrusin (1), (+)-allohydroxymata iresinol (2), (-)-hydroxymatairesinol (3), (+)-oxomatairesinol (4), (- )-alpha-conidendrin (5) and (+)-Pinoresinol (6) were determined or ide ntified by instrumental analysis The constituents (1)-(3), the assignm ent of proton and carbon atoms corrected by a series of NMR analyses, or their stereochemical configurations finally were solved. In additio n, Vanillic acid (7), catechin (8) and vanillin (9) were detected as m inor constituents causing the discoloration by co-TLC and/or HPLC with authentic specimens. Almost all of them were found to contain two com mon structure moieties, a guaiacyl ring structure and an oxigenation s tructure, at the neighboring alpha-position on the aromatic ring, whic h might be presumed to cause the photodiscoloration of western hemlock sapwood.