The constituents of Schizandra chinensis Baill. III. The structures of four new lignans, gomisin H and its derivatives, angeloyl-, tigloyl- and benzoyl-gomisin H.

Lignans from Schisandra sphenathera Rehd. et Wils. and semisynthetic schisantherin A analogues: Absolute configuration, and their estrogenic and anti-proliferative activity

“…The CD spectrum of 1 (Fig. 4) showed a negative band at 242 nm and a positive one at 227 nm, which is a distinctive feature of dibenzocyclooctadiene lignans with aS biphenyl configuration [14,24]. The consistency of this assignment for 1 and its confirmation by CD calculations are described below.…”

“…A CD sequence composed of a negative band around 240e250 nm and a positive one around 220e230 nm indicates a biphenyl M helicity, corresponding in most cases to aS configuration. Such a correlation was first observed by Ikeya et al [14,24] and has been applied to establish the absolute configuration of several dibenzocyclooctadiene lignans and related compounds. It is based on the more general and well-known biaryl helicity rule, established by Mislow [25] in the early 1960s and subsequently interpreted on a theoretical ground [26,27].…”

“…In fact, if we compare the CD spectrum of 1 (Fig. 4a) with those of lignans with similar skeleton but devoid of benzoate groups [17,24], large differences emerge. For example, Fig.…”

“…The EtOAc layer was repeatedly subjected to column chromatography on silica gel, Sephadex LH-20, and RP-18 to afford a new lignan, namely schisandrin A1 (1), together with 9 known ones. These known compounds were identified as schisantherin A (2) [12] (also known as gomisin C or wuweizi ester A) [14], wuweizisu C (3) [15], gomisin J (4) [16], schizandrin (5) [17], schisanbicolorin A (6) [18], (þ)-1-hydroxypinoresinol (7) [19], 8,8 0 -dihydroxypinoresinol (8) [20], clemaphenol A (9) [21], and (þ)-anwuligan (10) [22] (Fig. 1) by comparison with reported spectroscopic data.…”

“…On the contrary, it is expected that the two chromophores interact with each other according to the exciton-coupled CD mechanism [28], which may in principle generate strong CD signals [29]. In practice, it cannot be taken for granted that the helicity rule may be applied to benzoatecontaining lignans such as 1, as it is commonly done [3,14,24,30,31]. In fact, if we compare the CD spectrum of 1 (Fig.…”