Magnoshinin (1) was conveniently synthesized from E-asarone (5) under photochemical conditions. Photochemical conversion of cyclobutane type dimers was also described.
Previously, we reported the isolation and characterization of magnoshinin (1) and magnosalin (z), new neolignans from buds of Magnolia saZicifoZiaMAXIM. 1) Recently, both of 1 and ? were found to show inhibitory effects on adjuvantinduced inflammation in mice. 2) Of these compounds, 1 is particularly interesting, since the anti-inflammatory effect of 1 is fairly strong, being nearly half of that of hydrocortisone acetate when administered orally. We now report a convenient synthesis of 1 utilizing photochemical dimerization of E-asarone (5). 3) A typical synthetic operation is described below.
A degased solution of 5 (0.5 mmol) in acetonitrile (10 ml) containing pyromellitic acid (1 mmol) as an electron acceptor 4) was irradiated with a 300 W high-pressure mercury lamp for 70 h at room temperature. The reaction mixture was concentrated under reduced pressure. The residue was purified by preparative TLC on Merck Kieselgel 60 PF254 with AcOEt-benzene (1:9)to give dimeric products, magnoshinin (1) 5) and magnosalin (2) 6)in 14 and 6 % yields,respectively (Table I).
Identities of 1 and z were confirmed by comparisons of their spectral data with those of authentic samples. Results employing other electron acceptors are shown in Table I.