2 新規カーサミン生合成中間体アンヒドロサフロールイエロウBの構造と花弁色素群の生合成研究(口頭発表の部)

抄録

Safflower(Carthamus tinctorius L.)is well known as one of source plants of red pigments since ancient times. From the petals a red pigment, carthamin (4), several orange and yellow ones, precarthamin (3) and safflor yellow B (2) etc., and flavonol glycosides, 9 etc., were identified by us and other several groups. 3, an unstable orange yellow pigment, was confirmed to be a precursor of carthamin by us. However, the stereochemistry of the determined structural formulas and their biosynthetic path way are still unresolved. During the search study of biosynthetic intermediates into precarthamin, we now isolated a new compound, named as anhydrosafflor yellow B (1), as dark orange powder which was transformed into carthamin by standing the solution dissolved in the NMR solvent(methanol/pyridine=95/5) for a month at r.t.. It showed m/z 1045(FAB^+, [M+H]^+), λ_<max> 410nm (ε42000, Me0H), λ_<εxt>441nm (Δε+45.4) and λ_<ext>386nm (Δε-30.8). From ^1H, ^<13>C, and 2D NMR spectra(Table) the presence of two cinnamoyl, two 2,4,6-trihydroxy-4-C-glucosyl-cyclohexadienone, and a six carbon C-1 deoxyglycitol groups are confirmed. These data suggested that this compound also have a dimeric quinochalcone skeleton, such as 2 and 3, common in pigments of safflower. The δ values of the C-2 carbon of glycitol at 94.2 and the oxygen substituted sp^2 carbon at 171.3 are shifted to lower and higher field, respectively, compared with δ values of the corresponding carbon in 2. This suggested that these two carbon were binded through an ether bond and hence, a five membered ether ring was formed in 1. Since J_<H1-H2> and J_<H2-H3> in the glycitol were 8.5 and 3.4Hz respectively and it seems the glycitol was derived from D-glucose, it was determined that the juncture of the five membered ether ring was trans and the glycitol was 1-deoxy D-glucitol with a defined C-1 configuration. Because of a keto-enol tautomerism of carbonyl group to form an ether bond, two different ring closed structures are formed and furthermore two configurational isomers at C-4 in the cyclohexadienone ring should be considered. Therefore, the four structural isomers for the plane structural formula of 1 are inferred. The conformational analysis for them by a molecular mechanics simulation(Fig. 2) and the judgment for calculated structures based on the CD (plus chirality) and NOE(between glucitol and one cinnamoyl) were carried out. Consequently, a most expected structure is considered to be A shown in Fig. 2 with a extended arrangement of two cynnamoyl groups and trans configuration for the C-1 H of D-glucitol and D-glucose in the cyclohexane ring without ether bond.