3α-Acetyl-β-boswellic acid (1), 3α-acetyl-α-boswellic acid (2), 3α-acetyl-9,11-dehydro-β-boswellic acid (3), 3α-acetyl-9,11-dehydro-α-boswellic acid (4) and 3α-acetyl-11-keto-β-boswellic acid (5) were isolated from the gum resin of Boswellia serrata. 1D and 2D NMR (COSY45, HMQC, HMBC, ROESY) spectra at 500 MHz were used for shift assignments and structure verification. All boswellic acids investigated share the cis conformation at ring D/E and the 3α orientation of the acetyl ester group. Owing to high-order spectra, NMR could not determine the exact conformation of H-20/H-30 of the β-boswellic acids. 3α-Acetyl-β-boswellic acid methyl ester (1′) was synthesized for experiments with a shift reagent, Eu(fod)3, that enhanced the resolution considerably. The oxygen atoms of the 3α-acetyl group form the apparent complex binding site for the shift reagent. Copyright © 2003 John Wiley & Sons, Ltd.
3α-乙酰基-β-
乳香酸(1)、3α-乙酰基-α-
乳香酸(2)、3α-乙酰基-9,11-脱氢-β-
乳香酸(3)、3α-乙酰基-9,11-脱氢-α-
乳香酸(4)和3α-乙酰基-11-酮-β-
乳香酸(5)是从锯叶乳香(BOSwellia serrata)的树胶
树脂中分离出来的。500
MHz下的1D和2D NMR(COSY45、HMQC、HMBC、ROESY)光谱用于位移分配和结构验证。所有
乳香酸在D/E环和乙酰酯基团的3α方向上具有顺式构象。由于高阶光谱,NMR无法确定β-
乳香酸的H-20/H-30的确切构象。3α-乙酰基-β-
乳香酸甲酯(1′)是为实验合成的,使用位移试剂Eu(fod)3,可大大提高分辨率。3α-乙酰基的氧原子形成位移试剂的明显复合结合位点。版权 © 2003 John Wiley & Sons, Ltd.