用非亲核碱基 1,8-二氮杂双环[5,4,0]undec-7-ene (DBU) 处理 27-O-乙酰基withaferin A (2)，得到 5β,6β-环氧-4β-羟基- 1-oxo-witha-2(3),23(24),25(27)-trienolide (3) and 4，withaferin A 的同二聚体，由中间体 α 的 Diels-Alder [4 2] 型环加成反应产生， β-二亚甲基-δ-内酯(9)。使用 HRMS 以及一维和二维核磁共振波谱数据阐明了 3 和 4 的结构。 4的结构也通过其双-4-O-对硝基苯甲酸酯(8)的单晶X射线晶体学分析得到证实。作为主要产物的醉茄素 A 同型二聚体 (4) 的形成表明 9 的 Diels-Alder [4 2] 环加成反应具有区域选择性和立体选择性。2-4 的乙酰化分别得到其乙酰基衍生物 5-7。评估了化合物2-4和6-8对四种前列腺癌(PC)细胞系(LNCaP、22Rv1、DU-145和PC-3)和正常人包皮成纤维细胞(HFF)的细胞毒性活性。值得注意的是，与其他化合物相比，4 对大多数测试的细胞系表现出更高的活性。

Treatment of 27-O-acetylwithaferin A (2) with the non-nucleophilic base, 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU), afforded 5β,6β-epoxy-4β-hydroxy-1-oxo-witha-2(3),23(24),25(27)-trienolide (3) and 4, a homodimer of withaferin A resulting from a Diels-Alder [4 + 2] type cycloaddition of the intermediate α,β-dimethylene-δ-lactone (9). Structures of 3 and 4 were elucidated using HRMS and 1D and 2D NMR spectroscopic data. The structure of 4 was also confirmed by single crystal X-ray crystallographic analysis of its bis-4-O-p-nitrobenzoate (8). Formation of withaferin A homodimer (4) as the major product suggests regio- and stereoselectivity of the Diels-Alder [4 + 2] cycloaddition reaction of 9. Acetylation of 2-4 afforded their acetyl derivatives 5-7, respectively. Compounds 2-4 and 6-8 were evaluated for their cytotoxic activities against four prostate cancer (PC) cell lines (LNCaP, 22Rv1, DU-145, and PC-3) and normal human foreskin fibroblast (HFF) cells. Significantly, 4 exhibited improved activity compared to the other compounds for most of the tested cell lines.