Anhydrides of 3β,28-diacetoxy-21,22-secolup-18-ene-21,22-dioic acid (1) and (19R)-3β,28-diacetoxy-18β,19-epoxy-21,22-secolupane-21,22-dioic acid (11) undergo alkaline hydrolysis yielding the corresponding dicarboxylic acids. Depending on reaction conditions, these acids are further transformed yielding various lactones, liberating C-28 hydroxymethyl group, or undergoing decarboxylation leading to nor derivatives. This method has been used to prepare a diverse series of E-secolupane derivatives including lactonoacids (e.g. 2 and 15), lactones (4, 16 and 17), 28-nor derivatives (3 and 6) and 21,28-dinor derivatives (12 and 13). Derivatives of (19R)-3β,28-dihydroxy-18β,19-epoxy-21,22-secolupane-21,22-dioic acid 21,28-lactone (15c), bearing a free carboxylic group, are labile and can only be isolated as the corresponding dilactones 17. The C-22 carboxylic group forms a β-lactone by a nucleophilic α-directed attack on the C-18 epoxide ring carbon atom resulting in (19R)-3β,19-dihydroxy-21,22-secolupane-21,28:22,18α-dilactone (17b) and related derivatives. The structure and stereochemistry of the compounds discussed in this contribution were derived from IR, MS, 1H and 13C NMR spectra (1D and 2D COSY, TOCSY, NOESY, HSQC, HMBC). Using these NMR techniques and measuring the solvent influence on the IR carbonyl stretching frequencies of the dilactones 17, an equilibrium between the two E-ring conformations was shown to exist.
3β,28-二乙酰氧基-21,22-环氧鲁皮烯-18-烯-21,22-二羧酸(1)和(19R)-3β,28-二乙酰氧基-18β,19-环氧-21,22-环氧鲁皮烷-21,22-二羧酸(11)的酐在碱性水解条件下生成相应的二羧酸。根据反应条件的不同,这些酸进一步转化为各种内酯,释放C-28羟甲基基团,或经过脱羧反应生成诺尔衍生物。这种方法已被用来制备多种E-环氧鲁皮烷衍生物,包括内酯酸(例如2和15)、内酯(4、16和17)、28-诺尔衍生物(3和6)和21,28-二诺尔衍生物(12和13)。具有一个游离羧基的(19R)-3β,28-二羟基-18β,19-环氧-21,22-环氧鲁皮烷-21,22-二羧酸21,28-内酯(15c)的衍生物是不稳定的,只能以相应的二内酯17形式分离。C-22羧基通过对C-18环氧环碳原子的亲核α位攻击形成β-内酯,从而生成(19R)-3β,19-二羟基-21,22-环氧鲁皮烷-21,28:22,18α-二内酯(17b)及相关衍生物。本文讨论的化合物的结构和立体化学是通过IR、MS、1H和13C NMR光谱(1D和2D COSY、TOCSY、NOESY、HSQC、HMBC)推导的。利用这些NMR技术并测量溶剂对二内酯17中IR羰基伸展频率的影响,表明存在两种E环构象之间的平衡。