Structural flexibility in the biocatalyst-mediated functionalization of ring ‘A’ in salannin, a tetranortriterpene from Azadirachta indica
作者:K. Madhava Madyastha、Krishnamachari Venkatakrishnan
DOI:10.1039/b004260i
日期:——
Nocardia sp. quantitatively converts salannin 1 and 3-de-O-acetylsalannin 2 (C-seco limonoids) into 3-deacetoxy-1-de[(E)-2-methylbut-2-enoyloxy]salannin-1-en-3-one 10, a novel and potentially bioactive compound with an α,β-unsaturated ketone moiety in ring âAâ. In order to establish the sequence of events involved in this transformation and the structural specificity of this bacterial system, several new derivatives of salannin 1 have been prepared. These studies have indicated that the transformation is initiated by deacetylation at C-3, followed by oxidation of the secondary hydroxy group to 3-keto, which appears to facilitate the elimination of the tigloyloxy/acetoxy group at C-1 with the formation of an olefinic linkage between C-1 and C-2.
The organism very efficiently transforms some of the derivatives of salannin into their corresponding compounds possessing an enone system in ring âAâ, an essential pre-requisite for various biological activities. Some of the C-seco limonoids prepared in the present study, viz. 10, 1,2-didehydro-1,3-dideoxy-3-oxosalannic acid 18, 3-deacetoxy-1-de[(E)-2-methylbut-2-enoyloxy]-20,21,22,23-tetrahydrosalannin-1-en-3-one 15 and 1,2-didehydro-1,3-dideoxy-3-oxosalannol 23 were hitherto not known.
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诺卡氏菌(Nocardia sp.)能将丹宁1和3-de-O-乙酰基丹宁2(C-seco柠檬酸类)定量转化为3-deacetoxy-1-de[(E)-2-methylbut-2-enoyloxy]salannin-1-en-3-one 10,这是一种新型的、具有潜在生物活性的化合物,其δ,δ²-不饱和酮分子位于环§Aâ。为了确定这种转化所涉及的事件顺序以及这种细菌系统的结构特异性,我们制备了几种丹宁 1 的新衍生物。这些研究表明,这种转化是由 C-3 处的脱乙酰化开始的,随后仲羟基被氧化成 3-酮,这似乎促进了 C-1 处的惕格酰氧基/乙酰氧基的消除,并在 C-1 和 C-2 之间形成了烯烃连接。 该生物体能非常有效地将一些丹宁衍生物转化成相应的化合物,这些化合物在环§Aâ上拥有一个烯酮系统,这是各种生物活性的一个基本前提。本研究中制备的一些C-seco柠檬酸类化合物,即10、1,2-二脱氢-1,3-二脱氧-3-氧代丹宁酸18、3-脱乙酰氧基-1-脱[(E)-2-甲基丁-2-烯酰氧基]-20,21,22,23-四氢丹宁-1-烯-3-酮15和1,2-二脱氢-1,3-二脱氧-3-氧代丹宁醇23,迄今为止尚不为人所知。