Department of Chemistry and Vanderbilt Institute of Chemical Biology, Vanderbilt University, Nashville, Tennessee 37235, USA.
J Am Chem Soc. 2010 Feb 24;132(7):2222-32. doi: 10.1021/ja9080265.
Free radical chain oxidation of highly oxidizable 7-dehydrocholesterol (7-DHC), initiated by 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), was carried out at 37 degrees C in benzene for 24 h. Fifteen oxysterols derived from 7-DHC were isolated and characterized with 1D and 2D NMR spectroscopy and mass spectrometry. A mechanism that involves abstraction of hydrogen atoms at C-9 and/or C-14 is proposed to account for the formation of all of the oxysterols and the reaction progress profile. In either the H-9 or H-14 mechanism, a pentadienyl radical intermediate is formed after abstraction of H-9 or H-14 by a peroxyl radical. This step is followed by the well-precedented transformations observed in peroxidation reactions of polyunsaturated fatty acids such as oxygen addition, peroxyl radical 5-exo cyclization, and S(H)i carbon radical attack on the peroxide bond. The mechanism for peroxidation of 7-DHC also accounts for the formation of numerous oxysterol natural products isolated from fungal species, marine sponges, and cactaceous species. In a cell viability test, the oxysterol mixture from 7-DHC peroxidation was found to be cytotoxic to Neuro2a neuroblastoma cells in the micromolar concentration range. We propose that the high reactivity of 7-DHC and the oxysterols generated from its peroxidation may play important roles in the pathogenesis of Smith-Lemli-Opitz syndrome, X-linked dominant chondrodysplasia punctata, and cerebrotendinous xanthomatosis, all of these being metabolic disorders characterized by an elevated level of 7-DHC.
高度易氧化的 7-脱氢胆固醇（7-DHC）在 37°C 下于苯中，以 2,2'-偶氮双（4-甲氧基-2,4-二甲基戊腈）引发自由基链式氧化，持续 24 小时。从 7-DHC 衍生的 15 种氧化固醇通过 1D 和 2D NMR 光谱和质谱进行分离和表征。提出了一个涉及在 C-9 和/或 C-14 处夺取氢原子的机制，以解释所有氧化固醇的形成和反应进展情况。在 H-9 或 H-14 机制中，在过氧自由基夺取 H-9 或 H-14 后，形成戊二烯基自由基中间体。这一步之后是在多不饱和脂肪酸如氧气加成、过氧自由基 5-外消旋环化和 Si（H）碳原子自由基攻击过氧化物键的过氧化反应中观察到的熟知的转化。7-DHC 过氧化的机制也解释了从真菌、海洋海绵和仙人掌物种中分离出的许多氧化固醇天然产物的形成。在细胞活力测试中，发现 7-DHC 过氧化产生的氧化固醇混合物在微摩尔浓度范围内对 Neuro2a 神经母细胞瘤细胞具有细胞毒性。我们提出，7-DHC 的高反应性及其过氧化产生的氧化固醇可能在 Smith-Lemli-Opitz 综合征、X 连锁显性软骨发育不良点状和脑腱黄瘤病的发病机制中发挥重要作用，所有这些代谢紊乱都以 7-DHC 水平升高为特征。
