Williamson R Thomas, Boulanger Anna, Vulpanovici Alexandra, Roberts Mary A, Gerwick William H
College of Pharmacy, Oregon State University, Corvallis, Oregon 97331, USA.
J Org Chem. 2002 Nov 15;67(23):7927-36. doi: 10.1021/jo020240s.
The extract from a laboratory culture of an Indonesian isolate of the cyanobacterium Phormidium sp. displayed inhibitory activity in a Ras-Raf protein interaction assay. Assay-guided fractionation led to the isolation of both active and inactive materials of novel structure. The major inactive metabolite, phormidolide, was nevertheless highly toxic to brine shrimp (LC(50) = 1.5 microM), and hence, its structure was elucidated using various spectroscopic methods, primarily NMR. A series of partial structures were developed from standard experiments and then assembled using GHMBC, 2D INADEQUATE, and ACCORD-ADEQUATE data obtained on a (13)C-enriched sample. The relative stereochemistry at phormidolide's 11 chiral centers was established using the J-based configuration analysis method in concert with the G-BIRD(R)-HSQMBC NMR experiment. Absolute stereochemistry was determined on a bis-acetonide derivative using the variable temperature Mosher ester method. The robust number of NMR restraints provided from determination of most homonuclear and heteronuclear coupling constants in phormidolide, along with an abundance of NOE information, allowed construction of a refined lowest energy three-dimensional structure in Macromodel. Phormidolide is one of only a few macrolide-type natural products to be reported from marine cyanobacteria.
来自印度尼西亚蓝藻席藻属（Phormidium sp.）分离株实验室培养物的提取物在Ras-Raf蛋白相互作用试验中显示出抑制活性。通过试验引导的分级分离得到了具有新结构的活性和非活性物质。主要的非活性代谢产物，即席藻内酯，对卤虫具有高毒性（LC(50) = 1.5 microM），因此，使用各种光谱方法，主要是核磁共振（NMR）对其结构进行了阐明。通过标准实验得到了一系列部分结构，然后使用在富含(13)C的样品上获得的GHMBC、二维INADEQUATE和ACCORD-ADEQUATE数据进行组装。利用基于J的构型分析方法并结合G-BIRD(R)-HSQMBC NMR实验确定了席藻内酯11个手性中心的相对立体化学。使用可变温度Mosher酯法在双丙酮化物衍生物上确定了绝对立体化学。席藻内酯中大多数同核和异核耦合常数的测定以及丰富的NOE信息提供了大量的NMR限制条件，从而能够在Macromodel中构建精细的最低能量三维结构。席藻内酯是从海洋蓝藻中报道的为数不多的大环内酯类天然产物之一。
