Lee J, Wang S, Milne G W, Sharma R, Lewin N E, Blumberg P M, Marquez V E
Laboratory of Medicinal Chemistry, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
J Med Chem. 1996 Jan 5;39(1):29-35. doi: 10.1021/jm950277n.
Conformationally constrained analogues of diacylglycerol (DAG) built on a racemic 5(-)[(acyloxy)-methyl]-5-(hydroxymethyl)tetrahydro-2-furanone template were shown previously to have excellent binding affinities for protein kinase C (PK-C). Since the interaction of PK-C with DAG is stereospecific, it was anticipated that PK-C would bind tightly to only one enantiomeric form of the compounds constructed with this new lactone template. Separation of enantiomers by chiral HPLC was discarded due to the ease with which acyl migration occurs in these class of compounds, and a total chiral synthesis was undertaken. Prior to chemical synthesis, the selection of the "correct" enantiomeric template was predicted by a molecular conformational analysis that compared the two enantiomers of DAG in their presumed "active" conformation with the two enantiomeric lactone templates. This presumed "active" conformation for DAG was derived from a previously developed pharmacophore model that uses the molecule of a potent phorbol diester as the ideal rigid template. The results from this analysis indicated that the "correct" lactone template corresponded to the inactive (R)-isomer of DAG. This analysis also predicted that the lactone template corresponding to the active (S)-DAG enantiomer would not fit adequately into the pharmacophore. The chiral syntheses of target compounds 2, 4, and 6, constructed on the selected, and presumably "correct" lactone template, were achieved from a common bicyclic intermediate (5R,8R,9R)-8,9-O-isopropylidene-2-keto-1,7-dioxaspiro[4.4]nonane (10) that was synthesized from commercially available 1,2:3,5-di-O-isopropylidene-alpha-D-threo-apiofuranose (7) by a very effective spirolactonization approach. On the basis of their ability to inhibit the binding of [3H-20]phorbol 12,13-dibutyrate (PDBU) to PK-C alpha, the enantiomeric ligands 2, 4, and 6 were twice as potent as the corresponding racemates. These results confirm that binding of these lactones is stereospecific and consistent with a binding mechanism similar to that of DAG.
先前已表明，基于外消旋5-[(酰氧基)甲基]-5-(羟甲基)四氢-2-呋喃酮模板构建的二酰基甘油（DAG）构象受限类似物对蛋白激酶C（PK-C）具有出色的结合亲和力。由于PK-C与DAG的相互作用具有立体特异性，预计PK-C只会与用这种新内酯模板构建的化合物的一种对映体形式紧密结合。由于这类化合物中酰基迁移容易发生，因此放弃了通过手性HPLC分离对映体的方法，并进行了全手性合成。在化学合成之前，通过分子构象分析预测了“正确”对映体模板的选择，该分析将DAG的两种对映体在其假定的“活性”构象下与两种对映体内酯模板进行了比较。DAG的这种假定“活性”构象源自先前开发的药效团模型，该模型使用强效佛波醇二丁酸酯分子作为理想的刚性模板。该分析结果表明，“正确”的内酯模板对应于DAG的无活性（R）-异构体。该分析还预测，对应于活性（S）-DAG对映体的内酯模板将无法充分适配到药效团中。在选定的、可能是“正确”的内酯模板上构建的目标化合物2、4和6的手性合成，是通过一种非常有效的螺内酯化方法，从市售的1,2:3,5-二-O-异亚丙基-α-D-苏阿糖呋喃糖（7）合成的常见双环中间体（5R,8R,9R）-8,9-O-异亚丙基-2-酮-1,7-二氧杂螺[4.4]壬烷（10）实现的。基于它们抑制[3H-20]佛波醇12,13-二丁酸酯（PDBU）与PK-Cα结合的能力，对映体配体2、4和6的效力是相应外消旋体的两倍。这些结果证实了这些内酯的结合具有立体特异性，并与类似于DAG的结合机制一致。
