de Costa B R, Lewin A H, Rice K C, Skolnick P, Schoenheimer J A
Laboratory of Medicinal Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892.
J Med Chem. 1991 May;34(5):1531-8. doi: 10.1021/jm00109a002.
p-, m-, and o-isothiocyanate derivatives (1-3, respectively) of tert-butylbicycloorthobenzoate (TBOB) were synthesized from 3-tert-butyloxetane-3-methanol (4) as the starting material. While 2 was readily obtained in four steps via catalytic hydrogenation of the m-nitro-tert-butylbicycloorthobenzoate (9) intermediate, 1 and 3 could not be obtained this way. 1 and 3 were instead synthesized by an alternative four-step approach while made use of the stability of the isothiocyanate moiety to strong Lewis acids such as boron trifluoride etherate, conditions that would isomerize isothiocyanato oxetane ester intermediates to their corresponding orthoesters. The p-isothiocyanate derivative of TBOB, compound 1, inhibited [35S]-tert-butylbicyclophosphorothionate (TBPS) binding to rat cortical membranes with a potency (IC50 62 nM) comparable to the parent compound while 2 and 3 were approximately 10-fold less potent (IC50 values 570 and 609 nM, respectively). Preincubating tissue with radioligand further reduced the potencies of 2 and 3 by approximately 1 order of magnitude (IC50 values 5400 and 7500 nM, respectively) while the potency of 1 (IC50 90 nM) was only marginally affected by this procedure. Pretreatment of membranes with 1 and 2 followed by extensive washing resulted in a concentration-dependent inhibition of [35S]TBPS binding. In contrast, preincubating tissues with up to 2.4 microM of 3 did not elicit an apparent acylation of [35S]TBPS binding sites. Molecular modeling of the effective diameters of 1-3 in their thermodynamically most stable conformations indicates a relationship between these diameters and their relative efficacies as site-directed acylators; the smaller the diameter, the more potent the acylator. This hypothesis explains both the relative potencies of these compounds and their differential abilities to acylate the TBPS binding site.
以3-叔丁基氧杂环丁烷-3-甲醇（4）为起始原料，合成了叔丁基双环原苯甲酸酯（TBOB）的对-、间-和邻-异硫氰酸酯衍生物（分别为1-3）。虽然通过间硝基叔丁基双环原苯甲酸酯（9）中间体的催化氢化反应，经四步反应可轻松得到化合物2，但无法用这种方法得到1和3。相反，1和3是通过另一种四步方法合成的，该方法利用了异硫氰酸酯部分对强路易斯酸（如三氟化硼乙醚）的稳定性，在这种条件下，异硫氰酸根合氧杂环丁烷酯中间体可异构化为相应的原酸酯。TBOB的对异硫氰酸酯衍生物化合物1抑制[35S]-叔丁基双环硫代磷酸酯（TBPS）与大鼠皮层膜结合的效力（IC50为62 nM）与母体化合物相当，而2和3的效力约低10倍（IC50值分别为570和609 nM）。用放射性配体预孵育组织可使2和3的效力进一步降低约1个数量级（IC50值分别为5400和7500 nM），而1的效力（IC50为90 nM）仅受到轻微影响。用1和2预处理膜，然后大量洗涤，会导致对[35S]TBPS结合的浓度依赖性抑制。相比之下，用高达2.4 μM的3预孵育组织不会引起[35S]TBPS结合位点的明显酰化。对1-3在其热力学最稳定构象下的有效直径进行分子模拟，结果表明这些直径与其作为定点酰化剂的相对效力之间存在关联；直径越小，酰化剂的效力越强。这一假设解释了这些化合物的相对效力及其酰化TBPS结合位点的不同能力。
