Jones D W, Sowden J M
Cancer Biochem Biophys. 1976;1(6):281-8.
The crystal structure of the moderately active carcinogen 12-methylbenz[alpha]anthracene (12-MBA) has been determined by application of direct methods to X-ray single-crystal diffraction data. Least-squares refinement to a residual R = 0.09 over 929 independent reflections enabled carbon positions to be established with apparent e.s.d.s. of atomic coordinates about 0.008 A. Deviation from planarity is exemplified by the 15.5 degrees inclination of the benz ring (A) to the anthracene nucleus and by the 0.89 A distance of the methyl carbon out of the best plane through the whole benzanthracene nucleus. Comparison with the structure of the highly carcinogenic 7,12-dimethylbenz[alpha]anthracene (7,12-DMBA), and with the recently solved structures of the weak carcinogen 1-MBA and the extremely weak carcinogen 1,12-DMBA, shows a close similarity in the anthracene parts; in 1-MBA, and 1,12-DMBA, the phenanthrenic K-region bond is close to 1.34 A and the M-region bond about 1.38 A. In 12-MBA, overcrowding in the 'bay' region causes the central anthracene ring C and the benz ring A each to be bent about 10 degrees in opposite directions from the phenanthrenic B ring, much as in 1-MBA and 7,12-DMBA, but less than in 1,12-DMBA; the 12-methyl carbon lies about the same distance (0.55 A) above the anthracene plane in 12-MBA as in 1,12-MBA and 7,12-DMBA.
通过直接法对X射线单晶衍射数据进行分析，已确定中等活性致癌物12-甲基苯并[a]蒽（12-MBA）的晶体结构。对929个独立反射进行最小二乘法精修，残余R值为0.09，从而确定了碳原子位置，原子坐标的表观标准偏差约为0.008 Å。苯环（A）与蒽核的倾斜度为15.5度，以及甲基碳偏离贯穿整个苯并蒽核的最佳平面0.89 Å，这些都体现了与平面性的偏差。将其与高致癌性的7,12-二甲基苯并[a]蒽（7,12-DMBA）的结构，以及最近解析出的弱致癌物1-MBA和极弱致癌物1,12-DMBA的结构进行比较，结果表明蒽部分结构非常相似；在1-MBA和1,12-DMBA中，菲的K区域键接近1.34 Å，M区域键约为1.38 Å。在12-MBA中，“湾区”的过度拥挤导致中心蒽环C和苯环A各自相对于菲的B环向相反方向弯曲约10度，这与1-MBA和7,12-DMBA的情况非常相似，但弯曲程度小于1,12-DMBA；12-MBA中12-甲基碳在蒽平面上方的距离（0.55 Å）与1,12-MBA和7,12-DMBA中的大致相同。
