Eyer P, Schneller M
Biochem Pharmacol. 1983 Mar 15;32(6):1029-36. doi: 10.1016/0006-2952(83)90621-4.
Nitroso-chloramphenicol (NOCAP) was synthetized by reduction of chloramphenicol (CAP) with zinc dust in a modification of the procedure published by Corbett and Chipko. The radioactive derivative was similarly prepared from [dichloroacetamido-1-14C]CAP. NOCAP rapidly reacted with GSH with the formation of hydroxylamino-chloramphenicol (NHOHCAP), D-(-)-threo-1-(p-hydroxylaminophenyl)-2-dichloroacetamido-1,3-propanediol and glutathione disulfide (GSSG). In addition, a hydrophilic sulfinamide was formed (GSONHCAP), D-(-)-threo-1-(p-glutathionesulfinamidophenyl)-2-dichloroacetamido-1, 3-propanediol. Free amino-chloramphenicol (NH2CAP), D-(-)-threo-1-(p-aminophenyl)-2-dichloracetamido-1,3-propanediol, was not detected. The proportion of NHOHCAP formed increased with increasing GSH concn, at the expense of GSONHCAP. Analysis by stopped-flow spectroscopy revealed formation of a labile adduct in the reaction of NOCAP with GSH (k = 5500 M-1 sec-1 at 37 degrees, pH 7.4). This reaction was reversible because nearly all NOCAP could be extracted with ether from the labile intermediate. The equilibrium adduct/NOCAP was dependent on GSH concn (K = 4500 M-1 at 37 degrees, pH 7.4). The labile intermediate either isomerized to the sulfinamide, GSONHCAP (favoured by decreasing pH at constant GSH), or it was thiolytically cleaved by another GSH molecule to NHOHCAP and GSSG (favoured by increasing GSH at constant pH). At acid pH, GSONHCAP readily hydrolyzed to NH2CAP and glutathionesulfinic acid. Thus, NOCAP reacts with thiols similar to nitrosobenzene. A scheme is presented for the proposed reaction mechanism. It is concluded that most of the NOCAP, if formed in the intestine or liver, will be rapidly disposed by reactions with GSH. Hence, toxic concns at the sensitive target, i.e. the bone marrow, may usually be prevented.
亚硝基氯霉素（NOCAP）是通过用锌粉还原氯霉素（CAP）合成的，这是对Corbett和Chipko发表的方法的一种改进。放射性衍生物同样由[二氯乙酰氨基-1-¹⁴C]CAP制备。NOCAP与谷胱甘肽（GSH）迅速反应，生成羟氨基氯霉素（NHOHCAP）、D-(-)-苏式-1-(对羟基氨基苯基)-2-二氯乙酰氨基-1,3-丙二醇和谷胱甘肽二硫化物（GSSG）。此外，还形成了一种亲水性亚磺酰胺（GSONHCAP），即D-(-)-苏式-1-(对谷胱甘肽亚磺酰胺基苯基)-2-二氯乙酰氨基-1,3-丙二醇。未检测到游离氨基氯霉素（NH₂CAP），即D-(-)-苏式-1-(对氨基苯基)-2-二氯乙酰氨基-1,3-丙二醇。随着GSH浓度的增加，NHOHCAP的生成比例增加，而GSONHCAP的生成比例降低。停流光谱分析表明，NOCAP与GSH反应形成了一种不稳定的加合物（在37℃、pH 7.4时，k = 5500 M⁻¹ s⁻¹）。该反应是可逆的，因为几乎所有的NOCAP都可以用乙醚从不稳定的中间体中萃取出来。平衡加合物/NOCAP取决于GSH浓度（在37℃、pH 7.4时，K = 4500 M⁻¹）。不稳定的中间体要么异构化为亚磺酰胺GSONHCAP（在GSH浓度恒定的情况下，pH降低时更有利），要么被另一个GSH分子硫解裂解为NHOHCAP和GSSG（在pH恒定的情况下，GSH浓度增加时更有利）。在酸性pH下，GSONHCAP很容易水解为NH₂CAP和谷胱甘肽亚磺酸。因此，NOCAP与硫醇的反应类似于亚硝基苯。文中给出了所提出的反应机制的示意图。结论是，如果NOCAP在肠道或肝脏中形成，大部分将通过与GSH的反应迅速被清除。因此，通常可以防止在敏感靶点即骨髓处出现毒性浓度。
