Santillán A, Zhang X, Hardesty J, Widger W R, Kohn H
Department of Chemistry, University of Houston, Texas 77204, USA.
J Med Chem. 1998 Mar 26;41(7):1185-94. doi: 10.1021/jm9708386.
Bicyclomycin (1) is a commercial antibiotic whose primary site of action in Escherichia coli is the transcription termination factor rho. A recent structure-activity relationship study of 1 showed that replacing the C(6)-hydroxy group with alkoxy and thioalkoxy substituents led to dramatic losses of inhibitory activity in rho biochemical assays. The origin for this structural specificity has been explored by the synthesis and chemical, biochemical, and biological evaluation of C(6)-amino- (13), C(6)-(hydroxylamino)-(14), and C(6)-mercaptobicyclomycin (15). These compounds, like 1, are capable of entering into hydrogen bond donor interactions with rho and are capable of undergoing C(6) ring opening to generate alpha, beta-unsaturated carbonyl, imine, or thione systems. The chemical reactivity of 13-15 was compared with that of 1. We observed that 1, upon treatment with EtSH under moderate and basic conditions, readily underwent C(6) hemiaminal bond cleavage followed by conjugate addition to beta-methylene-alpha-ketoamide 2 to give Michael addition adducts whereas 13-15 reacted by initial cleavage of the C(1)-O(2) bond. Biochemical and biological assays of 13-15 and related analogues demonstrated that the C(6) hydroxy group in 1 was essential for activity. We found that replacing the C(6)-hydroxy group in 1 with weaker hydrogen bond donors led to low inhibitory activities in the rho-dependent ATPase and transcription termination assays. None of the bicyclomycin derivatives exhibited antibiotic activity against E. coli W3350 cells at a 32 mg/mL concentration. The apparent specificity for the C(6)-hydroxy group in 1 suggests that an efficient hydrogen bond donor interaction from the C(6)-hydroxy group to rho or the C(6) hemiaminal bond cleavage to 2 or both is necessary for drug function.
双环霉素（1）是一种商业抗生素，其在大肠杆菌中的主要作用位点是转录终止因子ρ。最近对1的构效关系研究表明，用烷氧基和硫代烷氧基取代基取代C（6）-羟基会导致在ρ生化分析中抑制活性急剧丧失。通过合成以及对C（6）-氨基-（13）、C（6）-（羟氨基）-（14）和C（6）-巯基双环霉素（15）进行化学、生化和生物学评估，探索了这种结构特异性的起源。这些化合物与1一样，能够与ρ形成氢键供体相互作用，并且能够发生C（6）环开环以生成α，β-不饱和羰基、亚胺或硫酮体系。将13 - 15的化学反应性与1的进行了比较。我们观察到，1在温和和碱性条件下用乙硫醇处理时，容易发生C（6）半缩醛胺键断裂，随后与β-亚甲基-α-酮酰胺2进行共轭加成，生成迈克尔加成加合物，而13 - 15则通过C（1）-O（2）键的初始断裂进行反应。对13 - 15及相关类似物的生化和生物学分析表明，1中的C（6）羟基对活性至关重要。我们发现，用较弱的氢键供体取代1中的C（6）-羟基会导致在ρ依赖性ATP酶和转录终止分析中抑制活性较低。在32 mg/mL浓度下，没有一种双环霉素衍生物对大肠杆菌W3350细胞表现出抗生素活性。1中对C（6）-羟基的明显特异性表明，从C（6）-羟基到ρ的有效氢键供体相互作用或C（6）半缩醛胺键断裂成2或两者对于药物功能都是必要的。
