Jaki Birgit U, Franzblau Scott G, Chadwick Lucas R, Lankin David C, Zhang Fangqiu, Wang Yuehong, Pauli Guido F
Institute for Tuberculosis Research and Department of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, University of Illinois at Chicago, 833 S. Wood Street, Chicago, Illinois 60612-7231, USA.
J Nat Prod. 2008 Oct;71(10):1742-8. doi: 10.1021/np800329j. Epub 2008 Sep 18.
The present study explores the variability of biological responses from the perspective of sample purity and introduces the concept of purity-activity relationships (PARs) in natural product research. The abundant plant triterpene ursolic acid (1) was selected as an exemplary natural product due to the overwhelming number yet inconsistent nature of its approximate 120 reported biological activities, which include anti-TB potential. Nine different samples of ursolic acid with purity certifications were obtained, and their purity was independently assessed by means of quantitative 1H NMR (qHNMR). Biological evaluation consisted of determining MICs against two strains of virulent Mycobacterium tuberculosis and IC50 values in Vero cells. Ab initio structure elucidation provided unequivocal structural confirmation and included an extensive 1H NMR spin system analysis, determination of nearly all J couplings and the complete NOE pattern, and led to the revision of earlier reports. As a net result, a sigmoid PAR profile of 1 was obtained, demonstrating the inverse correlation of purity and anti-TB bioactivity. The results imply that synergistic effects of 1 and its varying impurities are the likely cause of previously reported antimycobacterial potential. Generating PARs is a powerful extension of the routinely performed quantitative correlation of structure and activity ([Q]SAR). Advanced by the use of primary analytical methods such as qHNMR, PARs enable the elucidation of cases like 1 when increasing purity voids biological activity. This underlines the potential of PARs as a tool in drug discovery and synergy research and accentuates the need to routinely combine biological testing with purity assessment.
本研究从样品纯度的角度探讨了生物反应的变异性，并在天然产物研究中引入了纯度-活性关系（PARs）的概念。由于其约120种已报道的生物活性数量众多但性质不一致，其中包括抗结核潜力，丰富的植物三萜熊果酸（1）被选为典型的天然产物。获得了九种具有纯度认证的熊果酸不同样品，并通过定量1H NMR（qHNMR）独立评估其纯度。生物学评估包括测定对两种毒力结核分枝杆菌菌株的MIC以及在Vero细胞中的IC50值。从头算结构解析提供了明确的结构确认，包括广泛的1H NMR自旋系统分析、几乎所有J耦合的测定和完整的NOE模式，并导致对早期报道的修订。最终结果是获得了1的S形PAR曲线，证明了纯度与抗结核生物活性之间的负相关。结果表明，1及其不同杂质的协同作用可能是先前报道的抗分枝杆菌潜力的原因。生成PARs是常规进行的结构与活性定量相关性（[Q]SAR）的有力扩展。通过使用qHNMR等主要分析方法，PARs能够阐明像1这样纯度增加却导致生物活性消失的情况。这突出了PARs作为药物发现和协同作用研究工具的潜力，并强调了将生物学测试与纯度评估常规结合的必要性。
