Using HMBC and ADEQUATE NMR Data To Define and Differentiate Long-Range Coupling Pathways: Is the Crews Rule Obsolete?

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• 作者：Mary M. Senior ; R. Thomas Williamson ; Gary E. Martin
• 刊名：Journal of Natural Products
• 出版年：2013
• 出版时间：November 22, 2013
• 年：2013
• 卷：76
• 期：11
• 页码：2088-2093
• 全文大小：318K
• 年卷期：v.76,no.11(November 22, 2013)
• ISSN：1520-6025

文摘

It is well known that as molecules become progressively more proton-deficient, structure elucidation becomes correspondingly more challenging. When the ratio of ¹H to ¹³C and the sum of other heavy atoms falls below 2, an axiom that has been dubbed the 鈥淐rews rule鈥?comes into play. The general premise of the Crews rule is that highly proton-deficient molecules may have structures that are difficult, and in some cases impossible, to elucidate using conventional suites of NMR experiments that include proton and carbon reference spectra, COSY, multiplicity-edited HSQC, and HMBC (both ¹H鈥?sup>13C and ¹H鈥?sup>15N). However, with access to modern cryogenic probes and microcyroprobes, experiments that have been less commonly utilized in the past and new experiments such as inverted ¹J_CC 1,n-ADEQUATE are feasible with modest sized samples. In this light, it may well be time to consider revising the Crews rule. The complex, highly proton-deficient alkaloid staurosporine (1) is used as a model proton-deficient compound for this investigation to highlight the combination of inverted ¹J_CC 1,n-ADEQUATE with 1.7 mm cryoprobe technology.