Automated structure verification based on a combination of 1D ¹H NMR and 2D ¹H¹³C HSQC spectra

Abstract

A method for structure validation based on the simultaneous analysis of a 1D (1)H NMR and 2D (1)H - (13)C single-bond correlation spectrum such as HSQC or HMQC is presented here. When compared with the validation of a structure by a 1D (1)H NMR spectrum alone, the advantage of including a 2D HSQC spectrum in structure validation is that it adds not only the information of (13)C shifts, but also which proton shifts they are directly coupled to, and an indication of which methylene protons are diastereotopic. The lack of corresponding peaks in the 2D spectrum that appear in the 1D (1)H spectrum, also gives a clear picture of which protons are attached to heteroatoms. For all these benefits, combined NMR verification was expected and found by all metrics to be superior to validation by 1D (1)H NMR alone. Using multiple real-life data sets of chemical structures and the corresponding 1D and 2D data, it was possible to unambiguously identify at least 90% of the correct structures. As part of this test, challenging incorrect structures, mostly regioisomers, were also matched with each spectrum set. For these incorrect structures, the false positive rate was observed as low as 6%.

Structure elucidation of uniformly 13C labeled small molecule natural products

“…In the past decade, natural product-based drug discovery has fallen into disfavor with most major pharmaceutical research companies. [2] In this report, we present a streamlined approach to rapid structure characterization of natural products utilizing uniform (U) 13 C labeling. This strategy has become feasible because of the increased availability and affordability of labeled substrates such as U- 13 C labeled glucose.…”

“…[2] In this report, we present a streamlined approach to rapid structure characterization of natural products utilizing uniform (U) 13 C labeling. This strategy has become feasible because of the increased availability and affordability of labeled substrates such as U- 13 C labeled glucose. Using labeled substrates in fermentation media produces metabolites highly enriched with 13 C. With the 13 C label in place, the backbone of virtually any natural product can be quickly established by standard and longrange optimized 1 H-decoupled 13 C- 13 C COSY experiments.…”

“…This strategy has become feasible because of the increased availability and affordability of labeled substrates such as U- 13 C labeled glucose. Using labeled substrates in fermentation media produces metabolites highly enriched with 13 C. With the 13 C label in place, the backbone of virtually any natural product can be quickly established by standard and longrange optimized 1 H-decoupled 13 C- 13 C COSY experiments. [3][4][5] The 1 H NMR chemical shifts can be subsequently assigned through the use of an F 1 -decoupled HSQC experiment.…”

“…The constant time CT-HSQC described by Bax and coworkers [6] provides a method to achieve F 1 decoupling in the HSQC experiments of uniformly 13 C-labeled peptides and proteins. Herein, we expand the theoretical framework of the CT-HSQC approach to make it universally applicable to practically any U- 13 C labeled organic small molecule.…”

“…Herein, we expand the theoretical framework of the CT-HSQC approach to make it universally applicable to practically any U- 13 C labeled organic small molecule. The resulting structure elucidation strategy is demonstrated both theoretically and experimentally using the natural product enterocin, [7] 1, as an example.…”