Deuterated Modifiers in Sub/Supercritical Fluid Chromatography for Streamlined NMR Structure Elucidation

Abstract

Isolation and chemical characterization of target components in fast-paced pharmaceutical laboratories can often be challenging, especially when dealing with mixtures of closely related, possibly unstable species. Traditionally, this process involves intense labor and manual intervention including chromatographic method development and optimization, fraction collection, and drying processes prior to NMR analyses for unambiguous structure elucidation. To circumvent these challenges, a foundational framework for the proper utilization of supercritical carbon dioxide (scCO 2 ) and deuterated modifiers (CD 3 OD) in sub/supercritical fluid chromatography (SFC) is herein introduced. This facilitates a streamlined multicomponent isolation with minimized protic residues, further enabling immediate NMR analysis. In addition to bypassing tedious drying processes and minimizing analyte degradation, this approach (complementary to traditional reversed-phase liquid chromatography, RPLC) delivers highly efficient separations and automated fraction collection using readily available analytical/midscale SFC instrumentation. A series of diverse analytes across a wide spectrum of chemical properties (acid, basic, and neutral), combined with different stationary-phase columns in SFC are investigated using both a protic organic modifier (CH 3 OH) and its deuterated counterpart (CD 3 OD). The power of this framework is demonstrated with pharmaceutically relevant applications in the context of target characterization and analysis of complex multicomponent reaction mixtures from modern synthetic chemistry, demonstrating high isolation yields while reducing both the environmental footprint and manual intervention. This workflow enables unambiguous fast-paced structure elucidation on the analytical scale, providing results that are comparable to traditional, but time-consuming, RPLC purification approaches.

DELTA50: A Highly Accurate Database of Experimental 1H and 13C NMR Chemical Shifts Applied to DFT Benchmarking

“…Such calculations can aid in NMR peak assignments [ 9 , 10 ], as highlighted in our recent example of misassigned beta-lactam carbonyl chemical shifts [ 11 ]. They have been used to confirm organic [ 12 , 13 , 14 , 15 ], inorganic [ 16 , 17 ], and organometallic [ 18 , 19 ] reaction products, particularly those with unexpected or unusual molecular structures [ 20 , 21 , 22 ], and they have been applied in complex speciation studies [ 23 , 24 , 25 ]. Perhaps most notably, chemical shift calculations were used to revise incorrectly reported natural product structures: aquatolide [ 26 ], vannusal B [ 27 ], glabramycin C [ 28 ], and hexacyclinol [ 29 ].…”