CPSA Digest 2001

Proceedings -Wednesday, October 10, 2001

WOD1

Applications of Flow NMR to the Analysis of Combinatorial Products

Background:
Advances in new experimental techniques, improved hardware and more powerful software have allowed NMR spectroscopy to help solve important problems in the field of drug discovery including natural products research, synthetic medicinal chemistry, rational drug design and combinatorial chemistry. For example, NMR spectroscopy is now being used to analyze mixtures using LC-NMR, analyze solid-phase synthesis resins and determine the structures of organic small molecules.

Premise:
Flow-injection NMR offers a convenient means to analyze the large numbers of samples generated by combinatorial chemistry. Using Flow-NMR, a sample is pumped through a flow cell, eliminating the use of traditional glass tubes. NMR probes are available in tube configurations of 10, 5, 3 and 1.7 mm, and in flow configurations of 120, 60 and 2 uL. In "Direct Injection NMR," the direction of the flow path is described as "push and pull;" a 250 mL sample volume is used; a 5 mM sample concentration is created by diluting a mother well; 3 rinse volumes are used and total analysis time is 8.5 to 9 min/sample. In "Flow through NMR" using a modified configuration, the direction of the flow path is described as "flow through" rather than "push and pull;" a 200 mL sample volume is used; daughter plates are created; 1 rinse volume is used and total analysis time is 4 min/sample.

The routine acquisition of large amounts of spectral data can increase the rate of throughput for these NMR analyses but the technology can generate huge amounts of data with no appropriate manner to track and easily store the information. Data handling software is thus an essential component to optimizing the performance of flow-NMR. Third party software from companies such as ACD Labs ("CombiNMR"), Chemical Concepts, Groton Neochem and others is allowing for the indexing and storage of NMR spectral curves associated with molecular structures. Also, NMR prediction algorithms allow for the comparison of experimental and predicted spectra. Data can be accessed, processed and displayed in a 96-well plate format. The spectral curves generated can be stored directly in a database and associated with chemical structures and user-defined text fields.

Future
Flow NMR data acquisition can be rapid, even relative to some high throughput LC-MS methods. The technology provides for structural identity and quantification. Its current limitations include the amount of material required for analysis, software for data analysis, and the level of throughput now achieved (even higher throughput is desired).

Links
Paul A. Keifer, "NMR spectroscopy in drug discovery: Tools for combinatorial chemistry, natural products and metabolism research," Progress in Drug Research, Vol. 55 (Ernst Jucker, Editor). Birkhauser Verlag, Basel, Switzerland (2000).

Paul A. Keifer, Direct-injection NMR: A flow NMR technique for the analysis of combinatorial chemistry libraries. Jrnl. Comb. Chem. 2(2), 151-171 (2000).

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