Stretched Poly(methyl methacrylate) Gel Aligns Small Organic Molecules in Chloroform. Stereochemical Analysis and Diastereotopic Proton NMR Assignment in Ludartin Using Residual Dipolar Couplings and 3J Coupling Constant Analysis

Roberto R. Gil,* Chakicherla Gayathri, Nicolay V. Tsarevsky, and Krzysztof Matyjaszewski
Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213
J. Org. Chem., 2008, 73 (3), pp 840–848
DOI: 10.1021/jo701871g
Publication Date (Web): January 5, 2008
Copyright © 2008 American Chemical Society
*

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

, rgil@andrew.cmu.edu

Abstract

Abstract Image

Poly(methyl methacrylate) (PMMA) gels prepared by copolymerizing methyl methacrylate (MMA) and various amounts of ethylene glycol dimethacrylate (EGDMA) in the presence of the radical initiator V-70 (2,2‘-azobis(2,4-dimethyl-4-methoxyvaleronitrile)) can orient small organic molecules when swollen in NMR tubes with CDCl3. The aligning properties of the stretched PMMA gels were evaluated by monitoring the quadrupolar splitting of the 2H NMR signal of CDCl3, and the aligning degree is proportional to the cross-linking density. Natural abundance one-bond 1H−13C residual dipolar couplings (RDCs) for menthol measured in the gels depended on the cross-link density. The stereochemistry and assignment of the diastereotopic protons of the gastroprotective and nonsteroidal aromatase inhibitor sesquiterpene lactone ludartin, isolated from Stevia yaconensis var. subeglandulosa, were unambiguously determined using a combination of natural abundance one-bond 1H−13C RDCs measured in a PMMA gel and a 3J coupling constant analysis.

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History

  • Published In Issue February 01, 2008
  • Received August 26, 2007

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