Gil Roberto R, Gayathri Chakicherla, Tsarevsky Nicolay V, Matyjaszewski Krzysztof
Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, USA.
J Org Chem. 2008 Feb 1;73(3):840-8. doi: 10.1021/jo701871g. Epub 2008 Jan 5.
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 CDCl(3). The aligning properties of the stretched PMMA gels were evaluated by monitoring the quadrupolar splitting of the (2)H NMR signal of CDCl(3), and the aligning degree is proportional to the cross-linking density. Natural abundance one-bond (1)H-(13)C 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 (1)H-(13)C RDCs measured in a PMMA gel and a (3)J coupling constant analysis.
通过在自由基引发剂V - 70（2,2'-偶氮二（2,4 - 二甲基 - 4 - 甲氧基戊腈））存在下使甲基丙烯酸甲酯（MMA）与不同量的乙二醇二甲基丙烯酸酯（EGDMA）共聚制备的聚（甲基丙烯酸甲酯）（PMMA）凝胶，在装有CDCl₃的核磁共振管中溶胀时能够使小有机分子取向。通过监测CDCl₃的²H核磁共振信号的四极分裂来评估拉伸PMMA凝胶的取向性能，且取向程度与交联密度成正比。在凝胶中测量的薄荷醇的天然丰度一键¹H - ¹³C剩余偶极耦合（RDCs）取决于交联密度。从甜叶菊亚腺毛变种中分离出的具有胃保护作用的非甾体芳香酶抑制剂倍半萜内酯卢达汀的非对映体质子的立体化学和归属，通过结合在PMMA凝胶中测量的天然丰度一键¹H - ¹³C RDCs和³J耦合常数分析得以明确确定。
