Efficient Protocol for Accurately Calculating 13C Chemical Shifts of

Article Cite This: J. Nat. Prod. XXXX, XXX, XXX−XXX

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Efficient Protocol for Accurately Calculating 13C Chemical Shifts of Conformationally Flexible Natural Products: Scope, Assessment, and Limitations Warren Hehre,*,†,# Phillip Klunzinger,† Bernard Deppmeier,† Andy Driessen,† Noritaka Uchida,§ Masaru Hashimoto,*,‡,# Eri Fukushi,¶ and Yusuke Takata¶ †

Wavefunction, Inc., 18401 Von Karman Avenue, Suite 370, Irvine, California 92612-1542, United States Wavefunction Japan, 3-5-2, Koji-Machi, Chiyoda-Ku, Tokyo 102-0083, Japan ‡ Faculty of Agriculture and Life Science, Hirosaki University, 3-Bunkyo-cho, Hirosaki 036-8561, Japan ¶ Graduate School of Agriculture, Hokkaido University, Sapporo 060-8589, Japan

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ABSTRACT: An efficient protocol for calculating 13C NMR chemical shifts for natural products with multiple degrees of conformational freedom is described. This involves a multistep procedure starting from molecular mechanics and ending with a large basis set density functional model to obtain accurate Boltzmann conformer weights, followed by empirically corrected density functional NMR calculations for the individual conformers. The accuracy of the protocol (average rms