Saelli, Nicolaou, and Bagno point out in a recent article how the determination of the structure of vannusal B might have been guided by DFT computed 13C NMR chemical shifts, had they been available.1 The original structure was proposed in 1999 as 1,2 but was ultimately settled as 2 in 2010.3
The 13C NMR chemical shifts of 1 and 2 and some other alternatives were computed at M06/pcS-2//B3LYP/6-31g(d,p), where the pcS-2 basis set4 is one proposed by Jensen for computing chemical shifts. The computed chemical shifts of 1 poorly correlate with the experimental chemical shifts of vannusal B, with a low correlation coefficient of 0.9580 and a maximum error of 16.2 ppm. On the other hand, the correlation between the computed chemical shifts of 2 with the experimental values is excellent (R2=0.9948) and a maximum error of 3.0 ppm. Comparison of computed and experimental H-H coupling constants of model compounds of the “northeast” section of the molecule verified the correct structure is 2.
(1) Saielli, G.; Nicolaou, K. C.; Ortiz, A.; Zhang, H.; Bagno, A., "Addressing the Stereochemistry of Complex Organic Molecules by Density Functional Theory-NMR: Vannusal B in Retrospective," J. Am. Chem. Soc., 2011, 133, 6072-6077, DOI: 10.1021/ja201108a
(2) Guella, G.; Dini, F.; Pietra, F., "Metabolites with a Novel C30 Backbone from Marine Ciliates," Angew. Chem. Int. Ed., 1999, 38, 1134-1136, DOI: 10.1002/(SICI)1521-3773(19990419)38:8<1134::AID-ANIE1134>3.0.CO;2-U
(3) Nicolaou, K. C.; Ortiz, A.; Zhang, H.; Dagneau, P.; Lanver, A.; Jennings, M. P.; Arseniyadis, S.; Faraoni, R.; Lizos, D. E., "Total Synthesis and Structural Revision of Vannusals A and B: Synthesis of the Originally Assigned Structure of Vannusal B," J. Am. Chem. Soc., 2010, 132, 7138-7152, DOI: 10.1021/ja100740t
(4) Jensen, F., "Basis Set Convergence of Nuclear Magnetic Shielding Constants Calculated by Density Functional Methods," J. Chem. Theory Comput., 2008, 4, 719-727, DOI: 10.1021/ct800013z
vannusal B (2):