Prediction of a new pathway to presilphiperfolanol

Organic Letters

Volumn 10, Issue 21, 2008, Pages 4827-4830

  Wang, Selina C ^a   Tantillo, Dean J ^a  

^a UNIVERSITY OF CALIFORNIA   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ORGANIC COMPOUND; PRESILPHIPERFOLANOL; SESQUITERPENE; UNCLASSIFIED DRUG;

ARTICLE; CHEMICAL STRUCTURE; CHEMISTRY; SYNTHESIS; X RAY CRYSTALLOGRAPHY;

CRYSTALLOGRAPHY, X-RAY; MODELS, MOLECULAR; MOLECULAR STRUCTURE; ORGANIC CHEMICALS; SESQUITERPENES;

EID: 58149142845     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol801898v     Document Type: Article

References (31)

1. Isolation: (a) Bohlmann, F.; Zdero, C.; Jakupovic, J.; Robinson, H.; King, R. M. Phytochemistry 1981, 20, 2239-2244.
2. Stereochemistry and mechanistic proposals: (b) Coates, R. M.; Ho, Z.; Klobus, M.; Wilson, S. R. J. Am. Chem. Soc. 1996, 118, 9249-9254, and references therein; (correction) J. Am. Chem. Soc. 1996, 118, 13117.
3. Leading references on carbocation rearrangements in terpene biosynthesis: (a) Christianson, D. W. Curr. Opin. Chem. Biol. 2008, 12, 141-150.
4. (b) Christianson, D. W. Chem. Rev. 2006, 106, 3412-3442.
5. (c) Davis, E. M.; Croteau, R. Top. Curr. Chem. 2000, 209, 53-95.
6. (d) Cane, D. E. Comp. Nat. Prod. Chem. 1999, 2, 155-200.
7. (e) Cane, D. E. Chem. Rev. 1990, 90, 1089-1103.
8. (a) Peterson, E. A.: Overman, L. E. Proc. Natl. Acad. Sci. U.S.A. 2004, 101, 11943-11948.
9. (b) Douglas, C. J.; Overman, L. E. Proc. Natl. Acad. Sci. U.S.A. 2004, 101, 5363-5367.
10. (c) Denissova, I.; Barnault, L. Tetrahedron 2003, 59, 10105-10146.
11. Tantillo, D. J. J. Phys. Org. Chem. 2008, 21, 561-570.
12. Bradshaw, A. P. W.; Hanson, J. R.; Nyfeler, R.; Sadler, I. H. J. Chem. Soc., Perkin Trans, 1 1982, n/a, 2187-2192.
13. The GAUSSIAN 03 program suite was used for all calculations: Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajinia, T.; Honda, Y.; Kitao, O.; Nakai, H.; Kiene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, revision B.04; Gaussian, Inc.; Wallingford, CT, 2004. Geometries were optimized at the B3LYP/6-31+G(d,p) level: Becke, A. D. J. Chem. Phys. 1993, 98, 5648-5652;
14. Becke, A. D. J. Chem. Phys. 1993, 98, 1372-1377;
15. Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785-789;
16. Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J. J. Phys. Chem. 1994, 98, 11623-11627.
17. All structures were characterized by frequency calculations, and reported energies include zero-point energy corrections (unsealed). Single point energies for all structures were also computed at the mPW1PW91/6-31+G(d,p) level as recommended in Matsuda, S. P. T.; Wilson, W. K.; Xiong, Q. Org. Biomol. Chem. 2006, 4, 530-543.
18. These energies include unsealed zero-point energy corrections from B3LYP/6-31+G(d,p) frequency calculations. Intrinsic reaction coordinate (IRC) calculations were used to verify the identity of transition structures: Gonzalez, C.; Schlegel, H. B. J. Phys. Chem. 1990, 94, 5523-5527;
19. Fukui, K. Acc. Chem. Res. 1981, 14, 363-368.
20. Structural drawings were produced using Ball & Stick: N. Müller, N.; Falk, A. Ball & Stick, molecular graphics application for MacOS computers, version 3.7.6; Johannes Kepler University: Linz, Austria, 2000.
21. This report is part 4 in our "Theoretical Studies on Farnesyl Cation Cyclization" series. For parts 1-3 and leading references to related work, see: (a) Gutta, P.; Tantillo, D. J. J. Am. Chem. Soc. 2006, 128, 6172-6179.
22. (b) Hong, Y. J.; Tantillo, D. J. Org. Lett. 2006, 8, 4601-4604.
23. (c) Lodewyk, M. W.; Gutta, P.: Tantillo, D. J. J. Org. Chem. 2008, 73, 6570-6579.
24. 7 further details will be reported in due course. For the system described herein, a productive conformer of A was located that is 4.5 kcal/mol lower in energy than B' (Figure 1) at the B3LYP/6-31+G(d,p) level (see Supporting Information for details), but attempts to find a productive conformer of A' led to structures with six-membered rings. We are not comfortable speculating as to whether or not cations such as A and A' are formed as intermediates in terpene synthase active sites at this time, since these cations would be formed in the mechanistic step where pyrophosphate departs and is therefore close in space to the putative carbocation center that is generated. These cations are therefore most likely to be influenced by the departed pyrophosphate group that is not included in the models reported herein.
25. At the B3LYP/6-31+G(d,p) level. This comparison is based on the conformera of B and B' that are productive for ring closure to form C. A detailed study on the various conformera available to humulyl cations and their interconversious will be described in due course. Humulyl cation conformer B was also discussed in ref 7a.
26. The barrier for ring closure of B is computed to be 2.2 kcal/mol and the conformer of C that is formed is 3.9 kcal/mol lower in energy than that shown in Figure 1 (at the B3LYP/6-31+G(d,p) level). The transition structure for this reaction is also earlier than that for B'; see the Supporting Information and refs 4 and 7a for details and additional discussion.
27. For other examples of complex concerted rearrangements that may avoid possible secondary carbocation intermediates, see refs 4, 7b and 7c.
28. A similar transformation has been proposed previously for a nonbiological process; see: Koizumi, T; Harada, K.; Mochizuki, E.; Kokubo, K.; Oshima, T. Org. Lett. 2004, 6, 4081-4084
29. Wang, S. C.; Tantillo, D. J. J. Org. Chem. 2007, 72, 8394-8401.
30. This value is 8.5 kcal/mol based on experiment and ∼3 to 11 kcal/ mol based on quantum chemical calculations at various levels of theory, some of which suggest that an extremely shallow symmetrically bridged minimum occurs along the reaction coordinate: for leading references, see: Vrcek, I. V.; Vrcek, V.; Siehl, H.-U. J. Phys. Chem. A 2002, 106, 1604-1611. Note that two consecutive 1,2-hydride shifts would, here, lead to a diastereomer of cation F.
31. Theoretical studies on subsequent rearrangements of the presilphiperfolanyl cation are ongoing and will be reported in due course.