Sesquiterpene structure elucidation

Daniewski, W.M., A. Wawrzun, M. De Bernardi, G. Vidari, P. Vita-Finzi, G. Fronza, and G. Gatti Structural Studies on Lactarius Sesquiterpenes Structure Elucidation of Lactarorufins D and E and Conformational Analysis of Lactaran-5-olides. Tetrahedron, 40, 2757 (1984). 

Herz W, Subramaniam PS, Santhanam PS, Aota K, Hall AL. Structure elucidation of sesquiterpene dilactones from Mikania scandens (L.) Willd. J Org Chem 1970 35 1453-1464. 

The mangrove plant Heritiera littoralis (Stercullaceae) has been utlized by natives of the Philippines as a fish poison. The hexane extract of this plant has shown toxicity to fish (Tilapia nllotlca). A novel sesquiterpene which was assigned the name heritianin has been identified as one of the compounds with ichthyotoxicity. The structure elucidation of heritianin and other compounds in the hexane extract of Heritiera littoralis is presented with bioassay data. 

Okuda T, Yoshida T (1965) Absolute Configuration of Tutin. Tetrahedron Lett 2137 Kinoshita T, Itaki N, Hikita M, Aoyagi Y, Hitozuyanagi Y, Takeya K (2005) The Isolation and Structure Elucidation of a New Sesquiterpene Lactone from the Poisonous Plant Coriaria japonica (Coriariaceae). Chem Pharm Bull 53 1040... 

Structure elucidation of many Lactarius sesquiterpenes often requires interconversions of y-hydroxybutenolide, butenolide, and furan rings for confirming spectroscopic assignments. Examples of DIBAL reductions of y-lactones to the corresponding furans include the conversions of blennin C (14.5) to lactarol (19.3) (Scheme 12) (60) and of compound 11.20 to 3-dcoxy-3-cp/-furandiol (87) (Scheme 10). 

An example of the power of this method in structure elucidation is shown for the sesquiterpene lactone acetylisomontanolide (Fig. 5.74). The complete carbon skeleton of the molecule can be traced directly in the spectrum, with breakdown occurring only when heteroatom linkages arise. Unfortunately, it is rare indeed to have sufficient sample quantities at hand to consider employing this technique, and still it remains a little used method in its original form. However, greater potential exits for directly tracing carbon-carbon connectivities with recently developed methods based on proton excitation and observation combined with gradient selection see Section 5.8.4 below. 

Finally, mention should be made of the increasing application of the intramolecular Nuclear Overhauser Effect (NOE) which has played an important role not only as an aid to structural elucidation but also in the conformational determination of some of the germacrane sesquiterpenes. These results have a significant bearing on the understanding of transannular effects and chemical reactivity. 

The isolation and structural elucidation of the novel tetracyclic sesquiterpenes ishwarane (311, R = and ishwarone (311, R = O), obtained from the... 

The structural elucidation of these sesquiterpenes, given the difficulty in determining the linking sites of the respective ester groups when more than three kinds of acid are involved as esters in the molecule, necessitates the use of nmr experiments (selective INEPT [10], Coloc [11] or HMBC 2D [12]), selective hydrolysis processes or X-ray crystallographic methods [13], From comparison of the chemical shifts of similar compounds, it is not easy to establish the exact position of each ester. 

We have been interested in the toxic constituents of Illicium plants (Illiciaceae), and have reported on the isolation and structural elucidation of a series of sesquiterpenes possessing unique framework from these plants in Japan and China [1], As a continuous work on the chemical studies on the Illicium plants, we investigated the constituents of the bark of non-toxic Illicium difengpi K. I. B. et K. I. M., which was used as antiarthritic agent in China, and those of the fresh fruits of toxic Illicium anisatum L.. This paper deals with the isolation and structural elucidation of five new phenylpropanoid glycosides from the above plants. 

The fascinating lactone isolactarorufin (9.4), at first discovered in an EtOH extract of L. rufus (75, 76, 77) and later also in L. vellereus (5S) and L. necator, is the only known isolactarane sesquiterpene so far isolated from Lactarius species. Other compounds listed in Part 9 are synthetic derivatives that were prepared for structure elucidation of the parent compound or for investigation of their biological properties. 

Structure elucidation of 5-lactaranolides other relevant chemical transformations involved the conversion of the lactone into the furan ring and addition reactions to double bonds (hydrogenation, hydroboration, epo-xidation, osmylation). A brief account of these reactions will be included in the chapter on chemical conversions of Lactarius sesquiterpenes. 

Because of space limitations, standard reactions of Lactarius sesquiterpenes will not be described when usual reagents were employed and the outcome of the reactions was unexceptional. It must be said, however, that preparation of simple derivatives of sesquiterpenes of Lactarius was often an essential part of the work of structure elucidation. In several instances, for example, crystalline compounds suitable for X-ray analysis were produced. In addition, many semisynthetic derivatives often showed better biological activities than the natural products. Important synthetic derivatives are included in Parts 1 -20. 

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