Structure Elucidation of a Sesquiterpene

Mass spectrometry (MS) detects the molecular mass of a compound with a precision of 10 mass units. Owing to the isotope mass defect of elements the molecular formula of a terpene can be determined by high-resolution mass spectrometry of the molecular ion. For example, the molecular formula C17//22O4 of acanthifolin from Senecio acanthifolius (Asteraceae) is calculated from the molecular mass of 290.1525 determined by high-resolution mass spectrometry of the molecular ion. Additionally, partial structures of molecules can be derived from the masses of the ions arising from fragmentation of the molecular ion and detected in the mass spectrum. 

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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... 

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 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. 

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. 

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). 

The Philippine mangrove plant Heritiera Uttoralis (Steraliaceae) has been used as a fish and spearhead poisoa Crude extracts of this plant were shown to be toxic to the fish Tilapia nilotica. Four novel sesquiterpenes of the cadinane type with an unusual oxygenation pattern and an aromatic ring have been previously reported. A fito novel sesquiterpene of this type which was assigned the name Vallapianin has been identified. The structure elucidation of Vallapianin is reported. 

Chamaecynane type (223) was first encountered with the characterization of C]4 sesquiterpenes - e.g., dehydrochamaecynenol (232) from Chamaecyparis formosensis (14). Some half dozen compounds with this stereochemistry are known at present and all of these are C14 compounds isolated from C formosensis. The other cis fused type, 224, was uncovered with the structure elucidation of (+)-occidentalol (233), isolated from the heartwood of Thuja occidentalis (368). The aromatic compound occidol (234) co-occurs with occidentalol in the Thuja wood. Several compounds of intermedeane type (225) are known at present and some of these have been isolated from woody tissues. Intermedeol (235) itself was first isolated from the Indian race of the grass Bothriochloa intermedia (95). (-)-Callitrisin (236) is a constituent of Callitris columellaris heartwood (59, 158). 

Terpenes are characterized as being made up of units of isoprene in a head-to-tail orientation. This isoprene concept, invented to aid in the structure determination of terpenes found in natural products, was especially useful for elucidation of structures of more complex sesquiterpenes, diterpenes, and polyterpenes. The hydrocarbon, myrcene, and the terpene alcohol, OC-terpineol, can be considered as being made up of two isoprene units in such a head-to-tail orientation (1). 

A sesquiterpene thiocyanate, cavemothiocyanate (269) was isolated from Acanthella cf. cavernosa and the structure was elucidated on the basis of spectral data. The nudibranch Phyllidia ocellata also contained cavemothiocyanate [270]. Acanthene B (270) is a sesquiterpene isothiocyanate isolated from a British Columbian Acanthella sp. [271]. The sesquiterpene thiol, T-cadinthiol (271) was isolated from Cymbastela hooperi from Kelso Reef on the Great Barrier Reef [272]. A sesquiterpene isothiocyanate that displayed modest in vitro antimalarial activity, (-)-9-isothiocyanatopupukeanane (272) was isolated from an Axinyssa sp. from the Great Barrier Reef [273]. Great Barrier Reef samples of A. cavernosa contained 10-isothiocyanatocadin-4-ene (273) [274],... 

Artemisinin 1, a naturally occurring sesquiterpene peroxy-lactone, has been isolated in up to 0.25% yield from the dry leaves of Artemisia annua L.1 Interest in artemisinin is based on its phytomedicinal properties. In 168 b.c. China, as described in a Treatment of 52 Sicknesses, the leaves of A. annua (Qinghao) were used for the treatment of chills and fever.2 It was not until 1972 that the active antimalarial agent qinghaosu was isolated in pure form. This allowed for the unequivocal elucidation of its structure through the use of x-ray crystallography. This complex tetracyclic peroxide is now referred to as artemisinin in various sources such as Chemical Abstracts or the Merck Index. 

Chapters 3 and 4 (familiarity with which is assumed) provide us with powerful techniques and methods to elucidate the structures of organic compounds especially when combined with information derived from IR and mass spectrometry. These NMR methods are collectively referred to as one-dimensional techniques. To extend our capabilities, we turn once more to NMR. We will use four compounds as examples ipsenol (see Chapter 3), caryophyllene oxide (a sesquiterpene epoxide), lactose (a j3-linked disaccharide), and a small peptide (valine-glycine-serine-glutamate, VGSE). The structures of these compounds are shown in Figure 5.1. 

The fascinating lactone isolactarorufin (9.5) (Table 9) is the only example of isolactarane sesquiterpenes isolated from a Lactarius specie (43-45). The structure of isolactarorufin has been elucidated by spectroscopic data and confirmed by X-ray analysis of its p-bromobenzoate 9.8 (45). 

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