Sesquiterpenoids structures

Studies of terpenoid chemistry have also in volved syntheses. Several of the complex sesquiterpenoid structures have been confirmed or. in some cases, correctly established through synthesis. Many elegant new general synthetic methods have been developed asaresult of attempts to synthesize terpenoids. The chemistry of terpenoids present a continually growing area of chemical research, perhaps the equal of any in complexity, subtlety, and variety. 

Arata (14) and Kotake et al. (15) reported their results almost at the same time, showing deoxynupharidine to have a novel sesquiterpenoid structure of the quinolizidine type. 

Another alkaloid isolated from N. japonicum (35) is nupharamine (XXXII) which has a sesquiterpenoid structure with furan and piperidine rings. 

This chapter follows the pattern of previous Reports with the various sesquiterpenoids considered in structural groups based on their postulated or established biosynthesis. Interest in sesquiterpenoid structure, synthesis, and biosynthesis has continued at a high level during the period covered by the present Report. Two excellent reviews have been published one provides an up-to-date account of sesquiterpenoid biosynthesis while the other provides an authoritative description of studies on sesquiterpenoid stress compounds. Stress metabolites are produced by plants after infection with fungi, bacteria, and viruses or after mechanical wounding, irradiation with u.v. light, dehydration, cold, or treatment with phytotoxic agents. 

Chemical and spectroscopic evidence has been cited in support of the structure and absolute configuration of cybullol (383), a metabolite of Cyanthus bulleri Brodie. It has been suggestedthat the trisnor-sesquiterpenoid structure of cybullol is produced in nature by elimination of an isopropyl group from a eudesmane precursor, and the structural elucidation of a bicyclic sesquiterpenoid triol which co-occurs with cybullol could eventually provide indirect support for this proposal. 

A prenylated cadinene, biflora-4,10(19),15-triene (77), has been isolated from a termite soldier. Prenylated sesquiterpenoid structures have also been assigned to perrottetianal A (78) and B (79), which were isolated from Porella perrottetiana, and a further series of sacculatane diterpenoids including 18- and... 

An optically active piperidine ring has been constructed by an intramolecular aza-Wittig reaction allowing a concise enantiospecific synthesis of nuphar piperidine alkaloids, among them (-)-anhydronupharamine (118), which has a sesquiterpenoid structure... 

The heliannuols are a family of natural products isolated from the sunflower, Helianthus annuus, with unusual sesquiterpenoid structures. Heliannuol G was originally assigned the structure shown [Journal of Natural Products, 62 (1999) 1636-9]. When a compound with that structure was later synthesized, however, the NMR spectra of the synthetic compound did not match the data from the natural material. Using the following NMR data for the natural product, propose a different reasonable structure for heliannuol G. Note that the OH proton is not visible in the NMR spectrum. 

The beautiful saffron colored Jack-o -Lantern (CZ/focybe///wr/eos), a poisonous bioluminescent mushroom growing in large clusters during late summer and autumn particularly in the eastern United States, yields an antitumor substance illudin-S shown to possess a unique sesquiterpenoid structure. A total synthesis of Illudin-S has been reported by Matsumoto et al., and involves combination of cyclopropane (A) and cyclopentane (B) moieties of the molecule by Michael addition of a /3-keto sulfoxide, followed by an aldol condensation for completion of the six-membered ring. ... 

The organization of Part Two is according to structural type. The first section, Chapter Seven, is concerned with the synthesis of macrocyclic compounds. Syntheses of a number of heterocyclic target structures appear in Chapter Eight. Sesquiterpenoids and polycyclic higher isoprenoids are dealt with in Chapters Nine and Ten, respectively. The remainder of Part Two describes syntheses of prostanoids (Chapter Eleven) and biologically active acyclic polyenes including leukotrienes and other eicosanoids (Chapter Twelve). 

The terpenoid precursor isopentenyl diphosphate, formerly called isopentenyl pyrophosphate and abbreviated IPP, is biosynthesized by two different pathways depending on the organism and the structure of the final product. In animals and higher plants, sesquiterpenoids and triterpenoids arise primarily from the mevalonate pathway, whereas monoterpenoids, diterpenoids, and tetraterpenoids are biosynthesized by the 1-deoxyxylulose 5-phosphate (DXP) pathway. In bacteria,... 

Mono- and sesquiterpenoids are of limited use for the identification and classification of aged resins. Due to their volatility, they are rarely found in ancient samples except when they have been conserved in very particular conditions [88,98], On the other hand, the di-and triterpenoids enable us to identify resins thereby identifying their botanical origin [2,99]. Figures 1.1 and 1.2 show the main diterpenoid and triterpenoid structures. 

Figure 1.3 Structures of the main sesquiterpenoid shellac compounds...

Examining the structures of the sesquiterpenoid carbazole alkaloids, tubingensins A (379), B (380), aflavazole (381), and dihydrotubingensins A (382) and B (383), it is likely that they are biogenetically related, and could have originated from a common intermediate, nominine (448) (394). This hypothesis was supported by the isolation of nominine (448) and 20,25-dihydrooxyaflavinine (452) from the sclerotia of the same Aspergillus spp. (347). 

A new carotane sesquiterpenoid, linkiol, has been isolated from the plant Ferula linkii and assigned structure (96) on the basis of its chemical and spectroscopic properties. "... 

The structure of simularene (123), a new structurally interesting sesquiterpenoid isolated from soft coral (Simularia mayi), has been established by A-ray analysis. It has been suggested that the cyclosesquifenchene skeleton of simularene (123) is derived by rearrangement of the intermediate (122) proposed in the biosynthesis of a-and /8-copaene (124). 

Aduncin, a picrotoxane sesquiterpenoid isolated from Dendrobium aduncum, has been assigned structure (147) on the basis of its spectroscopic properties and their similarity to those of a- and /3-dihydropicrotoxinin (148). A full paper dealing with the previously reported synthesis of 4-epidendrobine (149) has been published (cf. Vol. 7, p. 74). 

Chemical and spectroscopic evidence has been provided for the structure of the longipinane sesquiterpenoid vulgarone B (156), a co-metabolite of vulgarone A (157) in the essential oil of Chrysanthemum vulgare. ° Vulgarone B (.156) can be... 

Sacculatal (155) and its C-9 epimer, isosacculatal, are two diterpenoid dialdehydes which contribute to the pungent odour of the liverwort, Trichocoleopsis sacculata. Their structures bear a resemblance to the sesquiterpenoid drimanes. A diterpenoid analogue of the cadinene group is found in the structure of dihy-droxyserrulatic acid (156), from Eremophila serrulata (Myoporaceae). 

Fedorov, S.N. Shubina, L.K. Kalinovsky, A.I. Lyakhova, E.G. Stonik, V.A. (2000) Structure and absolute configuration of a new rearranged chamigrane-type sesquiterpenoid from the sea hare Aplysia sp. Tetrahedron Lett., 41,1979-82. 

Izac, R.R. Poet, S. Fenical, W. van Engen, D. Clardy, J. (1982) The structure of pacifigorgiol, an ichthyotoxic sesquiterpenoid from the Pacific gorgonian coral Pacifigorgia cf. adamsi. Tetrahedron Lett., 23, 3743-6. 

Sesquiterpenoids isolated form Hibiscus tiliaceus and Thespesia populnea with highly oxygenated structures attracted many scientists attention. Nine oxygenated sesquiterpenoids were isolated from the heartwood of Hibiscus tiliaceus and they are shown in Figure 5. 

Sesquiterpenes are formed by the addition of one more isoprene units to a monoterpene molecule, and thus have the molecular formula C15H24 (see also Fig. 4.2). There are linear, branched or cyclic sesquiterpenes. Sesquiterpenes are unsaturated compounds. Cyclic sesquiterpenes may be monocyclic, bicyclic or tricyclic. They are the most diverse group among the volatile terpenoids [2, 3, 7-11, 13,14, 16, 20-24, 37-39, 49]. The DNP treats sesquiterpenoids in 147 different structural types [37]. Various types of sesquiterpenes (69-109) can also be seen in Structure 4.16. 

Methylene difluorocyclopropanes are relatively rare and their rearrangement chemistry has been reviewed recently [14]. In addition, electron deficient alkenes such as sesquiterpenoid methylene lactones may be competent substrates. Two crystal structures of compounds prepared in this way were reported recently [15,16]. Other relatively recent methods use dibromodifluoromethane, a relatively inexpensive and liquid precursor. Dolbier and co-workers described a simple zinc-mediated protocol [17], while Balcerzak and Jonczyk described a useful reproducible phase transfer catalysed procedure (Eq. 6) using bromo-form and dibromodifluoromethane [18]. The only problem here appears to be in separating cyclopropane products from alkene starting material (the authors recommend titration with bromine which is not particularly amenable for small scale use). Schlosser and co-workers have also described a mild ylide-based approach using dibromodifluoromethane [19] which reacts particularly well with highly nucleophilic alkenes such as enol ethers [20], and remarkably, with alkynes [21] to afford labile difluorocyclopropenes (Eq. 7). 

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