Humulene, structure

Humulene. structure of, 202 Hund s rule, 6 sp Hybrid orbitals. 17-18 sp2 Hybrid orbitals, 15. sp3 Hybrid orbitals, 12-14 Hydrate, 701... 

Regardless of Llieu apparent structural differences, all terpenoids are related. According to a formalism called the isoprene rule, they can be thought of as arising from head-to-tail joining of 5-carbon isoprene units (2-methyl-1,3-butadiene). Carbon 1 is the head of the isoprene unit, and carbon 4 is the tail. For example, myreene contains two isoprene units joined head to tail, forming an 8-carbon chain with two 1-carbon branches. a-Pinene similarly contains two isoprene units assembled into a more complex cyclic structure, and humulene contains three isoprene units. See if you can identify the isoprene units in a -pinene and humulene. 

Variation within a species was examined by looking at the chemistry of Z. dipetalum specimens collected from sites on three islands, Hawaii, Kauai, and Oahu. Of the seven compounds detected in this comparison, only two, caryophyl-lene [542] and humulene [543] (see Fig. 6.5 for structures 542-546), were present in all individuals. Trees from a site on Oahu were unique in their possession of... 

Humulene 109 (Structure 4.31) is isomeric with caryophyllene. First isolated from hops oil (Humulus lupulus), it is a common constituent of essential oils. 

You will notice that they are all aliphatic compounds with a scattering of double bonds and rings, few functional groups, and an abundance of methyl groups. A better definition (that is, a bio synthetically based definition) arose when it was noticed that all these compounds have 5n carbon atoms. Pinene and camphor are Cto compounds, humulene is Cl5> and phytol is C20 It seemed obvious that terpenes were made from a C5 precursor and the favourite candidate was isoprene (2-methylbuta-l,3-diene) as all these structures can be drawn by joining together 2-, 3-, or 4-isoprene skeletons end to end. Humulene illustrates this idea. 

A new tricyclic hydrocarbon, senoxydene, which has been isolated from Senecio oxyodontus, has been assigned the structure (304) on the basis of its n.m.r. spectrum together with that of the corresponding epoxide.It is suggested that once again humulene could act as the precursor (Scheme 48) see, however, p. 104. 

The proposed intermediacy of humulene (218) in the biosynthesis of sesquiterpenoids belonging to various structural groups (caryophyllane, protoilludane, etc.)... 

A complete account of the experimental evidence leading to the structural elucidation of the first members (244a—d) of the capnellane group of sesquiterpenoids has been provided in a recent paper cf. Vol. 5, p. 70). These compounds (244a—d) are found in soft coral (Capnella imbricata) and it has been suggested that their biosynthesis involves cyclization of humulene followed by methyl migration from C-5 to C-4 [cf. (245)]. 

There is a close correspondence between the conformation of humulene (1) and that of the tricyclic compound 3 as indicated from the X-ray crystal structure analysis of a silver(I) nitrate-humulene complex and by molecular mechanics (MMl) calculations. " Indeed, one of the preferred humulene conformations is that required to generate the stereochemistry of the product. ... 

Reaction of the 4,5-monoepoxide of humulene 8 with boron trifluoride-diethylether complex or trimethylsilyl triflate yielded two isomeric alcohols 6,6,9-trimethyltricyclo[6.3.0.0 ]un-dec-9-en-5-ol 9 and 6,6,9-trimethyltricyclo[6.3.0.0 ]undec-8-en-5-ol 10, in a 1 1 proportion with yields of 70 and 80%, respectively. The isomeric alcohols have the structure of the naturally occurring sesquiterpenes africene and africanol and of some of their derivatives. 

When the C1-C2 double bond is deactivated, for instance by oxidation of the methyl group to an aldehyde group as in 11, opening of the oxirane ring by trimethylsilyl triflate provided a homoallyl carbenium ion which then underwent transannular Ti-cyclization but with participation of the C8-C9 double bond leading to a mixture of secoprotoilludane derivatives 12 and 13. In this case the rearrangement took place from a different C-C conformation, where in an intermediate step an additional Z/ isomerization of the C1-C2 double bond occurred. Reaction of the 8,9-epoxide of humulene with tin(IV) chloride led initially to formation of a cationic center at C9, but internal 7r-cyclization yielded an alcohol with a hydroazulene structure. ... 

Irradiation performed with racemic substrate at room temperature, unless noted otherwise. Anisotropy (g) factor at or around irradiation wavelength, if reported or estimated. Extent of destruction. Maximum observed rotation a of irradiated solution, or specific rotation [a] of isolated sample or of residue obtained upon evaporation. Maximum observed ellipticity of irradiated solution or molar ellipticity of isolated sample. Enantiomeric excess of isolated sample. Not reported. Compound (mp 113 C) of unknown structure, obtained in a reaction of humulene with sodium nitrite, according to the reported procedure Chapman, AC. J. Chem. Soc. 1895 67 780. A mixed case of asymmetric destruction and photoderacemization irradiation performed at 0 C. Enantiomerically enriched sample used. Estimated g factor enhanced by two-quantum excitation with high intensity picosecond laser pulse. High-inten-sity laser of indicated pulse duration used. "Irradiation performed at 77 K in a hydrocarbon glass matrix. Optically pure sample photolyzed only to evaluate the enhanced g factor. Estimated g factor enhanced by two—quantum excitation with high-intensity femtosecond laser pulse. 

The microbial transformation of humulene, a substrate showing a structure similar to that of germacrone, was studied by Abraham and Stumpf using a screen of about 300 strains1175 . This led the authors to select the fungi Diplodia gossypina and Chaetonium cochlioides for preparative scale experiments. It was thus observed that the main reaction path starts with the epoxidation of the 1,2-double bond, as shown by direct biotransformation of this monoepoxide obtained by chemical synthesis. This is then further oxidized to yield a multitude of products including diepoxides and hydroxy-epoxides (Fig. 16.1-28). 

The relationship between these materials is clear from their biogenesis which is discussed in Chapter 2 (see Figure 2.11). Cyclisation of farnesyl pyrophosphate produces the 11-membered ring of the humulenes and this then can undergo ( -annular cyclisation to give the bicyclic structure of the caryophyllenes. 

Several monoterpenes [320,321], humulene (364) [320] and zerumbone (365) [322] have been reported from the essential oil from the rhizomes of Zingiber zerumbet. The characterization and elucidation of structure 365 of zerumbone was reported later [323]. The crystal structure of zerumbone isolated from the rhizomes of Z. zerumbet was determined by single-crystal X-ray diffraction [324]. The stereochemistry of the double bonds of humulene was established by crystallographic study of its silver nitrate adduct [325, 326]. The essential oil from the rhizomes of Z. 

Thus, for humulene we cleave at the three double bonds, giving three dicarbonyl compounds that we may draw by copying the structural portions from the starting molecule, as follows ... 

Figure 1. Structures of hop oil components. Key I, humulene II, humulene epoxide I III, humulene epoxide II IV, humulol V, humulenol II VI, humula-dienone VII, a-eudesmol VIII, -eudesmol IX, hop ether X, karahana ether XI, p-ionone and XII, j3-damascenone.

Sesquiterpenes (sesquiterpenoids). A structurally highly diverse class of terpenoids with 15 carbon atoms skeleton derived biosynthetically from famesyl pyrophosphate (FPP) ( famesol, isoprene rule, ter-penes). More than 70 different ring systems are formed by enzyme-catalyzed cyclization of the linear parent structure these cyclic structures can be further modified by 1,2- and 1,3-hydride shifts, renewed cycliza-tions, hydroxylations, and other subsequent reactions. S. are widely distributed in plants, fiingi, and animals but are less common in bacteria. Specific biosynthetic routes are often characteristic for certain organisms. Thus, basidiomycetes preferentially use humulene as the basis for the syntheses of protoilludanes, illu-danes, lactaranes, hirsutanes, and related S. skeletons. Individual S. systems are also known for liverworts and marine organisms. In addition, liverworts often contain the optical antipodes of S. known from plants. 

Alcohol 2.1 is the only example of this class, and was isolated from Lactarius camphoratus (79) which belongs to Section Olentes (2). The compound is presumably the product of 1-9 cyclization of a humulene precursor. The structure and absolute configuration of this new caryophyllene oxide (2.1) was determined by a combination of spectral data and a single-crystal X-ray analysis of the p-bromobenzoate derivative 2.3. The NMR spectrum of 2.1 exhibited only two methyl signals, one of them at 51.20, together with one-proton doublet of doublets centred at 52.93, strongly suggesting the presence of the 4,5-epoxide. The C-12 methylene protons were shifted downfield (5 3.84) in the 220 MHz NMR spectrum of the acetyl derivative (2.2). Moreover,... 

Sukh Dev Studies in Sesquiterpenes. XVIII. The Proton Magnetic Resonance Spectra of Some Sesquiterpenes and the Structure of Humulene. Tetrahedron 9, I (1960). 

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