Structure of a sesquiterpene, cuauhtemone, and its derivative. Application of partially relaxed Fourier transform carbon-13 nuclear magnetic resonance

Structures, Occurrences and Biosynthesis of 11,12,13-Tri-nor-Sesquiterpenes, an Intriguing Class of Bioactive Metabolites

The compounds 11,12,13-tri-nor-sesquiterpenes are degraded sesquiterpenoids which have lost the C₃ unit of isopropyl or isopropenyl at C-7 of the sesquiterpene skeleton. The irregular C-backbone originates from the oxidative removal of a C₃ side chain from the C₁₅ sesquiterpene, which arises from farnesyl diphosphate (FDP). The C₁₂-framework is generated, generally, in all families of sesquiterpenes by oxidative cleavage of the C₃ substituent, with the simultaneous introduction of a double bond. This article reviews the isolation, biosynthesis and biological activity of this special class of sesquiterpenes, the 11,12,13-tri-nor-sesquiterpenes.

Eudesmane-type sesquiterpene derivatives from Laggera alata

Ten eudesmane-type sesquiterpene derivatives (1-10), including six cuauhtemone derivatives (1-6), one di-norsesquiterpene (3-oxo-di-nor-eudesma-4-en-11-oic acid, 7), and three eudesmane glycosides (alatoside F-H, 8-10) were isolated from the whole plants of Laggera alata together with 12 known compounds. Their structures were elucidated on the basis of extensive spectroscopic analysis, acid hydrolysis, and compounds 1 and 7 were studied by single-crystal X-ray diffraction analysis. The absolute configuration of 1 was determined by the application of the modified Mosher's method. All of the isolated eudesmane-type sesquiterpenes were evaluated for their cytotoxic activities on six human cancer cell lines, but all of the compounds were inactive on the tested cell lines in the concentration of 100 μg/mL.

A New Eudesmane Sesquiterpene from Pluchea arguta

A new eudesmane sesquiterpene, pluchargen A (3-β-[3′-chloro-2′-hydroxy-2′-methyl butyroyl]-cuauhtemone), was isolated from the whole plant of Pluchea arguta, and the structure was elucidated on the basis of 1- and 2-D NMR spectroscopic studies.

One-Dimensional Zigzag Chains of Cs-: The Structures and Properties of Li+(Cryptand[2.1.1])Cs- and Cs+(Cryptand[2.2.2])Cs-

The crystal structure and properties of lithium (cryptand[2.1.1]) ceside, Li+ (C211)Cs-, are reported. Li+ (C211)Cs- is the second ceside and third alkalide with a one-dimensional (1D) zigzag chain of alkali metal anions. The distance between adjacent Cs- anions, 6 A, is shorter than the sum of the van der Waals radii, 7 A. Optical, magic angle spinning NMR, two-probe alternating and direct current conductivity, and electron paramagnetic resonance measurements reveal unique physical properties that result from the overlap of adjacent Cs- wave functions in the chain structure. The properties of cesium (cryptand[2.2.2]) ceside, Cs+ (C222)Cs-, were also studied to compare the effects of the subtle geometric changes between the two 1D zigzag chain structures. Li+ (C211)Cs- and Cs+ (C222)Cs- are both low-band-gap semiconductors with anisotropic reflectivities and large paramagnetic 133Cs NMR chemical shifts relative to Cs- (g). An electronic structure model consistent with the experimental data has sp2-hybridized Cs- within the chain and sp-hybridized chain ends. Ab initio multiconfiguration self-consistent field calculations on the ceside trimer, Cs3(3-), support this model and indicate a net bonding interaction between nearest neighbors. The buildup of electron density between adjacent Cs- anions is visualized through an electron density difference map constructed by subtracting the density of three cesium atoms from the short Cs3(3-) fragment.

Barium azacryptand sodide, the first alkalide with an alkaline Earth cation, also contains a novel dimer, (Na(2))(2-)

The first barium sodide, with stoichiometry Ba(2+)(H(5)Azacryptand[2.2.2](-))Na(-).2MeNH(2), was synthesized by the reaction of Ba, Na, and H(6)Azacryptand[2.2.2] in NH(3)-MeNH(2) solution. It was characterized by X-ray crystallography, (23)Na MAS NMR, hydrogen evolution, DSC, optical spectroscopy, and magnetic susceptibility. This is the first sodide in which the sodium anions form (Na(2))(2)(-) dimers. Previous theoretical predictions were verified by a calculation of the potential energy curve for the dimer in the field of the surrounding charges, whose positions were determined from the crystal structure.