Origin of the axial-alkyl preference of (R)-α-phellandrene and related compounds investigated by high-level ab initio MO calculations. Importance of the CH/π hydrogen bond

Ab initio MO calculations were carried out, at the MP2/6-311++G(d,p)//MP2/6-311G(d,p) level, to investigate the Gibbs energy of conformational isomers of (R)-α-phellandrene and related 5-alkyl-1,3-cyclohexadienes. It has been found that the conformer bearing the 5-alkyl group in axial orientation is more stable than the equatorial congener. The result is consistent with experimental evidence that the axial-isopropyl conformer prevails in the conformational equilibrium of α-phellandrene. The reason for the stability of the folded conformer has been sought in the context of the CH/π hydrogen bond. A number of short non-bond distances have been disclosed in the axial conformers, between CHs in the 5-alkyl group and sp²-carbons of the cyclohexadiene ring. We suggest that the stability of the folded conformation often observed in conjugated diene compounds of natural origin, such as α-phellandrene and levopimaric acid, is attributed to an attractive molecular force, the CH/π hydrogen bond.     

Application of the taraxerane–oleanane rearrangement to the synthesis of seco-oleanane triterpenoids from taraxerone

Synthetic oleananes and seco-oleananes form a group of promising anti-inflammatory and cancer chemopreventive agents with an excellent safety profile. These compounds are usually prepared by semi-synthesis from natural oleanane triterpenoids. Since a taraxer-14-ene was reported to be rearranged into an olean-12-ene under mild reaction conditions, a rapid synthesis of seco-oleananes from taraxerone, which is a readily available starting material, was explored by us. Treatment of taraxerone with m-chloroperoxybenzoic acid gave 14,15-epoxy lactones, which underwent the taraxerane–oleanane rearrangement leading to new seco-oleanane triterpenoids.     

Medicinal Flowers. XXXV. Nor-oleanane-type and acylated oleanane-type triterpene saponins from the flower buds of Chinese Camellia japonica and their inhibitory effects on melanogenesis(1))

The methanolic extract and its 1-butanol-soluble fraction from the flower buds of Camellia japonica, cultivated in Yunnan Province, China, showed inhibitory effects on melanogenesis in theophylline-stimulated B16 melanoma 4A5 cells. From the 1-butanol-soluble fraction, a new 28-nor-oleanane-type and three new oleanane-type triterpene saponins, sanchakasaponins A-D, were isolated together with four known triterpene saponins. Their chemical structures were elucidated on the basis of chemical and physicochemical evidence. The inhibitory effects on melanogenesis in theophylline-stimulated B16 melanoma 4A5 cells and structure-activity relationships of the saponins were investigated.     

Medicinal flowers. XXXVI.1) Acylated oleanane-type triterpene saponins with inhibitory effects on melanogenesis from the flower buds of Chinese Camellia japonica

Four acylated oleanane-type triterpene oligoglycosides, sanchakasaponins E-H, were isolated from the flower buds of Camellia japonica cultivated in Yunnan province, China, together with four known triterpene oligoglycosides. The chemical structures of the new triterpene oligoglycosides were elucidated on the basis of chemical and physicochemical evidence. The inhibitory effects of the triterpene oligoglycoside constituents on melanogenesis in theophylline-stimulated B16 melanoma 4A5 cells were investigated.     

Annonamine, a new aporphine alkaloid from the leaves of Annona muricata

Atypical Parkinsonism in the Caribbean Island Guadeloupe is thought to be associated with the consumption of plants of the Annonaceae family, especially Annona muricata (soursop). In this study, a new aporphine alkaloid named annonamine (1) was isolated from the leaves of A. muricata L. together with four known benzylisoquinoline alkaloids (2-5). The structures of the isolated compounds were elucidated by the spectroscopic method.     

One new and several minor diarylheptanoids from Amomum muricarpum

A new natural diarylheptanoid, designated muricarpin, together with four diarylheptanoids were isolated from the rhizomes of Amomum muricarpum Elmer (Zingiberaceae) growing in Vietnam. Three known compounds, 1,7-bis(3,4-dihydroxyphenyl)heptan-3-yl acetate, 1-(4'-hydroxyphenyl)-7- (3″,4″-dihydroxyphenyl)heptan-3-yl acetate and 1-(3',4'-dihydroxyphenyl)-7-(4″-hydroxyphenyl)-heptan-3-one were isolated for the first time from the genus Amomum, meanwhile (5R)-5-hydroxy-1,7-bis(4-hydroxyphenyl)-heptan-3-one was found for the first time in plants. Their structures were determined using spectroscopic analyses.     

A new nondestructive approach to chemical analysis of potsherds using an X‐ray fluorescence microscope: Case study about the past pottery manufacture in the Yaeyama Islands

In archeology, pottery represents an important class of artifacts giving information on the past human activity, the ecology, and ancient cultural groups. Some chemical analytic methods, including X‐ray fluorescent analysis, were adopted for the archeological study of pottery. However, these techniques also involve problems, including the destructive analysis of materials, and cannot analyze the original clay condition of pottery. To address this, we carried out nondestructive chemical analysis of 13 potsherds excavated from the Yaeyama Islands in the southern Japan archipelagos using X‐ray fluorescence microscopy. Two analytic methods were used, elemental mapping and multipoint spectral measurement, making it possible to obtain a visualized elemental distribution on potsherd surface and a detailed multipoint elemental composition of the same sample for the multivariate statistical analysis. In this study, the visualized images suggested that calcium particles were mixed to temper the materials, and their size and quantity differed between potsherds, whereas the uniformity of clay substrate, including the quantities of iron and silicon on multipoint measurement, was a characteristic of each potsherd. Therefore, principal component analysis and nonmetric multidimensional scaling analysis of the potsherds suggest that the differences between the Yaeyama Islands in terms of pottery manufacturing technology are due to chronological factors in this case. Our method represents an effective new approach to the pottery study for technological change.     

Zinc phyllosilicates containing amino pendant groups

Two new zinc silicate hybrids were synthesized via sol-gel process from the reaction of zinc ions with trialkoxyaminesilanes in aqueous basic medium at room temperature and at 373 K. The inorganic-organic hybrids obtained, named SILZn (x=1 or 2) are related to 3-aminopropyl- and N-propylethylenediaminetrimethoxysilane, respectively. From nitrogen content, the number of pendant moles of organic groups in the matrices SILZnx (x=1 to 2) were determined as 5.14 and 3.25 mmol g⁻¹, respectively. The thermogravimetric curves showed mass losses of 50.7% and 58.0% for the same sequence of hybrids, to give the oxides as residue. X-ray diffraction patterns gave basal distances of 2065 and 2814 pm for SILZnx (x=1, 2), with well-formed particles of irregular shapes and sizes, as a characteristic of such material obtained from sol-gel process. The infrared spectra confirmed the attachment of the organic moieties on siloxane groups on the inorganic framework.