New volatile sulfur-containing constituents in a simultaneous distillation-extraction extract of red bell peppers (Capsicum annuum).

An extract of red bell peppers ( Capsicum annuum) was prepared by simultaneous distillation-extraction (SDE, Likens-Nickerson). In addition to the already known (3 E)-3-hepten-2-one ( 1), the unsaturated C9-ketones 1-nonen-4-one ( 2), (2 E)-2-nonen-4-one ( 3), and (2 E,5 E)-2,5-nonadien-4-one ( 4), 2-methoxy-3-isobutylpyrazine ( 5), and heptane-2-thiol ( 6), we identified 19 new thiols (the aliphatic saturated and unsaturated thiols 14- 16, and 22- 27, the mercapto-ketones 12 and 13, the mercapto-alcohols 17, 18, and 30, the dithiols 19 and 28, the methylthio-thiols 20 and 21, and the thiophene-thiol 31) and the two new dithiolanes 10 and 29. All of them are structurally related to the unsaturated C7- and C9-ketones 1- 4. The free thiols were enriched using Affi-Gel 501 ( p-aminophenyl-mercuric acetate grafted on an agarose gel). The new compounds were confirmed by syntheses and were organoleptically evaluated.

From linden flower to linden honey. Part 2: Glycosidic precursors of cyclohexa-1,3-diene-1-carboxylic acids.

The presence of two unusual, recently identified terpene acids, i.e., 4-(1-hydroxy-1-methylethyl)cyclohexa-1,3-diene-1-carboxylic acid (1) and 4-(1-methylethenyl)cyclohexa-1,3-diene-1-carboxylic acid (2), was now also confirmed in (Swiss) linden honey, after solid-phase extraction and HPLC purification. NMR Spectroscopy, in combination with UPLC/MS analysis, showed the presence of several glycosides of 1, which accounted for ca. 0.6 weight-% of the honey, as quantified by UPLC-UV. The major 'glycoside' of 1, compound 5, could be isolated and identified by 2D-NMR experiments as the corresponding beta-gentiobiosyl ester (rather than the classical compound with a glycosidic bond between an aglycone OH group and the sugar). The same diglycosides found in linden honey were also detected in linden nectar; also, chestnut and fir honeys contained these glycosides in minor quantities, but not colza, acacia, or dandelion honeys (Table 2).

New constituents related to 3-methyl-2,4-nonanedione identified in green tea.

The volatile constituents of two exquisite green tea varieties, Kiyosawa tea from Japan and Long Jing tea from China, were investigated in order to identify new compounds responsible for the characteristic flavor of a green tea brew. The extracts were prepared by solid-phase extraction using Oasis-HLB-cartridges. Besides the common compounds of green tea chemistry, the already described compounds 3-methyl-2,4-nonanedione (1) and 3-hydroxy-3-methyl-2,4-nonanedione (2), products of degradation of furan fatty acids, as well as three new compounds related to compound 1 were identified. These were 1-methyl-2-oxopropyl hexanoate (3), 1-methyl-2-oxoheptyl acetate (4) and 2-butyl-4,5-dimethyl-3(2H)-furanone (5). Their syntheses and spectroscopic data are reported. Compound 2 increases the sweet, creamy aroma and the characteristic mouthfeel of a green tea flavor, compounds 3 and 4 contribute to its floral, juicy notes and compound 5 exhibits an interesting sweet, buttery flavor.

Volatile constituents of Semnostachya menglaensis Tsui.

Semnostachya menglaensis Tsui (Acanthaceae) is a rare plant indigenous to Mengla in the tropical rainforest of the Xishuangbanna prefecture in the south of Yunnan province, People's Republic of China. When the leaves are crushed, a characteristic smell of basmati rice or pandan leaves develops. Their hexane extract, prepared from a specimen growing in a greenhouse of the botanical garden of the Kunming Institute of Botany, contains 1-(3,4,5,6-tetrahydro-2-pyridyl)-1-propanone (41.2%) and 1-(1,4,5,6-tetrahydro-2-pyridyl)-1-propanone (37.5%) which constitute the main part of the volatile compounds. Minor components are 1-(3,4,5,6-tetrahydro-2-pyridyl)-1-ethanone (4.9%), 1-(1,4,5,6-tetrahydro-2-pyridyl)-1-ethanone (4.8%), 1-(2-piperidyl)-1-propanone (5.2%), 1-octen-3-ol (3.2%), 1-octen-3-one (1.9%), and 3-octanol and 1-(2-pyridyl)-1-propanone in trace amounts.

From the linden flower to linden honey--volatile constituents of linden nectar, the extract of bee-stomach and ripe honey.

Honey is produced by honeybees (Apis mellifera), which collect nectar from flowers, digest it in their bodies, and deposit it in honeycombs, where it develops into ripe honey. We studied the evolution of the volatile constituents from the nectar of linden blossoms (Tilia cordata) to honey via the 'intermediate' honeybee. The sampling of the contents of the honey stomach or honey sack of the bee is unique. Extracts were prepared from nectar, from the liquid of the honey stomach, and from ripe honey. The chemistry is extremely complex, and compounds spanning from monoterpenes (hydrocarbons, ethers, aldehydes, acids, and bifunctional derivatives), isoprenoids, aromatic compounds (phenylpropanoids, phenols), and products degraded from fatty acids to alkaloids, were identified. Some compounds definitely stem from the plants, whereas other interesting constituents can be attributed to animal origin. Two derivatives of decanoic acid, 9-oxodec-2-enoic acid (12) and 9-hydroxydec-2-enoic acid, identified in the honey are known to be constituents of the so-called 'Queen's pheromone'. Two metabolites of these acids were identified in the extract of the honey stomach: 8-oxononanal (10), a new natural product, and 8-oxononanol (11). There structures were confirmed by synthesis. Nectar and honey stomach contain many aldehydes, which, due to the highly oxidative atmosphere in the honeycomb, are found as corresponding acids in the honey. Two acids were newly identified as 4-isopropenylcyclohexa-1,3-diene-1-carboxylic acid (14) and 4-(1-hydroxy-1-methylethyl)-cyclohexa-1,3-diene-1-carboxylic acid (15).