Identification of new, odor-active thiocarbamates in cress extracts and structure-activity studies on synthesized homologues

Effective End-Group Modification of Star-Shaped PNVCL from Xanthate to Trithiocarbonate Avoiding Chemical Crosslinking

In this study, six-arm star-shaped poly(N-vinylcaprolactam) (PNVCL) polymers prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization were subjected to aminolysis reaction using hexylamine. Chemically crosslinked gels or highly end-functionalized star polymers can be obtained depending mainly on the type of solvent used during the transformation of the RAFT functional group. An increase in the viscosity of the solution was observed when the aminolysis was carried out in THF. In contrast, when the reaction was conducted in dichloromethane, chain-end thiol (PNVCL)6 star polymers could be obtained. Moreover, when purified (PNVCL-SH)6 star polymers are in contact with THF, the gelation occurs in just a few minutes, with an obvious increase in viscosity, to form physical gels that become chemically crosslinked gels after 12 h. Interestingly, when purified (PNVCL-SH)6 star polymers were stirred in distilled water, even at high aqueous solution concentration (40 mg/mL), there was no increase in the viscosity or gelation, and no evident gels were observed. The analysis of the hydrodynamic diameter (Dh) by dynamic light scattering (DLS) did not detect quantifiable change even after 4 days of stirring in water. On the other hand, the thiol groups in the (PNVCL-SH)6 star polymers were easily transformed into trithiocarbonate groups by addition of CS2 followed by benzyl bromide as demonstrated by UV-Vis spectroscopical analysis and GPC. After the modification, the (PNVCL)6 star polymers exhibit an intense yellow color typical of the absorption band of trithiocarbonate group at 308 nm. To further demonstrate the highly effective new trithiocarbonate end-functionality, the PNVCL polymers were successfully chain extended with N-isopropylacrylamide (NIPAM) to form six-arm star-shaped PNIPAM-b-PNVCL block copolymers. Moreover, the terminal thiol end-functionality in the (PNVCL-SH)6 star polymers was linked via disulfide bond formation to l-cysteine to further demonstrate its reactivity. Zeta potential analysis shows the pH-responsive behavior of these star polymers due to l-cysteine end-functionalization. By this using methodology and properly selecting the solvent, various environment-sensitive star polymers with different end-groups could be easily accessible.

Characterization of volatile compounds of Indian cress absolute by GC-olfactometry/VIDEO-sniff and comprehensive two-dimensional gas chromatography

Indian cress (Tropaeolum majus L.) has been consumed in salad or soup for decades, but its odor's detailed molecular composition is still unknown. Here we report on the study of the odorant profile and odor-impact compounds of Indian cress absolute by GC-olfactometry/vocabulary-intensity-duration of elementary odors by sniffing (GC-O/VIDEO-Sniff) on an eight-way multiport system, combined with GCxGC-MS analyses for the identification of odorant trace constituents. Odor impact compounds of Indian cress absolute were determined by GC-O, and the overall influence of sulfury and fruity notes stood out. Forty-four odorant compounds were identified among which 22 (50% of the identified odorant molecules) were identified by using comprehensive two-dimensional GC coupled to a time-of-flight-mass spectrometer (TOFMS). These trace compounds were not detected by 1D-qMS or could only be found with specific searches once they were detected by comprehensive 2D-GC, although they were well perceived by the judges in GC-O. This was amongst others the case for the two molecules having the highest odor impact, (E)-hex-2-enal (fruity) and diethyl trisulfide (alliaceous, sulfury, cabbage). A powerful sulfur-containing odor compound whose first identification in cress was recently reported by the authors was detected by GC-O: O,S-diethyl thiocarbonate (fruity/red fruit and sulfury odor).

First identification of O,S-diethyl Thiocarbonate in Indian Cress absolute and odor evaluation of its synthesized homologues by GC-sniffing

Indian cress (Tropaeolum majus L.) absolute was studied by GC-olfactometry (VIDEO-Sniff method) in order to identify odor-active aroma compounds. Because of its fruity-sulfury odor note, a compound that has never been identified in plant extracts before stood out: O,S-diethyl thiocarbonate, present at 0.1% (percentage of the total GC/FID area) in the extract. GCxGC-TOFMS allowed for a clean mass spectrum to be obtained, and isolation by preparative GC followed by NMR studies allowed its identification. Here, we report on the first detection of O,S-diethyl thiocarbonate in Indian cress absolute by GC-olfactometry/VIDEO-Sniff and on its isolation and identification. The synthesis and odor evaluation of its homologues are presented.

Volatile organic nitrogen-containing constituents in ambrette seed Abelmoschus moschatus Medik (Malvaceae)

A detailed investigation of the basic fraction of a CO2 extract of ambrette seeds (Abelmoschus moschatus) revealed a total of 58 nitrogen-containing compounds. The identification of these compounds was carried out by GC-MS and NMR. All the identified nitrogen-containing compounds are reported here for the first time in ambrette seeds. Among these are 27 pyrazine derivatives and 12 pyridines, including the tentative identification of four new natural compounds, 1-(6-ethyl-3-hydroxypyridin-2-yl)ethanone (1), 1-(3-hydroxy-5,6-dimethylpyridin-2-yl)ethanone (2), 1-(3-hydroxy-6-methylpyridin-2-yl)ethanone (3), and 1-(3-hydroxy-5-methylpyridin-2-yl)ethanone (4). The odor of the basic fraction was assumed to be due to these pyrazines and pyridines and also the presence of seven thiazoles. The odors described suggest that these N-compounds contribute to what is described in perfumery terms as the "natural and rounded" character of the ambrette extract.