What's Hot,What's Not: The Trends of the Past 20 Years in the Chemistry of Odorants

This review is the sequel to the 2000 report on the recent advances in the chemistry of odorants and it summarizes the developments in fragrance chemistry over the past 20 years. Following the olfactory spectrum set out in that report, trendsetting so‐called captive odorants (patent‐protected ingredients unavailable to the market) are presented according to the main odor families: “fruity”, “marine”, “green”, “floral”, “spicy”, “woody”, “amber”, and “musky”. The design of odorants, their chemical synthesis, and their use in modern perfumery are illustrated with prominent examples. Featured are new fruity odorants that provide signature in the top note, as well as precursor technology. In the green domain, focus is on leafy notes and green pear. New benzodioxepines and benzodioxoles have modernized the marine family and required a revision of the existing olfactophore models. The replacement of Lilial and Lyral kept the industry busy in the floral domain with a plethora of new “muguets”. There was continued activity in the domain of rose odorants, especially in the area of rose ketones. Biotechnology became significant, for example, with Clearwood and Ambrofix, and the principal odorants of vetiver oil in the woody family have been found. Fourth and fifth families of musk odorants were also discovered and populated. Thus, new avenues for further explorations into fragrance chemistry have been opened.     

Determination of 2-mercaptopropionylglycine and its metabolite, 2-mercaptopropionic acid, in plasma by ion-pair reversed-phase high-performance liquid chromatography with post-column derivatization.

A simple and fast high-performance liquid chromatographic method was developed for the simultaneous measurement of 2-mercaptopropionylglycine (Tiopronine) and its metabolite (2-mercaptopropionic acid) in human plasma after the administration of a pharmaceutical dosage form (Acadione). The sample treatment before high-performance liquid chromatographic analysis consisted of the reduction of the corresponding disulphides by tri-n-butylphosphine and protein precipitation with ethanol. Separation was achieved by ion-pair high-performance liquid chromatography on a reversed-phase column (LiChrospher RP 18e) with cetrimonium bromide as counter ion and detection by fluorimetry after post-column derivatization with a selective thiol reagent, i.e. pyrenemaleimide. The high frequency of the analyzed samples and validation results make the method suitable for pharmacokinetic studies, and this was demonstrated by the first results obtained after the administration of an oral dose of 500 mg of Tiopronine to two healthy subjects.     

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Use of monomer fraction data in the parametrization of association theories

Association theories such as the CPA (cubic-plus-association), NRHB (non-random hydrogen bonding) equations of state and the various variants of SAFT (statistical associating fluid theory) have been extensively applied to phase equilibrium calculations. Such models can also be used for estimating the monomer fraction of hydrogen bonding compounds and their mixtures. Monomer fraction data are obtained from spectroscopic measurements and they are available for a few compounds such as pure water and alcohols as well as for some alcohol–alkane and similar mixtures. These data are useful for an understanding of the capabilities and limitations of association models. The purpose of this work is two-fold: (i) to compare the performance of three models, CPA, NRHB and sPC-SAFT, in predicting the monomer fraction of water, alcohols and mixtures of alcohol-inert compounds and (ii) to investigate whether “improved” model parameters can be obtained if monomer fraction data are included in the parameter estimation together with vapor pressures and liquid densities. The expression “improved” implies parameters which can represent several pure compound properties as well as monomer fraction data for pure compounds and mixtures. The accuracy of experimental monomer fraction data is discussed, as well as the role of monomer fraction data in clarifying which association scheme should be used in these equations of state. The results reveal that the investigated association models (CPA, sPC-SAFT and NRHB) can predict, at least qualitatively correct, monomer fractions of associating compounds and mixtures. Only, small differences are observed between the models. In addition, it has been shown that, using a suitable association scheme, a single set of parameters can describe satisfactorily vapor pressures, liquid densities and monomer fractions of water and alcohols. The 4C scheme is the best choice for water, while for methanol there is small difference between the 2B and 3B association schemes.     

Synthesis and Crystal Structure of the Novel Compound Mg4.5Pr79.5Mo126O312 Containing Mo3, Mo7 and Mo19 Clusters

The synthesis and crystal structure of the novel reduced molybdenum oxide Mg_4.5Pr_79.5Mo₁₂₆O₃₁₂ are presented. This compound crystallizes in the trigonal space group R-3 m with a = 11.3061(2) Å, c = 58.242(1) Å, V = 6447.5(2) Å³, and Z = 1. Refinements yield R(F ²) = 0.0433 and wR(F ²) = 0.0931 for 2827 unique reflections. The structure is built up from alternating slabs made up of molybdenum forming Mo₃, Mo₇ and Mo₁₉ clusters, praseodymium and oxygen atoms, and slabs containing isolated MoO₆ octahedra. The Pr³⁺ cations are localized either within the slabs or at their borderlines to ensure the cohesion between the slabs. Of the six crystallographically independent sites occupy by the Pr³⁺ cations, two of them also contain randomly about 15% and 20% of Mg²⁺ cations while the remaining four are fully occupied by the Pr³⁺ cations.     

Synthesis and polymerization of racemic and optically active β-substituted β-propiolactones. II: β-monosubstituted and β-disubstituted monomers and polymers with different optical purities

β-(trichloromethyl)-β-propiolactone (CCl₃-PL), β-(trifluoromethyl,methyl)-β-propiolactone (CF₃, Me-PL) and β-(trifluoromethyl,ethyl)-β-propiolactone (CF₃,Et-PL) have been obtained by the reaction of ketene with chloral, 1,1,1-trifluoroacetone and 1,1,1-trifluorobutanone, respectively. Chiral catalysis lead to optically active monomers. The enantiomeric excess of the lactones has been measured by ¹H-NMR spectroscopy, in the presence of 2,2,2-trifluoro-1-(9-anthryl)ethanol or an europium chiral shift reagent. Polymerizations have been carried out in bulk or in toluene, at 60°C or 80°C, using mainly organometallic initiators. The Polymers become insoluble and crystalline at enantiomeric excesses over 80% for CCl₃-PL and 70% for CF₃,Me-PL. Melting temperatures were recorded from 238 to 268°C for poly(CCl₃-PL) and from 78 to 100°C for poly(CF₃,Me-PL), depending upon the molecular weight and the enantiomeric excess. The ¹³C-NMR specroscopy of poly(CCL₃-PL) indicates that the polymerization of the corresponding lactone leads to polymers of increasing degrees of isotacticity with the enantiomeric excess of the monomer.     

Ice photolysis of 2,2′,4,4′,6-pentabromodiphenyl ether (BDE-100): Laboratory investigations using solid phase microextraction

Here, we report for the first time a laboratory investigation into the photochemical degradation of 2,2′,4,4′,6-pentabromodiphenyl ether (BDE-100) in ice solid samples using an artificial UV light source. Solid phase microextraction (SPME) was used as a sensitive extraction technique for monitoring trace amounts of the hydrophobic pollutant and its photoproducts. The results showed that ice photolysis kinetics for BDE-100 is similar to the one observed in the aqueous counterpart. The eight photoproducts identified consisted of brominated diphenyl ethers with lower bromine content and polybrominated dibenzofurans, suggesting two important photodegradation pathways for BDE-100 in ice solid samples: (i) stepwise reductive debromination and (ii) intramolecular elimination of HBr. Similarities in photochemical product arrays observed in the ice and water photolysis of BDE-100 were attributed to a similar mechanism for photochemical decomposition for both phases. Possible involvement of the water molecules in the reactions has been excluded by performing photolysis in D₂O ice solid and water samples. Taking advantage of the high preconcentration factor obtained with SPME at low temperatures, a SPME fiber cooled with liquid carbon dioxide down to 0 °C was used as a photoreaction support for BDE-100 allowing the identification of a greater number of photoproducts.     

Production of the Bengamide Class of Marine Natural Products in Myxobacteria: Biosynthesis and Structure–Activity Relationships

The bengamides, sponge‐derived natural products that have been characterized as inhibitors of methionine aminopeptidases (MetAPs), have been intensively investigated as anticancer compounds. We embarked on a multidisciplinary project to supply bengamides by fermentation of the terrestrial myxobacterium M. virescens, decipher their biosynthesis, and optimize their properties as drug leads. The characterization of the biosynthetic pathway revealed that bacterial resistance to bengamides is conferred by Leu 154 of the myxobacterial MetAP protein, and enabled transfer of the entire gene cluster into the more suitable production host M. xanthus DK1622. A combination of semisynthesis of microbially derived bengamides and total synthesis resulted in an optimized derivative that combined high cellular potency in the nanomolar range with high metabolic stability, which translated to an improved half‐life in mice and antitumor efficacy in a melanoma mouse model.