Fluorinated Musk Fragrances: The CF2 Group as a Conformational Bias Influencing the Odour of Civetone and (R)-Muscone

Selectively Fluorinated Citronellol Analogues Support a Hydrogen Bonding Donor Interaction with the Human OR1A1 Olfactory Receptor

C-2 fluorinated and methylated stereoisomers of the fragrance citronellol 1 and its oxalate esters were prepared from (R)-pulegone 11 and explored as agonists of the human olfactory receptor OR1A1 and assayed also against site-specific mutants. There were clear isomer preferences and C-2 difluorination as in 18 led to the most active compound suggesting an important hydrogen bond donor role for citronellol 1. C-2 methylation and the corresponding oxalate ester analogues were less active.

Synthesis of Cyclic Fragrances via Transformations of Alkenes, Alkynes and Enynes: Strategies and Recent Progress

With increasing demand for customized commodities and the greater insight and understanding of olfaction, the synthesis of fragrances with diverse structures and odor characters has become a core task. Recent progress in organic synthesis and catalysis enables the rapid construction of carbocycles and heterocycles from readily available unsaturated molecular building blocks, with increased selectivity, atom economy, sustainability and product diversity. In this review, synthetic methods for creating cyclic fragrances, including both natural and synthetic ones, will be discussed, with a focus on the key transformations of alkenes, alkynes, dienes and enynes. Several strategies will be discussed, including cycloaddition, catalytic cyclization, ring-closing metathesis, intramolecular addition, and rearrangement reactions. Representative examples and the featured olfactory investigations will be highlighted, along with some perspectives on future developments in this area.

Biomimetic enantioselective synthesis of β,β-difluoro-α-amino acid derivatives

Although utilization of fluorine compounds has a long history, synthesis of chiral fluorinated amino acid derivatives with structural diversity and high stereoselectivity is still very appealing and challenging. Here, we report a biomimetic study of enantioselective [1,3]-proton shift of β,β-difluoro-α-imine amides catalyzed by chiral quinine derivatives. A wide range of corresponding β,β-difluoro-α-amino amides were achieved in good yields with high enantioselectivities. The optically pure β,β-difluoro-α-amino acid derivatives were further obtained, which have high application values in the synthesis of fluoro peptides, fluoro amino alcohols and other valuable fluorine-containing molecules.

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

Due to their intrinsic physical properties, which includes being able to perform as volatile liquids at room and biological temperatures, fragrance ingredients/intermediates make ideal candidates for continuous-flow manufacturing. This review highlights the potential crossover between a multibillion dollar industry and the flourishing sub-field of flow chemistry evolving within the discipline of organic synthesis. This is illustrated through selected examples of industrially important transformations specific to the fragrances and flavours industry and by highlighting the advantages of conducting these transformations by using a flow approach. This review is designed to be a compendium of techniques and apparatus already published in the chemical and engineering literature which would constitute a known solution or inspiration for commonly encountered procedures in the manufacture of fragrance and flavour chemicals.

Fluorinated Rings: Conformation and Application

The introduction of fluorine atoms into molecules and materials across many fields of academic and industrial research is now commonplace, owing to their unique properties. A particularly interesting feature is the impact of fluorine substitution on the relative orientation of a C-F bond when incorporated into organic molecules. In this Review, we will be discussing the conformational behavior of fluorinated aliphatic carbo- and heterocyclic systems. The conformational preference of each system is associated with various interactions introduced by fluorine substitution such as charge-dipole, dipole-dipole, and hyperconjugative interactions. The contribution of each interaction on the stabilization of the fluorinated alicyclic system, which manifests itself in low conformations, will be discussed in detail. The novelty of this feature will be demonstrated by presenting the most recent applications.

Study of compositions of musks in different types secreted by forest musk deer (Moschus berezovskii)

Musk is a secretion of the forest musk deer (Moschus berezovskii). Normal musk is a brown solid secretion with a light fragrance. In this study, abnormal types of musk, namely, white and black musks, were discovered during the musk collection process. Researchers have long been concerned with the components of musk. Herein, GC-MS, headspace solid-phase microextraction (HS-SPME), and nonmetric multidimensional scaling (NMDS) were used to analyze the nonpolar organic components, volatile organic components, and sample similarities among different musks, respectively. Abundant steroid hormones and proteins were also found in the musk. The steroid hormone concentrations were detected using a radioimmunoassay (RIA). Proteins in the samples were hydrolyzed and the amino acids concentrations were detected. The steroid hormone and amino acid concentrations in white musk were significantly lower than in normal and black musks (p<0.05). The components were subjected to NMDS analysis to understand the differences in components among different types of musk, with the results suggesting that white musk was different from normal and black musks.

Pharmacological effects and mechanisms of muscone

Musk, the dried secretion from the preputial follicles of the male musk deer (genus Moschus), possesses various pharmacological activities and has been used extensively in traditional Chinese medicine for thousands of years. Muscone is the main active ingredient of musk and exerts pharmacological effects similar to those of musk. Although muscone was notably used to treat various disorders and diseases, such as neurological disorders, chronic inflammation and ischemia-reperfusion injury, most of the mechanisms of the pharmacological action of muscone remain unclear because of slow progress in research before the 21st century. In recent years, the pharmacological activities and mechanisms of muscone have been clarified. The present article summarizes the pharmacological and biological studies on cerebrovascular disease, cardiovascular disease, neurological effects, cancer and others and the associated mechanisms of the action of muscone to date.

Catalytic Enantioselective Synthesis of Difluorinated Alkyl Bromides

We report an iodoarene-catalyzed enantioselective synthesis of β,β-difluoroalkyl bromide building blocks. The transformation involves an oxidative rearrangement of α-bromostyrenes, utilizing HF-pyridine as the fluoride source and m-CPBA as the stoichiometric oxidant. A catalyst decomposition pathway was identified, which, in tandem with catalyst structure-activity relationship studies, facilitated the development of an improved catalyst providing higher enantioselectivity with lower catalyst loadings. The versatility of the difluoroalkyl bromide products was demonstrated via highly enantiospecific substitution reactions with suitably reactive nucleophiles. The origins of enantioselectivity were investigated using computed interaction energies of simplified catalyst and substrate structures, providing evidence for both CH-π and π-π transition state interactions as critical features.

Drastic fluorine effect: complete reversal of the selectivity in the Au-catalyzed hydroalkoxylation reaction of fluorinated haloalkynes

The gold-catalyzed hydration reaction of haloalkynes is highly regioselective producing 2-halomethylketones as the sole products. Herein, we document a drastic fluorine effect where the reaction of 1-halo-3,3-difluoroalkynes as substrates leads to a complete reversal of selectivity and produces 3,3-difluoroesters as the unique products.

Muscone Ameliorates Ovariectomy-Induced Bone Loss and Receptor Activator of Nuclear Factor-κb Ligand-Induced Osteoclastogenesis by Suppressing TNF Receptor-Associated Factor 6-Mediated Signaling Pathways

Postmenopausal osteoporosis is caused by the deficiency of estrogen, which breaks bone homeostasis and induces levels of pro-inflammatory cytokines. Muscone is a potent anti-inflammatory agent and is used to treat bone fracture in traditional Chinese medicine. However, its anti-osteoclastogenic effects remain unclear. For in vitro study, morphology tests of osteoclastogenesis were firstly performed. And then, factors in RANK-induced NF-κB and MAPK pathways were examined by RT-PCR and Western blot, and the binding of TNF receptor–associated factor (TRAF)6 to RANK was inspected by coimmunoprecipitation and immunofluorescence staining. For in vivo experiments, C57BL/6 ovariectomized (OVX) mice were used for detection, including H&E staining, TRAP staining, and micro CT. As a result, muscone reduced OVX-induced bone loss in mice and osteoclast differentiation in vitro, by inhibiting TRAF6 binding to RANK, and then suppressed NF-κB and MAPK signaling pathways. The expression of the downstream biomarkers was finally inhibited, including NFATc1, CTR, TRAP, cathepsin K, and MMP-9. The inflammatory factors, TNF-a and IL-6, were also reduced by muscone. Taken together, muscone inhibited the binding of TRAF6 to RANK induced by RANKL, thus blocking NF-kB and MAPK pathways, and down-regulating related gene expression. Finally, muscone inhibited osteoclastogenesis and osteoclast function by blocking RANK-TRAF6 binding, as well as downstream signaling pathways in vitro. Muscone also reduced ovariectomy-induced bone loss in vivo.

Highly selective macrocyclic ring-closing metathesis of terminal olefins in non-chlorinated solvents at low dilution

New ruthenium complexes featuring two unsymmetrical NHCs proved to be highly selective in macrocyclic RCM performed in green solvents at low dilution.

Molecular mechanism of activation of human musk receptors OR5AN1 and OR1A1 by (R)-muscone and diverse other musk-smelling compounds

Understanding olfaction at the molecular level is challenging due to the lack of crystallographic models of odorant receptors (ORs). To better understand the molecular mechanism of OR activation, we focused on chiral (R)-muscone and other musk-smelling odorants due to their great importance and widespread use in perfumery and traditional medicine, as well as environmental concerns associated with bioaccumulation of musks with estrogenic/antiestrogenic properties. We experimentally and computationally examined the activation of human receptors OR5AN1 and OR1A1, recently identified as specifically responding to musk compounds. OR5AN1 responds at nanomolar concentrations to musk ketone and robustly to macrocyclic sulfoxides and fluorine-substituted macrocyclic ketones; OR1A1 responds only to nitromusks. Structural models of OR5AN1 and OR1A1 based on quantum mechanics/molecular mechanics (QM/MM) hybrid methods were validated through direct comparisons with activation profiles from site-directed mutagenesis experiments and analysis of binding energies for 35 musk-related odorants. The experimentally found chiral selectivity of OR5AN1 to (R)- over (S)-muscone was also computationally confirmed for muscone and fluorinated (R)-muscone analogs. Structural models show that OR5AN1, highly responsive to nitromusks over macrocyclic musks, stabilizes odorants by hydrogen bonding to Tyr260 of transmembrane α-helix 6 and hydrophobic interactions with surrounding aromatic residues Phe105, Phe194, and Phe207. The binding of OR1A1 to nitromusks is stabilized by hydrogen bonding to Tyr258 along with hydrophobic interactions with surrounding aromatic residues Tyr251 and Phe206. Hydrophobic/nonpolar and hydrogen bonding interactions contribute, respectively, 77% and 13% to the odorant binding affinities, as shown by an atom-based quantitative structure-activity relationship model.

Kinetic Benchmarking Reveals the Competence of Prenyl Groups in Ring-Closing Metathesis

A series of prenyl-containing malonates are kinetically benchmarked against the standard allyl-containing congeners using a ruthenium benzylidene precatalyst for ring-closing metatheses. The prenyl grouping is found to be a superior acceptor olefin compared to an allyl group in RCM processes with ruthenium alkylidenes derived from terminal alkenes. The prenyl group is also found to be a highly competent acceptor for a ruthenium alkylidene derived from a 1,1-disubstituted olefin in a RCM process.

Organofluorine chemistry: Difluoromethylene motifs spaced 1,3 to each other imparts facial polarity to a cyclohexane ring

2,2-Dimethyl-5-phenyl-1,1,3,3-tetrafluororocyclohexane has been prepared and characterised as an example of a facially polarised cyclohexane containing 1,3 related CF₂ groups. The dipolar nature of the ring arises from the axial orientation of two of the C-F bonds pointing in the same direction, and set by the chair conformation of the cyclohexane. This electrostatic profile is revealed experimentally both in the solid-state (X-ray) packing of the rings and by solution (NMR) in different solvents. A computationally derived electrostatic profile of this compound is consistent with a more electronegative and a more electropositive face of the cyclohexane ring. This placing of CF₂ groups 1,3 to each other in a cyclohexane ring is introduced as a new design strategy which could be applicable to the preparation of polar hydrophobic cyclohexane motifs.

Muscone Induces CYP1A2 and CYP3A4 Enzyme Expression in L02 Human Liver Cells and CYP1A2 and CYP3A11 Enzyme Expression in Kunming Mice

AIM

To examine the effect of synthetic muscone on the expression of CYP1A2 and CYP3A4 enzymes in human liver L02 cells and in the liver tissue of Kunming mice.

METHODS

The L02 hepatic cell line was used to study the effect of low (10-4 μmol/L), middle (10-3 μmol/L), and high concentrations (10-2 μmol/L) of muscone on the expression of CYP1A2 and CYP3A4 enzymes. In addition, the cytochrome P450 (CYP) expression was investigated in Kunming mice after the administration of 10 mg/kg (low), 50 mg/kg (middle), and 100 mg/kg (high) dose of muscone for 6 days. A mixture of phenobarbital (30 mg/kg) and β-napthoflavone (80 mg/kg) was used as positive control and the effects of the compounds on CYP expression were investigated at the end of 6- and 12-day periods.

RESULTS

Muscone induced the expression of CYP1A2 (middle and low concentrations) and of CYP3A4 (high concentration) enzymes in L02 cells. In vivo, administration of muscone in Kunming mice revealed significant weight reduction at the end of 6- and 12-day periods (middle and high doses, respectively), compared to the control group (p < 0.05). Liver toxicity scores indicated that the liver injuries in the positive control and high doses of muscone group were significantly higher in the 6- and 12-day periods, compared to those in the blank control group (p < 0.05). Furthermore, muscone induced CYP1A2 and CYP3A11 expressions in Kunming mice at the middle dose and all doses during the 12-day period as demonstrated by immunoblotting experiments. A low dose of mucone induced the CYP enzyme expression more rapidly, whereas a high dose of muscone caused the longest inductive effect. The results were confirmed by immunohistochemistry experiments and real-time PCR studies, where similar patterns of muscone-mediated inductive effects were noted.

CONCLUSIONS

Muscone induces CYP1A2 and CYP3A4 expression in liver cells in vitro and in vivo. In addition, it exhibits liver toxicity in Kunming mice at concentrations higher than 50 mg/kg. The CYP-inductive effect that is caused by muscone encompasses a 6- to 12-day period of activity after drug administration as demonstrated by follow-up in vivo studies.