A Highly Selective and Sensitive Chiral Derivatization Method for High- Performance Liquid Chromatographic Determination of the Stereoisomer Composition of Natural Products With Chiral Branched Alkyl Chains

In the study of chiral biologically active compounds such as pheromones, the analysis of the stereoisomer composition is essential to gain more insight into their stereochemical diversity, which affects the pheromone communication channels and therefore the diversification of species. This mini-review summarizes the development of fluorescence derivatization reagents for high-performance liquid chromatographic (HPLC) determination of the absolute configuration and stereoisomer composition of natural products with a chiral branched alkyl chain. The diastereomeric separation of anteiso fatty acids bearing a branched methyl group up to the C-26 position was achieved by reversed-phase HPLC under very low column temperature conditions using (1S,2S)-2-(2,3-anthracenedicarboximido)cyclohexanol as a derivatization reagent, enabling fluorescent detection of these compounds at femtomole levels. This method was also applicable to chiral alcohols and amines with chiral branched methyl groups using similar reagents containing a carboxyl group. These reagents were successfully applied to determine the absolute configurations and stereoisomer composition of the chiral alkyl chain of natural compounds including some insect pheromones, miyakosyne A, and plakoside A. The combination of these reagents and two-dimensional HPLC constitutes a very powerful tool for the analysis of the stereoisomers of natural crude samples. Furthermore, the analysis of some natural bioactive substances using this method demonstrated that natural substances are not always optically pure, consisting instead of stereoisomer mixtures exhibiting stronger activity than optically pure enantiomers. These results cast doubts on the concept of biological homochirality and demonstrate that natural pheromones do not always show the highest activity among all stereoisomers.

     

Synthesis of alkyl‐branched fatty acids

Alkyl‐branched fatty compounds are of interest for industrial products in the cosmetics and lubricant areas. In this review, clay‐ and zeolite‐catalyzed isomerizations of unsaturated fatty compounds, especially of oleic acid, are discussed. While clay‐catalyzed reactions give most complex mixtures of dimeric fatty acids and of monomeric so‐called “isostearic acid”, the zeolite‐catalyzed process yields preferentially an isomeric mixture of isostearic acids having the methyl branch on the 8–14 positions of the alkyl chain. Synthetically useful additions of alkyl radicals can only be performed on ω‐unsaturated fatty compounds, whereas perfluoroalkyl iodides were added to fatty compounds with terminal as well as internal double bonds using electron transfer‐initiated radical addition reactions. Electrophilic additions of alkyl carbenium ions generated by decomposition of alkyl chloroformates by ethylaluminum sesquichloride give well‐defined alkyl‐branched oleochemicals with good yields.     

Lubricity-Enhancing Low-Temperature Diesel Fuel Additives

Branched chain alkyl esters have lower crystallization temperatures than those with straight chain headgroups. We investigated the effect of branched chain headgroups on the cold flow properties and lubricity of alkyl esters. Commercial grade canola methyl ester was transformed into branched chain alkyl esters through a two or three-stage base-catalyzed transesterification reaction with 1-methoxy-2-propanol and 3-methyl-1-butanol. Conversion rates between 85 and 95% were achieved. The alkyl esters exhibited improved cold flow properties. The pour points were reduced from −12 to −27 °C as a result of incorporating branched headgroups. Addition of 0.1 or 0.2% (v/v) 1-methoxy-2-propyl alkyl ester improved the lubricity of a commercial pre-production ultra low sulfur diesel (ULSD) fuel, as determined by increased lubricity number and reduced wear scar diameter. The inclusion of methyl-tert butyl ether or ethanolamides additives to ULSD containing alkyl esters had an antagonistic effect on lubricity. The branched-chain alkyl esters have the potential to be used as lubricity-enhancing and low-temperature fuel additives.     

Cholesteryl ester compounds containing alkyl branched acyl groups — their preparations,properties and applications

Cholesterol having a reactive hydroxyl group at C₃-position can react with fatty acids to give the corresponding cholesteryl esters. Most of the natural cholesteryl esters consist of straight alkyl chain fatty acids with a high melting point. In oleochemistry it is well known that alkyl branched fatty acids, which are derived from petroleum or the fat and oil industry, have low melting points (mp.) and are chemically more stable if they are saturated acids. We designed alkyl branched fatty acid cholesteryl esters by means of common esterification and found some esters having a low mp. (mostly as a liquid). They had no irritative effect on both animal and human skin. They showed characteristic emulsification properties, namely the formation of either O/W or W/O emulsion coexistence together with other lipid components. Applying them onto human skin, they were able to penetrate towards the stratum corneum and improve the water-retaining ability and the barrier function of the stratum corneum. Based on these properties we have been applying the alkyl branched fatty acid cholesteryl ester, especially the methyl branched isostearic acid cholesteryl ester (IS-CE), to a shampoo and a rinse as hair cosmetics, skin care cosmetics and bath-additive products in the past decade.     

Rhodium‐Catalyzed Oxidative ortho‐Acylation of Aryl Ketone O‐Methyl Oximes with Aryl and Alkyl Aldehydes

The rhodium‐catalyzed oxidative ortho‐acylation of aryl ketone O‐methyl oximes with aryl and alkyl aldehydes via C H bond activation is described. The cross‐coupling reaction exhibits high functional group tolerance and regioselectivity under relatively mild conditions and constitutes a versatile route to a diverse library of diaryl ketones, which are difficult to obtain by the classical Friedel–Crafts acylation. Moreover, this reaction proceeds via an unprecedented Rh‐catalyzed oxidative ortho‐acylation of aryl ketone O‐methyl oximes with highly electron‐deficient aryl aldehydes followed by a direct addition of the second ortho C H bond to aldehydes in a one‐pot reaction, to generate two C C bonds simultaneously.     

Assessment of branching in polymers from small angle X-ray scattering (SAXS): SAXS from model comb-branched polystyrenes

Comb-branched polystyrenes having both fixed backbone length and number of branches but variable branch lengths were prepared anionically. Small angle X-ray scattering of the model polystyrenes from methyl ethyl ketone (MEK) solutions at 25°C was examined and it is shown that the mass per unit length and cross-sectional radius of gyration increase with increasing branch length. A maximum appears in the Kratky plot for the branched polymers. While the linear polymer displays an essentially Gaussian segment distribution in solution, the branched polymers deviate considerably from the behaviour of the linear polymer under the same conditions.     

Low temperature complete combustion of dilute toluene and methyl ethyl ketone over Mn‐doped ZrO2 (cubic) catalysts

Combustion of dilute toluene and methyl ethyl ketone over Mn‐doped ZrO₂ catalysts prepared using different precipitating agents, such as tetra‐alkyl ammonium hydroxides and NH₄OH, having Mn/Zr ratios from 0.05 to 0.67, and calcined at different temperatures has been thoroughly investigated. The Mn‐doped ZrO₂ catalyst shows high toluene or methyl ethyl ketone combustion activity, particularly when its ZrO₂ is in cubic form, when its Mn/Zr ratio is close to 0.2, and when it is prepared using tetra‐methyl ammonium hydroxide as a precipitating agent and calcined at 773 K. Copyright © 2005 Society of Chemical Industry     

Low-temperature properties of alkyl esters of tallow and grease

The low-temperature properties of mono-alkyl esters derived from tallow and recycled greases were determined for neat esters and 20% ester blends in No. 2 low-sulfur diesel fuel. Properties studied included cloud point, pour point, cold filter plugging point, low-temperature flow test, crystallization onset temperature, and kinematic viscosity. Compositional properties of the alkyl esters determined included water, residual free fatty acids, and free glycerol content. In general, the secondary alkyl esters of tallow showed significantly improved cold-temperature properties over the normal tallow alkyl ester derivatives. The low-temperature flow test did not show a 1:1 correlation with cloud point as previously observed with methyl soyate and methyl tallowate. For the homologous series methyl to n-butyl tallowate, ethyl tallowate had the best broad-spectrum low-temperature properties, both neat and when blended in diesel fuel. For the greases studied, both the normal and branched alkyl ester derivatives showed improved properties over corresponding tallow esters, especially with neat esters.     

Mixed Dialkylaluminum Chlorides and Mixed Trimethylorganoaluminates in Chemoselective 1,4 Addition Reactions to Alkylidene Malonic Acid Diethyl Ester

Mixed alkyl‐methyl‐ and aryl‐methylorganoaluminum chlorides 6 were formed by reaction of methylaluminum dichloride with organolithium or Grignard compounds and used for chemoselective 1,4 addition of higher alkyl, aryl, alkenyl and alkinyl groups to alkylidine malonic esters 1 and 2 . As an alternative, mixed trimethylorganoaluminates 7 can also be applied for these Michael addition reactions. For conjugate addition of alkenyl groups to alkylidene malonates 1 and 2 , alkenyl diisopropylalanes 10 obtained from alkynes and diisopropylaluminum hydride proved the most efficient reagents. Using these novel mixed organoaluminum compounds, β‐branched malonic (carboxylic) acid derivatives 3c , 8 , 9 and 1 1 were obtained in good yields. The method offers a general access to β‐branched carboxylic derivatives of quite diverse structure not dependent on the commercial availability of the organoluminum chlorides.     

Iron‐Catalyzed Cross‐Coupling of 1‐Alkynylcyclopropyl Tosylates and Related Substrates

1‐Alkynylcyclopropyl tosylates react with alkylmagnesium halides in the presence of catalytic ferric acetylacetonate [Fe(acac)₃] under net propargylic substitution; allene formation, which is the prevalent reactivity mode of propargylic substrates otherwise, was noticed as a side reaction only when branched alkyl‐ or aryl‐Grignard reagents were used. These transformations represent the first successful iron‐catalyzed cross‐coupling reactions of tert‐alkyl electrophiles.

     

具有特征香味的丙烯基烷基甲酮合成

利用烷基酯与烯丙基氯进行格氏反应得到烷基二烯丙基甲醇,在碱性条件下对叔醇进行分解,再通过用对甲苯磺酸催化异构得到丙烯基烷基甲酮。此方法可应用于合成含丙烯基酮结构的特征香味料和香料中间体。     

Effects of solvent basicity on free radical polymerizations of N,N′‐bismaleimide‐4,4′‐diphenylmethane initiated by barbituric acid

The polymerizations of N,N′‐bismaleimide‐4,4′‐diphenylmethane (BMI) initiated by barbituric acid (BTA) carried out in a variety of solvents at 130°C were studied. The nitrogen‐containing cyclic solvents such as N‐methyl‐2‐pyrrolidinone acted as a catalyst to promote the formation of the three‐dimensional crosslinked network structure. By contrast, the polymerization in a cyclic solvent that did not contain nitrogen such as γ‐butyrolactone resulted in nil gel content. The higher the solvent basicity, the larger the amount of insoluble polymer species formed. The molar ratio of BTA to BMI also played an important role in the polymerizations. The resultant polymers, presumably having a hyper‐branched structure, exhibited much narrower molecular weight distributions than those prepared by conventional free radical polymerizations. The BMI polymerizations using BTA as the initiator could not be adequately described by conventional free radical polymerization mechanisms. A polymerization mechanism that took into account the generation of a ketone radical pair between BTA and BMI and the subsequent initiation, propagation and termination reactions was proposed. It was concluded that the nitrogen‐containing cyclic solvents were capable of participating in the ketone radical pair formation process, thereby increasing the extent of polymer crosslinking reactions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The synthesis of sucrose esters from telomer monocarboxylic acids

Glycolipid biosurfactants possess excellent surfactant properties and can be useful model compounds for the synthesis of surfactants from materials available in large quantities. The incorporation of a long, branched alkyl group, which is a feature of glycolipids, into a synthetic surfactant was achieved by the transesterification of sucrose with the methyl ester of a selected telomer monocarboxylic acid mixture, in a solution reaction. Characterisation showed the product to be a mixture of mono- and diesters each comprising a different ratio of linear to branched alkyl chains in the substituted group. Surfactant properties of the mixture, and the chromatographically-separated components, when evaluated in both distilled water and a salt solution, were found to be superior to a range of sucrose stearates. In addition the biosurfactant analogues were found to be more effective than surfactants derived from β-keto alkyl esters of various sugars (including sucrose) but were not as efficient as these latter compounds.     

C18‐unsaturated branched‐chain fatty acid isomers: Characterization and physical properties

Iso‐oleic acid is a mixture of C₁₈‐unsaturated branched‐chain fatty acid isomers with a methyl group on various positions of the alkyl chain, which is the product of the skeletal isomerization reaction of oleic acid and is the intermediate used to make isostearic acid (C₁₈‐saturated branched‐chain fatty acid isomers). Methyl iso‐oleate, a mixture of C₁₈‐unsaturated branched‐chain fatty acid methyl ester isomers, is obtained via acid catalyzed esterification of iso‐oleic acid with methanol. The branched‐chain materials are liquid at room temperature and their “oiliness” property makes them an attractive candidate for the lubricant industry. In this paper, we report characterization of these branched‐chain materials using comprehensive two‐dimensional GC with time‐of‐flight mass spectrometry (GC × GC/TOF‐MS) and their physical and lubricity properties using tribology measurements.     

Copper(I)‐Mediated Highly Stereoselective syn‐Carbometalation of Secondary or Tertiary Propargylic Alcohols with Primary Grignard Reagents in Toluene with a High Linear Regioselectivity

A highly regio‐ and stereoselective syn‐carbometalation of terminal secondary or tertiary propargylic alcohols with primary alkyl Grignard reagents in toluene or phenylmagnesium bromide in Et₂O was developed, in which the alkyl or phenyl group from the Grignard reagents is introduced into the terminal position of the alcohols. The organometallic intermediate formed may be used directly for the coupling reaction with organic halides. Upon treatment with I₂ after the carbometalation, iodides may be obtained, which may undergo Sonogashira coupling reaction and highly stereoselective Novozym‐435‐catalyzed kinetic resolution to afford the optically active products.     

Organocatalytic Asymmetric Vinylogous Michael Addition of Dicyanoolefins to Imine Intermediates Generated in situ from Arenesulfonylalkylindoles

An organocatalytic asymmetric vinylogous Michael addition of dicyanoolefins to vinylogous imine intermediates generated in situ from arenesulfonylalkylindoles has been developed. This protocol provides an easy and convenient approach to C‐3 alkyl‐substituted indole derivatives with high yields (up to 93%), diastereomeric ratios (up to 99:1 dr) and enantioselectivities (up to 99% ee). The resulting adducts can be also readily converted to pyrazolo derivatives or α‐alkylation products of ketones without any decrease of the diastereoselectivities and enantioselectivities.     

Synthesis of Chloro Alkoxy and Alkoxy Derivatives of Methyl Oleate

Vegetable oil based lubricants typically have improved lubricity and biodegradability over their mineral oil based counterparts. However, vegetable oil lubricants often fail to meet the performance standards of mineral based oils with respect to cold temperature and resistance to oxidation. Olefins are an oxidatively weak point for vegetable based compounds. Removal of the olefin in a vegetable based lubricant through functionalization may increase resistance to oxidation. If the added functionality also causes branching of the alkyl chain, cold temperature properties may be improved. Any chemical modifications considered must be scalable and cost-effective to be useful in a commercial application. In this study, methyl oleate was functionalized into a chloro alkoxy derivative. Sodium hypochlorite (household bleach) and calcium hypochlorite were both used to generate hypochlorous acid in situ. Hypochlorous acid and a series of alcohols (methanol, ethanol, and butanol) were reacted with methyl oleate to make chloro alkoxy compounds in 29.8–77.9 % yields. In an effort to make a branched saturated ether we removed the chlorine moiety of the chloro alkoxy compounds. Dehalogenation was achieved under basic conditions over a Pd/C catalyst in 2-propanol. Reaction times increased substantially as the size of the adjacent alkoxy group increased. The reaction rate could be improved by heating the reactions above 100 °C in a pressure reactor. Increased reaction temperature also resulted in an increase in ketone side products from the competing elimination reactions. Saturated ether yields were 4.1–43.2 %.     

Gold‐Catalyzed Carbenoid Transfer Reactions of Diynes – Pinacol Rearrangement versus Retro‐Buchner Reaction

Aromatic diyne systems bearing one terminal propargylic acetate moiety and one tertiary propargylic alcohol subunit were converted in the presence of a gold catalyst. After an initial 1,2‐migration of the acetoxy group at the terminal alkyne, a gold carbenoid is formed which is then transferred onto the internal alkyne of the propargylic alcohol. This combination enables the use of propargylic acetates as precursors for a gold‐catalyzed pinacol‐type rearrangement. In the final pinacol‐like step the shift of an alkyl or aryl moiety onto an electrophilic gold carbenoid/cation terminates the reaction and 1‐naphthyl ketones are obtained as products. If electron‐rich aromatic backbones are used, a mechanistically interesting alternative pathway including a retro‐Buchner reaction is opened.

     

Clay nanolayer reinforcement of cis‐1,4‐polyisoprene and epoxidized natural rubber

Conditions were established for dispersing clay nanolayers into both cis‐1,4‐polyisoprene (synthetic) natural rubber (NR) and epoxidized natural rubbers (ENR) having 25 or 50 mol % epoxide. The clay was a sodium montmorillonite and was used as a pristine layered silicate or as organically modified layered silicates to make the galleries more hydrophobic and thus more compatible with the elastomers. The chemical modifications were carried out using an ion‐exchange reaction with alkyl ammonium cations. Incorporation of the clays into the elastomers was achieved by mixing the components themselves in a standard internal blender or by mixing dispersions of them in toluene or methyl ethyl ketone. X‐ray diffraction results indicated intercalation of NR and ENR into the silicate interlayers, followed by exfoliation of the silicate layers into the elastomer matrices. Of primary interest was the effect of the intercalated and exfoliated clays on the mechanical properties of the elastomers. The reinforcing effects obtained were found to depend strongly on the extent of the dispersion of the silicate layers into the rubber matrices. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1391–1403, 2001     

Effect of benzohydroxamato-ethylenediamine-titanium complex on modification of jute and cotton yarns by UV-radiation-induced urethane acrylate

Several formulations were developed consisting of an aliphatic-based urethane triacrylate oligomer (Ebcryl 264) combined with N-vinyl pyrrolidone (NVP), a carboamide monomer, and tripropylene glycol diacrylate (TPGDA) at different proportions. A plasticizing agent, diallyl phthalate (DP), and methyl ethyl ketone (MEK), an antibubbling solvent, were incorporated into the solutions. Thin polymer films prepared with these solutions under UV radiation were characterized. Jute and cotton yarns were treated with these solutions and cured with UV radiation. As a result, the rheological properties of jute and cotton were improved. The effect of ethylenediamine–titanium (EDA–titanium) complex and its ligands was studied. A very minute amount (0.1%) of the complex enhanced rheological properties of jute and cotton very significantly. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1571–1580, 1997