Enatiomeric Separation of Branched Fatty Acids after Conversion with trans-2-(2,3-Anthracenedicarboximido)cyclohexanol, a Highly Sensitive Chiral Fluorescent Conversion Reagent

Sex Pheromone of the Azalea Mealybug: Absolute Configuration and Kairomonal Activity

The sex pheromone of the azalea mealybug, Crisicoccus azaleae (Tinsley, 1898) (Hemiptera: Pseudococcidae), includes esters of a methyl-branched medium-chain fatty acid, ethyl and isopropyl (E)-7-methyl-4-nonenoate. These compounds are exceptional among mealybug pheromones, which are commonly monoterpenes. Determination of the absolute configuration is challenging, because both chromatographic and spectrometric separations of stereoisomers of fatty acids with a methyl group distant from the carboxyl group are difficult. To solve this problem, we synthesized the enantiomers via the Johnson-Claisen rearrangement to build (E)-4-alkenoic acid by using (R)- and (S)-3-methylpentanal as chiral blocks, which were readily available from the amino acids L-(+)-alloisoleucine and L-(+)-isoleucine, respectively. Each pure enantiomer, as well as the natural pheromone, was subsequently derivatized with a highly potent chiral labeling reagent used in the Ohrui-Akasaka method. Through NMR spectral comparisons of these derivatives, the absolute configuration of the natural pheromone was determined to be S. Field-trap bioassays showed that male mealybugs were attracted more to (S)-enantiomers and preferred the natural stereochemistry. Moreover, the synthetic pheromones attracted Anagyrus wasps, indicating that the azalea mealybug pheromone has kairomonal activity.

Branched medium-chain fatty acid profiling and enantiomer separation of anteiso-forms of teicoplanin fatty acyl side chain RS3 using UHPLC-MS/MS with polysaccharide columns

This work reports on targeted UHPLC-tandem mass spectrometry methods for the chiral separation of anteiso-methyl branched fatty acids (aiFAs). The methods involve precolumn derivatization with 1-naphthylamine and chiral separation on Chiralpak IG-U. anteiso-Methyl branched fatty acids with up to eight carbons can be separated. A method was used for the assignment of the absolute configuration of an aiFA present as fatty acyl residue of the teicoplanin mixture, namely teicoplanin RS3. Furthermore, the excellent methylene selectivity and improved selectivity for constitutional isomers of the polysaccharide columns was exploited for the elucidation and structural confirmation of previously unknown fatty acyl residues in teicoplanin. This shows the versatility and practical applicability of polysaccharide columns as orthogonal stationary phases to reversed-phase for structural elucidation of natural compounds. The developed methods are useful tools for related subdisciplines such as targeted metabolomics and lipidomics.

Metabolic Isolation, Stereochemical Determination, and Total Synthesis of Predominant Native Cholesteryl Phosphatidyl-α-glucoside from Carcinogenic Helicobacter pylori

We report the isolation and stereochemical determination of the predominant native cholesteryl 6-O-phosphatidyl α-glucoside (CPG) from Helicobacter pylori via an integrated biological and chemical strategy. The strategy employed (i) the metabolic isolation of a CPG analogue and (ii) the enzymatic degradation of the analogue to obtain the native lactobacillic acid for the stereochemical determination. The absolute stereochemistry of the acid was found to be 11R and 12S. Using the new stereochemical data, we accomplished the total synthesis of predominant native CPG and other predominant αCG derivatives.

The tridecaptins: non-ribosomal peptides that selectively target Gram-negative bacteria

Tridecaptins are a re-emerging class of non-ribosomal antibacterial peptides (NRAPs) with potent activity against highly problematic strains of Gram-negative bacteria. An intricate mode of action has been reported to explain the bactericidal activity of these NRAPs, wherein they bind selectivity to the Gram-negative version of the peptidoglycan precursor lipid II on the outer leaflet of the inner membrane and disrupt the proton-motive force. Tridecaptins are highly amenable to synthetic modification owing to their linear structure, therefore, various synthetic analogues have been reported, several of which have enhanced antimicrobial activity, reduced cost of synthesis and/or improved stability towards d-peptidase mediated hydrolysis. It has also been demonstrated that unacylated tridecaptins can act synergistically with clinically relevant antibiotics by sensitizing the outer membrane. This review will summarize past literature on the development/discovery of novel tridecaptin analogues (up until the end of 2020), some of which may be useful therapeutic agents to treat insidious Gram-negative bacterial infections.

Biosurfactants from Marine Cyanobacteria Collected in Sabah, Malaysia

Chemical investigation of the organic extract from Moorea bouillonii, collected in Sabah, Malaysia, led to the isolation of three new chlorinated fatty acid amides, columbamides F (1), G (2), and H (3). The planar structures of 1-3 were established by a combination of mass spectrometric and NMR spectroscopic analyses. The absolute configuration of 1 was determined by Marfey's analysis of its hydrolysate and chiral-phase HPLC analysis after conversion and esterification with Ohrui's acid, (1S,2S)-2-(anthracene-2,3-dicarboximido)cyclohexanecarboxylic acid. Compound 1 showed biosurfactant activity by an oil displacement assay. Related known fatty acid amides columbamide D and serinolamide C exhibited biosurfactant activity with critical micelle concentrations of about 0.34 and 0.78 mM, respectively.

Structure elucidation of bacterial nonribosomal lipopeptides

We provide a summary of the tools, which allow elucidate the structures of nonribosomal lipopetides.

Studies on tridecaptin B(1), a lipopeptide with activity against multidrug resistant Gram-negative bacteria

Previously other groups had reported that Paenibacillus polymyxa NRRL B-30507 produces SRCAM 37, a type IIA bacteriocin with antimicrobial activity against Campylobacter jejuni. Genome sequencing and isolation of antimicrobial compounds from this P. polymyxa strain show that the antimicrobial activity is due to polymyxins and tridecaptin B1. The complete structural assignment, synthesis, and antimicrobial profile of tridecaptin B1 is reported, as well as the putative gene cluster responsible for its biosynthesis. This peptide displays strong activity against multidrug resistant Gram-negative bacteria, a finding that is timely to the current problem of antibiotic resistance.

Total Synthesis and Stereochemical Assignment of the Antimicrobial Lipopeptide Cerexin A1

The isolation and total synthesis of the antimicrobial lipopeptide cerexin A1 is reported. This synthesis includes the preparation of orthogonally protected γ-hydroxylysine, utilizing a nitrile Reformatsky-type reaction as a key step to yield both diastereomers more efficiently than previously reported methods. The configuration of the β-hydroxyl in the lipid tail was determined by the use of a modified Ohrui-Akasaka approach. Furthermore, new cerexin analogues from Bacillus mycoides ATCC 21929 were isolated and characterized, revealing an ε-amino succinylation of a hydroxylysine residue that is unusual in a nonribosomal peptide synthetase product.

Development of Highly PotentD-Glucosamine-Based Chiral Fluorescent Labeling Reagents and a Microwave-Assisted β-Selective Glycosidation of a Methyl Glycoside Reagent

We synthesized new chiral fluorescence labeling reagents having a 2,3-anthracenedicarboximide group from D-glucosamine, and it was possible to introduce target alcohols at the anomeric positions of the reagents with beta-selectivity by glycosidations. Especially, it was possible to use methyl glycoside reagent as a glycosyl donor with a Lewis acid and microwave irradiation, and it gave selectively beta-glycoside while the reaction without microwave irradiation gave alpha- and beta-mixed glycosides. Those reagents showed very high chiral discrimination ability, and they made it possible to separate the eight stereoisomers of 4,8,12,16-tetramethylheptadecanol by HPLC after derivatizations.

Direct Determination of the Stereoisomeric Composition of Callosobruchusic Acid, the Copulation Release Pheromone of the Azuki Bean Weevil, Callosobruchus chinensis L., by the 2D-Ohrui-Akasaka Method

The stereoisomeric composition of the copulation release pheromone of the azuki bean weevil, Callosobruchus chinensis L., was determined to be R:S=3.3-3.4:1 by the 2D-Ohrui-Akasaka method.

Selectivity Enhancement for trans-2-(2,3-Anthracenedicarboximido)-cyclohexane-derived Diastereomers in HPLC by Using an Ordered Organic Stationary Phase

2-(2,3-anthracenedicarboximido)cyclohexane derivatives (AC) have been known as the evolutionary diastereomerizing reagents for enantiomer discrimination in HPLC with ODS. However, a substantial separation of diastereomers can be observed only at lower temperatures, such as -40 degrees C. Therefore, in this work, poly(octadecyl acrylate)-grafted silica, ODAn was applied as an alternative stationary phase to ODS for the separation of AC-derived diastereomers. As a result, complete separation was achieved even under the conventional condition: for example, methanol as the mobile phase and 0 degrees C as the column temperature. An investigation on the temperature dependency of the selectivity demonstrated that ODAn shows a remarkable increase in selectivity at temperatures below 30 degrees C, which almost agreed with the peak-top temperature of the endothermic peak in a DSC thermogram for ODA35 immersed in a mobile phase. The better separation would be derived from a highly ordered structure of ODAn and a carbonyl-pi interaction with AC-derived diastereomers.

Chiral discrimination of primary amines by HPLC after labeling with a chiral derivatization reagent,trans-2-(2,3-anthracenedicarboximido)-cyclohexanecarbonyl chloride

Enantiomeric discrimination of chiral primary amines was performed by both reversed-phase HPLC and normal-phase HPLC after labeling with a chiral fluorescent derivatization reagent, (1R,2R)- and (1S,2S)-trans-2-(2,3-anthracenedicarboximido)cyclohexanecarbonyl chloride. Use of HPLC permits separation of diastereomeric derivatives of amines up to C30 which have a primary amino group at the middle of the alkyl chain. The derivatives of primary amines having an anteiso alkyl chain, which has a chiral branched-methyl at the n-3 position of the alkyl chain, were also separated by HPLC, and it was also possible to separate niphatesine D by reversed-phase HPLC after derivatization.

Chiral discrimination of secondary alcohols by both1H-NMR and HPLC after labeling with a chiral derivatization reagent, 2-(2,3-anthracenedicarboximide)cyclohexane carboxylic acid

Enantiomeric discrimination of chiral secondary alcohols was performed by both reversed-phase HPLC and 1H-NMR after labeling with a chiral fluorescent derivatization reagent, 2-(2,3-anthracenedicarboximide)cyclohexanecarboxylic acid. It was possible to discriminate by HPLC the chirality of alcohols up to C30 having a chiral hydroxyl group at the middle of the straight alkyl chain, and, by 1H-NMR, alcohols up to C16. For alcohols having one straight alkyl and one isoalkyl group with the same carbon numbers at both sides of a hydroxyl group, it was possible to discriminate the chiralities of alcohols up to C19 by both 1H-NMR and HPLC. The 1H-NMR methods also made it possible to determine absolute configurations empirically.

Resolution of chiral drugs by liquid chromatography based upon diastereomer formation with chiral derivatization reagents

Chiral derivatization reagents for resolution of biologically important compounds, such as chiral drugs by high-performance liquid chromatography (HPLC), based upon pre-column derivatization and diastereomer formation, are reviewed. The derivatization reagents for various functional groups, i.e., amine, carboxyl, carbonyl, hydroxyl and thiol, are evaluated in terms of reactivity, stability, wavelength, handling, versatility, sensitivity, and selectivity. The applicability of the reagents to the analyses of drugs and bioactive compounds are included in the text.

Absolute configuration of a ceramide with a novel branched-chain fatty acid isolated from the epiphytic dinoflagellate, Coolia monotis

The absolute configuration of the chiral center at the C15 position of a novel branched-chain fatty acid derived from a new ceramide isolated from the epiphytic dinoflagellate Coolia monotis was determined to be of R from by reversed-phase HPLC after cleavage to 12-methylpentadecanoic acid and subsequent conversion with the chiral fluorescent reagent, (1R,2R)-2-(2,3-anthracenedicarboximido)cyclohexanol.