Determination Of Absolute Stereochemistry Research Articles

Absolute Stereochemistry Determination of Bioactive Marine-Derived Cyclopeptides by Liquid Chromatography Methods: An Update Review (2018-2022).

Cyclopeptides are considered as one of the most important classes of compounds derived from marine sources, due to their structural diversity and a myriad of their biological and pharmacological activities. Since marine-derived cyclopeptides consist of different amino acids, many of which are non-proteinogenic, they possess various stereogenic centers. In this respect, the structure elucidation of new molecular scaffolds obtained from natural sources, including marine-derived cyclopeptides, can become a very challenging task. The determination of the absolute configurations of the amino acid residues is accomplished, in most cases, by performing acidic hydrolysis, followed by analyses by liquid chromatography (LC). In a continuation with the authors' previous publication, and to analyze the current trends, the present review covers recently published works (from January 2018 to November 2022) regarding new cyclopeptides from marine organisms, with a special focus on their biological/pharmacological activities and the absolute stereochemical assignment of the amino acid residues. Ninety-one unreported marine-derived cyclopeptides were identified during this period, most of which displayed anticancer or antimicrobial activities. Marfey's method, which involves LC, was found to be the most frequently used for this purpose.

Cryptocaryoic acids A – C: New phenyl alkyl acids isolated from the leaves of Australian rainforest plant Cryptocarya mackinnoniana

Phytochemical investigation of the leaves of the Australian rainforest tree Cryptocarya mackinnoniana led to the discovery of three new oxygenated phenyl alkyl acids, cryptocaryoic acids A – C and two known compounds, cryptocaryone and 2′,6′-dihydroxy-4′-methoxychalcone. The structures of all the compounds were determined by detailed spectroscopic analysis. Mosher's analysis was used for absolute stereochemistry determination at C-11, while the remaining stereochemistry determination of the one remaining stereocenter C-13 was based on NOESY correlations. All compounds isolated were also evaluated for their anti-inflammatory properties by assessing their inhibitory effects on LPS and interferon-γ induced nitric oxide (NO) production and TNF- α release in RAW 264.7 macrophages. The new cryptocaryoic acids exhibited weak to moderate anti-inflammatory activity (NO inhibition) ranging from (18.4–56 μM).

Direct determination of absolute stereochemistry of α-methylselenocysteine using the Mosher method

Mosher amides of α-methylselenocysteine were synthesized to determine the absolute stereochemistry of the sterically hindered α-carbon utilizing 1H, 13C, 19F, and 77Se NMR spectroscopies. After analysis of these spectra using the established Mosher method, the stereochemistry of the α-carbon was determined to be (R), which was subsequently confirmed using x-ray crystallography.

Asymmetric Synthesis of Griffipavixanthone Employing a Chiral Phosphoric Acid-Catalyzed Cycloaddition.

Asymmetric synthesis of the biologically active xanthone dimer griffipavixanthone is reported along with its absolute stereochemistry determination. Synthesis of the natural product is accomplished via dimerization of a p-quinone methide using a chiral phosphoric acid catalyst to afford a protected precursor in excellent diastereo- and enantioselectivity. Mechanistic studies, including an unbiased computational investigation of chiral ion-pairs using parallel tempering, were performed in order to probe the mode of asymmetric induction.

Instrumentation for Vibrational Circular Dichroism Spectroscopy: Method Comparison and Newer Developments.

Vibrational circular dichroism (VCD) is a widely used standard method for determination of absolute stereochemistry, and somewhat less so for biomolecule characterization and following dynamic processes. Over the last few decades, different VCD instrument designs have developed for various purposes, and reliable commercial instrumentation is now available. This review will briefly survey historical and currently used instrument designs and describe some aspects of more recently reported developments. An important factor in applying VCD to conformational studies is theoretical modeling of spectra for various structures, techniques for which are briefly surveyed.

Mini review: Instrumentation for vibrational circular dichroism spectroscopy, still a role for dispersive instruments.

Vibrational circular dichroism (VCD) has become a standard method for determination of absolute stereochemistry, particularly now that reliable commercial instrumentation has become available. These instruments use a now well-documented Fourier transform infrared-based approach to measure VCD that has virtually displaced initial dispersive infrared-based designs. Nonetheless, many papers have appeared reporting dispersive VCD data, especially for biopolymers. Instrumentation designed with these original methods, particularly after more recent updates optimizing performance in selected spectral regions, has been shown still to have advantages for specific applications. This article presents a mini-review of dispersive VCD instrument designs and includes sample spectra obtained for various biopolymer (particularly peptide) samples. Complementary reviews of Fourier transform-VCD designs are broadly available.

43 1,3-ポルオールの立体化学 : 相対配置を決めないで絶対配置を決定する方法(口頭発表の部)

43 1,3-ポルオールの立体化学 : 相対配置を決めないで絶対配置を決定する方法(口頭発表の部)

Resolution of Thiele’s acid

Thiele’s acid has been resolved for the first time by diastereomeric salt formation with brucine. Determination of absolute stereochemistry was accomplished by X-ray crystallography of the corresponding diester. We anticipate that access to optically resolved Thiele’s acid will stimulate its use in a diverse range of applications requiring chiral molecular clefts.

Application of Unusual Grignard Reaction for the Stereoselective Synthesis of Antidepressant Drug (R)-(–)-Venlafaxine

An enantioselective synthesis of antidepressant drug (R)-(–)-venlafaxine is accomplished as an application of recently explored unusual Grignard reaction. An innovative method for the generation of chirality at extremely reactive benzylic center along with determination of absolute stereochemistry has been discussed. The key steps involved in the synthesis include Sharpless asymmetric dihydroxylation for the induction of chirality and an unusual Grignard reaction.

Optical Resolution of Flavor/Fragrance Compounds by Chiral Supercritical Fluid Chromatography (SFC), and Determination of Absolute Stereochemistry using Vibrational Circular Dichroism (VCD)

Optical Resolution of Flavor/Fragrance Compounds by Chiral Supercritical Fluid Chromatography (SFC), and Determination of Absolute Stereochemistry using Vibrational Circular Dichroism (VCD)

2-および3-ヒドロキシアーキオールの立体選択的合成と水酸基の絶対立体配置の推定

2-および3-ヒドロキシアーキオールの立体選択的合成と水酸基の絶対立体配置の推定

Asymmetric Synthesis and CD Investigation of the 1,4-Benzodioxane Lignans Eusiderins A, B, C, G, L, and M

The enantioselective synthesis of (-)-eusiderins A (1), B (2), G (25), L (23), M (5) and (+)-eusiderin C (20) and a range of analogues was undertaken using an efficient, divergent synthesis all from a single chiral aldehyde 15, which was derived from (S)-ethyl lactate 9. A comprehensive set of NMR data along with ECD spectra and optical rotation measurements of the synthesized natural products and analogues were then obtained. This data confirmed the absolute stereochemistry of eusiderins A (1) and C (20) and for the first time gives the ECD and optical rotation for eusiderins B (2), G (25), L (23), and M (5) and a range of other substituted 1,4-benzodioxanes. This data will now allow for the determination of absolute stereochemistry of other members in this class of compound.

Determination of Absolute Stereochemistry of Natural Alicyclic Glycosides by 1H NMR Spectroscopy without Application of Chiral Reagents – An Indication

A study has been made of the 1H NMR spectra of peracetylated beta-glucopyranosides and alpha-arabinopyranosides obtained by reaction of D- and L-glucoses, and L- and D-arabinoses with either (R)- or (S)-2-octanols. The obtained and literature data show that 1H NMR spectra may be used to determine the absolute configuration of the aglycone moieties of some alicyclic glycosides without the need to synthesize derivatives with chiral reagents, as long as the absolute configuration of their monosaccharide moiety is known or vice versa. Spectra of marine steroid glycosides and their acetates containing glycosylated side chains as alicyclic fragments were also examined. It was shown that analysis of 1H NMR spectra for the determination of the absolute configuration is more applicable in the cases when glycosides have the same substitution in the D-ring of the aglycone moiety.

The Use of Co-crystals for the Determination of Absolute Stereochemistry: An Alternative to Salt Formation

Absolute stereochemistry of oils and viscous liquids can be difficult to determine. Co-crystallization involves generating a crystalline material consisting of more than one neutral compound. The combination of co-crystallization with both X-ray diffraction and chiral HPLC was particularly powerful in overcoming these difficulties for a series of chiral 3-arylbutanoic acids. Co-crystallization offers advantages over salt formation because co-crystals dissociate in solution, meaning identical HPLC conditions can be used for both the materials of interest and their co-crystals.

ChemInform Abstract: Quadrone Structural and Synthetic Studies. Total Synthesis of Natural ( -)-Quadrone, the (+)-Enantiomer, and the Racemate. Conformational Analysis, Circular Dichroism, and Determination of Absolute Stereochemistry.

A concise (17 steps, 1.8% overall yield) and highly stereoselective synthesis of the architecturally novel, cytotoxic sesquiterpene (−)-quadrone has been achieved, together with parallel constructions of the unnatural (+)-enantiomer and the racemate. The cornerstone of the strategy involved generation of the tricarbocyclic quadrone skeleton via an efficient, acid-promoted rearrangement of [4.3.2] propellane derivative

Total Syntheses of (+)-Echinopine A and B: Determination of Absolute Stereochemistry

The first total syntheses of the novel 3,5,5,7-sesquiterpenoids (+)-Echinopine A (1) and B (2) were achieved. Thereby the proposed structures were confirmed, and the absolute stereochemistry was determined. The key features are (1) the stereoselective installation of the vinyl-moiety on the concave side of the bicyclo[3.3.0]octane core via Myers' [3,3]-sigmatropic rearrangement, (2) the finding that the substituent on the C7 position next to the ketone can be epimerized to the desired concave face under basic conditions, (3) the closure of the highly strained seven-membered ring via RCM, and (4) the unusual C2-homologation of a vinyltriflate with a ketene silyl acetal.

α-メチル-α-アミノ酸エステルの絶対構造決定法としての CFTA法の応用研究

α-メチル-α-アミノ酸エステルの絶対構造決定法としての CFTA法の応用研究

The first synthesis of a 12-membered macrolide natural product via a RCM protocol: determination of absolute stereochemistry

The first synthesis of (10 S,12 R)-10-hydroxy-12-methyl-1-oxacyclododecane-2,5-dione and its C12 epimer is reported, thereby assigning the absolute stereochemistry of the natural product. The strategy utilizes a syn selective reduction, Yamaguchi esterification, and ring-closing metathesis as the key steps.

Determination of absolute stereochemistry for regulatory submission

Determination of absolute stereochemistry for regulatory submission

Enantiomeric separation and determination of absolute stereochemistry of asymmetric molecules in drug discovery—Building chiral technology toolboxes

The application of Chiral Technology, or the (extensive) use of techniques or tools for the determination of absolute stereochemistry and the enantiomeric or chiral separation of racemic small molecule potential lead compounds, has been critical to successfully discovering and developing chiral drugs in the pharmaceutical industry. This has been due to the rapid increase over the past 10-15 years in potential drug candidates containing one or more asymmetric centers. Based on the experiences of one pharmaceutical company, a summary of the establishment of a Chiral Technology toolbox, including the implementation of known tools as well as the design, development, and implementation of new Chiral Technology tools, is provided.