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(3R)-Gobiusxanthin stereoisomers (1a–d) were synthesized by stereoselective Wittig reaction of the (3R)-C15-acetylenic tri-n-butylphosphonium salt 7 with C25-apocarotenal stereoisomers 5a,b and 14a,b bearing four kinds of 3,6-dihydroxy-ε-end groups. The validity of the reported stereochemistry of gobiusxanthin was demonstrated by the fact that the reported spectral data of natural gobiusxanthin were in agreement with those of synthetic (3R,3'S,6'R)-gobiusxanthin (1a). On the other hand, the reported CD spectral data of natural epigobiusxanthin, which has been assigned as (3R,3'R,6'R)-isomer (3'-epigobiusxanthin), were identical with those of synthetic (3R,3'S,6'S)-isomer 1d (6'-epigobiusxanthin) rather than those of the corresponding synthetic 3'-epi-isomer 1b. It was found that the stereochemistry at C3-position has little effect on the shape of their CD spectra. Thus, in order to reinforce the validity of the absolute configurations at C3-position of natural specimens, (3S,3'S,6'R)- and (3S,3'S,6'S)-stereoisomers 1e and 1f were also synthesized and a HPLC analytical method for four stereoisomers was established by using a column carrying a chiral stationary phase. The HPLC analysis has proven that the stereochemistry of the natural epigobiusxanthin is 3R,3'S,6'S.

In order to determine the absolute configuration of naturally occurring alloxanthin, a HPLC analytical method for three stereoisomers 1a–c was established by using a chiral column. Two authentic samples, (3S,3′S)- and meso-stereoisomers 1b and 1c, were chemically synthesized according to the method previously developed for (3R,3′R)-alloxanthin (1a). Application of this method to various alloxanthin specimens of aquatic animals demonstrated that those isolated from shellfishes, tunicates, and crucian carp are identical with (3R,3′R)-stereoisomer 1a, and unexpectedly those from lake shrimp, catfish, biwa goby, and biwa trout are mixtures of three stereoisomers of 1a–c.

Twelve pairs of sesquineolignan enantiomers (1a / 1b − 6a / 6b and 1c / 1d − 6c / 6d), including twenty one undescribed and three known (2b , 3b , and 4b) sesquineolignans were isolated from an ethanol extract of the stems and leaves of Neoshirakia japonica (Euphorbiaceae). The successful separation of twelve pairs of enantiomers with mirror image-like electronic circular dichroism (ECD) curves and opposite specific rotation values, as one of the most important steps in compound isolation, was carried out by chiral HPLC columns. The absolute configurations of all undescribed sesquineolignans were elucidated by comprehensive analysis of their experimental ECD spectra. The effects of all the isolates on antineuroinflammatory and radical scavenging activity were evaluated. Compared with the positive control minocycline (IC 50 = 1.2 μM), compounds 1a / 1b / 1c / 1d − 6a / 6b / 6c / 6d with IC 50 values being greater than 50 μM displayed almost no effect on the inhibition of NO production in LPS-induced BV-2 microglial cells. The results of DPPH-radical scavenging activity for them showed that compound 3c had moderate radical scavenging ability (EC 50 = 48.47 μM), while the EC 50 value of positive control vitamin C was 18.21 μM. Twelve pairs of sesquineolignan enantiomers, including twenty one undescribed and three known sesquineolignans were isolated from Neoshirakia japonica. The effects of all the sesquineolignans on antineuroinflammatory and antioxidant activities were evaluated. [Display omitted] • Twelve pairs of sesquineolignan enantiomers were isolated from Neoshirakia japonica. • The separation of these enantiomers were carried out successfully by chiral HPLC columns. • The absolute configurations of all sesquineolignans were established by analysis of their ECD spectra. [ABSTRACT FROM AUTHOR]

Chiral high-performance (HPLC) separation of trans-bis[2-(2-pyridyl)aminophenolato] dichlorocyclotriphosphazene 1 was achieved and the absolute configuration of (+)-1 was assigned to be S,S by single-crystal X-ray structural analysis. The optically pure 1,2-diphenyl-1,2-ethanediolate derivatives (+)- 2a and (−)- 2b were synthesized by the reactions of (+)-1 and (-)-1 with ( R,R)-hydrobenzoin, respectively, in refluxing toluene in the presence of an excess amount of triethylamine and a catalytic amount of 4-(dimethylamino)pyridine. The of the enantiomers of 1 and the of diastereomers of 2 were not observed in refluxing toluene neither under acidic nor basic conditions. The stereochemistry of (+)-1 was confirmed by the crystal structure of (+)- 2a and bis[(4-methyl-2-pyridyl)oxy]cyclotriphosphazene (+)-3 derived from (+)-1. Chirality 28:556-561, 2016. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

We report here a practical and efficient synthesis of diethyl 1,2,3,4-tetrahydroisoquinoline-3-phosphonate derivatives. The target compounds were prepared in good yield using a Pictet-Spengler reaction involving α-amino phosphonates that were easily obtained. We have paid special attention to the synthesis of (R)- and (S)-1,2,3,4-tetrahydroisoquinoline-3-phos- phonic acid (TicP) 2a, a conformationally constrained analogue of phosphophenylalanine PheP. The procedure is based on the preparation of racemic phosphophenylalanine (PheP) diethyl ester followed by chiral chromatographic separation and subsequent Pictet-Spengler chemistry. [ABSTRACT FROM AUTHOR]

(3R)-Gobiusxanthin stereoisomers (1a-d) were synthesized by stereoselective Wittig reaction of the (3R)-C15-acetylenic tri-n-butylphosphonium salt 7 with C25-apocarotenal stereoisomers 5a,b and 14a,b bearing four kinds of 3,6-dihydroxy-ε-end groups. The validity of the reported stereochemistry of gobiusxanthin was demonstrated by the fact that the reported spectral data of natural gobiusxanthin were in agreement with those of synthetic (3R,3'S,6'R)-gobiusxanthin (1a). On the other hand, the reported CD spectral data of natural epigobiusxanthin, which has been assigned as (3R,3'R,6'R)-isomer (3'-epigobiusxanthin), were identical with those of synthetic (3R,3'S,6'S)-isomer 1d (6'-epigobiusxanthin) rather than those of the corresponding synthetic 3'-epi-isomer 1b. It was found that the stereochemistry at C3-position has little effect on the shape of their CD spectra. Thus, in order to reinforce the validity of the absolute configurations at C3-position of natural specimens, (3S,3'S,6'R)- and (3S,3'S,6'S)-stereoisomers 1e and 1f were also synthesized and a HPLC analytical method for four stereoisomers was established by using a column carrying a chiral stationary phase. The HPLC analysis has proven that the stereochemistry of the natural epigobiusxanthin is 3R,3'S,6'S. [ABSTRACT FROM AUTHOR]

The aim of the study was to develop a new HPLC method for direct chiral separation of Ofloxacin enantiomers using polar non-aqueous mobile phase by application of response surface methodology. Rotatable central composite design (CCD) with eight factorial points, six axial points and six replications in central point was used to evaluate the influence of three independent variables (concentration of methanol, diethylamine and flow rate) on the output responses (capacity factor of first peak, tailing factors of both the enantiomers, resolution between the Ofloxacin enantiomers, retention time of the last peak and chromatographic optimization function). Further, CCD data were combined with multiple response optimization in order to obtain a set of optimal experimental conditions (% methanol/hexane/acetonitrile-43.33/10/46.62 (v/v), % acetic acid/diethylamine-0.4/0.2 and flow rate as 1.4 mL min) leading to the most desirable compromise between resolution and analysis time. The method demonstrated good correlation between observed and predicted responses. The developed method was validated according to ICH guidelines and applied for quantitative analysis of two commercially available tablets Zenoflox (Ofloxacin) and Glevo (Levofloxacin). Good agreement was found between the assay results and the label claim of the marketed formulations by showing good %recovery and %CV. The study resulted in a better chromatographic system for the determination of Ofloxacin enantiomers. [ABSTRACT FROM AUTHOR]

Abstract: A sensitive and specific high performance liquid chromatography method for the separation and determination of tapentadol enantiomers has been developed and validated. Ten different chiral columns were tested in a normal phase system. Excellent enantioseparation with the resolution more than 2.5 for all enantiomers was achieved on Chiralpak AD-H using mixture of heptane–propan-2-ol–diethylamine (980:20:1, v/v/v). The detection was carried out using fluorescence detector at excitation wavelength of 295nm and emission wavelength of 273nm. The influence of mobile phase composition, namely organic modifiers, additives, aliphatic alkanes and water content in mobile phase, on retention and enantioseparation was studied. Validation of the developed method including linearity, limit of detection, limit of quantification, precision, accuracy and selectivity was performed according to the International Conference on Harmonization guidelines. The advantage of the method is a good enantioseparation, short analysis time (less than 20min) and therefore this method is suitable for routine determination of chiral purity of (R,R)-tapentadol in enantiopure active pharmaceutical ingredient. [Copyright &y& Elsevier]