Naphthyl Groups in Chiral Recognition: Structures of Salts and Esters of 2‐Methoxy‐2‐naphthylpropanoic Acids

The crystal structures of salt 8 , which was prepared from (R)‐2‐methoxy‐2‐(2‐naphthyl)propanoic acid ((R)‐MβNP acid, (R)‐ 2 ) and (R)‐1‐phenylethylamine ((R)‐PEA, (R)‐ 6 ), and salt 9 , which was prepared from (R)‐2‐methoxy‐2‐(1‐naphthyl)propanoic acid ((R)‐MαNP acid, (R)‐ 1 ) and (R)‐1‐(p‐tolyl)ethylamine ((R)‐TEA, (R)‐ 7 ), were determined by X‐ray crystallography. The MβNP and MαNP anions formed ion‐pairs with the PEA and TEA cations, respectively, through a methoxy‐group‐assisted salt bridge and aromatic CH???π interactions. The networks of salt bridges formed 2₁ columns in both salts. Finally, (S)‐(2E,6E)‐(1‐²H₁)farnesol ((S)‐ 13 ) was prepared from the reaction of (2E,6E)‐farnesal ( 11 ) with deuterated (R)‐BINAL‐H (i.e., (R)‐BINAL‐D). The enantiomeric excess of compound (S)‐ 13 was determined by NMR analysis of (S)‐MαNP ester 14 . The solution‐state structures of MαNP esters that were prepared from primary alcohols were also elucidated.     

Development and validation of a high-precision capillary electrophoresis method for main component assay of ragaglitazar

The ability of a developed capillary electrophoresis (CE) method for fast, efficient and reliable main component assay of ragaglitazar [NNC 61-0029/DRF(-)2725] has been demonstrated through documentation of the analytical performance and the results of a successful validation. The fast analysis time of around 1.2 min ensures a high analytical capacity, and the validation results show that the CE method is robust and gives reliable and precise results. The results from the validation of the CE method meet the acceptance criteria that are normally set for other main component assays such as high-performance liquid chromatography assays.     

The synthesis of isoquinoline alkaloid and its related compounds using alanine derivatives as chiral auxiliaries

Chiral 1-substituted isoquinoline derivatives, which were obtained by the reaction using alanine derivatives as chiral auxiliaries, were transformed to (S)-2,3,9,10,11-pentamethoxyhomoprotoberberine (7) and a synthetic intermediate for O-methylkreysigine (9) in good yields and high stereoselectivity. The corresponding chiral allyl derivative of isoquinoline was transformed to a pyrrolidinoisoquinoline (16) in a highly enantioselective manner.     

Strategy for structural elucidation of drugs and drug metabolites using (MS)n fragmentation in an electrospray ion trap

Triple-stage quadrupole (TSQ) electrospray ionization (ESI) tandem mass spectrometry (MS/MS) and ion trap ESI-MS/MS can be used to cleave protonated molecules to produce carbocations and neutral molecules in the positive ion mode. Dissociation products which correspond to protonated forms of neutral fragment molecules can also be trapped and detected. These protonated molecules in turn can cleave via carbocation cleavage, ipso cleavage, onium cleavage or McLafferty or related rearrangements. One can elucidate the structures of metabolites from the differences in m/z ratios of the fragments arising from the original drug compound and its metabolite. This strategy for structural elucidation is further facilitated by estimates of the reactivity of drugs with oxygen diradicals involved in cytochrome P-450 cycles.     

Sigmasigma* transition in anti,cisoid alternating oligosilanes: clear-cut evidence for suppression of conjugation effect by a cisoid turn

On the basis of the UV absorption spectra of the anti,cisoid alternating oligosilanes, the first experimental clear-cut evidence was presented for the generally accepted idea that the sigma conjugation in polysilanes does not effectively extend through a tetrasilane fragment with a small dihedral angle such as a cisoid turn.     

Controlling coupling reaction of EDC and NHS for preparation of collagen gels using ethanol/water co-solvents

To control the crosslinking rate of the collagen gel, ethanol/water co-solvent was adopted for the reaction solvent for the collagen microfibril crosslinking. Collagen gel was prepared by using EDC and NHS as coupling agents. Ethanol did not denaturate the helical structure of the collagen and prevented the hydrolysis of EDC, but showed the protonation of carboxylate anions. In order to control the intra- and interhelical crosslink of the collagen triple helix, variations of the mole ratio of carboxyl group/EDC/NHS, and of the ethanol mole concentration were investigated. Increase in the EDC ratio against the carboxyl group increased the crosslinking rate. Furthermore, an increase in the ethanol mole concentration resulted in an increase of the crosslinking rate until ethanol mole concentration was 0.12, but showed gradual decrease as the ethanol mole concentration was further increased. This is because the adsorption of solvent by the collagen gel, protonation of carboxylate anion, and hydrolysis of EDC is at its most optimum condition for the coupling reaction when the ethanol mole concentration is 0.12. The re-crosslinking of the collagen gel showed an increase in the crosslinking rate, but did not show further increase when the coupling reaction was executed for the third time. This implied that the highest possible crosslinking rate for the intra- and interhelical is approximately 60% when EDC/NHS is used.     

The unusual micelle micropolarity of partially fluorinated gemini surfactants sensed by pyrene fluorescence

New gemini surfactants having two fluorocarbon chains were prepared by refluxing partially fluorinated alkyl bromide with N,N,N',N'-tetramethyl-1,6-diaminohexane in acetonitrile. The partially fluorinated gemini surfactants containing a six-methylene spacer chain are easily soluble in water. The critical micelle concentrations (cmc's) were determined by various fluorescent probe methods. The hydrophobicity of a CF2 group was estimated to be 1.5 times that of a CH2 group according to the cmc values. The micelle micropolarity of a fluorocarbon gemini sensed by pyrene fluorescence was unusually high, suggesting an apparent iceberg-like environment in the location of pyrene. The significantly small micelle aggregation numbers of fluorinated gemini surfactants were ascertained by the pyrene fluorescence quenching method. The micelle ionization degree estimated by fluorescence quenching of 6-methoxy-N-(3-sulfopropyl)quinolinium (SPQ) gave tendencies similar to those of the corresponding hydrocarbon geminis.     

Enantiodifferentiating Photodimerization of a 2,6-Disubstituted Anthracene Assisted by Supramolecular Double-Helix Formation with Chiral Amines

A novel 2,6-anthrylene-linked bis(m-terphenylcarboxylic acid) strand ( 1 ) self-associates into a racemic double-helix. In the presence of chiral mono- and diamines, either a right- or left-handed double-helix was predominantly induced by chiral amines sandwiched between the carboxylic acid strands with accompanying stacking of the two prochiral anthracene linker units in an enantiotopic face-selective way, as revealed by circular dichroism and NMR spectral analyses. The photoirradiation of the optically active double helices complexed with chiral amines proceeded in a diastereo- (anti or syn) and enantiodifferentiating way to afford the chiral anti-photodimer with up to 98 % enantiomeric excess when (R)-phenylethylamine was used as a chiral double-helix inducer. The resulting optically active anti-photodimer can recognize the chirality of amines and diastereoselectively complex with chiral amines.