Controlled ring-opening polymerization of cyclic esters with phosphoric acid as catalysts

(R)-(?)-1,1′-Binaphthyl-2,2′-diyl hydrogen phosphate (BPA) has been demonstrated as an efficient organocatalyst for controlled ring-opening homopolymerization of ε-caprolactone (ε-CL) and copolymerization of ε-CL with glycolide and lactide. High molar mass PCL with narrow molar mass distribution has also been synthesized from the bulk ring-opening polymerization (ROP) of ε-CL with BPA as catalysts; the highest molar mass of PCL is 4.35?×?10⁴ g/mol with polydispersity index of 1.20. The successful synthesis of high molar mass PCL is attributed to the bifunctional activation mechanism for the ROP of ε-CL catalyzed by BPA. More interestingly, ppm level of BPA is sufficient to catalyze controlled ROP of ε-CL.     

Determinations of traces of calcium in phosphoric acid and its salts by atomic-absorption spectrometry

A method for the determination of traces of calcium by atomic-absorption spectrometry after extraction into an organic solvent, has been investigated for the determination of traces of calcium in phosphoric acid and its salts. Calcium is extracted as the hydroxy-quinolate complex, the extract is introduced into the flame, and the calcium atomic-absorption is measured. The effects of pH, concentration of reagent, and diverse ions on the calcium extraction were investigated.     

Synthesis,stereochemistry and conformational properties of diastereomeric cyclic dipeptides containing tetrahydro-1,4-thiazine-3,5-dicarboxylic acid

The synthesis of linear dipeptides containing N-protected L-phenylalanine and (3R-cis)-tetrahydro-1,4-thiazine-3,5-dicarboxylic acid dialkyl diester residues is described. N-Deprotection of these dipeptides by hydrogenolysis on palladium afforded directly a mixture of cis and trans dioxopiperazines. The stereochemistry and the solution conformational properties of the cyclic dipeptides are determined.     

Structures of deoxypeganine salts

The structures of deoxypeganine (DOP) hydrochloride and oxalate were solved by x-ray structure analysis. An infinite chain along the crystallographic c axis was formed in the crystal structure of DOP oxalate. A molecular framework consisting of Cl anions and DOP cation protonated at N1 was found in the structure of unhydrated DOP hydrochloride. The molecular packing of the “host” (DOP cation) was pseudoisostructural in the studied ion-molecular crystals but differed from other known DOP salts. The “guest” molecules (acid anions) in the studied and known DOP salts formed different intermolecular contacts. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 280–283, May–June, 2006.     

Synthesis of a novel sterically hindered chiral cyclic phosphoric acid derived from l-tartaric acid and application to the asymmetric catalytic Biginelli reaction

A novel sterically hindered chiral cyclic phosphoric acid derived from l-tartaric acid was designed and synthesized based on highly regioselective cyclosulfitation of chiral 1,1,4,4-tetraphenylbutanetetraol. The asymmetric Biginelli reaction catalyzed by this newly synthesized chiral phosphoric acid was examined, and enantioselectivities up to 99% ee was obtained.     

New cyclic phosphonium salts derived from the reaction of phosphine-aldehydes with acid

Various cyclic phosphonium structures are formed in high yield by the deprotection of unstable phosphine-aldehydes in acidic solution. When there is a methylene spacer between the phosphine and the aldehyde, a phosphonium ion [PHR₂CH₂CH(OEt)₂]Br₂, R=iPrOH, Et is obtained. Reaction of these phosphonium salts with water produces the dimers [-PR₂CH₂CH(OH)-]₂[Br]₂ R = iPr, Et. When there is an ethylene spacer as in PPh₂CH₂CH₂CH(OCH₂CH₂O), a remarkable tetramer with a 16-membered ring [-PPh₂CH₂CH₂CH (OH)-]₄[Cl]₄ forms as one diastereomer in hydrochloric acid solution. Reaction of HCl with the protected phosphine-aldehyde with a propylene spacer (PPh₂CH₂CH₂CH₂CH(OCH₂CH₂O)) results in the formation of the monomeric phosphonium salt [-PPh₂ CH₂CH₂CH₂CH(OH)-]Cl with a 5-membered ring. Solid state structures of different ring types were determined using X-ray diffraction experiment.     

The effect of SDE on the separation of diastereomeric salts: a case study for the resolution of mandelic acid derivatives with Pregabalin

A resolution method has been elaborated for mandelic acid and 2-chloromandelic acid applying the (R)-(−)-3-(aminomethyl)-5-methylhexanoic acid (Pregabalin) as the resolving agent. The formation of the corresponding diastereomers was kinetically controlled. This observation was rationalized by the behavior of enantiomeric mixtures of mandelic acid, 2-chloromandelic acid, and 3-(aminomethyl)-5-methylhexanoic acid. It was found that the eutectic composition of Pregabalin influenced the diastereomeric excess of the diastereomers formed under kinetic control.     

Quininium mandelates--a systematic study of chiral discrimination in crystals of diastereomeric salts

The selectivity profile for the resolution of mandelic acid by quinine is dominated by structures comprising (QUIN(+))(MAND(-)) salts with Z' = 3 which contain (R)-, (R)- and (S)-mandelate anions.     

Configurational analysis of diastereomeric open-chain and cyclic nitro-substituted diols by NMR spectroscopy

Nitro-substituted 1,3-dioxanes and pyrans with potential biological activity were synthesized. The relative configurations of the threo and erythro isomers of 2-nitro-1-phenylpropane-1,3-diol (the starting materials) and of 5-nitro-2,4-diphenyl-1,3-dioxane, the products formed with benzaldehyde, were determined by ¹H and ¹³C NMR spectroscopy. Cinnamaldehyde and nitroethanol give a homologue of nitrophenylpropanediol, which exists as a mixture of two diastereomeric cyclic hemiacetals. After dissolving in CDCl₃, the ratio of these components changes from approximately 10:1 to 3:2 in a few days. The ethyl acetal of the hemiacetal is stereohomogeneous, and the ethoxy group is axial to the pyran ring owing to the anomeric effect. This configuration was proved by two-dimensional NMR measurement, permitting separate observation of the originally overlapping multiplets and direct reading of the H,H coupling constants.     

Liquid crystalline polyaniline and phthalocyanine-based polysiloxanes bearing lateral fluoro-substituted benzoic acid groups

A series of novel liquid crystalline polymers (PI, PII, PIII and PIV) containing lateral fluoro-substituted benzoic acid groups was synthesised using cholesteryl 4-(2-propenyloxy)-benzoate, 4-(allyloxy)-3-fluorobenzoic acid and poly(methylhydrogeno)siloxane. PI and PII showed smectic phase, but PIII and PIV showed chiral nematic phase due to more lateral fluoro-substituted benzoic acid groups in the polymer systems. Liquid crystalline polyaniline (PAN) and phthalocyanine (Pc)-based polysiloxanes showing chiral nematic phase were prepared by use of Pc, PAN and these liquid-crystalline polymers via hydrogen bond. PAN-based polysiloxanes showed different liquid crystalline behaviours from Pc-based polysiloxanes due to the difference of molecular structure. PAN-based polysiloxanes showed greater d-spacings between the side mesogenic groups than Pc-based polysiloxanes due to long rod-like geometrical shapes. Hydrogen bond based on lateral fluoro-substituted benzoic acid groups was formed to different geometrical shapes (strip or roundness) between PAN and Pc-based polysiloxanes.     

Prediction of solid solution formation in a family of diastereomeric salts. A molecular modeling study

The possibility of solid solution behavior of diastereomeric salts, containing multiple resolving agents of the same family (Dutch Resolution), is predicted by molecular modeling. Super-cells containing different ratios of resolving agents in the diastereomeric salt are constructed and optimized, and their lattice energy is computed. The energy difference between these "simulated solid solutions" and the native structures is related in an understandable fashion to the probability of solid solution formation. This procedure is applied to a family of diastereomeric salts of ephedrine and cyclic phosphoric acids, for which the ternary diagrams have been determined experimentally at 25 degrees C in ethanol. Good agreement between experimental and computational results indicates that this relatively simple and fast method could predict the stable character of solid solution behavior in binary systems.     

The effect of structure on the thermodynamic properties of a liquid crystalline diastereomeric pair of chiral alkanoates

The thermodynamic properties of a diastereomeric pair of a cholesteryl chiral alkanoate were investigated. Studies on the thermal behavior, optical activity and the phase diagram confirmed that the diastereomeric pair exhibit similar mesomorphic behavior. It is concluded that the structural effects due to the chiral ester moiety do not contribute significantly to the mesomorphic structure of the diastercomers, but are pronounced in the crystalline structure.     

Synthesis of a diastereomeric mixture of deuterium-labeled lovastatin and its acid ammonium salt

In this communication, a facile synthesis for (2S/2R)-[²H₃]lovastatin and (2S/2R)-[²H₃]lovastatin acid ammonium salt was described. The stable isotope-labeled (2S/2R)-lovastatin and its acid ammonium salt were prepared from butyric acid via several reaction steps with 11.1 and 6.3 % overall yield, respectively.     

Optical resolution of N-formylphenylalanine succeeds by crystal growth rate differences of diastereomeric salts

Optical resolution of racemic-phenylalanine through its N-formyl derivative with a 1-phenylethylamine resolving agent is an effective procedure. Differential scanning calorimetry, single crystal X-ray diffraction and optical microscopy were used in the investigation of the resolution process. It was found that the thermodynamic properties of the given system would not allow the efficient enantiomer separation. Kinetic effects during the crystal formation have been discovered by the comparison of the crystal morphologies of the two diastereomers. The crystal structure of the less soluble diastereomer (S)-(−)-1-phenylethylammonium (S)-(+)-N-formylphenylalaninate salt has been determined and discussed.