Epoxide Hydrolase-catalyzed Resolution of Ethyl 3-Phenylglycidate

Epoxide hydrolase-catalyzed resolution of ethyl 3-phenylglydidate was investigated using resting cells ofPseudomonas sp. BZS21. Under the present conditions 26.2 % of (2R, 3S)-ethyl 3-phenylglycidate with ee value of 94.6 % was obtained from the racemic mixture.     

Synthesis of Bicyclooctane Derivatives for Kinetic Resolution

Theracemicdiacetaterac-l[l]hasprovedtobeaversatilestartingmaterialforthesgnthesisofracemicprostaglandins,suchasll-deoxyPG.,1l-deoxyPGfy,PGA:,PGE,,andPGF.l:1.Bothenantiomerslandent-lcanbetransformedbyenantioc0nvergentroutCsintoenantiomericallypureprostaglandinswiththenatualconfigurationt'].Therefore,thekineticresolutionofitSprecursorrac-2(Schemel)evoked0urinterestinthisfield.CycliccompoundsofthetyPe3shouldbeidealsubstratesforkineticres0luti0noftheendo,endo,bicyclo[3.3.0]octal-2,6-diol2ri…     

Resolution of β-aminophosphines with chiral cyclopalladated complexes

Resolution of the racemic chiral β-aminophosphines Ph₂PCH₂CH(Ph)NH(Ar) (L¹ for Ar = C₆H₅ and L² for Ar = 2,6-C₆H₃ⁱPr₂) has been investigated by use of different cyclopalladated complexes as chiral agents. The resulting complexes afford diastereomeric adducts in a 1:1 ratio. After successive crystallizations from ethanol, a d.e. of 98% was achieved for one aminophosphine palladium complex, while no significant d.e. was obtained after crystallizations from chlorinated solvents. The X-ray structure analysis has pointed out intermolecular hydrogen interactions N-H?Cl between the P,N ligand and the chloride ion, which are responsible for the formation and stabilization of the diastereomeric adducts. Thus, the use of oxygenated solvents cancels such hydrogen interactions by their stronger donor character and makes the diastereomers separation possible, allowing to isolate the optically pure (R)-Ph₂PCH₂CH(Ph)NH(Ph) L¹ of which the absolute configuration has been determined from the X-ray structure analysis of the related palladium dichloride complex.     

Resolution of α-phenylethylamine by its acidic derivatives

α-Phenylethylamine was resolved by its own derivatives formed with a homologous series of dicarboxylic acids. The structure of the oxalamic acid diastereoisomeric salts was investigated by the single-crystal X-ray diffraction method.     

Isothiourea-Catalyzed Acylative Kinetic Resolution of Tertiary α-Hydroxy Esters

A highly enantioselective isothiourea-catalyzed acylative kinetic resolution (KR) of acyclic tertiary alcohols has been developed. Selectivity factors of up to 200 were achieved for the KR of tertiary alcohols bearing an adjacent ester substituent, with both reaction conversion and enantioselectivity found to be sensitive to the steric and electronic environment at the stereogenic tertiary carbinol centre. For more sterically congested alcohols, the use of a recently-developed isoselenourea catalyst was optimal, with equivalent enantioselectivity but higher conversion achieved in comparison to the isothiourea HyperBTM. Diastereomeric acylation transition state models are proposed to rationalize the origins of enantiodiscrimination in this process. This KR procedure was also translated to a continuous-flow process using a polymer-supported variant of the catalyst.     

Crystal Structure of Crotin Ⅱ at 2.5  Resolution

1INTRODUCTIONTheplanttoxin,CrotinIisoneoftheribosomeinactivatingproteins(RIPs)[l3.AccordingtothemolecularmechanismofactiontheRIPscanbedividedintotwokinds[2:.OnebelongstoRNAN-glycosidasewhichisclassifiedastwotypes.TypeIconsistsofasinglepolypeptidechain,forexample,trichosanthinandsaporin-Typellconsistsoftwochains,suchasricinandabrin'ThiskindofRIPshydrolysesasingleN-glycosidicbondbetweenanadenineandriboseatspecificnu-cleotide(A4324)of28SrRNAintheribosomes[3i.ThesecondkindofRIPsbel…     

Candida rugosa Lipase－catalyzed Kinetic Resolution of Hydroxyalkanephosphonates

An efficient lipase-catalyzedenantioselective hydrolysis of butyryloxyalkanephosphonates in water-equillbrated diisopropyl ether was developed. The relationship between the substrates‘ structure and the reactivity, as well as the enantioselectivlty of this enzymatic transformation was studied. The catalytic preference of crude Candida rugosa lipase toward such molecules was assigned according to modified Mosher‘s method and Xray crystallographic analysis. Optically pure 2-hydroxy-2-arylethanephosphonates, 3-hydroxy-3-phenylpropanephosphonate, and 3, 3, 3-trifluoro-2-hydroxypropanephosphonates were conveniently prepared in this manner.     

Resolution method for overlapping peaks based on the fractional-order differential

Equations between the differential order and the maximum of the fractional-order differential for the specified peak signals are developed based on the variation of the maximum of the specified peak signals at different orders. Also, equations between the differential order and the zero-crossing of the fractional-order differential of the specified peak signals are proposed according to the variation of the zero-crossing of the specified peak signals at different orders. Characteristic paramters of the Gaus- sian peak, Lorentzian peak, and Tsallis peak can be estimated using estimator I and estimator II which are obtained by the equations above. As a result, a new method is presented to resolve the overlapped peaks signal. Firstly, a fractional-order differential of the specified peak signals is obtained with the fractional-order differentiation filter. Then, characteristic paramters of the specified peak signals can be extracted using estimator I and estimator II. Finally, the Tsallis peak is used as a model to assign the overlapping peak signals correctly. Experimental results show that the proposed method is efficient and effective for the simulated overlapping peaks and detected overlapping voltammetric peak signals.     

The Direct Resolution of the Enantiomers of Four Chiral Pesticides

Cellulose-tris(3,5-dimethylphenylcarbamate)(CDMPC) were synthesized as highperformance liquid chromatography (HPLC) chiral stationary phase(CSP). The successful resolution of four chiral pesticides on the CSP was realized and the influence of the temperature on the separation was studied.     

Practical Tactics in Resolution of Racemates via Diastereomeric Salt Formation

A practical tactics in the classical resolutions was illustrated for affording the desired isomers in maximum yields. According to the practical tactics resolution of racemic ethyl nipecotate, Corey lactone and huperzine A intermediate was successfully practiced. The basis of this practicability is the well-known Marckwald principle.     

Resolution of β-unsaturated amines with isopropylidene glycerol hydrogen phthalate

1-Phenyl-2-propenylamine 2, 1-phenyl-2-propinylamine 3, 1-(1-cyclohexenyl)ethylamine 4, (E)-2-ethylidenecyclohexylamine 5 and α-methylallylamine hydrochloride 6 were selected as candidates for resolution with isopropylidene glycerol hydrogen phthalate 1, previously described as an efficient resolving agent of 1-arylalkylamines. With only the exception of 5, all these substrates were resolved by (S)-1. In particular both the enantiomers of 2 and 3 were obtained in excellent yields and with very high enantiomeric excesses. The absolute configurations of non-racemic forms of 2, 3 and 4, not prepared before except those of 3, were established by correlation with the respective hydrogenation products. The enantiomeric excesses of all the resolved substrates were accurately determined by chiral HPLC analysis. The fact that 1 resolves 4 and 6 but not their saturated analogues and shows higher efficiency in resolving 2 and 3 than 1-phenylpropylamine indicates the positive influence of the presence of β-unsaturation on the resolvability of aminic substrates with such an acid.     

Synthesis and Resolution of 10, 11-Dihydro- 10-hydroxycyproheptadine

10, 11-Dihydro-10-hydroxycyproheptadine was synthesized in a new and facile synthetic route and resolved by L-(-)-2-(1, 3)-dioxo-1, 3-dihydroisoindol-2-yl)-propionic acid and D-( )-tartaric acid, respectively. The free base of the two enantiomers has the same absolute specific rotation value.     

Asymmetric Aminations and Kinetic Resolution of Acyclic α-Branched Ynones

An efficient method for asymmetric synthesis of acyclic α-tertiary amine derivatives has been achieved through enantioselective aminations of α-branched ynones with azodicarboxylates enabled by chiral phosphoric acid catalysis.Moreover,kinetic resolution of racemic starting material was realized under these conditions,which gave access to valuable enantioenriched α-substituted ketones.     

Sulfonyl-PYBOX Ligands Enable Kinetic Resolution of α-Tertiary Azides by CuAAC

We report the first highly selective kinetic resolution of racemic α-chiral azides via Cu-catalyzed azide-alkyne cycloaddition (CuAAC). Newly developed pyridine-bisoxazoline (PYBOX) ligands, bearing a C4 sulfonyl group, enable effective kinetic resolution of racemic azides derived from privileged scaffolds such as indanone, cyclopentenone, and oxindole, and their asymmetric CuAAC to afford α-tertiary 1,2,3-triazoles with high to excellent ee values. DFT calculations and control experiments reveal that the C4 sulfonyl group decreases the Lewis basicity of the ligand and increases the electrophilicity of the copper center for better recognition of azides, and functions as a shielding group to make the chiral pocket of the catalyst more effective.     

The Crystal and Molecular Structure of Trichosanthin at 2.6 Resolution

The crystallographic refinement of trichosanthin has been performed at 2.6 resolution. The crystal and molecular structure of trichosanthin is described in detail in this paper. On summarizing the regularity of the amino acid sequences of eight kinds of ribosome inactivating proteins and combining with the crystal and molecular structure of trichosanthin, fifteen most conservative amino acid residues are analyzed. It is found that four most conservative polar amino acid residues Gln156, Glu160, Arg163 and Glu189 gather on the molecular surface on the boundary of the large and small domains, thus forming the active center of the protein molecule.     

Enantioselective Synthesis of δ-Lactones with Lipase-Catalyzed Resolution and Mitsunobu Reaction

Both enantiomers of a series of δ-lactones (e.g., δ-decalactone, δ-dodelactone, and δ-hexadecalactone) were synthesized stereoselectively by Novozym 435–catalyzed resolution. Furthermore, only (S)-enantiomers of δ-lactones were synthesized with a combination of Novozym 435–catalyzed resolution and Mitsunobu reaction.     

Enzymatic Resolution of Ethyl α-Hydroxyphosphinates in a Modified Reaction Environment

The enzymatic resolutions of two racemic ethyl hydroxyalkane(P-phenyl)phosphinates were performed by both esterification and hydrolysis approaches. The first reaction was performed in anhydrous diisopropyl ether with triethylamine or pyridine as additives by using lipases from three different sources (Candida cylindracea, Aspergillus niger, and Mucor javanicus). The increase in enantioselectivity was observed when NEt₃ was applied. The second reaction—lipase-catalysed hydrolysis of ethyl butyryloxyalkane(P-phenyl)phosphinates—was carried out by Candida cylindracea lipase in diisopropyl ether saturated with water or in aqueous solutions containing MgCl₂, LiCl, or Triton X-100. The usefulness of biphasic systems consisting of diisopropyl ether and water or aqueous solution of MgCl₂, LiCl, or Triton X-100 also were tested. The use of biphasic system in the presence of Triton X-100 resulted in the higher conversion of the substrates.     

Resolution of 1,3-alkanediols via chiral spiroketals derived from ℓ-menthone

Ketalization reaction of racemic 1,3-alkanediols with ℓ-menthone gave a mixture of diastereomeric spiroketals that was easily separated by silica gel column chromatography and converted into enantiomerically pure diols by acid-catalyzed hydrolysis.     

Resolution of 8′-alkoxy- and hydroxy-1,1′-binaphthalen-8-ols

Enantiopure 8′-ethoxy-, 8′-hydroxy-, and 8′-methoxy-1,1′-binaphthalen-8-ol were readily resolved by separating the corresponding chiral camphanic esters [derived from the esterification of the alcohols with (−)-(1S)-camphanic chloride] based upon their differing solubility in diethyl ether and their differing chromatographic behavior.