Novel 8a-aza-8a-homoerythromycin--4''-(3-substituted-amino)propionates with broad spectrum antibacterial activity.

Fifteen-membered 8a-aza-8a-homoerythromycins derived from either erythromycin or clarithromycin have been acylated to form 4''-O-propenoyl derivative. These functionalized analogues underwent Michael reaction with primary or secondary amines to afford novel 8a-aza-8a-homoerythromycin-4''-(3-substituted-amino)propionates. This preparative sequence was adapted so that analogues could be made by parallel synthesis. Among them, 4-quinolone derivatives show particularly good antibacterial potency against macrolide resistant bacteria, comparable or better than azithromycin and telithromycin.

Determination of aqueous stability and degradation products of series of coumarin dimers.

The stability in aqueous solution of five classes of coumarin dimers (I-V, compounds 1-29) was studied by HPLC-MS/MS at various pH values. The relationship between chemical structure and stability is discussed. It was found that dimeric compounds with strong electron withdrawing groups (EWGs) on the α-carbon to the bridging C-atom are stable at all pH values, whereas other derivatives undergo retro-Michael addition at rates which are also affected by the substituents on the aromatic rings. In some cases formation of stable isomers or oxidation products was observed. In order to evaluate their developability and potential for progression to in vivo studies, representative compounds were tested in an in vitro microsomal stability assay.

Determination of the absolute configuration of flexible molecules by ab initio ORD calculations: a case study with cytoxazones and isocytoxazones.

Ab initio calculations of the optical rotatory power of the natural cytokine modulator cytoxazone 1 and its trans-diastereomer 2, as well as the structural isomers cis-3 and trans-4 isocytoxazones, have been performed at four different wavelengths (589, 546, 435, and 405 nm) by Density Functional Theory. The calculation of ORD curves provides a reliable method for the assignment of absolute configuration of these conformationally flexible molecules. The absolute configurations of isocytoxazones has been established as (+)-(4R,5S)-cis-3 and (+)-(4S,5S)-trans-4.

Chemoenzymatic synthesis and properties of Schiff bases containing (R)-1-(9-anthryl)ethylamine.

Racemic 1-(9-anthryl)ethylamine (10), obtained in 70% overall yield from commercial 9-cyanoanthracene, was kinetically resolved by the Candida antarctica A lipase-catalyzed acetylation with isopropyl acetate as acyl donor, affording (R)-(+)-10 with 95.8% enantiomeric excess (e.e.) (E-value 43.5), which afforded Schiff bases (R)-4 and(R)-8. (1)H-NMR, CD, and MM2 calculations offer a consistent picture of the conformational properties of these potential ligands and an explanation for the limited enhancement of enantioselectivity in cyclopropanation of styrene by their Cu(I) complexes, as compared with previously studied ligands in this series.

Two-step asymmetric synthesis of disubstituted N-tosyl aziridines having 98-100% ee: use of a phosphazene base.

Unknown diaryl (1-3) and alkyl-phenyl (4, 5) N-tosyl aziridines have been successfully synthesized from pure (R,R,R,S(S))-(-)-sulfonium salt derived from Eliel's oxathiane, tosylimines 11a-f, and using a phosphazene base (EtP(2)) to generate the ylide. Both cis and trans aziridines have exceptionally high enantiomeric purities (98.7-99.9%). The (2R,3R)-configuration of trans-3 and the (2R,3S)-configuration of cis-4 have been determined by X-ray analysis using the Bijvoet method. The R-configuration found at C2 is consistent with the model and all previous results, therefore all trans-aziridines and cis-aziridines have been assigned the (2R,3R)- and the (2R,3S)-configurations, respectively. This two-step asymmetric synthesis can be easily used on gram quantities and involves no unstable/hazardous reagent. The chiral auxiliary is used in a stoichiometric amount but is recovered in high yield and reused.

Separation, conformation in solution and absolute configuration of ethopropazine enantiomers.

Enantiomers of ethopropazine x HCl (10-(2-diethylaminopropyl)phenothiazine hydrochloride) were prepared by fractional crystallization of diastereomeric dibenzoyltartaric acid salts, and their optical purity (enantiomeric excess, ee) determined by HPLC on Chiralcel OJ column. With a solvent mixture n-hexane/t-butanol/triethylamine (100:3:0.5) as eluent a very good enantioseparation (alpha = 1.68) for racemic ethopropazine was obtained. Enantiomeric purity for (-)-enantiomer was 99.1% and for (+)-enantiomer 97.9%. Combined data from NMR and CD spectra of both enantiomers, along with previously reported X-ray structure analyses of racemic ethopropazine, revealed skewed conformation of tricyclic system in solution, and (S)-configuration on the stereogenic center for (-)-enantiomer, and (R)-configuration for (+)-enantiomer.

Enantiomerization of 3-carbethoxy-l,4-benzodiazepin-2-one: combined chiral HPLC and spectroscopic study.

Recently developed chiral HPLC columns CHIRIS AD1 and CHIRIS AD2 have been demonstrated to separate racemic, configurationally unstable ethyl-7-chloro-2-oxo-5-phenyl-2,3-dihydro-1H-1,4-benzodiazepine-3-carboxylate (1) and its 3-methyl congener 2; fast on-column enantiomerization of configurationally unstable 1 was observed, however. Addition of 0.1% of AcOH to the eluting mixture inhibits enantiomerization, whereas the same percentage of Et(3)N completely precludes enantioseparation, suggesting base-catalysis by free beta-aminoethyl groups, present in low percentage in chiral stationary phase (CSP). When both CSPs were prepared under conditions of nonexhaustive acylation by N-DNB-alpha-aminoacids, no separation of 1 was observed. The rate of enantiomerization on CHIRIS AD2 was determined at 25 degrees C, the mechanism is discussed, and experimental results correlated with calculated relative stabilities of the tautomers la-c. Absolute (3S) configuration of (+) enantiomers of 1 and 2 was determined by comparison of their eluation profile to that of (+/-)-3 and (3S)-(+)-3, taking into account relative (psia or psie) configuration of the prevailing conformer in solution.

Enantioseparation of racemic 4-aryl-3,4-dihydro-2(1H)-pyrimidones on chiral stationary phases based on 3,5-dimethylanilides of N-(4-alkylamino-3,5-dinitro)benzoyl L-alpha-amino acids.

Three novel chiral packing materials for high-performance liquid chromatography were prepared by covalently binding of (2S)-N-(3,5-dimethylphenyl)-2-[(4-chloro-3,5-dinitrophenyl)carbonylamino]propan-amide (7), (2S)-N-(3,5-dimethylphenyl)-2-[(4-chloro-3,5-dinitrophenyl)carbonylamino]-4-methylpentanamide (8), and (2S)-N-(3,5-dimethylphenyl)-2-[(4-chloro-3,5-dinitrophenyl)carbonyl-amino]-2-phenylacetamide (9) to aminopropyl silica. The resulting chiral stationary phases (CSPs 1-3) proved effective for the resolution of racemic 4-aryl-3,4-dihydro-2(1H)-pyrimidone derivatives (TR 1-14). The mechanism of their enantioselection, supported by the elution order of (S)-TR 13 and (R)-TR 13 and molecular modeling of the complex of the slower running (S)-TR 13 with CSP 1 is discussed.