Mechanism of chiral recognition in the enantioseparation of 2-aryloxypropionic acids on new brush-type chiral stationary phases.

New brush-type chiral stationary phases (CSP I-IV) comprising N-3,5,6-trichloro-2,4-dicyanophenyl-L-alpha-amino acids (1-4) were prepared by binding of chiral selectors 1-4 to gamma-aminopropyl silica gel. To check the role of excess free aminopropyl groups, CSP V was prepared by binding N-3,5,6-trichloro-2,4-dicyanophenyl-L-alanyl-(3-triethoxysilyl)propylamide to unmodified silica gel. The best separation of racemic 2-aryloxypropionic acids (TR-1-13) was obtained with CSP I; the -(-)-S enantiomer were regularly eluted first, as determined by a CD detector. The mechanism of chiral recognition implies a synergistic interaction of carboxylic acid analyte with the chiral selector and achiral free gamma-aminopropyl units on silica. In fact, CSP V, which is lacking an achiral aminopropyl spacer, shows a lower separation ability for 2-aryloxypropionic acids, but a similar enantioselective discrimination of esters TR-19-20, in comparison with CSP I. CSP I-IV retain unaltered separation ability after a few months of continuous work using a large number of various mobile phases.

Enantiomers of 2-[(Acylamino)ethyl]-1,4-benzodiazepines, potent ligands of kappa-opioid receptor: chiral chromatographic resolution, configurational assignment and biological activity.

Compounds 2a and 3a-e are racemic 2-[(acylamino)ethyl]-1,4-benzodiazepines, tifluadom analogs, with high affinity and selectivity towards the kappa-opioid receptor. We describe the enantiomeric separation of all compounds through liquid chromatography with chiral stationary phases, as well as the resolution of the enantiomers of the most interesting compounds, 2a and 3a, by the semipreparative column Chiralpak AD. The configuration of the resolved enantiomers was investigated: the comparative study of CD and (1)H NMR spectra shows that compounds (-)-2a and (-)-3a have the same absolute configuration of (+)-(S)-tifluadom. A study on the stereoselective interaction with opiate receptors is reported.

Synthesis and antinociceptive activity of pyrrolidinylnaphthalenes.

In this paper the synthesis of the racemates (2R,3S/2S,3R)-1,2-dimethyl-3-[2-(6-substituted naphthyl)]-3-hydroxypyrrolidine 1b-d [(2R,3S/2S,3R)-1b-d] are reported. Compounds 1b-d were prepared by reaction of the racemic 1,2-dimethyl-3-pyrrolidone 2 with the lithiation product obtained from 2-bromo-6-substituted naphthalene 3b-d. Pharmacological properties of (2R,3S/2S,3R)-1a-d are also described. Analgesic activity was investigated by the hot plate test and binding affinities towards mu, delta and kappa opioid receptors were evaluated. A preliminary evaluation of the in vivo side-effects was also accomplished using the rota-rod test. Interesting antinociceptive activity was shown by all compounds and in particular by 1d, which is the most active compound, since it is six-fold more potent than morphine and has lower side effects on the locomotory activity.

Dialkylaminoalkylnaphthalenes as novel opioid-like analgesics.

The study of dialkylaminoalkylnaphthalenes as novel opioid-like analgesics is reported. In particular, the synthesis of (1R,2R/1S,2S)-1-ethyl-1-[2-(6-hydroxynaphthyl)]-1-hydrox-2-m ethyl-2-dimethylaminoethane and its structural analogue (1R,2R/1S,2S)-1-ethyl-1-[2-(6-fluoronaphthyl)]-1-hydroxy-2-methyl- 2-dimethylaminoethane and the configurational analysis by X-ray and 1H NMR spectroscopy are described. Pharmacological profiles are discussed on the basis of the experimental results of analgesia tests (hot plate and writhing test) and rota-rod test, which was performed to distinguish analgesia from drug-induced motor changes. The compounds showed dose-dependent antinociception, with less potency than morphine. Motor coordination appeared to be less involved.

Synthesis of pyrrolinylnaphthalenes and evaluation of their antinociceptive activity.

In this paper the regioselective preparation of (R/S)-1,2-dimethyl-3-[2-(6-substituted naphthyl)]-2H,5H-pyrrolines 2a-d is reported. These compounds were prepared by thermal dehydration of the corresponding alcohols (2R,3S/2S,3R)-1,2-dimethyl-3-[2-(6-substituted naphthyl)]-3-hydroxy-pyrrolidines (2R,3S/2S,3R)-1a-d with anhydrous FeCl3-SiO2, under vacuum. Pharmacological properties of (R/S)-2a-d are also described. Analgesic activity was investigated by the hot plate test, also in the presence of selective antagonists of mu, delta and kappa opioid receptors. Preliminary analysis of the side-effects was also accomplished using the rota-rod test. Interesting antinociceptive activity was shown by all compounds and in particular by (R/S)-2a (AD50 = 0.31 mg/kg); delta opioid receptors were found to be mainly involved in the pharmacological process and, in general, it was found that the compounds influenced locomotory activity to a much lesser extent than did morphine.

Preparation and configuration of racemic and optically active analgesic cycloaminoalkylnaphthalenes.

Cycloaminoalkylnaphthalene 3 shows interesting opioid-like analgesic properties. It possesses two chiral centers and can exist as two racemic pairs and four diastereomers. Since the binding of opioids with receptors is stereoselective, it was important to have the two racemic pairs as well as the four diastereomers. In this paper the synthesis of the (2R,3S/2S,3R) racemate and the (2R,3S) and (2S,3R) enantiomers of the 1,2-dimethyl-3-[2-(6-hydroxynaphthyl)]-3-hydroxypyrrolidine 3 is considered and the determination of absolute configuration is described. The (2R,3S/2S,3R)-3 racemate and the (2R,3S)-3 and (2S,3R)-3 enantiomers were prepared by reaction of the racemic and optically active 1,2-dimethyl-3-pyrrolidone 2, respectively, with the lithiation product obtained from 2-bromo-6-tetrahydropyranyloxy-naphthalene 1 and acidic hydrolysis. The above-mentioned enantiomers of 3 were also obtained by optical resolution via fractional crystallization of the salts with D- and L-tartaric acids. The configuration of the optically active compounds was determined by X-ray analysis of a crystal of (-)-(2S,3R)-3.HCl.H2O. The pharmacological test HPT showed that (-)-(2S,3R)-3.HCl.H2O enantiomer is able to induce opioid-like analgesia with a relative potency 1.5 times that of (2R,3S/2S,3R)-3 and approximately 1.5 times that of morphine.

Chiral resolution, configurational study and pharmacological profile of 2-phenoxypropionic acids.

The racemates and several enantiomers of 2-phenoxypropionic acids, bearing alkyl, acetyl, benzyl, benzoyl, phenyl, difluorophenyl, Cl, NO2 groups on the aromatic moiety, were investigated as potential analgesic-antiinflammatory drugs. The enantiomers, whose absolute configuration has been previously determined by us, were prepared by chiral resolution of the diastereoisomeric salts of the racemates with cynchonidine. The enantiomeric excess was determined by chiral chromatography. The chiroptical properties of the dextroisomers were investigated by CD. The pharmacological properties of the racemates and the enantiomers were monitored by analgesic-antiinflammatory activity tests as well as by gastrotolerability and acute toxicity tests. Some compounds were shown to be superior to ASA and ketoprofen because they have higher or similar analgesic properties, with less gastroulcerogenetic activity. Furthermore low acute toxicity was found for the compounds with high values of ED50. Correlations between the configuration of the enantiomers and their activity are not evident. For the most active compounds, the activity of one of the enantiomers is superior to that of the racemates. This is particularly true for (S)-3, (R)-15 and (S)-18.

Chiral resolution and absolute configuration of the enantiomers of 5-acetyl-2-methyl-4-methylsulfinyl-6-phenyl-3(2H)-pyridazinone and evaluation of their platelet aggregation inhibitory activity.

In a series of 5-acyl-6-phenyl-2,4-substituted-3(2H)-pyridaziones the derivative 1a, with a sulfur stereogenic center, had the most potent activity as human platelet aggregation inhibitor. The resolution of rac-1a was successfully performed by chiral chromatography on Chiralcel OD-R, OD-H, and Chiralpak AD columns and scaled up to a preparative level. The absolute configuration of (-)-(S)-1a was determined by X-ray crystallographic analysis. In vitro human platelet aggregation inhibitory activity was evaluated. Both the enantiomers showed IC50 values in the same micromolar range, but the (-)-(S) isomer was slightly more potent [(S)/(R) potency ratio was 4/1].

Preparation and configuration of racemic and optically active analgesic dialkylaminoalkylnaphthalenes.

The alkylaminoalkylnaphthalene 3 shows interesting opioid-like analgesic properties, mu-selective ligand competition, and enkephalin hydrolyzing enzyme inhibition. 3 possesses two chiral centers and can exist as two racemic pairs and four diastereomers. Since the binding of opioids with the receptor is stereoselective, it was important to have the two racemic pairs as well as the four diastereomers. In this paper the synthesis of the (1R,2R/1S,2S)- and (1R,2S/1S,2R)-racemates and the (1R,2R)- and (1S,2S)-enantiomers of the 1-ethyl-1-hydroxy-1-[2-(6-hydroxynaphthyl)]-2-methyl-3- dimethylaminopropane 3 is considered and the determination of absolute configuration is described. The (1R,2R/1S,2S)-3 and (1R,2S/1S,2R)-3 racemates and the (1R,2R)-3 and (1S,2S)-3 enantiomers were prepared by reaction of the racemic and optically active 1-dimethylamino-2-methylpentan-3-one 2, respectively, with the lithiation product obtained from 2-bromo-6-tetrahydropyranyloxynaphthalene and acidic hydrolysis. The optical resolution of aminoketone 2 was carried out via fractional crystallization of salts (+)- and (-)-dibenzoyltartrates. The configuration of the optically active compounds was determined by X-ray analysis of a crystal of (+)-(1R,2R)-3.HCl.H2O. Preliminary pharmacological tests showed that (+)-(1R,2R)-3 enantiomer is able to induce opioid-like analgesia with a relative potency 2.5 times that of (1R,2R/1S,2S)-3 and about 4 times that of morphine.

Antiphlogistic aryloxypropionic acids: configurational study.

Configurational relationships of a series of antiphlogistic 2-aryloxypropionyl derivatives by means of 1H-NMR and HPLC methods were demonstrated. NMR spectra of racemic mixtures and optically active esters were recorded by adding suitable quantities of Eu(hfc)3 chiral shift reagent. The chemical shift values of the non-equivalent signals were unambiguously assigned to R and S enantiomers and the sign of the delta delta parameter was shown to be the same for all compounds. Chiral resolution of (1-naphthyl)methylamides on R-DNBPG and S-DNBL analytical columns was carried out. The alpha and K' values of the chromatographic separations by means of S-DNBL phase were generally better than those using R-DNBPG. The elution order could be determined: S isomers are generally eluted last from both columns. For all compounds the solute-CSP interaction was studied by molecular models to verify if the interacting conformation is the same for the enantiomers which have equal configuration. This control is essential to validate the configurational assignment method by means of HPLC analysis. Finally, we hypothesized the interactions of the compounds showing inversion of the elution order or lack of chiral resolution.

Optical resolution of benzodiazepine esters by HPLC.

The separation of the enantiomers of 11-26 esters of oxazepam 1, temazepam 2, lorazepam 3 and lormetazepam 4 whith the acids benzoic 6, 2-methyl-3-nitrobenzoic 7, cynnamic 8 and hydrocynnamic 9 by HPLC on analytical columns with chiral stationary phases of (R)-N-(3,5-dinitrobenzoyl)phenylglycine (R)-DNBPG and (S)-N-(3,5-dinitrobenzoyl)leucine (S)-DNBL was described. The diastereoisomeric mixtures of esters 27-30 of the overmentioned benzodiazepines with (S)(+)-2-(6-methoxy-2-naphthyl)propionic acid have been also separated by HPLC on analytical column of SiO2. Some of the best separations have been repeated on semipreparative scale in order to isolate and characterize the optically pure enantiomers or diastereoisomers. Configurational assignment and elution order are established by a chiral recognition model. On the basis of the study by molecular models of the interaction between solute and chiral stationary phases, the conformers more interacting with these phases have been individuated and it has been possible to conclude that for any enantiomers couple the (S) isomer is always more retained by the chiral stationary phase of (R)-DNBPG and the (R) isomer by (S)-DNBL. Regarding to the interaction of diastereoisomeric esters 27-30 with SiO2, the esters more retained should result those of the benzodiazepines having (S) configuration.

Optical resolution and configuration of 2-(4-dimethylvinylphenyl)propionic acid.

Optical resolution of (+/-)-2-(4-dimethylvinylphenyl)propionic acid (I) was performed through fractional crystallization of its salts with (S)-(-)- and (R)-(+)-alpha-phenylethylamine. 2-(4-Dimethylvinylphenyl)propionic acid, in comparison to ibuprofen, has greater antiinflammatory, analgesic and antipyretic activities, as well as a higher therapeutic index. Absolute configuration was determined by comparison of the (S)-(-)-alpha-phenylethylamide 1H-N.M.R. spectra of the enantiomers of (I) and of the enantiomers of ibuprofen whose configuration was already known. Thus, the absolute configuration (S) was assigned to (+)-(I).

[Clathrates of unsaturated hydroxamic acids with antifungal acitivity]. / Clatrati di acidi idrossammici insaturi ad attività antifungina.

Urea complexes of 10-undecen-hydroxamic acid (III) and trans-2-dodecen-hydroxamic acid (IV) were prepared with the aim of testing antifungal activity. No significant difference of activity between the complexes and corresponding hydroxamic acids was demonstrated.