共查询到20条相似文献,搜索用时 15 毫秒
1.
C. G. Overberger C. C. Chen 《Journal of polymer science. Part A, Polymer chemistry》1987,25(1):389-403
Polynucleotide analogs consisting of poly(vinylamine) as the backbone and optically active thymine and adenine derivatives as the pendants were synthesized. The pendants were prepared by the addition reaction of the nucleic acid base to ethyl crotonate followed by hydrolysis. The pendants were resolved using brucine as the resolving agent and an acetone-water mixture as the fractional crystallization solvent. The active esters of the pendants also were prepared. Poly(vinylamine) was isolated from water employing a weak acid, N-hydroxysuccinimide (HOSu), to protect the amino group of the poly(vinylamine). Model reactions for grafting were examined. Grafting reactions were carried out by reacting the active esters with the PVAm.6HOSu complex at room temperature. 相似文献
2.
Single enantiomers of 1,8-di(1-adamantyl)naphthalenes were synthesized by the [4+2]cycloaddition reaction of 6-adamantylbenzyne and 2-adamantylfuran. The enantiomers were resolved by conversion into diastereomeric ketopinic acid esters. The absolute configuration was determined by X-ray analysis. Kinetic studies by CD revealed an enantiomerization barrier of 29 kcal mol(-1) for 1,8-(1-adamantyl)naphthalenes. 相似文献
3.
The (+)- and (-) enantiomers of potassium α-phenylglycidate, an irreversible inhibitor of the enzyme mandelate racemase, were synthesized by resolution of the diastereomeric esters with R-(-)-2-octanol. Base-catalyzed ring-opening of the resolved α-phenylglycidate esters gave the enantiomers of 2,3-dihydroxy-2-phenylpropanoic acid, also obtained by resolution of the racemic dihydroxy acid using ephedrine. A comparison of the chiroptical properties of the esters of α-phenylglycidic and 2,3-dihydroxy-2-phenylpropanoic acids with those of the structurally similar atrolactic and mandelic acids and their 2-methoxy-derivatives showed that the (-)-methyl 2,3-dihydroxy-2-phenylpropanoate corresponding to the (+)-enantiomer of potassium α-phenylglycidate, as well as the esters of α-phenylglycidic acid derived from the same (+)-potassium salt, were all configurationally related to S-(+)-atrolactic and mandelic acids. The configurational assignments made on the basis of the chiroptical data were confirmed by lithium aluminum hydride reduction of the (-)-2-octyl S- and R-α-phenylglycidates, which led exclusively to the R-(-)- and S-(+)-2-phenyl-1, 2-propanediols, respectively, previously related configurationally to R-(-)- and S-(+)-atrolactic acids. 相似文献
4.
《Tetrahedron: Asymmetry》1999,10(22):4331-4341
The syntheses and resolutions of enantiomerically enriched 4-phenyl, 4-tert-butyl, and 4-isopropyl pipecolic acids are described. Optically active diastereomers were prepared by diastereomeric salt formation with the chiral base, l-tyrosine hydrazide, to provide Cbz or Boc protected 4-cis-d-pipecolic acid derivatives in >98% ee. Subsequent esterification followed by sodium methoxide catalyzed epimerization provided the isomeric 4-trans-l-pipecolic esters. In addition, an efficient synthesis of 4-phenyl-cis-pipecolic acid is described. 相似文献
5.
《Journal of organometallic chemistry》1986,301(3):289-297
Phenylphosphonous acid dimenthylester and its dibornylester react with bulky nucleophiles to give diastereomeric phosphinous acid esters. The asymmetric induction is as high as 95% d.e. If reaction conditions favouring inversion at phosphorus are used then the (R)-menthoxy group of the prochiral starting material is substituted. The phosphinous acid esters can be converted, with partial racemization, into optically active Horner-phosphines. 相似文献
6.
C. G. Overberger Ji Young Chang V. E. Gunn 《Journal of polymer science. Part A, Polymer chemistry》1989,27(1):99-106
Polynucleotide analogs with polytrimethylenimine backbones and optically active 2-(thymin-1-yl)propionic acids as pendants were prepared. Linear polytrimethylenimines were obtained by ring-opening polymerization of 2-phenyl-5,6-dyhydro-4H-1,3-oxazine and subsequent hydrolysis of the resulting polymers. 2-(Thymin-1-yl)propionic acids were reacted with N-hydroxy succinimide to form active esters. Optical purities of active esters were determined by NMR with chiral chemical shift reagents. The polynucloetide analogs and related monomer and dimer model compounds were prepared by grafting reactions using active esters. 相似文献
7.
Ohno T Yano S Yamada H Shirasaka T Yamamoto A Kobayashi K Ogawa K 《Chemical & pharmaceutical bulletin》1999,47(11):1549-1554
The enantiomers of (+/-)-4-[1-(4-tert-butylphenyl)-2-oxo-pyrrolidine- 4-yl]methyloxybenzoic acid (S-2), a new antilipidemic agent having dual action on the plasma triglyceride (TG) and cholesterol (Cho) lowering effects, were prepared via separation by Chiralcel OJ column chromatography of their methyl ester and also by the same method as the described racemate's synthesis from optically active 1-(4-tert-butylphenyl)-2-oxo-pyrrolidine-4-carboxylic acid respectively. These optically active carboxylic acids were prepared by the resolution of diastereomeric N-[(S)-(-)-[4-methyl-(alpha-methyl)benzyl]]-1-(4-tert-butylphenyl)-2-oxo - pyrrolidine-4-carboxyamide using silica gel column chromatography, followed by deamination with N2O4. The absolute configurations for the enantiomers of S-2 were indirectly determined using X-ray analysis of the 4-bromo-2-fluorobenzamide of the (+)-4-[1-(4-tert-butylphenyl)-2- oxo-pyrrolidine-4-yl]-methyloxybenzoic acid. S-2 and its enantiomers showed an essentially equipotent activity on the fatty acid- and sterol-biosynthesis inhibition in vitro. On the other hand, in the in vivo activity, (S)-(+)-4-[1-(4-tert-butylphenyl)-2-oxo-pyrrolidine- 4-yl]methyloxybenzoic acid (S-2E) was superior in the lowering abilities of the plasma TG and phospholipid(PL) and was chosen as a candidate for a novel antilipidemic agent. The difference in the in vivo activity among S-2 and its enantiomers was explained from the pharmacokinetics after administration p.o. 相似文献
8.
Liquid chromatographic separation of enantiomers of beta-amino acids using a chiral stationary phase
O W Griffith E B Campbell W H Pirkle A Tsipouras M H Hyun 《Journal of chromatography. A》1986,362(3):345-352
The enantiomers of both alpha-substituted beta-alanines and beta-substituted beta-alanines may be chromatographically separated using silica-bonded chiral stationary phases derived from N-acetylated alpha-arylalkylamines. The amino acids are chromatographed as alkyl esters of N-3,5-dinitrobenzoyl derivatives; separability factors range from 1.11 to 1.65 for nine alpha-substituted beta-alanines and from 1.08 to 1.20 for nine beta-substituted beta-alanines. The enantiomers of beta-aminoisobutyrate and beta-leucine, chiral beta-amino acids occurring in animal tissues and physiological fluids, are among those resolved. The enantiomers of R,S-beta-aminoisobutyrate and several related alpha-alkyl-beta-alanines were prepared by chromatographic resolution of diastereomeric dipeptides. 相似文献
9.
New chiral derivatization reagent for the resolution of amino acids as diastereomers by TLC and HPLC
Summary The applicability of a new chiral reagent to the resolution of amino acid enantiomers has been investigated. The new reagent,
S(-)-N-1-(2-naphthylsulphonyl)-2-pyrrolidinecarbonyl chloride (NSP-C1), was synthesized by the chlorination of S(-)-N-1-(2-naphthylsulphonyl)-2-pyrrolidinecarboxylic
acid which was prepared by the reaction of 2-naphthalene sulphonyl chloride with L-proline. Derivatization of the amino acids
proceeds rapidly at ambient temperature and no racemization takes place during the reaction. The resolution of the diastereomeric
amides was performed by TLC and normal phase HPLC. Complete resolutions were observed for the enantiomers of all amino acids
examined except cysteine, cystine and histidine. The favourable UV absorption of the derivatives enabled the optical antipode
to be determined down to the 0.1% level. 相似文献
10.
Two new syntheses of spiro[4.4]nonane-1, 6-dione (I) are described: one by rearrangement of 1,6-epoxy-bicyclo[4.3.0]-nonane-2-one (IV) with boron trifluoride, the other by an acid catalyzed, intramolecular Claisen condensation of 4-(2-oxocyclopentyl)-butyric acid. Spiro[4.4]-nonane-1,6-dione is converted into trans, trans-spiro[4.4]nonane-1,6-diol which is resolved into enantiomers via the diastereomeric esters with (?)-camphanic acid. (+)-(5S)-Spiro[4.4]nona-1,6-diene (III) is prepared from (1R, 6R)-trans,trans-spiro[4.4]nonane-1,6-diol (II) by pyrolysis of the corresponding bis-4-methylphenyl-thionocarbonate. This modification of the Chugaev reaction is particularly useful with sterically hindered alcohols which cannot be converted into S-me-thylxanthates. The circular dichroism, UV.- and NMR.-spectrum of optically active spiro[4.4]-nonane-1,6-diene are discussed. 相似文献
11.
Péter Bagi Réka Herbay Péter Ábrányi-Balogh Béla Mátravölgyi Elemér Fogassy György Keglevich 《Tetrahedron》2018,74(40):5850-5857
A dynamic kinetic resolution method based on the formation of covalent diastereomeric intermediates was elaborated for the preparation of enantiomerically enriched 1-substituted-3-methyl-3-phospholene oxides. The 3-phospholene oxides were first converted to the corresponding chloro-3-phospholenium chlorides. The dynamic interconversion between the enantiomers of the chlorophospholenium salts was verified experimentally, as it is the key step for a dynamic resolution. The cyclic chlorophospholenium salts were reacted with a chiral auxiliary bearing a hydroxy function to form the corresponding diastereomeric alkoxyphospholenium salts in unequal amounts. The diastereomeric species then rearranged into the corresponding optically active 3-phospholene oxides upon heating. After a screening of chiral auxiliaries and the optimization of the reaction conditions, several scalemic 1-aryl- or 1-alkyl-3-methyl-3-phospholene oxides were prepared in excellent yields and with ee-s up to 35%. The key steps of this resolution were investigated by quantum chemical calculations to get some insights into the factors responsible for the stereoselection. 相似文献
12.
Kamimura A Okawa H Morisaki Y Ishikawa S Uno H 《The Journal of organic chemistry》2007,72(9):3569-3572
Optically active N-sulfinimines underwent stereoselective Michael/nucleophilic addition domino reaction triggered by magnesium thiolate to give alpha-phenylthiomethyl-beta-(N-sulfinylamino) esters in high diastereomeric excess. The adducts were readily converted into optically active alpha-methylene-beta-(N-sulfinylamino)esters so that this reaction provides a useful asymmetric aza-Baylis-Hillman-equivalent method. 相似文献
13.
Kukula P Matousek V Mallat T Baiker A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(9):2699-2708
The kinetics and mechanisms of one-pot cascade reactions of racemic beta-keto esters to give chiral ketones in the presence of Pd/C-chiral amino alcohol catalyst systems were studied. Transformation of 2-methyl-1-tetralone-2-carboxylic acid benzyl ester (1) into 2-methyl-1-tetralone (4) in the presence of Pd/C and cinchona alkaloids or ephedrine was chosen as a model reaction. After the first reaction step, the Pd-catalysed debenzylation of 1 to afford the corresponding beta-keto acid (2), there are two possible reaction routes that may be catalysed by the chiral amino alcohol in solution or by Pd(0) sites on the metal surface in cooperation with the adsorbed amino alcohol. The reaction intermediate 2 was synthesized, and the kinetics of decarboxylation were followed by NMR, UV and IR spectroscopy. The studies revealed that the role of Pd is to trigger the reaction series by deprotection of 1. The subsequent dominant reaction route from the racemic beta-keto acid 2 to the chiral ketone 4 is catalysed by the chiral amino alcohol in the liquid phase. It is shown that kinetic resolution of the diastereomeric salt of rac-2 and the chiral amino alcohol plays a key role in the enantioselection. High enantioselectivity necessitates an amino alcohol/rac-2 ratio of at least 2. A high ratio favours the formation of 1:1 amino alcohol/acid diastereomeric complexes, and the second amino alcohol molecule may be responsible for the enantioselective protonation of 2 in the diastereomeric complex. 相似文献
14.
Thermodynamic studies were performed on 12 pairs of N-trifluoroacetyl-O-alkyl nipecotic acid ester enantiomers on diluted permethylated beta-cyclodextrin stationary phase (CP Chirasil-Dex CB). The influence of ester alkyl group structure on interaction with permethylated beta-cyclodextrin (Me-CD) and enantioselectivity was studied. The types of alkyl groups studied included n-alkyl (C1-C5) and groups containing branching at differing locations relative to the chiral center of the molecule. The results show that for a given molecular weight, the n-alkyl esters have stronger interactions with Me-CD than esters containing branched alkyl groups. However, although having weaker interactions with Me-CD, esters containing alpha-branched alkyl groups exhibit higher enantioselectivity than the corresponding n-alkyl or beta-branched isobutyl esters. From the retention data, thermodynamic parameters were estimated using the retention increment method and enthalpy-entropy compensation plots (ln R' versus deltaH) were constructed. The results suggest that ester enantiomers with branching at the alpha-carbon of the ester alkyl group have additional and/or different types of enantioselective interactions with Me-CD than the C1-C5 n-alkyl esters or beta-branched isobutyl ester. In order to obtain a qualitative sense of the interaction with Me-CD, structures of the diastereomeric complexes formed between Me-CD and some of the ester enantiomers were modeled using simulated annealing molecular dynamics. 相似文献
15.
Paul Pfffli Wolfgang Oppolzer Roland Wenger Hartmut Hauth 《Helvetica chimica acta》1975,58(4):1131-1145
Vincamine ( 13 ) was prepared from the aldehyde 8 in 5 steps using methyl dimethyl-phosphono-methoxy-acetate as a synthon for the pyruvic ester residue. A method to convert apovincamine ( 12 ) into vincamine ( 13 ) has hen worked out. Optically active 8 was synthesized from ethyl-malonaldehydic acid ethyl ester in 9 steps including optical revolution of the acid intermediate 3 by means of salt formation with L-(+)-pseudoephedrine. The two diastereomeric salts were distinguishable by NMR. in carbontetrachloride. 相似文献
16.
Enantioselective gas chromatographic assays for the quantitation of methylphenidate and its major metabolite ritalinic acid in plasma are described. The procedures involved the extraction of methylphenidate enantiomers from alkanised plasma. The plasma was then washed to ensure complete removal of methylphenidate before saturation with sodium carbonate to promote the extraction of ritalinic acid enantiomers with ethyl acetate-isopropanol (60:40) solvent mixture. Subsequently, ritalinic acid enantiomers were converted back into methylphenidate enantiomers by Fisher-Speier esterification. N-Heptafluorobutyryl-L-prolyl chloride, a chiral acylating reagent, was used to convert the enantiomers of methylphenidate into their corresponding diastereomeric amide derivatives, which were separated cleanly on an achiral capillary column (OV-225) and quantitated with electron-capture detection. The assays were sensitive, reliable and reproducible. 相似文献
17.
C. G. Overberger Ji Young Chang 《Journal of polymer science. Part A, Polymer chemistry》1989,27(12):4013-4033
A new family of polynucleotide analogs were prepared by grafting nucleic acid base derivatives onto polytrimethylenimine. Several new optically pure α-nucleic acid base substituted propanoic acids were prepared as pendant groups. The (R)-ethyl adeninylpropanoate was obtained from adenine and (S)-ethyl lactate by utilizing a diethyl azodicarboxylate-triphenyl phosphine method. Subsequent hydrolysis of the ester in aqueous acid gave the (R)-adeninylpropanoic acid without racemization. The reaction of cytosine sodium salt with (S)-ethyl 2-[(methylsulfonyl)oxy] propanoate produced the 20% racemized (R)-ethyl 2-(cytosin-1-yl)propanoate. The optically pure ester was obtained by recrystallization from ethyl alcohol, which was hydrolyzed in aqueous acid to give the (R)-acid with 66% enantiomeric excess. The (R)-2-(hypoxanthin-9-yl)propanoic acid was prepared by reaction of (R)-2-(adenin-9-yl)propanoic acid with sodium nitrite. The pendant groups were allowed to react with N-hydroxy compounds in the presence of dicyclohexylcarbodiimide to give the active esters. These active esters underwent reaction with N,N-dipropylamine to provide monomer model compounds. The pendant groups were grafted onto polytrimethylenimine by using the active ester method. The racemization reactions were observed in the grafting reactions. The resulting polymers showed a range of percent grafting from 60 to 80%. 相似文献
18.
Tamiko Takahashi Hiroaki Kameda Tomoyo Kamei Jyunichi Koyanagi Fabio Pichierri Kenji Omata Miyuki Ishizaki Hiroshi Nakamura 《Tetrahedron: Asymmetry》2013,24(17):1001-1009
Optically active 1-fluoroindan-1-carboxylic acid (FICA) was designed and prepared as its methyl ester for determining the absolute configuration of chiral molecules by both 1H and 19F NMR spectroscopies. Enantiomerically pure isomers of FICA methyl esters (FICA Me esters) were obtained by chromatographic separation using HPLC with a Daicel Chiralcel OJ-H column. The absolute configuration of the (+)-FICA Me ester was deduced to be (S) by X-ray crystallographic analysis of the (+)-FICA amide of (R)-α-phenethylamine. Both enantiomers were derived to the diastereomeric esters of chiral secondary alcohols by an ester exchange reaction. In the 1H NMR spectra, the signs of ΔδH (δR ? δS) were consistent on each side of the FICA molecular plane. Therefore, the concept of the modified Mosher’s method could be successfully applied to the FICA-based procedure. Moreover, the consistency in the signs of ΔδF (δR ? δS) values suggests that the FICA method would be reliable in assigning the absolute configurations of secondary alcohols based on 19F NMR spectroscopy. 相似文献
19.
The compound (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid (I) and its ytterbium(III) complex are evaluated as chiral NMR discriminating agents. The crown ether is a useful chiral discriminating agent for protonated amino acid esters, amines, and amino alcohols. The crown can also be used with neutral primary amines since amines are protonated through a neutralization reaction with a carboxylic acid moiety of the crown. Enantiodiscrimination with the crown is observed in methanol and acetonitrile. Addition of ytterbium(III) nitrate to crown-substrate mixtures causes upfield shifts in the NMR spectrum of the substrate and often enhances the enantiomeric discrimination. Evidence indicates that the ytterbium(III) bonds to the carboxylic acid moieties of the crown, but enhancements in enantiomeric discrimination result from either the different association constants of the enantiomers with the crown or diastereomeric nature of the resulting crown-substrate complexes. The ytterbium complex with the crown is suitable for use in methanol but precipitates in acetonitrile. 相似文献
20.
Federico Berti Cristina Forzato Giada Furlan Patrizia Nitti Giuliana Pitacco Ennio Valentin Ennio Zangrando 《Tetrahedron: Asymmetry》2009,20(3):313-321
The cis- and trans-4-benzylparaconic acids and their ethyl esters were synthesized with high enantiomeric excess by hydrolysis of the corresponding diastereomeric lactonic esters using α-chymotrypsin. Thus, at low conversion values, cis- and trans-4-benzyl-5-oxo-3-tetrahydrofurancarboxylic acids were separately isolated with 99% ee and 92% ee, respectively. Both ethyl ester diastereomers were also obtained in enantiopure form. The absolute configuration of the trans-lactonic acid was assigned by 1H NMR analysis of its ester derivatives with both enantiomers of 1-(9-anthryl)-2,2,2-trifluoroethanol, while that of the cis-lactonic acid was assigned by means of X-ray analysis of a crystalline derivative. The circular dichroism curves of the products obtained are also reported. 相似文献