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At least 19 recordsLinked to original sources
PubMed1998

Monosubstituted Oxazoles. 1. Synthesis of 5-Substituted Oxazoles by Directed Alkylation.

A general method is presented for synthesis of 2-(methylthio)-5-substituted oxazoles 2. Deprotonation of the readily available 2-(methylthio)oxazole (1) with n-BuLi occurs smoothly in the presence of TMEDA and regiospecifically at C5. The organometallic 1a added rapidly to aldehydes and other electrophiles to provide 5-substituted-2-(methylthio)oxazoles in very good to excellent yields. Reductive removal of the MeS group gave the desired 5-monosubstituted oxazoles 3 in good yield.

Journal Article↗
PubMed2005

A convenient oxazole C-2 protecting group: the synthesis of 4- and 5-substituted oxazoles via metalation of 2-triisopropylsilyloxazoles.

[reaction: see text] Metalation of oxazoles at the 4 and 5 position was achieved after regioselective C-2 silyl protection. Removal of the protecting group was then accomplished under mild conditions allowing for a straightforward preparation of C-5 monosubstituted and C-4,5 disubstituted oxazoles. The first practical C-2 protecting group of oxazoles has been demonstrated.

Lithium↗
PubMed1998

Synthesis of the C(26)-C(32) Oxazole Fragment of Calyculin C: A Test Case for Oxazole Syntheses.

The synthesis of the C(26)-C(32) oxazole fragment 4 and its C(32) epimer 20 of serine/threonine protein phosphatase PP1 and PP2A inhibitor calyculin C is presented. The syn methyl arrangement in 4 was established through cyclic stereocontrol. Several methods for oxidizing the intermediate oxazolines 18 and 19 to the finished oxazole fragments were explored. The best results were obtained with oxidations proceeding through the corresponding ester enolate when the carbamate NH side chain was temporarily protected with a TMS group, or with CuBr(2)/DBU/HMTA-based oxidations. The finished oxazole fragment 4 was obtained in 21% overall yield, starting from Boc-D-alaninal.

Journal Article↗
PubMed2003

1-Acetyl-4'-ethyl-2a'-phenyl-2',2a',5',5a'-tetrahydrospiro[1H-indole-3,2'-oxeto[5,4-b]oxazol]-2(3H)-one and 1-acetyl-4',5a'-diphenyl-2',2a',5',5a'-tetrahydrospiro[1H-indole-3,2'-oxeto[5,4-b]oxazol]-2(3H)-one.

In the title compounds, C(21)H(18)N(2)O(4) and C(25)H(18)N(2)O(4), respectively, the five-membered ring of the indole system is almost planar. The oxetane and oxazole rings are individually planar. The orientations of the indole, oxetane, oxazole and phenyl moieties are conditioned by the sp(3) nature of the spiro-C atoms. In both compounds, the relative orientation of the indole and oxazole rings is opposite.

Journal Article↗
PubMedDate not supplied

5-(hydroxymethyl)oxazoles: versatile scaffolds for combinatorial solid-phase synthesis of 5-substituted oxazoles.

A scheme combining the preparation of building blocks in solution followed by solid-phase combinatorial chemistry has been developed to side-chain diversify 5-(hydroxymethyl)oxazole scaffold (1) into aryl ethers, thioethers, sulfones, sulfonamides, and carboxamides. Protected heterocyclic scaffolds 2 were linked to the solid phase and N-terminal derivatized using active ester chemistry, providing chemset 4¿1-4,1-4¿. The free side-chain hydroxyl of 4 was smoothly converted to aryl ethers 6 under Mitsunobu conditions, with a broad range of substituted phenols. Alternatively, quantitative conversion of hydroxyl to bromide followed by displacement with alkyl and aryl thiols gave thioethers 8. Thioethers were optionally oxidized to sulfones 9. Bromide displacement by azide, followed by reduction to amine and acylation with a range of carboxylic acids and sulfonyl chlorides gave carboxamides 11 and sulfonamides 13, respectively. Crude purity at typically >90% was observed for each of the five modifications detailed. A series of 20 compounds, exemplifying each modification, was reprepared, purified, and fully characterized.

Chromatography, High Pressure Liquid↗
PubMed1987

[2-Amino-oxazoles as potential bonding agents in virostatic research. 1. N-unsubstituted and n-substituted 2-amino-oxazoles].

2-Amino-oxazoles with the semicyclic amidine structure are able in principle to form hydrogen bonds with native components for example with viral nucleic acids or viral enzymes. In this way the inhibition of viral replication seems to be possible. The syntheses of 39 compounds with amidine structure are described and the results of the antiviral agar diffusion plaque inhibition test are discussed in relation to the chemical structures.

Antiviral Agents↗
PubMed2002

11-Methyl-12a-phenyl-9a,12a-dihydrophenanthro[9',10':5,6][1,4]dioxino[2,3-d]oxazole and 9a-(10-hydroxyphenanthren-9-yl)-11,12a-diphenyl-9a,12a-dihydrophenanthro[9',10':5,6][1,4]dioxino[2,3-d]oxazole.

In the title compounds, C(24)H(17)NO(3), (I), and C(43)H(27)NO(5), (II), the dioxine ring is not planar and tends toward a boat conformation. The oxazoline ring adopts a twisted conformation in molecule (I) but is essentially planar in molecule (II). The configuration of the dioxine-oxazoline system is determined by the sp(3) state of the two shared atoms. The phenanthrene moiety is nearly coplanar with the dioxine ring, while the phenyl ring is perpendicular to the attached oxazole ring. The triclinic unit cell of (II) contains two crystallographically independent molecules related by a pseudo-inversion centre.

Journal Article↗
PubMed2005

The diazo route to diazonamide A. Studies on the indole bis-oxazole fragment.

[structure: see text] Various approaches to the indole bis-oxazole fragment of the marine secondary metabolite diazonamide A are described, all of which feature dirhodium(II)-catalyzed reactions of diazocarbonyl compounds in key steps. Thus, 3-bromophenylacetaldehyde is converted into an alpha-diazo-beta-ketoester, dirhodium(II)-catalyzed reaction of which with N-Boc-valinamide resulted in N-H insertion of the intermediate rhodium carbene to give a ketoamide that readily underwent cyclodehydration to give (S)-2-(1-tert-butoxycarbonylamino)-2-methylpropyl]-5-(3-bromobenzyl)oxazole-4-carboxamide, after ammonolysis of the initially formed ester. This aryl bromide was then coupled to a 3-formyl-indole-4-boronate under Pd catalysis to give the expected biaryl. Subsequent conversion of the aldehyde group into a second alpha-diazo-beta-ketoester gave a substrate for an intramolecular carbene N-H insertion, although attempts to effect this cyclization were unsuccessful. A second approach to an indole bis-oxazole involved an intermolecular rhodium carbene N-H insertion, followed by oxazole formation to give (S)-2-[1-tert-(butoxycarbonylamino)-2-methylpropyl]-5-methyloxazole-4-carboxamide. A further N-H insertion of this carboxmide with the rhodium carbene derived from ethyl 2-diazo-3-[1-(2-nitrobenzenesulfonyl)indol-3-yl]-3-oxopropanoate gave a ketoamide, cyclodehydration of which gave the desired indole bis-oxazole. Finally, the boronate formed from 4-bromotryptamine was coupled to another diazocarbonyl-derived oxazole to give the corresponding biaryl, deprotection and cyclization of which produced a macrocyclic indole-oxazole derivative. Subsequent oxidation and cyclodehydration incorporated the second oxazole and gave the macrocyclic indole bis-oxazole.

Heterocyclic Compounds, 4 or More Rings↗
PubMed2005

A two-stage iterative process for the synthesis of poly-oxazoles.

[reaction: see text]. Methodology has been developed to prepare bis-oxazoles via a two-stage iterative process. The sequence begins with C(2)-chlorination of a lithiated oxazole using hexachloroethane. Generation of the C(2)-C(4)(') bond by S(N)Ar substitution with TosMIC anion, followed by conversion to the heterocycle in a one-pot reaction with glyoxylic acid monohydrate, affords the desired bis-oxazole in good yield and purity. The two-stage process allows for efficient synthesis of a tris-oxazole and the first iterative preparation of a tetra-oxazole.

Combinatorial Chemistry Techniques↗
PubMed1993

Separation of amino acid-oxazole derivatives of the redox coenzyme pyrroloquinoline quinone by capillary zone electrophoresis.

Condensation products (oxazole derivatives) from the reaction of the coenzyme pyrroloquinoline quinone (PQQ) with several alpha-amino acids were successfully separated by capillary zone electrophoresis. Addition of a certain organic solvent such as dimethyl sulphoxide to the electrolyte solution is essential for reproducible and complete separation. The organic modifier appears to prevent the oxazole derivatives from absorbing on the capillary wall. Product analysis of the condensation reactions of PQQ with amino acids was performed by this method and the mechanism is discussed briefly. PQQ-spiked bovine serum was also analysed. Unsubstituted type 1 oxazole derivative was predominantly detected. This result suggests that most of the PQQ in mammalian fluids, if any, exists as PQQ derivatives, probably as a type 1 oxazole derivative.

Amino Acids↗
PubMed1993

Effects of pyrroloquinoline quinone (PQQ) and PQQ-oxazole on DNA synthesis of cultured human fibroblasts.

The effects of pyrroloquinoline quinone (PQQ) and PQQ-oxazole (PQQ-glycine adduct) on DNA synthesis were examined using cultured human fibroblasts. Confluent fibroblasts were cultured in serum-free Dulbecco's modified Eagle's media, and various concentrations of PQQ and PQQ-oxazole were added to the media. After incubation for 24 h, [3H]thymidine was added to the media as an indicator for DNA synthesis of the cells. The thymidine incorporation into the cells was significantly enhanced even in the presence of very low concentrations of PQQ (0.003-0.03 microM); it remained significantly enhanced, up to 30 microM PQQ. However, the incorporation remarkably decreased at 750-1500 microM of PQQ. In contrast to the results for PQQ, DNA synthesis was not stimulated by addition of 0.003-3 microM PQQ-oxazole, but it was slightly enhanced at concentrations 15-750 microM. In morphological examination of the cultured human fibroblasts, cell density was increased by addition of 0.003-30 microM PQQ when compared with that of the control, supporting the above biochemical data. However, there were no distinct differences in morphological effect between PQQ and PQQ-oxazole.

Adult↗
PubMed1994

C-glycosyl bond conformation in oxazofurin: crystallographic and computational studies of the oxazole analogue of tiazofurin.

Oxazofurin is the inactive oxazole analogue of the C-glycosyl thiazole antitumor agent tiazofurin. Replacement of the thiazole sulfur in tiazofurin with the oxazole oxygen in oxazofurin produces conformational effects that are examined using crystallographic and computational methods. The crystal structure of oxazofurin contains six molecules in the asymmetric unit and has been refined to a standard R value of 6.8% for all data. The six oxazofurin conformers show an average C-glycosidic torsion angle of 70(9) degrees. This value is significantly higher than the average absolute C-glycosidic torsion angle of 24(10) degrees obtained from previous thiazole nucleoside structures. Previous studies suggest that, in tiazofurin, an electrostatic interaction between a positively charged thiazole sulfur and negatively charged furanose oxygen constrains the C-glycosidic torsion angle to a relatively small value. Ab initio molecular orbital studies presented here suggest that the higher C-glycosidic angles observed in the oxazofurin structures result from a repulsive interaction between negatively charged oxazole and furanose oxygens. Thus, it is likely that differences in activity between oxazo- and tiazofurin are either (1) due directly to differences in electronic properties between the thiazole and oxazole rings or (2) due to the variation in C-glycosidic bond conformation resulting from the alteration in the charge distribution of the heterocycle.

Antineoplastic Agents↗
PubMed2006

New easy approach to the synthesis of 2,5-disubstituted and 2,4,5-trisubstituted 1,3-oxazoles. The reaction of 1-(methylthio)acetone with nitriles.

The reaction of 1-(methylthio)acetone with different nitriles in the presence of triflic anhydride led to the one-pot formation of 2-substituted 5-methyl-4-methylthio-1,3-oxazoles in good yield. 1,2- and 1,4-Bisozaxolyl-substituted benzenes were obtained when the reaction was carried out using aromatic dinitriles. The methylthio group at the C4 position of the oxazole ring was easily removed with Raney nickel to form 2-substituted 5-methyl-1,3-oxazoles in good yields. 4-Methylsulfonyl derivatives were prepared by the oxidation of the MeS group with m-CPBA. The proposed mechanism for the formation of oxazoles involves an unstable 1-(methylthio)-2-oxopropyl triflate, which was detected from the low-temperature NMR spectra.

Acetone↗
PubMed2003

Synthesis and biological activity of novel 5-(omega-aryloxyalkyl)oxazole derivatives as brain-derived neurotrophic factor inducers.

A novel series of 5-(omega-aryloxyalkyl)oxazole derivatives was prepared and their effects on brain-derived neurotrophic factor (BDNF) production were evaluated in human neuroblastoma (SK-N-SH) cells. Syntheses were performed by construction of an oxazole ring as a key reaction. Most of the 5-(omega-aryloxyalkyl)oxazole derivatives markedly increased BDNF production in SK-N-SH cells. 4-(4-Chlorophenyl)-2-(2-methyl-1H-imidazol-1-yl)-5-[3-(2-methoxyphenoxy)propyl]-1, 3-oxazole, one of the most promising compounds, showed potent activity (EC(50)=7.9 microM) and the improvement of the motor nerve conduction velocity and the tail-flick response accompanied by a recovery of the brain-derived neurotrophic factor level in the sciatic nerve of streptozotocin (STZ)-diabetic rats.

Alkanes↗
PubMed2004

Synthesis and antioxidative activity of 2-substituted phenyl-5-(3'-indolyl)-oxazole derivatives.

AIM: To study the synthesis of 5-(3'-indolyl)-oxazoles and their antioxidative activity. METHODS: The amides were prepared from tryptophan and different acid derivatives by the catalytic dehydration of dicyclohexyl carbodiimide (DCC). The characteristic heterocyclic ring system of 5-(3'-indolyl)-oxazoles was constructed by oxidative cyclization of amide, using dicholorodicyanoquinone (DDQ). Their antioxidative activity in vitro was tested using DPPH system. RESULTS: Eleven 2-substituted phenyl-5-(3'-indolyl)-oxazoles were prepared, the compounds 21 and 22 have shown antioxidative activity 3-4 times stronger than that of Vit E, and the compound 29 showed antioxidative activity almost as same as Vit E. CONCLUSION: Three 5-(3'-indoyl)-oxazole compounds synthesized showed potent antioxidative effect and they would be a good antioxidants.

Antioxidants↗
PubMed2004

Study on the second-order optical behavior of 4-(substituted-benzylidene)-2-phenyl-4H-oxazol-5-one.

The maximum absorption wavelengths (lambda(a-max)), absorption coefficient (epsilon), maximum emission wavelengths (lambda(e-max)) of 4-benzo[1,3]dioxol-5-ylmethylene-2-phenyl-4H-oxazol-5-one (1), 4-(3,4-dimethoxybenzylidene)-2-phenyl-4H-oxazol-5-one (2) and 4-(3,4,5-trimethoxy-benzylidene)-2-phenyl-4H-oxazol-5-one (3) were measured, their second-order nonlinear polarization values (beta(xxx)) were determined by solvatochromic method. Although the spectral nature (lambda(a-max), epsilon, lambda(e-max)) and beta(xxx) values of 1, 2 and 3 were close to each other in the same solvent, the second-order harmonic generation (SHG) value of sample 1 is higher obviously than that of sample 2 or 3 in solid state. The crystal structures of 1 and 2 characterized by single crystal X-ray diffraction technique indicated the reason why the SHG value of 1 is higher.

Crystallography, X-Ray↗