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1.
An efficient enantioselective synthesis of (−)-cytoxazone (1) and (+)-epi-cytoxazone (2) using proline-catalyzed asymmetric α-amino-oxylation of aldehydes followed by Rh-catalyzed diastereoselective oxidative C-H amination as the key steps is described. syn or anti 1,2-aminoalcohols were obtained by Rh-catalyzed intramolecular amidation of the C-H bonds of carbamates or sulfamate esters with good to excellent diastereoselectivity.  相似文献   

2.
In Su Kim 《Tetrahedron》2006,62(40):9349-9358
A concise synthesis of (−)-cytoxazone and its stereoisomer (−)-4-epi-cytoxazone, novel cytokine modulators, has been accomplished each in six steps from readily available p-anisaldehyde with good diastereoselectivity. Key steps in the synthesis include the regioselective and diastereoselective amination of anti- and syn-1,2-dimethyl ethers with chlorosulfonyl isocyanate and the subsequent regioselective cyclization of the diol to construct the oxazolidin-2-one core. The diastereoselectivity of amination reaction using CSI was explained by the Cieplak electronic model via SN1 mechanism and neighboring group effect, leading to the retention of the configuration.  相似文献   

3.
《Tetrahedron: Asymmetry》2001,12(14):2009-2011
A novel stereoselective synthesis of (−)-cytoxazone 1 was achieved via addition of p-methoxyphenylmagnesium bromide to the benzylimine derived from (S)-2,3-O-isopropylidene glyceraldehyde followed by one-step regioselective cyclization of N-Boc amino diol 7.  相似文献   

4.
《Tetrahedron: Asymmetry》2007,18(7):803-813
A variety of synthetic routes to (−)-cytoxazone 1, a cytokine modulator isolated from Streptomyces cultures, and its stereomers 2 and regioisomers 3 have been reviewed.  相似文献   

5.
A short and efficient method for synthesizing epi-cytoxazone via the corresponding oxazoline intermediate was developed. The formation of the oxazoline ring, which proceeds through an SN1 mechanism to ensure that the trans-oxazoline stereochemistry is retained, was induced by intramolecular benzylic substitution of a 1,2-bis-trichloroacetimidate, starting from the known enantiomerically pure diol.  相似文献   

6.
The diastereoselective imino 1,2-Wittig rearrangement of hydroximates provides a novel method for the construction of optically active α-hydroxy oxime ethers. Upon treatment with LDA, allyl p-methoxyphenylhydroximate carrying a chiral auxiliary smoothly underwent diastereoselective rearrangement to give the (R)-α-hydroxy oxime ether which was effectively converted into (+)-cytoxazone.  相似文献   

7.
A short and efficient enantioselective synthesis of (−)-cytoxazone and its stereoisomer (+)-epi-cytoxazone, novel cytokine modulators, has been described with good yield and enantioselectivity. Ti-catalyzed Sharpless asymmetric epoxidation of allyl alcohol and l-proline catalyzed three-component Mannich reaction constitute the key steps in introducing stereogenicity into the molecule.  相似文献   

8.
Imine auxiliaries including chiral N-tert-butanesulfinyl imines have been successfully utilized to provide stereochemical control to the reductive cross-coupling of imines with aldehydes or ketones. This methodology has been applied to the synthesis of (−)-cytoxazone.  相似文献   

9.
Om V. Singh 《Tetrahedron letters》2007,48(40):7094-7098
Ir(I)-catalyzed intermolecular allylic amidation of ethyl allyl carbonates with soft nitrogen nucleophiles under completely ‘salt-free’ conditions is described. A combination of [Ir(COD)Cl]2, a chiral phosphoramidite ligand L, and DBU as a base in THF effects the reaction. The reaction appears to be quite general, accommodating a wide variety of R-groups and soft nitrogen nucleophiles, and proceeds with excellent regio- and enantioselectivities to afford the branched N-protected allylic amines. The developed reaction was conveniently utilized in the asymmetric synthesis of N-Boc protected α- and β-amino acids as well as (−)-cytoxazone.  相似文献   

10.
The NaIO4-mediated asymmetric bromohydroxylation of α,β-unsaturated carboxamides was achieved using lithium bromide as the bromine source under acidic conditions at rt to afford the corresponding chiral α-bromo-β-hydroxy carboxamides. Excellent yields (77-90%) and diastereoselectivities (up to 10:1) along with exclusive control over regio- as well as anti-selectivity are the main features with a good scope of substrates. The method has successfully been applied in the enantioselective syntheses of two biologically important molecules, viz (−)-cytoxazone and l-threo-DOPS (droxidopa).  相似文献   

11.
A short and efficient strategy for the synthesis of (?)-cytoxazone, (?)-4-epi-cyoxazone and their analogues by using DDQ mediated diastereoselective intermolecular benzylic amination has been described. Immunological evaluation of their cytokine modulating activity revealed that the change of hydroxy methyl to methyl group increased the cellular immunity in in-vitro cultures. Changes in the stereochemistry of oxazolidine haven't influenced the biological activity.  相似文献   

12.
A convenient and efficient synthesis of 1,2-azido alcohols has been achieved by regioselective ring opening of epoxides using NaN3 and 4 Å molecular sieves in acetonitrile. The utility of this method has been demonstrated by achieving a short synthesis of (−)-cytoxazone in 48% overall yield.  相似文献   

13.
Kim JD  Kim IS  Jin CH  Zee OP  Jung YH 《Organic letters》2005,7(18):4025-4028
The total synthesis of (-)-cytoxazone 1 was achieved in six linear steps (34% overall yield) from p-anisaldehyde. The key steps in this route are the regioselective and stereoselective introduction of a N-protected amine group, using the CSI reaction of the anti-1,2-dimethyl ether 3, and the subsequent regioselective cyclization of the N-protected amino diol 13 to give the 2-oxazolidinone unit of (-)-cytoxazone 1. [reaction: see text]  相似文献   

14.
The synthetic correlation between two different antibiotic frameworks, the beta-lactams and 2-oxazolidinones, is described for the first time. In this approach, 2-oxazolidinones are prepared in stereomerically pure form from 3-hydroxy beta-lactams by a ring-opening-cyclization isomerization process. Application of this methodology to the total synthesis of the cytokine modulator, (-)-cytoxazone, and its three stereoisomers is demonstrated. [reaction: see text].  相似文献   

15.
A copper catalyst with a chiral pyridine-2,6-bisoxazoline (pybox) ligand was used to convert a variety of propargylic esters with different side chains (R=Ar, Bn, alkyl) into their amine counterparts in very high yields and with good enantioselectivities (up to 90% enantiomeric excess (ee)). Different amine nucleophiles were applied in the reactions and the highest enantioselectivities were obtained for aniline and its analogues. Interestingly, some carbon nucleophiles could also be used and with indoles excellent ee values were obtained (up to 98% ee). The versatility of the propargylic amines obtained was demonstrated by their further elaboration to formal total syntheses of the antibiotic (+)-anisomycin and the cytokine modulator (-)-cytoxazone.  相似文献   

16.
The sol-gel transition in aqueous gellan gum solutions induced upon cooling was investigated by rheology measurements. The gelation temperature was determined from the crossover point of storage and loss moduli, i.e., G′ = G′′ (Tc) and from the Winter’s criterion (Tgel), respectively, which increased with gellan concentration. Tgel was higher than Tc and the difference became larger as the gellan concentration got higher. The relaxation critical exponent n was estimated with the Winter’s method and the self-similarity was observed from the critical gel. The scaling for the zero-shear viscosity η0 before the gel point and the equilibrium modulus Ge after the gel point was established against the relative distance ε from the gel point over the gellan concentration Cg of 1.0-2.5 wt%, giving the critical exponents k and z. The critical exponent n calculated from k and z agrees well with n from the Winter’s criterion. However, no universal n was found for the gelation in aqueous gellan gum solutions, indicating that this gelation should be classified into the cross-linking category for the physical gelation. The critical exponent n decreased with increasing Cg for the gellan gum solution. The fractal dimension df calculated from n with the screened hydrodynamic interaction and the excluded volume effect suggested a denser structure in the critical gel with higher Cg.  相似文献   

17.
Phase relations of rutile, freudenbergite, and hollandite structures were examined in the pseudobinary system NaCrO2-TiO2 (i.e., NaxCrxTi8−xO16) at 1350 °C. The hollandite structure was obtained in the composition range 1.7?x?2.0. The symmetry of the samples at room temperature was tetragonal for x=1.7 and 1.75, and monoclinic for x=1.8 and above. Single crystals of monoclinic hollandite Na2Cr2Ti6O16 were grown and the structure refinement has been carried out using an X-ray diffraction technique. The space group was I2/m and cell parameters were a=10.2385(11), b=2.9559(9), c=9.9097(11)Å, and β=90.545(9)° with Z=1. The Na ion distribution in the tunnel was markedly deformed from that in the tetragonal form. It was suggested that Cr/Ti ratios were different between the two framework metal sites.  相似文献   

18.
The temperature dependence of the viscosity of dilute polybutadiene solutions has been described by an Arrhenius expression according to Moore's treatment. The activation energy of flow was found to depend on both concentration and molecular weight through an empirical parameter, Ke. This parameter was positive in toluene, zero in decalin and negative in dioxane. This behaviour is discussed in connection with the temperature dependence of the expansion coefficient (xη) and the excluded volume parameter (z). A recent Yamakawa-Tanaka expression relating xη and z was used in the theoretical calculation of Ke.  相似文献   

19.
The solid solution of YMn1−xFexO3 (x=0.0, 0.1, 0.2, 0.3, 0.5, 1.0) was synthesized from the citrate precursor route. The hexagonal crystal structure related to YMnO3 was stable for x?0.3. Rietveld refinement was carried out on the composition for x=0.3 and was refined to a major hexagonal phase (∼97%) with 3% of orthorhombic Y(Fe/Mn)O3 phase. The a-axis lattice constant increases and the c-axis lattice constant decreases with x for x?0.2. The increase in the c-axis lattice constant at x=0.3 could be due to the doping of significant amount of d5 ion (high spin Fe3+ ion) in a trigonal bipyramidal crystal field. The detailed structural, magnetic and dielectric properties are discussed.  相似文献   

20.
《Tetrahedron: Asymmetry》1998,9(7):1171-1178
The levorotatory enantiomer of t-butylsulfinylacetic acid 3 was obtained in the reaction of the α-carbanion of (+)-t-butyl methyl sulfoxide 1 with carbon dioxide. The same enantiopure form of the acid 3 was isolated from its diastereomerically pure levorotatory salt 5 with (−)-(1R,2S)-ephedrine. The structure of this salt was determined by X-ray analysis and the absolute configuration (S) at sulfur was ascribed to the t-butylsulfinylacetate anion. Consequently, the absolute configuration (S) was assigned to the acid (−)-3 and its precursor (+)-t-butyl methyl sulfoxide 1.  相似文献   

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