6884-01-1Relevant academic research and scientific papers
Total Synthesis of the Naturally Occurring Glycosylflavone Aciculatin
Yao, Chun-Hsu,Tsai, Chi-Hui,Lee, Jinq-Chyi
, p. 1719 - 1723 (2016/08/02)
The new flavone-glycoside aciculatin (1), from Chrysopogon aciculatus, has been shown to have cytotoxic, anti-inflammatory, and antiarthritis activity. Further biological studies have been limited because of the limited availability of 1 from natural sources. Herein the first total synthesis of 1 in an overall yield of 8.3% is described. The synthesis involved the regio- and stereoselective glycosylation-Fries-type O-to-C rearrangement to construct the C-aryl glycosidic linkage, followed by a Baker-Venkataraman rearrangement and cyclodehydration to form the flavone scaffold.
Evidence of cation-coordination involvement in directing the regioselective di-inversion reaction of vicinal di-sulfonate esters
Hevey, Rachel,Ling, Chang-Chun
, p. 1887 - 1895 (2013/04/23)
Direct evidence has been obtained to confirm the unusual nucleophilic attack of an alkoxide at the S-center of sp3-hybridized sulfonyl esters. The unusual reaction pathway leads to S-O bond scission which is crucial for the regio- and stereoselective conversion of 2,3-di-O-sulfonates of 4,6-O-benzylidene-β-d-galactopyranosides into β-d-idopyranosides. In addition, strong evidence has been provided to clarify the role of the alkali counter-cation in the transformation. The cation is believed to influence the reaction rate via coordination to an oxygen in the sulfonate ester; the presence of a neighboring ring oxygen oriented in a cis-relationship greatly enhances reactivity of the sulfonyl ester.
A scalable approach to obtaining orthogonally protected β-d-idopyranosides
Hevey, Rachel,Morland, Alizee,Ling, Chang-Chun
scheme or table, p. 6760 - 6772 (2012/09/25)
A practical method to obtain orthogonally protected d-idopyranose from d-galactose has been developed, which is the first method to enable synthesis of the challenging β-d-idopyranoside linkage. The method relies on a key double inversion at O-2 and O-3 in an easily prepared d-galactose derivative, which proceeds regio- and stereoselectively through a 2,3-anhydrotalopyranoside; reaction using a selection of alkoxides affords exclusively the 3-O-alkylidopyranoside, which can be used to generate an orthogonally protected monosaccharide. The process is scalable and requires minimal purification, so it could be used to produce building blocks to aid in the synthesis of various β-idopyranose-containing oligosaccharide targets to further probe their biological functions.
A rapid and facile preparation of methyl 4,6-O-benzylidene-α-D-glucopyranoside and some related compounds
Joseph, Cosam C.,Zwanenburg, Binne,Chittenden, Gordon J. F.
, p. 493 - 497 (2007/10/03)
A simple and rapid benzylidenation procedure for preparing the title compound and other related derivatives using tin(II) triflate and other triflate salts as catalysts is described.
2-Diphenylarsino-, 2-diphenylphosphinyl-, and 2-triphenylstannyl-derivatives of methyl 4,6-O-benzylidene-2-deoxy-α-D-altropyranoside. Crystal structure of the phosphinyl derivative
Brown, Martyn A.,Cox, Philip J.,Howie, R. Alan,Melvin, Olga A.,Taylor, Oonah J.,Wardell, James L.
, p. 275 - 282 (2007/10/02)
Reaction of methyl 2,3-anhydro-4,6-O-benzylidene-α-D-allopyranoside (3) with PhnMLi gives methyl 4,6-O-benzylidene-2-deoxy-2-M-α-D-altropyranoside (4; M=Ph2As, Ph2P or Ph3Sn).Compound (4, M=Ph2P) is readily oxidised in air to the phosphinyl derivative (4, M=Ph2P(O)).Characterisation of (4, M=Ph2As, Ph2P(O), or Ph3Sn) was achieved by NMR spectroscopy, including solid state NMR spectroscopy, for (4, M=Ph2As) and (4, M=Ph3Sn), and by X-ray crystallography for .In the solid state both the benzylidene and pyranose rings in , adopt chair conformations.The pentavalent phosphorus atom has a distorted tetrahedral geometry with C-P-C valency angles in the narrow range from 105.7(3) to 106.0(3) deg and the C-P-O valency angles ranging from 111.3(3) to 115.6(2) deg; the P-Caryl bond lengths are 1.808(5) and 1.815(6) Anagstroem, while the P-Calkyl bond length is slightly larger, being 1.829(6) Angstroem.Intermolecular H-bonding, involving HO and O(P) centres, links the molecules in the crystal.Keywords: Tin; Phosphorus; Arsinic; Pyranosides; Crystal structure
Studies of the Mechanistic Diversity of Sodium Cyanoborohydride Reduction of Tosylhydrazones
Miller, Vaughn P.,Yang, Ding-yah,Weigel, Theresa M.,Han, Oksoo,Liu, Hung-wen
, p. 4175 - 4188 (2007/10/02)
Reduction of tosylhydrazone derivatives of ketones and aldehydes with sodium cyanoborohydride in acidic medium is a mild, albeit versatile, deoxygenation reaction.The reaction mechanism has been proposed to proceed via either a direct hydride attack route or a tautomerization-then-reduction route.By using a mild reduction procedure (NaBH3CN, THF-MeOH, 0 deg C), it has been possible to stop the deoxygenation halfway and isolate the nascent tosylhydrazine product.Characterization of the resulting hydrazine to define the origin of the hydrogen being delivered to theformer carbonyl carbon has allowed us to unambiguously distinguish between these two possible mechanisms.Studies of reduction of tosylhydrazones derived from conjugated and saturated ketones confirmed earlier speculation that these reductions occur through a direct hydride attack mechanism.The reduction of para-substituted methyl phenyl ketone tosylhydrazones revealed a competition between these two mechanisms.Substrates bearing electron-donating substituents prefer to direct hydride attack pathway, while those with electron-withdrawing substituents favor an initial tautomerization prior to reduction.Sugar and hydroxyl ketone tosylhydrazones are also reduced by competing mechanisms.The mechanistic diversity in those cases may be attributed to the inductive effects compelled by the α substituents and the conformational constraints imposed by the ring structure.The mechanistic insights gained from these studies indicate that the direct hydride attack mechanism is the main reaction pathway due to the propensity of NaBH3CN to selectively attack the iminium ion.The tautomerization-then-reduction mechanism prevails only when the tautomerization of hydrazon to azohydrazine is facilitated.
Total Synthesis of (+)-Colletodiol: New Methodology for the Synthesis of Macrolactones
Keck, Gary E.,Boden, Eugene P.,Wiley, Michael R.
, p. 896 - 906 (2007/10/02)
Synthetic efforts directed toward two different structures suggested for the macrocyclic bis(lactone) colletodiol are detailed.The initial approach to an incorrect structure (C11 epi) relies upon the manipulation of methyl α-D-glucopyranoside to set the required stereochemistry for the C8-C14 segment of the C11 epi structure.The second approach, initiated after structural revision based upon X-ray crystallographic evidence, employs a Lewis acid mediated addition of allylstannane 33 to β-alkoxy aldehyde 34 to set the stereochemistry of the C8-C14 subunit.This route, which employs a number of new synthetic reactions developed specifically for this problem, gives (+)-colletodiol in nine linear operations and 8.2percent overall yield.
SYNTHESIS OF 3,6-DIDEOXY-3-(METHYLAMINO)HEXOSES FOR G.L.C.-M.S. IDENTIFICATION OF RHIZOBIUM LYPOSACCHARIDE COMPONENTS
Hollingsworth, Rawle I.,Hrabak, Estelle M.,Dazzo, Frank B.
, p. 103 - 114 (2007/10/02)
A direct synthetic route from methyl α-D-glucopyranoside to 3,6-dideoxy-3-(methylamino)hexoses having the D-gluco, D-galacto, and D-manno configurations has been developed.Methyl α-D-glucoside was converted into the 4,6-O-benzylidene-2,3-di-O-tosyl derivative, which was then transformed into the 4-O-benzyl-6-deoxy 2,3-ditosylate (5) by successive reductive cleavage of the acetal ring, iodination, and reduction.The intermediate 5 was readily converted into the allo 2,3-epoxide, which yielded the pivotal intermediate methyl 4-O-benzyl-3,6-dideoxy-3-(methylamino)-α-D-glucopyranoside (7) by cleavage of the oxirane ring with methylamine.The amino compound 7 can be directly converted into the derivatized galacto and manno derivatives for mass-spectrometric identification by selective inversion at C-4 and C-2, respectively, followed by hydrolysis, reduction, and acetylation.
Stereochemical dependence of the mechanism of deoxygenation, with lithium triethylborohydride, in 4,6-O-benzylidenehexopyranoside p-toluenesulfonates
Baer, Hans H.,Mekarska-Falicki, Miroslawa
, p. 3043 - 3052 (2007/10/02)
Lithium triethylborohydride was shown to react with methyl 4,6-O-benzylidene-α-D-hexopyranoside 2- and 3-tosylates, and 2,3-ditosylates, in the manno, allo, and altro configurational series both by O-S fission (O-desulfonylation) and by C-O fission (C-desulfonyloxylation), to produce carbinol and deoxy functions, respectively.The results were compared with those previously obtained with the corresponding gluco and galacto isomers, and the degree of facility of the cleavage reactions was seen to depend on the position of the sulfonic ester groups and the overall configuration of the molecules.The mechanism of reductive desulfonyloxylation also depended on configuration and was demonstrated to involve intermediary epoxide formation or displacement by internal hydride shift as the principal paths; competing elimination and direct nucleophilic displacement were found to occur in the allo series, whereas reduction accompanied by ring contraction has thus far been encountered only in the conformationally less constrained, cis-fused acetal system of the galacto series.Like the borohydride reagent, lithium aluminum hydride was found to react (though much more slowly) with the altro 2,3-ditosylate by the epoxide-mediated mechanism, although the latter hydride is known to desulfonyloxylate the α-D-gluco-isomer by a different, intramolecular reduction mechanism.
SELECTIVE ESTERIFICATION OF METHYL 4,6-O-BENZYLIDENE-α-D- AND β-D-GALACTOPYRANOSIDE IN A CATALYTIC TWO-PHASE SYSTEM
Szeja, Wieslaw
, p. 1803 - 1808 (2007/10/02)
Selective tosylation of methyl 4,6-O-benzylidene-α-D- (1) and β-D-galactopyranoside (8) in a catalytic two-phase system (CTP system) yields preferentially 2-O-p-toluenesulfonate and 3-O-p-toluenesulfonate, respectively.In the course of unimolar benzoylation of 1 and 8, under similar conditions, a migration of the acyl group takes place and an equilibrium mixture is obtained.Esterification of 1 and 8 with benzoyl chloride under CTP conditions, in presence of an aqueous sodium hydroxide solution, saturated with sodium perchlorate, afforded in preponderant yields 2-O-benzoate and 3-O-benzoate, respectively.
