Approaches to the Synthesis of Glycosides

<p>In a search for better synthetic routes to O- and S-glycosides, a number of mercury(II) containing derivatives of 1-thio-D-glucose were synthesised, and their reactions with thiols and acids were investigated as well as their pyrolytic behaviour. A new route to O-acetylated glycosyl thiols involving specific S-deacetylation of peracetylated 1-thioglycoses was developed by the conversion of 1-thio-Beta-D-glucopyranose pentaacetate into tetra-O-acetyl-1-S-phenylmercury (II) thio-Beta-D-glucopyranose and subsequent demercuration of this by hydrogen sulphide. A range of acylated alkyl and aryl 1,2-trans-1-thioglycosides was prepared by one step processes from peracylated 1,2-trans-related sugars by a procedure which involved the use of equimolar proportions of thiols together with boron trifluoride. A similar procedure was used to obtain benzoylated 1,2-cis-O-glucosides from penta-O-benzoyl-Beta-D-glucopyranose. Partial desulphurisation of acetylated glucosyl phenyl disulphide with tris(diethylamino)phosphine led to both phenyl tetra-O-acetyl-1-thio-alpha-D-glucopyranoside and the alpha, beta-linked thiotrehalose peracetate. Phenyl 1-thiohex-1-enopyranosid-3-ulose esters were obtained from the light induced reactions of N-bromosuccinimide with acetylated and benzoylated phenyl 1-thiogluco- and galacto-pyranosides; the acetylated 1-thioglycosides gave mixtures of 2-O-acetyl and 2-O-monobromoacetyl 1-enosid-3-uloses. Methyl hexuronate derivatives were brominated alpha to the carbonyl function by N-bromosuccinimide, and a new synthetic route to L-ascorbic acid has been proposed following the successful bromination of methyl tri-O-acetyl-2,6-anhydro-L-gulonate.</p>

Approaches to the Synthesis of Glycosides

<p>In a search for better synthetic routes to O- and S-glycosides, a number of mercury(II) containing derivatives of 1-thio-D-glucose were synthesised, and their reactions with thiols and acids were investigated as well as their pyrolytic behaviour. A new route to O-acetylated glycosyl thiols involving specific S-deacetylation of peracetylated 1-thioglycoses was developed by the conversion of 1-thio-Beta-D-glucopyranose pentaacetate into tetra-O-acetyl-1-S-phenylmercury (II) thio-Beta-D-glucopyranose and subsequent demercuration of this by hydrogen sulphide. A range of acylated alkyl and aryl 1,2-trans-1-thioglycosides was prepared by one step processes from peracylated 1,2-trans-related sugars by a procedure which involved the use of equimolar proportions of thiols together with boron trifluoride. A similar procedure was used to obtain benzoylated 1,2-cis-O-glucosides from penta-O-benzoyl-Beta-D-glucopyranose. Partial desulphurisation of acetylated glucosyl phenyl disulphide with tris(diethylamino)phosphine led to both phenyl tetra-O-acetyl-1-thio-alpha-D-glucopyranoside and the alpha, beta-linked thiotrehalose peracetate. Phenyl 1-thiohex-1-enopyranosid-3-ulose esters were obtained from the light induced reactions of N-bromosuccinimide with acetylated and benzoylated phenyl 1-thiogluco- and galacto-pyranosides; the acetylated 1-thioglycosides gave mixtures of 2-O-acetyl and 2-O-monobromoacetyl 1-enosid-3-uloses. Methyl hexuronate derivatives were brominated alpha to the carbonyl function by N-bromosuccinimide, and a new synthetic route to L-ascorbic acid has been proposed following the successful bromination of methyl tri-O-acetyl-2,6-anhydro-L-gulonate.</p>

Glycyrrhetinic amides and their cytotoxicity

3-<em>O</em>-Acetyl-glycyrrhetinic amides were prepared, and sulforhodamine B assays investigated their cytotoxicity. Their cytotoxicity strongly depended on the substitution pattern of the respective compounds. Thereby, an ethylenediamine-derived compound <strong>2</strong> performed the best, acting mainly by apoptosis. As far as heterocyclic amides are concerned, ring enlargement and the replacement of the distal nitrogen invariably led to a more or less complete loss of cytotoxic activity. Thus, the presence of a carbonyl function (C-30) seems necessary for providing significant cytotoxicity.

Crystal structure of 2-oxo-1,2-diphenylethyl diisopropylcarbamate

The title compound, C21H25NO3, crystallized as a racemic twin in the Sohnke space group P21. In the molecular structure of the title compound, both enantiomers show a highly similar conformation with the urethane function and the benzoyl group showing an almost perpendicular arrangement [the dihedral angle is 72.46 (8)° in the S-enantiomer and 76.21 (8)° in the R-enantiomer]. In the crystal structure, molecules of both enantiomers show infinite helical arrangements parallel to the b axis formed by weak C—H...O hydrogen bonds between the phenyl ring of the benzoyl group and the carbamate carbonyl group. In case of the R-enantiomer, this helix is additionally stabilized by a bifurcated hydrogen bond between the carbonyl function of the benzoyl group towards both phenyl groups of the molecule.

Wittig Reactions of Maleimide Derived Stabilized Ylides with Alkyl Pyruvates: Concise Approach to Methyl Ester of (±)-Chaetogline A

A facile synthesis of methyl ester of chaetogline A is reported starting from the corresponding methyl 1-methyltryptophanate derived maleimide. A stereoselective Wittig olefination with a carbonyl function in methyl pyruvate followed by phosphorous pentoxide induced regioselective dehydrative cyclization are the essential reactions. An acid induced thermodynamically driven stereoselective β- to α-position migration of the exocyclic carbon−carbon double unit in ethyl tetrahydroindolizinoindolylidenepropanoate is described.

Recent Advances in Chemistry and Biological Activity of 2,6-Diphenyl piperidines

: The review discusses different methods for preparation of 2,6-diphenyl-piperidin-4-one derivatives. 2,6-Diphenyl-piperidin-4-one is prepared from aromatic aldehyde and acetone in ammonium acetate. Reaction of 1-phenylsulfinylpropan-2-one or 1-(4-chlorophenylsulfinyl)propan-2-one, aromatic aldehyde and ammonium acetate gives a series of 2,6-diaryl-2,3-dihydro-1H-pyridin-4-one 6a,b. 4-Phenyl-2-amino-1,3-butadienes reacts with N-allyl benzaldimine through Diels-Alder reaction to afford 2,6-diphenyl-4-piperidinone derivative 7. Also, reactions of 2,6-diphenyl-piperdin-4-one are discussed. The reactions of latter compounds can be on nitrogen atom or carbonyl function group or methylene group adjacent to carbonyl group. In addition, different applications of 2,6-diphenyl-piperidin-4-one are summarized.

Inter- and Intramolecular [2+2+2] Cycloaddition of Alkyne Triple Bonds to the Carbonyl Function of Aldehydes and Ketones Enabled by η5-Cyclopentadienylcobalt(L)(L′)

Abstract1,7-Octadiyne underwent [2+2+2] cycloaddition to acetone in the presence of η5-cyclopentadienylcobalt(L)(L′) complexes to give (η5-cyclopentadienyl)[(1,4,4a,8a-η4)-5,6,7,8-tetrahydro-3,3-dimethyl-3H-2-benzopyran]cobalt, in which the two triple bonds and the carbonyl moiety have combined to engender a 2H-pyran ring complexed to CpCo. The scope of this reaction was explored, including cocyclizations of ynals and ynones with bis(trimethylsilyl)acetylene, as well as all-intramolecular reorganizations of α,ω-diynals and -diynones. Two major trajectories were observed in the case of aldehydes, the (often minor) [2+2+2] pathway and a competing trail featuring a formal 1,5-hydride shift that results in CpCo–dienones. The latter is obviated for ketone substrates. Preliminary chemistry of selected complexes uncovered unprecedented reactions, such as acid-catalyzed ring openings and additions of amines, the latter providing access to novel carbon frames.

Mild Deprotection of Dithioacetals by TMSCl / NaI Association in CH3CN

<p><a>We showed for the first time, the fundamental role<b> </b>of CH₃CN associated to TMSCl/NaI combination to deprotect S,S-ethylene- and S,S-propylene-ketals into ketones. Indeed, if the TMSCl/NaI association leads to the reduction of dithioketals in CH₂Cl₂, we have demonstrated that this association can be used to deprotect a large variety of various dithioketals into ketones in CH₃CN. Otherwise, under mild experimental conditions, O,O-acetals as well as O,S-oxathianes were cleanly deprotected with high yields. It is also possible to easily regenerate the carbonyl function of various hydrazones and imines using this novel protocol. We believe that this metal-free process is a good alternative to other known methodologies used to deprotect dithioketals into ketones.<b></b></a></p><table></table><br>

Mild Deprotection of Dithioacetals by TMSCl / NaI Association in CH3CN

<p><a>We showed for the first time, the fundamental role<b> </b>of CH₃CN associated to TMSCl/NaI combination to deprotect S,S-ethylene- and S,S-propylene-ketals into ketones. Indeed, if the TMSCl/NaI association leads to the reduction of dithioketals in CH₂Cl₂, we have demonstrated that this association can be used to deprotect a large variety of various dithioketals into ketones in CH₃CN. Otherwise, under mild experimental conditions, O,O-acetals as well as O,S-oxathianes were cleanly deprotected with high yields. It is also possible to easily regenerate the carbonyl function of various hydrazones and imines using this novel protocol. We believe that this metal-free process is a good alternative to other known methodologies used to deprotect dithioketals into ketones.<b></b></a></p><table></table><br>

Synthesis and Investigation of Pinane-Based Chiral Tridentate Ligands in the Asymmetric Addition of Diethylzinc to Aldehydes

A library of pinane-based chiral aminodiols, derived from natural (−)-β-pinene, were prepared and applied as chiral catalysts in the addition of diethylzinc to aldehydes. (−)-β-Pinene was reacted to provide 3-methylenenopinone, followed by a reduction of the carbonyl function to give a key allylic alcohol intermediate. Stereoselective epoxidation of the latter and subsequent ring opening of the resulting oxirane with primary and secondary amines afforded aminodiols. The regioselectivity of the ring closure of the N-substituted secondary aminodiols with formaldehyde was examined and exclusive formation of oxazolidines was observed. Treatment of the allylic alcohol with benzyl bromide provided the corresponding O-benzyl derivative, which was transformed into O-benzyl aminodiols by aminolysis. Ring closure of the N-isopropyl aminodiol derivative with formaldehyde resulted in spirooxazolidine. The obtained potential catalysts were applied in the reaction of both aromatic and aliphatic aldehydes to diethylzinc providing moderate to good enantioselectivities (up to 87% ee). Through the use of molecular modeling at an ab initio level, this phenomenon was interpreted in terms of competing reaction pathways. Molecular modeling at the RHF/LANL2DZ level of theory was successfully applied for interpretation of the stereochemical outcome of the reactions leading to display excellent (R) enantioselectivity in the examined transformation.