Stereoselective syntheses of polyhydroxylated azepane derivatives from sugar-based epoxyamides. Part 1: synthesis from d-mannose

An approach to the synthesis of polyhydroxyazepane derivatives from sugar-based epoxyamides or epoxyalcohols, in which the total regioselective epoxide opening by nitrogen nucleophiles is the key step, is described. Thus, novel polyhydroxyazepane carboxamides and aminomethyl polyhydroxyazepanes, with potential pharmacological interest, are synthesized from diacetone d-mannose. Configurational assignments of the obtained products were determined.     

Fourier transform Raman studies of materials and compounds of biological importance—II. The effect of moisture on the molecular structure of the alpha and beta anomers of d-glucose

The effects of small amounts of water added to the alpha and beta anomers of d-glucose have been investigated. The monohydrate of alpha-d-glucose was formed under these conditions and its FT-Raman spectrum has been recorded for the first time. The combination of crystallographic data and vibrational spectroscopy, based on the study of alpha and beta d-glucose, with special emphasis on conformation and configuration sensitive modes, enabled band assignments to be made for the monohydrate of alpha-d-glucose.     

Iminosugars from α,β-epoxyamides. Part 1: Synthetic approach to hydroxylated piperidine derivatives

A new synthetic route towards iminosugars starting from chiral epoxyamides is described. The strategy, by which a single precursor, the α,β-epoxyamide obtained from 6-O-trityl-2,3-O-isopropylidene-d-ribose and a sulphur ylide, can be transformed into different iminosugars, is based on the combination of a regioselective epoxide opening and stereospecific intramolecular displacements.     

Iminosugars from α,β-epoxyamides. Part 2: Synthetic approach to hydroxylated pyrrolidine and azepane derivatives

This paper describes a new synthetic route towards hydroxylated pyrrolidines and azepane derivatives starting from chiral epoxyamides. The alternate transformations on a ribose derivative α,β-epoxyamide permit the construction of five or seven member rings leading to different precursors of homoiminosugars.     

Amperometric simultaneous sensing system for d-glucose and l-lactate based on enzyme-modified bilayer electrodes

An amperometric biosensor system which uses screen-printed electrodes to simultaneously detect d-glucose and l-lactate has been developed and applied for simple and rapid determination of d-glucose and l-lactate levels in lactic fermenting beverages. The system was constructed from three-dimensionally layered electrodes. Taking into consideration the effects of easily oxidized substances contained in the samples, ferricyanide ions, which are electrochemically oxidized at a lower voltage, were chosen as a mediator. A linear relationship between steady-state current and concentration was found over a range of 1-100 mM (d-glucose) and 1-50 mM (l-lactate); the variation coefficients were 1.43% (n = 10) and 3.50% (n = 10) for the d-glucose and l-lactate sensors, respectively. When applied to lactic fermenting beverages, there was good agreement between the results obtained by the proposed sensing system and those obtained by the HPLC method. Using the proposed method, assays were completed within 5 min.     

Isomerization of E-α,β-epoxyamides to Z-α,β-epoxyamides and synthetic applications based on regio- and stereoselective oxirane ring openings

The regioselective opening reaction of 2,3-epoxyamides with various nucleophiles offers a variety of β-hydroxyamides with diverse synthetic utility depending on the introduced nucleophile. Due to the exclusive stereoselectivity in the formation of trans epoxyamides in reactions of aldehydes with stabilized sulfur ylides, we studied the isomerization of trans epoxyamides into the cis isomers with the objective of obtaining the corresponding syn opening products, which together with the anti isomers represent a variety of enantiomerically pure building blocks.     

Highly enantioselective darzens reaction of a camphor-derived sulfonium amide to give glycidic amides and their applications in synthesis

The reaction of an amide-stabilized sulfonium ylide bearing chiral groups on sulfur has been investigated. We have discovered that the camphor-derived amide-stabilized ylide reacts with aldehydes at -50 degrees C in ethanol to give glycidic amides in one step with up to 99% ee and complete diastereoselectivity. From analyzing reactions of different ratios of diastereomers at sulfur it was found that the major diastereomer gave very high enantioselectivity, while the minor one gave much lower selectivity (54% ee). Further mechanistic studies have revealed that enantioselectivity is controlled not in the betaine-forming step (C-C bond formation is reversible) but in the different barriers to bond rotation around the newly formed C-C of the two diastereomeric betaines. Further transformations of epoxyamides were investigated. It was found that epoxyamides could be converted into epoxyketones by reaction with organolithium reagents and that they could be ring-opened by nucleophiles with complete regioselectivity using Yb(OTf)3. The practicality of the process has been exemplified in the synthesis of SK&F 104353, a leukotriene D4 antagonist in the potential treatment of bronchial asthma.     

Carbohydrate-based approach to four enantiomerically pure 2-naphthylmethyl 3-hydroxy-2-methylbutanoates

Chiral pool approach using d-glucose, l-xylose, and d- and l-arabinoses was used to obtain four stereoisomeric 3-hydroxy-2-methylbutanoic acids with well defined configurations. The acids were isolated as fluorescent 2-naphthylmethyl esters after reaction with 2-naphthyldiazomethane.     

Assembly state of catalytic modules as chiral switches in asymmetric Strecker amino acid synthesis

Self-assembled chiral polymetallic complexes often demonstrate novel properties as asymmetric catalysts. We report the three-dimensional structures of two such asymmetric catalysts (crystals A and B) for Strecker alpha,alpha-disubstituted amino acid synthesis. These complexes are constructed via assembly of the same chiral modules derived from d-glucose, but their assembly modes differ. The enantioselectivity in the Strecker reaction was dramatically switched, depending on which assembly mode was used: the catalyst generated in situ whose structure is represented by crystal B, or by crystal A. These findings provide insight into the functional importance of higher-order structures of an artificial catalyst.     

Parallel synthesis of modular chiral Schiff base ligands and evaluation in the titatium(IV) catalyzed asymmetric trimethylsilylcyanation of aldehydes

Highly modular tridentate Schiff base ligands arising from enantiopure epoxyalcohols have been prepared and evaluated in catalysis using parallel methods. The key structural motifs and experimental parameters have been identified, allowing enantioselectivities of up to 77% ee in the titatium-catalyzed trimethylsilyl cyanide addition to aldehydes.     

Asymmetric dihydroxylation of d-glucose derived alpha,beta-unsaturated ester: synthesis of azepane and nojirimycin analogues

The asymmetric dihydroxylation of a d-glucose derived alpha,beta-unsaturated ester 3 afforded syn vicinal diols in good to high diastereoselectivity. The conversion of these vicinal diols to the corresponding cyclic sulfate, regio-, stereoselective nucleophilic ring opening by sodium azide, and LAH reduction afforded amino heptitols 7a,b that were converted to azepane 1c,d and nojirimycin analogues 2c,d.     

Fluorination of carbinols with 2,2-difluoro-1,3-dimethylimidazolidine in ionic liquid

The utility of ionic liquids for fluorination using 2,2-difluoro-1,3-dimethylimidazolidine (DFI) is described. Further, the fluorination of chiral epoxyalcohols gave the chiral monofluoromethylated epoxides.     

Electronically promoted Payne rearrangement of 3-CF3-2,3-epoxyalcohols

[reaction: see text] Smooth and selective Payne rearrangement was achieved for the above types of epoxyalcohols with a CF(3) group so as to form thermodynamically more stable alkoxides, where the strongly electron-withdrawing nature of this moiety played a significantly important role and was proved to overcome increased steric instability of epoxides from syn-E to anti-Z isomers.     

Radiation-induced molecular imprinting of d-glucose onto poly(2-hydroxyethyl methacrylate) matrices using various crosslinking agents

Radiation-induced molecular imprinting of d-glucose onto poly(2-hydroxyethyl methacrylate) matrix was achieved to create three-dimensional cavities to recognize and bind d-glucose. The optimization of imprinting capability of matrices was achieved by investigating the effects of various parameters such as the type and amount of crosslinking agent, type of solvent, template to monomer ratio and total absorbed dose. Crosslinking agents with increasing chain lengths and different flexibilities were used in an attempt to elucidate the impact of relevant imprint parameters on the effectiveness of imprinting technique. The absorbed dose varied from 1 to 15 kGy. Cavity sizes of MIPs were measured by positron annihilation lifetime (PAL) experiments. Control matrices were synthesized with exactly the same composition in the absence of d-glucose. Separation of d-glucose has been shown to be successfully achieved in HPLC columns filled with MIPs whereas no separation was observed for non-imprint matrices.     

Synthesis of ertugliflozin from d-glucose

A new synthesis of ertugliflozin from d-glucose in 7% overall yield is reported. The reaction sequence involves conversion of d-glucose to a fully protected open chain d-glucose aldehyde in 4 steps, further installation of the aglycon group by a Grignard reaction, introduction of the hydroxymethyl group by a sequential oxidation/aldol reaction/Canizzarro reduction, and finally benzylic oxidation and global deprotection.     

Stereo-conserved synthesis of syn-diarylheptanoids, active principles of Zingiber, starting from d-glucose

A highly efficient and stereo-controlled synthetic strategy has been developed to access syn-diarylheptanoids, for example, 2,3, 4, and 5b starting from d-glucose as a chiral pool. The 3-(R), 5-(S)-syn-diol stereochemistry present in these heptanoids was obtained after conserving C2 and C4 stereochemistry of d-glucose during the course of synthetic transformation. The key features of this synthetic strategy include: (i) conversion of d-glucose to a known chiral template 6 armored with the required 1,3-syn-diol stereochemistry as well as two terminal aldehyde functionalities for building up customized ‘diaryl wings’; (ii) conversion of 6 to 7 via an initial Wittig olefination at the C5-aldehyde; (iii) use of the hemiacetal 7 as a common intermediate to obtain the individual heptanoids via a second Wittig reaction at its anomeric center using appropriately chosen ylides.     

A diversity-oriented synthetic approach to bengamides

A new approach to the bengamides, a new class of antitumor natural products of marine origin, is reported from epoxyamides, prepared by reaction of aldehydes with sulfur ylides. The synthetic strategy has been designed for the delivery of a wide array of analogues. Thus, the terminal alkyl substituent is introduced by a cross olefin metathesis from the corresponding terminal olefin. The combination of cross olefin metathesis, introduction of different nucleophiles by the oxirane ring opening and the introduction of different amines via amide bond formation, can produce a wide array of bengamides analogues.     

Synthesis of polyhydroxylated carbo-bicyclic compounds from sugar allyltins

A highly functionalized polyhydroxylated dienoaldehyde, readily obtained from a d-glucose allyltin, served as a convenient precursor for a variety of configurationally different carbo-bicyclic polyols available in a free (deprotected) form. The activity of the free polyols against glycosidases was also tested.     

Synthesis of polyhydroxylated aza-bicyclic compounds from sugar allyltins

Highly functionalized polyhydroxylated dienoaldehyde, readily obtained from allyltin and d-glucose, served as a convenient precursor for a variety of configurationally different aza-bicyclic polyols. Such derivatives were deprotected and the activity of these free compounds against glycosidases was also tested.     

Carbohydrate pyrolysis mechanisms from isotopic labeling: Part 2. The pyrolysis of d-glucose: General disconnective analysis and the formation of C1 and C2 carbonyl compounds by electrocyclic fragmentation mechanisms

The flash pyrolysis of d-glucose was investigated by the use of isotopic labeling with ¹³C, in conjunction with GC/MS. Co-pyrolysis of uniformly labeled and unlabeled d-glucose established the extent of unimolecular formation of each of the pyrolysis products. A complete set of singly labeled d-glucose isotopologs was used to determine the origin of specific carbons within each of the pyrolysis products. The Cyclic Grob 1,3-diol fragmentation and the tandem alkaline pinacol rearrangement/retro-aldol fragmentation (TAPRRAF) discovered from the pyrolysis of glycerin were applied to the analysis of pyrolytic fragmentation pathways for d-glucose. These mechanisms provide means of initial carbon–carbon bond breakage, and are consistent with the high proportion of carbon-unimolecularity observed for many of the volatile low-molecular weight products of the reaction. These and other reactions, including the retro-aldol fragmentation, carbonyl migration, dehydration, ene-reaction, retro-Claisen cleavage, hydrolysis, or alcoholysis were applied conceptually to the initial fragments resulting from either mechanism to ascertain the ultimate fate of the carbons of d-glucose. The “predicted” results were then compared with labeling patterns observed by experiment. The most promising rationalizations provided by this exercise are presented herein, for the formation of five C₁ and C₂ carbonyl-containing pyrolysis products: formaldehyde, formic acid, acetaldehyde, glycolaldehyde and acetic acid.