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A total synthesis of tiacumicin B, a natural macrolide whose remarkable antibiotic properties are used to treat severe intestinal infections, is reported. The strategy is in part based on the prior synthesis of the tiacumicin B aglycone, and on the decisive use of sulfoxides as anomeric leaving groups in hydrogen-bond-mediated aglycone delivery (HAD). This new HAD variant permitted highly β-selective rhamnosylation and noviosylation. To increase convergence, the rhamnosylated C1–C3 fragment thus obtained was anchored to the C4–C19 aglycone fragment by adapting the Suzuki–Miyaura cross-coupling used for the aglycone synthesis. Ring-size-selective macrolactonization provided a compound engaged directly in the noviolysation step with virtually total β selectivity. The final efficient removal of all the protecting groups provided synthetic tiacumicin B.

The development of an N-heterocyclic carbene (NHC) catalysed intercepted dehomologation of aldoses is reported. The unique selectivity of NHCs for aldehydes is exploited in the complex context of reducing sugars. Examples of strong substrate governance for either intercepted dehomologation or a subsequent redox-lactonisation were identified and mechanistically understood. More importantly, it was shown that catalyst design allowed the tuning of the selectivity of the reaction with structurally unbiased starting materials towards either of the two scenarios.

Sugar-based low-molecular-weight gelators (LMWGs) have been used for various applications for a long time. Herein, structurally simple, ester-protected arabinosides are reported as low-molecular-weight organogelators (LMOGs) that are able to gel aromatic solvents, as well as petrol and diesel. Studies on the mechanical strength of the gels, through detailed rheological experiments, indicate that gels from the 1,2-dibenzoylated arabinose gelator possess better mechanical properties than those from the 1,2-diacetylated gelator. These results are interpreted in terms of the tendency of the former to form fibers with comparatively lower diameter than those of the latter, based on detailed field-emission SEM and AFM studies. Investigations of the interactions responsible for the self-assembly of gelators through IR spectroscopy and wide-angle X-ray scattering reveal that the primary interactions responsible are hydrogen bonds between the hydroxyl groups and ester C=O, which is absent in the solid state of the gelators. In addition, π interactions present in the 1,2-dibenzoylated derivative result in a more regular arrangement, which, in turn, leads to better mechanical properties of the gels compared with those of the 1,2-diacetylated gelator.

A novel C-branched polyhydroxylated cyclic nitrone 25, which could be a valuable intermediate for the synthesis of C-branched pyrrolidine iminosugars, was synthesized starting from the commercially available L-arabinose in 29.0% total yield.

Two new biotin analogues, biotin carbonate 5 and biotin carbamate 6, have been synthesized. These molecules were designed to reversibly bind with streptavidin by replacing the hydrogen-bond donor NH group(s) of biotin's cyclic urea moiety with oxygen. Biotin carbonate 5 was synthesized from L-arabinose (7), which furnishes the desired stereochemistry at the 3,4-cis-dihydroxy groups, in 11% overall yield (over 10 steps). Synthesis of biotin carbamate 6 was accomplished from L-cysteine-derived chiral aldehyde 33 in 11% overall yield (over 7 steps). Surface plasmon resonance analysis of water-soluble biotin carbonate analogue 46 and biotin carbamate analogue 47 revealed that KD values of these compounds for binding to streptavidin were 6.7×10-6M and 1.7×10-10M, respectively. These values were remarkably greater than that of biotin (KD=10-15M), and thus indicate the importance of the nitrogen atoms for the strong binding between biotin and streptavidin.

Six chiral hydroxylated pyrrolidine catalysts were synthesized from commercially available D-arabinose in seven steps. Various aromatic substituents α to the amine can be introduced readily by a Grignard reaction, which enables facile optimization of the catalyst performance. The stereoselectivities of these catalysts have been assessed by comparing with those of MacMillan's imidazolidinone in a known intramolecular Diels-Alder (IMDA) reaction of a triene. Two additional IMDA reactions of symmetrical dienals with concomitant desymmetrisation further established the potential use of these novel amine catalysts. These pyrrolidines are valuable catalysts for other synthetic transformations.

It is an object of the present invention to provide a mutant streptavidin with a reduced affinity for natural biotin, and also to provide a modified biotin having a high affinity for the mutant streptavidin with a reduced affinity for natural biotin. Acco

Enantiomeric d- or l-arabinose based low molecular-weight organogelators (LMOGs), accessible in a single synthetic step from d-/l-arabinose have been found to be efficient gelators for aromatic solvents and refined and crude oil. The organogel has also been successfully used as a micro-reactor for a photochemical reaction. This journal is

Divergent syntheses of two 14-membered resorcylic acid lactones (RALs), cochliomycin B (6) and zeaenol (22), have been accomplished. The key feature in our strategy was the facile construction of three contiguous stereogenic centers in the title molecules

New chiral monoaza-15-crown-5 type macrocycles anellated to 3,4-O-isopropylidene-β-L-arabinopyranose (5a-b), to β-L- arabinopyranose (6) and to 3,4-O-benzyliden-β-L-arabinopyranose (11) have been synthesized. The cation binding ability of the new lariat e

Our goal in the search for potentially bioactive analogues of KRN 7000 was to design an easy synthetic approach to a library of analogues using a strategy recently developed in our laboratory based on a Nucleophilic addition followed by an Epoxide Opening

Epoxypiperidine derivatives bearing a dehydroamino acid unit were designed and synthesized as novel DNA alkylating agents based on the structure of azinomycins. A relaxation assay of plasmid DNA revealed that the epoxypiperidine derivative 3 has a DNA cle

The allene-diyne natural product nemotin was synthesized for the first time through an enantioselective route with the stereogenic center at the lactone moiety derived from l-glutamic acid and the allene axis constructed from the corresponding propargylic

The fibrous polymer-supported sulfonic acid catalyst Smopex-101 H+ proved to be an efficient catalyst for the preparation of O-isopropylidene derivatives from a series of rare sugars. Acetonation of the reducing sugars l-arabinose, l-ribose, l-xylose, l-fucose, and l-rhamnose in N,N-dimethylformamide by 2,2-dimethoxypropane or 2-methoxypropene led to the formation of the kinetically favored di-O- and/or mono-O-isopropylidene derivatives in 46-88% yields. The method consists of a simple experimental procedure which does not require predried solvents or reagents. The catalyst is easily recovered and can be regenerated making the procedure economically viable even for large-scale synthesis.

Various 4-deoxy-4-fluoro-xylosides were prepared using click chemistry for evaluating their potential utility as inhibitors of glycosaminoglycan biosynthesis. 2,3-Di-O-benzoyl-4-deoxy-4-fluoro-β-d-xylopyranosylazide, obtained from l-arabinopyranose by six

Efforts directed toward a total synthesis of cepacin A is presented in full detail. The C-7, C-8, and C-9 stereogenic centers in the target molecule were derived from d-arabinose. The configuration of the allene axis was controlled at the bromoallenation step by the C-10 configuration of the precursor. An unexpected yet very interesting phenomenon was observed with the bromoallenation, where the α-isomer of the propargylic alcohol 31 was entirely resistant to the conditions that worked so well for its β-counterpart. The problem was eventually solved by careful tuning of the size of the neighboring groups based on the clue obtained from conformational analysis. The diyne moiety was incorporated into the molecular framework through a coupling of the TMS protected diyne with a proper bromoallene under the Sonogashira conditions with EtOAc as the solvent. Use of other solvents at this step led to complete failure.

Tuberculosis is an increasing threat, owing to the spread of AIDS and to the development of resistance of the causative organism, Mycobacterium tuberculosis, to the currently available drugs. Dihydrofolate reductase (DHFR) is an important enzyme of the folate cycle; inhibition of DHFR inhibits growth and causes cell death. The crystal structure of M. tuberculosis DHFR revealed a glycerol tightly bound close to the binding site for the substrate dihydrofolate; this glycerol-binding motif is absent from the human enzyme. A series of pyrimidine-2,4-diamines was designed with a two-carbon tether between a glycerol-mimicking triol and the 6-position of the heterocycle; these compounds also carried aryl substituents at the 5-position. These, their diastereoisomers, analogues lacking two hydroxy groups and analogues lacking the two-carbon spacing linker were synthesised by acylation of the anions derived from phenylacetonitriles with ethyl (4S,5R)-4-benzyloxymethyl-2,2-dimethyl-1,3-dioxolane-4-propanoate, ethyl (4S,5S)-4-benzyloxymethyl-2,2-dimethyl-1,3-dioxolane-4-propanoate, tetrahydrooxepin-2-one and 2,3-O-isopropylidene-d-erythronolactone, respectively, to give the corresponding α-acylphenylacetonitriles. Formation of the methyl enol ethers, condensation with guanidine and deprotection gave the pyrimidine-2,4-diamines. Preliminary assay of the abilities of these compounds to inhibit the growth of TB5 Saccharomyces cerevisiae carrying the DHFR genes from M. tuberculosis, human and yeast indicated that 5-phenyl-6-((3R,4S)-3,4,5-trihydroxypentyl)pyrimidine-2,4-diamine selectively inhibited M. tuberculosis DHFR and had little effect on the human or yeast enzymes.

Two new long-chain ceramides, trametenamides A (1) and B (2), were isolated from the methanolic extract of the fruiting body of the fungus Trametes menziesii. The structures were elucidated by spectroscopic analyses and chemical transformations, and the absolute stereochemistry of trametenamide B (2) was determined by stereoselective total synthesis of four possible diastereomers. The acetyl derivative of the natural ceramide (1a) and synthetic ceramides (24-27) showed cytotoxicity on the human melanoma cell line SK-MEL-1, which was caused by induction of apoptosis as determined by DNA fragmentation, poly-(ADP-ribose) polymerase cleavage, and procaspase-9 and -8 processing.

A concise and convergent synthesis of the C-glycoside analogue 2b of immunomodulating α-galactosylceramide OCH 1b starting from readily available 2,3,4,6-tetra-O-benzyl-d-galactose 3 and l-arabinose 6 is described. The synthesis features the nucleophilic addition of an α-ethynyl sugar 5 to the phytosphingosine-precursor aldehyde 9 and would be applicable to a variety of C-glycoside analogues of interest.

Deoxyxylulose 5-phosphate (DXP) analogs were synthesized and evaluated as alternative substrates and inhibitors of recombinant Synechocystis PCC6803 DXP reductoisomerase (DXR; EC 1.1.1.267). Five of the compounds tested (1,2-dideoxy-d-threo-3-hexulose 6-phosphate, 1-deoxy-l-ribulose 5-phosphate, 2S,3R-dihydroxybutyramide 4-phosphate, 4S-hydroxypentan-2-one 5-phosphate, and 3S-hydroxypentan-2-one 5-phosphate) acted as relatively weak competitive inhibitors when compared to fosmidomycin. A sixth compound, 3R,4S-dihydroxy-5- oxohexylphosphonic acid, served as an alternate substrate, as has recently been reported for the same compound with Escherichia coli DXR.

Representative diastereomeric, erythritol and threitol polyhydroxylated pyrrolidine imine scaffolds have been rapidly elaborated to diversely functionalized aza-sugars through highly diastereoselective organometallic (RM) additions (R = Me, Et, allyl, hex

A stereoselective synthesis of thioxylo-di-, -tri-, -tetra- and -penta-saccharides from S-glycosyl isothiourea precursors is described. The synthesis was performed starting from 2,3,4-tri-O-acetyl-β-D-xylopyranosyl isothiouronium bromide using a triethylamine promoted reaction with 1,2,3-tri-O-benzoyl-4-O-trifluoromethanesulphonyl-β-L-arabinopyranose. The resulting 4-thioxylobiose was then converted into the corresponding isothiouronium bromide and used for the synthesis of 4,4′-dithioxylotriose. Higher homologues of the series and their α-methyl glycosides were also prepared.

3',4'-Seco-nucleosides as well as their derivatives lacking C-3', all retain the carbon framework and chirality of the β-D-ribofuranosyl moiety of the nucleosides occurring in nucleic acids, have been synthesized and their antiviral properties examined.Mo