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Proteus mirabilis is a pathogenic Gram‐negative bacterium that causes several kinds of infections in human beings. Herein, we present the first total synthesis of the O‐antigen tetrasaccharide repeating unit of P. mirabilis OC (CCUG 10702) serogroup O75 with an aminoethyl linker appended at the reducing end. The tetrasaccharide comprising D‐glucosamine, L‐rhamnose, D‐galactose and D‐galactosamine with a key (1→4)‐α‐glycosidic linkage between D‐galactose and L‐rhamnose was assembled by three stepwise [1+1+1+1], [1+2+1] and [2+2] assembly approaches and one one‐pot [1+2+1] assembly. The respective routes provided the tetrasaccharide in yields of 23 %, 18 %, 20 %, and 26 % from suitably protected monosaccharide building blocks. [ABSTRACT FROM AUTHOR]

The bleomycins (BLMs) are known antitumor antibiotics composed of the tumoricidal and tumor seeking domains. The peptide structure of BLMs is responsible for the cytotoxicity by selective oxidative cleavage of DNA (and RNA), while the tumor cell selectivity and internalization resides in the disaccharide moiety (i.e. BLM disaccharide). This has prompted researchers to utilize BLM disaccharide and its derivatives as constituents for the selective recognition of tumor cells, which may find further applications as new tumor imaging tools or drug delivery vehicles. In the present study a high yielding synthesis of an alkyne modified BLM disaccharide precursor that may be used as a useful agent for the click conjugation, its conversion to a 18F‐labeled radiotracer, and preliminary in vivo PET imaging studies of the tracer with breast cancer (MCF‐7) xenograft mouse models are described. An alkyne modified bleomycin disaccharide has been synthesized from diacetone‐α‐d‐glucose and converted to a 18F radiotracer. Preliminary in vivo‐PET imaging studies has been described. [ABSTRACT FROM AUTHOR]

A concise synthesis of C-furanosides has been achieved, starting from unprotected D-xylose and D-arabinose. Both sugars reacted with hydroxylamine 6 to give the respective nitrones. These underwent in-situ intramolecular 1,3-dipolar cycloaddition reactions to give, in each case, a pair of diastereomeric derivatives of 7-oxa-1-aza-bicyclo[2.2.1]heptane 7 and 8. The ratio of chromatographically separable diastereoisomers could be changed by carrying out the reaction in the presence of weak Lewis acid. Both D-xylose-derived stereoiso-mers 7a and 8a were converted into D-erythro-C-furanosides by tosylation or mesylation followed by catalytic hydrogenolysis. On the other hand, the formation of D-threo-C-furanosides from D-arabinose derivatives 7b and 8b under similar conditions was accompanied by the formation of minor amounts of polyhydroxyquinolizidines as a result of competitive N-alkylation. The polyhydroxyquinolizidine side-products were useful for the assignment of the configuration of the new compounds. [ABSTRACT FROM AUTHOR]

Hexacarbonyldicobalt-C-3-alkynyl-substituted glycal derivatives, when treated with BF3 ·OEt2 give rise to Nicholas-stabilized Ferrier cation intermediates (Ferrier-Nicholas cations) that react with alcohols or C-nucleophiles to give C-3-branched 2,3-unsaturated glycosides or C-glycosides, respectively. α- C-Glycosides were the sole compounds obtained when allyltrimethylsilane was used as the nucleophile. On the contrary, the reaction of C-3-alkynylglycals with heteroaryl or alcohol nucleophiles led to anomeric mixtures in which the β-anomers prevailed. The presence of the hexacarbonyldicobalt-C-3-alkynyl substituent seems to be of key importance in the stereoselectivity of these transformations, since the reaction of C-3-alkynylglycals - devoid of the hexacarbonyldicobalt moiety - showed a preferred α-stereoselectivity. Furthermore, a bis(indolyl) linear compound was obtained from the reaction of a hexacarbonyldicobalt-C-3-alkynylglycal with 2 equiv. of indole. [ABSTRACT FROM AUTHOR]

An efficient strategy for synthesis of a spacer-armed tetrasaccharide related to galactan I of Klebsiella pneumoniae is described, which uses newly developed acid-free conditions for the pyranoside-into-furanoside (PIF) rearrangement of a digalactoside bearing a 4-pentenyl group at the anomeric position. The 4-pentenyl aglycon was successfully used both as a leaving group in the glycosylation of 3-(trifluoroacetamido)propanol, and as a temporary anomeric protecting group, allowing conversion into an imidate donor. Regioselective coupling of the disaccharide blocks gave the desired tetrasaccharide sequence required for investigation of the interaction of galactan I with immune-system proteins. [ABSTRACT FROM AUTHOR]

Functionalization of C-H bonds has received significant attention in organic chemistry during the last decade and it is still a 'hot' topic. In particular, C-H modification of natural products has benefitted from this development. Carbohydrates are densely functionalized natural products, and methods for their functionalization are therefore very attractable. This review presents methods from the last five decades and gives an overview of the developments in C-H functionalization of carbohydrates. It covers all methods in which a C-H bond is broken: from radical abstractions and carbene insertion to new metal-catalyzed approaches. The review systematically covers the carbohydrates position-by-position and hence gives a quick overview. [ABSTRACT FROM AUTHOR]

A novel set of L-gulose and L-guluronic acid building blocks, comprising both monosaccharide and disaccharide synthons, was assembled to investigate how structural changes in these synthons influence the outcome of glycosylation reactions in which they are involved. Our studies corroborate previous reports that identified the gulosyl C4-OH group as a relatively poor nucleophile. We did not find a major influence of the neighboring C5 functionality on the reactivity of the alcohols, and the gulose acceptors did not provide more productive glycosylation reactions than their guluronic acid counterparts. The conformational behavior of the synthons was found to be of prime importance to the outcome of the reactions. [ABSTRACT FROM AUTHOR]

Seven-membered ring 'septanose' sugars have been used as surrogates of pyranoses in biochemical investigations. Septanoses are homologs of pyranoses in the same way that beta amino acids are for alpha amino acids or hexose nucleosides for deoxyribose nucleosides. Methods for their synthesis have undergone significant development recently, following two complementary strategies. In one, glycals are cyclopropanated which are later opened in addition reactions with nucleophiles. The other follows traditional glycosylation strategies where electrophilic donors are prepared and reacted with nucleophiles. Unsaturated seven membered ring oxepines play a key role in both of the approaches, which are highlighted. [ABSTRACT FROM AUTHOR]

2-Deoxy-2-amino-substituted glycosides are ubiquitous compounds in biochemistry and biology. Therefore, the development of new synthetic pathways to access natural and non-natural derivatives is highly desirable. In that context, 2-nitroglycals appeared as versatile building blocks for reaching those targets. Since their first introduction almost forty years ago, their synthetic utility has been widely demonstrated and they have been used to access natural and non-natural compounds with potent biological activity. The aim of this review is to summarize the developed routes to these versatile intermediates as well as their reactivity. The main applications of the chemistry developed with 2-nitroglycal derivatives is also highlighted in this first review. [ABSTRACT FROM AUTHOR]

Carbohydrates have been widely used for stereochemical control, either as chiral auxiliaries or as ligands. Their natural abundance and rigidity of structure, together with the presence of many functional groups, have also in recent years made them attractive chiral modular units for the assembly of bifunctional organocatalysts. Applications have ranged from the more complex bifunctional carbohydrate-based amine-(thio)ureas and prolinamides to simple amino alcohols. The presence of many hydroxy groups and their consequent water solubility has allowed for the study of reactions in aqueous media. Nowadays they have been applied to many reactions such as the aldol, Michael, Stetter, Biginelli, Morita-Baylis-Hillman, decarboxylative Mannich and other reactions, and even to the multistep synthesis of known drugs. This review provides an overview of developments in this field in the period from 2009 to mid-2014. [ABSTRACT FROM AUTHOR]

A diastereoselective, metal-free, one-pot domino synthetic strategy was developed for the transformation of glycals into new chiral scaffolds. Optimization of the reaction conditions to exclude normal Ferrier products, characterization of the new entities, and a plausible mechanism were investigated. [ABSTRACT FROM AUTHOR]