The synthesis of tetrafluorinated aminosugars

The synthesis of two tetrafluorinated 4-aminosugars, 4-amino-2,3,4-trideoxy-2,2,3,3-tetrafluoro-d-erythro-hexopyranose hydrochloride (7•HCl) and 4-amino-2,3,4-trideoxy-2,2,3,3-tetrafluoro-d-threo-hexopyranose hydrochloride (8•HCl), is described. The amino group in ?-position of a CF2(CF2) group is proposed as a mimic for the hydrogen bond accepting capacity of an alcohol group in an unfluorinated sugar. The synthesis of the two sugars was achieved in 4 steps each from the sulfinylimine diastereoisomers of d-glyceraldehyde

Heavily fluorinated carbohydrates as enzyme substrates: oxidation of tetrafluorinated galactose by galactose oxidase

Galactose oxidase (GOase) was shown to oxidise several C2/C3 fluorinated galactose analogues. Interestingly, the enzyme was able to distinguish between the 2,3-tetrafluorinated galactose and its epimeric glucose analogue, and this represents the first reported biotransformation of a heavily fluorinated suga

Enzymatic glycosylation involving fluorinated carbohydrates

Fluorinated carbohydrates, where one (or more) fluorine atom(s) have been introduced into a carbohydrate structure, typically through deoxyfluorination chemistry, have a wide range of applications in the glycosciences. Fluorinated derivatives of galactose, glucose, N-acetylgalactosamine, N-acetylglucosamine, talose, fucose and sialic acid have been employed as either donor or acceptor substrates in glycosylation reactions. Fluorinated donors can be synthesised by synthetic methods or produced enzymatically from chemically fluorinated sugars. The latter process is mediated by enzymes such as kinases, phosphorylases and nucleotidyltransferases. Fluorinated donors produced by either method can subsequently be used in glycosylation reactions mediated by glycosyltransferases, or phosphorylases yielding fluorinated oligosaccharide or glycoconjugate products. Fluorinated acceptor substrates are typically synthesised chemically. Glycosyltransferases are most commonly used in conjunction with natural donors to further elaborate fluorinated acceptor substrates. Glycoside hydrolases are used with either fluorinated donors or acceptors. The activity of enzymes towards fluorinated sugars is often lower than towards the natural sugar substrates irrespective of donor or acceptor. This may be in part attributed to elimination of the contribution of the hydroxyl group to the binding of the substrate to enzymes. However, in many cases, enzymes still maintain a significant activity, and reactions may be optimised where necessary, enabling enzymes to be used more successfully in the production of fluorinated carbohydrates. This review describes the current state of the art regarding chemoenzymatic production of fluorinated carbohydrates, focusing specifically on examples of the enzymatic production of activated fluorinated donors and enzymatic glycosylation involving fluorinated sugars as either glycosyl donors or acceptors

Profiling substrate promiscuity of wild-type sugar kinases for multifluorinated monosaccharides

Fluorinated sugar-1-phosphates are of emerging importance as intermediates in the chemical and biocatalytic synthesis of modified oligosaccharides, as well as probes for chemical biology. Here we present a systematic study of the activity of a wide range of anomeric sugar kinases (galacto- and N-acetylhexosamine kinases) against a panel of fluorinated monosaccharides, leading to the first examples of polyfluorinated substrates accepted by this class of enzymes. We have discovered four new N-acetylhexosamine kinases with a different substrate scope, thus expanding the number of homologs available in this subclass of kinases. Lastly, we have solved the crystal structure of a galactokinase in complex with 2-deoxy-2-fluoro galactose, giving insight into changes in the active site that may account for the specificity of the enzyme towards certain substrate analogues

Synthesis and diastereoselective Diels–Alder reactions of homochiral C2-symmetric butane-1,2-diacetal-based 1,3-dienes

The C2-symmetric, butane diacetal (BDA) auxiliary-based dienes 2 and 3 are described, which display moderate to excellent diastereoselectivities in Diels–Alder reactions with a range of dienophiles under thermal and Lewis acid-catalysed conditions

Enantioselective synthesis and selective monofunctionalization of (4R,6R)-4,6-dihydroxy-2,8-dioxabicyclo[3.3.0]octane

An efficient, enantioselective synthesis of a disubstituted bis-THF scaffold 5 is described, as well as an efficient differentiation of the 1,3-diol unit

Stereocontrol by quaternary centres: a stereoselective synthesis of (?)-luminacin D

Very high diastereoselectivity can be achieved by 1,3-chelation-controlled allylation of aldehydes that possess a non-chelating ?-ether substituent, even if the ?-position is a quaternary centre and/or a spiro-epoxide. This reaction was used as a key step in an enantioselective synthesis of the angiogenesis inhibitor luminacin?

Efficient desymmetrization of "Pseudo"-C-2-symmetric substrates: illustration in the synthesis of a disubstituted butenolide from arabitol

A short synthesis of the homochiral disubstituted butenolide 1 is described in four steps from arabitol. The key steps are the selective kinetic protection of arabitol and the cyclization of 11 to form the butenolide ring. This last transformation represents a rare example of a fully stereoselective cyclitive desymmetrization process of a "pseudo"-C-2-symmetric substrate