Study on fluorination of 2,3-dideoxy-2,3-(N-tosylepimino)-alpha-D-allopyranosides, and synthesis of 3'-deoxy-3'-fluorokanamycin B and 3',4'-dideoxy-3'-fluorokanamycin B

Synthesis of 4′-deoxy-4′-fluoro neamine and 4′-deoxy-4′-fluoro 4′-epi neamine

The syntheses of 4′-deoxy-4′-fluoro neamine and 4′-deoxy-4′-fluoro 4′-epi neamine from the readily available neamine and paromamine are described.

Recent trends in the synthesis of O-glycosides of 2-amino-2-deoxysugars

The discovery of new methods for stereoselective glycoside synthesis and convergent oligosaccharide assembly has been critical for the area of glycosciences. At the heart of this account is the discussion of the approaches for stereoselective synthesis of glycosides of 2-amino-2-deoxysugars that have emerged during the past two decades. The introductory part provides general background information and describes the key features and challenges for the synthesis of this class of compounds. Subsequently, major approaches to the synthesis of 2-amino-2-deoxyglycosides are categorized and discussed. Each subsection elaborates on the introduction (or protection) of the amino functionality, synthesis of glycosyl donors by introduction of a suitable leaving group, and glycosidation. Wherever applicable, the deprotection of a temporary amino group substituent and the conversion onto the natural acetamido functionality is described. The conclusions part evaluates the current standing in the field and provides a perspective for future developments.

The mild cleavage of 2-amino-2-deoxy-D-glucoside methoxycarbonyl derivatives

The conversion of methyl carbamate to the corresponding free amine is described for a series of 2-amino-2-deoxy-D-glucosamine derivatives. Cleavage of methoxycarbonyl moiety with MeSiCl(3) and triethylamine in dry THF at 60 degrees C and subsequent aqueous hydrolysis yields the free amine in 54 to 93% yields. The selective cleavage of methyl carbamates with MeSiCl(3) in the presence of a 2,2,2-trichloroethoxycarbonyl group or 2-azido glycosides affords selectively, orthogonal N-deprotected carbohydrates.

Synthesis of deoxyfluoro sugars from carbohydrate precursors

Results obtained over the past decade concerning the introduction of the fluorine atom into carbohydrate molecules, either by nucleophilic substitution or electrophilic addition reactions, are summarised. The first section mainly deals with the triflate/fluoride tandem sequence and the DAST-reaction. In the discussion, emphasis is given to the dependency of the reaction course on the stereochemical and protecting group features. Possible reaction pathways are direct substitution (with inversion or retention of configuration), rearrangement (combined with substitution and inversion of configuration at both of the centres involved) and elimination. Based on the assumption of cyclic transition states or transient intermediates (formed through participation of neighbouring groups), far-reaching mechanistic generalisations were made. On this basis, isolated examples from the literature, which are not in accordance with these generalisations, are specifically brought to attention. Results from the recently introduced reaction of safe and easy to handle N-F fluorinating agents with glycals are also reported. This approach allows the simple and stereoselective access to a series of 2-deoxy-2-fluoro aldopyranoses, as well as the synthesis of various C-1-substituted derivatives by an easy one-pot reaction. However, the same method applied to furanoid glycals is rather poor with respect to stereoselectivity. Finally, considerations on the importance of fluorine-specific reactions of the S(N)-type in related fields of organic synthesis are made.

NMR spectra of fluorinated carbohydrates

Recent advances in structural and conformational analysis of fluorinated carbohydrates by NMR spectroscopy are reviewed. Characteristic 1H, 13C, and 19F NMR chemical shifts and coupling constants for selected examples are given and the spectral data of a series of fluorinated carbohydrates were collected in continuation of the review of Csuk and Glänzer [Adv. Carbohydr. Chem. Biochem., 46 (1988) 73-177].

Synthesis of 1-N-[(2S,4S)- and (2S,4R)-5-amino-4-fluoro-2-hydroxypentanoyl]dibekacins (study on structure-toxicity relationships)

(2S,4S)- and (2S,4R)-5-azido-2-O-benzyl-4-fluoro-2-hydroxypentanoic acids (15 and 19) have been prepared from L-malic acid (1), and coupled to the H2N-1 group of 3,2',6'-tris(N-benzyloxycarbonyl)-3"-N-(trifluoroacetyl)dibekacin (23), to give, after reduction and deblocking, 1-N-[(2S,4S)- and (2S,4R)-5-amino-4-fluoro-2-hydroxypentanoyl]dibekacins (26 and 27). The fluorinated arbekacin analogs showed almost the same antibacterial activities as that of arbekacin, but lower toxicity. Comparison of the toxicity between 26 (and 27) and the arbekacin analogs (28-30) with change of the 1N-side-chain indicates that the observed decrease in toxicity was a function of the chain length rather than the introduction of fluorine.

Study on fluorination-toxicity relationships. Syntheses of 1-N-[(2R,3R)- and (2R,3S)-4-amino-3-fluoro-2-hydroxybutanoyl] derivatives of kanamycins

(2R,3R)- And (2R,3S)-4-azido-3-fluoro-2-hydroxybutanoic acids (11 and 22) have been prepared from 3-deoxy-3-fluoro-1,2-O-isopropylidene-alpha-D-glucofuranose (1) and 3,5-di-O-benzyl-1,2-O-isopropylidene-alpha-D-xylofuranose (12), respectively. They were then coupled to the N2N-1 group of suitably protected kanamycin A or kanamycin B analogs to give, 1-N-[(2R,3R)- and (2R,3S)-4-amino-3-fluoro-2-hydroxybutanoyl]kanamycins (32-35). This group of compounds (32-34) exhibited similar antibacterial activity and toxicity level as those of the corresponding 1-N-[(S)-4-amino-2-hydroxybutanoyl] (AHB) derivatives of kanamycins. The base strength of the H2N-4"' group of 32 and 34, as determined by 13C NMR spectroscopy (in D2O) at varying pD values, was found to be lower when compared to the basicity for the corresponding AHB analogs. The relationship between observed toxicity and base strength of the H2N-4"' group is discussed.

Synthesis of 5-deoxy-5-fluoro and 5-deoxy-5,5-difluoro derivatives of kanamycin B and its analogs. Study on structure-toxicity relationships

5-Deoxy-5-fluoro- (1), 5.3'-dideoxy-5-fluoro- (2), and 5,3',4'-trideoxy-5-fluoro-kanamycin B (3) have been prepared by treatment of 5-epihydroxyl precursors (prepared by the Mitsunobu reaction) with DAST as the key step. 5,3'-Dideoxy-5,5-difluoro- (26) and 5,3',4'-trideoxy-5,5-difluoro-kanamycin B (27) were also prepared by treatment of the corresponding 5-oxo derivatives with DAST. These 5-deoxy-5-fluoro and 5-deoxy-5,5-difluoro derivatives showed markedly decreased toxicity as compared with the parent compounds.

Synthesis of 4'-deoxy-4'-fluorokanamycin A and B

4'-Deoxy-4'-fluorokanamycins A (17) and B (25) have been prepared through fluorinative ring-opening of the D-galacto-3',4'-oxiranes (8 and 21) derived from kanamycin A and B with potassium hydrogenfluoride in ethane-1,2-diol. The mechanism of preponderant formation of the 4'-deoxy-4'-fluoro-D-gluco (9 and 22) over the 3'-deoxy-3'-fluoro-D-gulo derivatives was discussed. In the synthesis of 25, the unusual 3',6'-epimine (23) was the main product along with the 4'-deoxy-4'-fluoro derivative. The mechanism of this reaction is also discussed. Both 17 and 25 were active against resistant bacteria producing aminoglycoside-adenylylating enzymes for HO-4'.