Glycosyl carbamates

Glycosyl 6>-xanthates 247, activated with BF3-Et20, have been reported by Pougny [528]. Similarly, glycosyl carbamates 248 also provided glycosides in BF3-Et20-promoted reactions [529]. 

Praia, C, Mora, N, Lacombe, J-M, Maurizis, J C, Pucci, B, Stereoselective synthesis of glycosyl carbamates as new surfactants and glycosyl donors. Tetrahedron Lett., 38, 8859-8862, 1997. 

Glycosyl-carbamates, -isothiocyanates, thioureas and Related Compounds... 

New routes to glycosyl carbamates and esters have been described. Reaction of 1 with the amino-sugar 2 gives the carbamate 3 in 92% yield (Scheme 1). Four new tetraacetyl glucosyl esters of 5-aryl-2-furoic acids 4 (R = 2-NO2, 3-NO2, 4-NO2, H) were also prepared by glycosylation of the acids under phase transfer catalysis [CH3(CH2)i5Me3NBr]. ... 

Carbamate glycosyl donors are another useful class of compounds, which pre sent significant variability in chemical structures (Scheme 3.24). In an early example by Kunz and Zimmer, the N-allyl carbamate donors were used in a remote activation protocol to furnish pyranoside and furanoside products. In this reaction, the N-allyl carbamate donor 146 is activated with dimethyl methylthiosulfonium... 

Representative Procedure for TMS Triflate Promoted Clycosylation with Glycosyl N-Tosyl Carbamate Donors [343]... 

After selective cyclic carbamate formation, the 3 -OH can be selectively protected using THP (Scheme 4.14). The 5-OH was then glycosylated with a thiofuranose, creating a ribostamycin analog, 78. However, compound 78 was... 

To monitor tumor response to capecitabine therapy noninvasively, Zheng and co-workers, from the Indiana University School of Medicine, developed the synthesis of the fluorine- 18-labeled capecitabine as a potential radiotracer for positron emission tomography (PET) imaging of tumors.28 Cytosine (20) was nitrated at the C-5 position with nitric acid in concentrated sulfuric acid at 85°C, followed by neutralization to provide 5-nitrocytosine (27) in moderate yield. This nitro pyrimidine was then carried through the glycosylation and carbamate formation steps, as shown in the Scheme below, to provide the 6/s-protected 5-nitro cytidine 28 in 47% for the three-step process. Precursor 28 was then labeled by nucleophilic substitution with a complex of 18F-labeled potassium fluoride with cryptand Kryptofix 222 in DMSO at 150 °C to provide the fluorine-18-labe led adduct. This intermediate was not isolated, but semi-purified and deprotected with aqueous NaOH in methanol to provide [l8F]-capecitabine in 20-30% radiochemical yield for the 3-mg-scale process. The synthesis time for fluorine-18 labeled capecitabine (including HPLC purification) from end of bombardment to produce KI8F to the final formulation of [18F]-1 for in vivo studies was 60-70 min. 

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