Synthesis of fluorinated Thomsen–Friedenreich antigens: direct deoxyfluorination of αGalNAc-threonine tert-butyl esters

Abstract

Selectively 6-fluorinated analogs of the tumor-associated T(N) antigen Fmoc-Thr(α-O-GalNAc)-OtBu can be efficiently prepared using DAST-mediated de(hydr)oxyfluorination reactions of preformed and orthogonally protected glycosyl amino esters without affecting the labile protecting groups and O-glycosidic linkages. The resulting mono- and difluorinated T(N) analogs are interesting building blocks for non-hydrolyzable mucin-type antigen mimetics, as illustrated by the unprecedented synthesis of two different multiply fluorinated Thomsen-Friedenreich derivatives. The reported deoxyfluoro antigen analogs represent important functional probes for carbohydrate-binding proteins and glycosyl-processing enzymes.

Chemoenzymatic synthesis of mono- and di-fluorinated Thomsen–Friedenreich (T) antigens and their sialylated derivatives

“…Compared to a previously reported chemical synthesis of protected C6-fluorinated T-antigen from Gal and GalNAcαSer which required at least 8 steps with a less than 30% total yield, 14 the current chemoenzymatic synthesis of a similar C6-fluorinated T-antigen 8 from Gal and GalNAcαProN 3 only required 4 steps and resulted in a total yield of higher than 60%.…”

“…As shown in Table 1, C6′-fluorinated T-antigens 9–11 were synthesized in very good yields (80–87%). Compared to a previously reported chemical synthesis of C6′, C6-difluorinated T-antigen which required at least 9 steps from Gal and GalNAcαSer with a less than 25% total yield even with an optimization of the glycosylation reaction using microwave radiation (100W, 80°C, 4 h), 14,16 the two-step one-pot two-enzyme system synthesis of a similar di-fluorinated T-antigen 11 resulted in a total yield of greater than 50% in 7 steps including chemical synthesis of Gal6F ( 5 ) and GalNAc6FαProN 3 ( 4 ) from non-fluorinated Gal and GalNAcαProN 3 using similar processes. 14,16 …”

“…14 A solution of compound 3 (1.42 g, 4.69 mmol) and CSA (0.15 g, 0.66 mmol) in 2,2-dimethoxypropane (55 mL) was heated and kept reflux at 110 °C for 70 min. Et 3 N (0.8 mL) was added and the reaction mixture was concentrated.…”

“…12,13 Recently, T-MUC1 glycopeptide analogs containing one or two fluorine substituents on the sugar were synthesized. 14–17 They have been conjugated to tetanus toxoid carrier protein and the conjugate vaccines elicited strong and specific immune responses in mice. 18–19 These “foreign” fluorinated TACA-based vaccines not only provided enhanced immunogenicity and metabolic stability but also improved bioavailability.…”

“…), 20,21 only a few fluorinated T-antigens and derivatives have been synthesized so far. 14–17,22–24 Chemical synthesis of fluorinated oligosaccharides including T-antigens and other Galβ1–3GalNAc-containing O -glycans is challenging. 14,23,25 It involves multiple protection and deprotection processes and has to deal with the low reactivity of fluorinated acceptors or donors during glycosylation.…”