Efficient synthesis of a 6-deoxy-talose containing tetrasccharide found in Franconibacter helveticus LMG23732 T

Total Synthesis of 6-Deoxy-l-talose Containing a Pentasaccharide Repeating Unit of Acinetobacter baumannii K11 Capsular Polysaccharides

“…After those failed attempts, we shifted our focus to oxidation followed by reduction to get the l -talose . Treating the l -rhamnose derivative 21 with DMSO, PhPOCl 2 , and Et 3 N at 0 °C produced the corresponding ketone intermediate, which on reduction with NaBH 4 in MeOH at room temperature produced the 2,3-isopropylidene- l -taloside 22 with an excellent 98% yield. One-pot isopropylidene removal and acetylation were carried out by treating compound 22 with AcOH/Ac 2 O/H 2 SO 4 (25:4:1, v/v/v) to get the desired p -tolyl-2,3,4-tri- O -acetyl-1-thio-α- l -talopyranoside with an 89% yield (Scheme ).…”

“…After complete consumption of the starting material, the reaction was quenched with Et 3 N and concentrated under reduced pressure. The crude product was purified by column chromatography over silica gel (100−200 mesh) (hexane/EtOAc = 3:1, v/v) to obtain compound 21 (0.738 g, 96% yield in two steps) as a white solid: [α] D 20 + 85.0 (c 1.1, CHCl 3 ); mp 99−101 °C; IR (CHCl 3 ): ν 3414, 2925, 1445, 1085, 1013, 968, 813, 762 cm −1 ; 1 H NMR (400 MHz, CDCl 3 ): δ 7.37 (d, J = 8.2 Hz, 2H, Ar−H), 7.13 (d, J = 7.9 Hz, 2H, Ar−H), 5.66 (d, J = 0.4 Hz, 1H, H-1), 4.34 (dd, J = 5.5, 0.7 Hz, 1H, H-2), 4.12−4.06 (m, 2H, H-3, H-4), 3.47 (ddd, J = 9.8, 7.7, 3.7 Hz, 1H, H-5), 2.34 (s, 3H, CH 3 ), 2.14 (s, 1H, OH), 1.53 (s, 3H, CH 3 ), 1.37 (s, 3H, CH 3 ), 1.24 (d, J = 6.2 Hz, 3H, CCH 3 ); 13 C { 1 H} NMR (100 MHz, CDCl 3 ): δ 137.9−129.5 (Ar−C), 84.0 (C-1), 78.4 (C-3), 76.5 (C-2), 75.2 (C-4), 66.8 (C-5), 28 p-Tolyl-2,3-O-isopropylidene-1-thio-α-L-talopyranoside (22). A solution of compound 21 (0.730 g, 2.35 mmol) in anhydrous CH 2 Cl 2 (28 mL) was cooled at 0 °C under a nitrogen atmosphere.…”

“…[α] D20 − 99.1 (c 1.0, CHCl 3 ); mp 144−146 °C; IR (CHCl 3 ): ν 2921, 2852, 1734, 1366, 1242, 1209, 1081, 1017, 971, 812, 740, 598 cm −1 ; 1 H NMR (400 MHz, CDCl 3 ): δ 7.35 (d, J = 8.2 Hz, 2H, Ar− H), 7.12 (d, J = 7.9 Hz, 2H, Ar−H), 5.48 (d, J = 1.2 Hz, 1H, H-1 E ), 5.34−5.31 (m, 1H, H-2 E ), 5.28 (t, J = 4.0 Hz each, 1H, H-3 E ), 5.22 (d, J = 3.5 Hz, 1H, H-4 E ), 4.65−4.60 (m, 1H, H-5 E ), 2.33 (s, 3H, CH 3 ), 2.16 (s, 3H, COCH 3 ), 2.13 (s, 3H, COCH 3 ), 2.01 (s, 3H, COCH 3 ), 1.21 (d, J = 6.5 Hz, 3H, CCH 3 );13 C { 1 H} NMR (100 MHz, CDCl 3 ): δ 170.5 (COCH 3 ), 169.9 (COCH 3 ), 169.6 (COCH 3 ), 138.0−129.3 (Ar−C), 86.4 (C-1 E ), 69.0 (C-4 E ), 68.6 (C-2 E ), 66.5 (C-3 E ), 66.2 (C-5 E ), 21.1 (CH 3 ), 20.9 (COCH 3 ), 20.7 (COCH 3 ), 20.6 (COCH 3 ), 16.1 (CCH 3 ); HRMS (ESI-TOF) m/z: [M + Na] + calcd for C 19 H 24 O 7 NaS, 419.1135; found, 419.1123. PMP-3-O-acetyl-2-azido-4,6-O-benzylidene-2-deoxy-α-D-glucopyranosyl-(1 → 2)-3,4,6-tri-O-benzyl-β-D-glucopyranoside (23).…”