Chapter 6 Stereocontrolled Synthesis of Mannans and Rhamnans

Chemoenzymatic synthesis of ADP-d-glycero-β-d-manno-heptose and study of the substrate specificity of HldE

“…The primary hydroxyl of compound 13 was subjected to Dess–Martin oxidation to provide the desired aldehyde, which can be directly used for Wittig reaction without further purification to afford alkene 14 in 61% yield over two steps. 19, 20 Dihydroxylation of alkene 14 with OsO 4 and N -methylmorpholine N -oxide (NMNO) gave a 5:1 mixture of diastereomers that can be separated by silica gel column to give predominant D, D-heptose 15 with 63% separated yield. The stereochemical outcome of this dihydroxylation was in accordance with Kishi’s empirical rule.…”

Methodology Development and Physical Organic Chemistry: A Powerful Combination for the Advancement of Glycochemistry

“…Much of this synthetic work has been reviewed 67 and we limit ourselves here to a single example taken from the recent work of the Kobayashi group on the synthesis of the antibiotic TMC 151C (Scheme 10). 68 The intramolecular aglycone delivery method provides a useful alternative in many cases to the benzylidene directed mannosylation and has also been widely applied in synthesis, but it does require the extra step of tethering the donor to the acceptor prior to glycosylation.…”

“…This limitation is most apparent in the synthesis of the 6-deoxy-β-mannosides, otherwise known as the β-rhamnosides, 67b,69e,86 a class of glycosides that are commonly found, in the form of either enantiomer, in bacterial capsular and lipopolysaccharides. We considered that the use of a 4,6- O -benzylidene protected donor followed by regioselective deoxygenation after β-selective glycosylation, by a modification of either the Hanessian-Hullar 87 or the Roberts’ 88 acetal fragmentation chemistries, would be a suitable way to address this problem.…”

“…91 This methodology, which has been reviewed, 67b,92 was subsequently applied to the synthesis of a β-1,3-D-rhamnan 93 and to the 6-deoxy-β-D-mannoheptosides. 94 Seeking a perhaps more practical third generation method we turned to 6-deoxy-6-thia mannosyl donors with the 4,6-hydroxythiol unit tied up in a monothioacetal.…”

Synthesis of Staphylococcus aureus Type 5 Trisaccharide Repeating Unit: Solving the Problem of Lactamization

“…15 Recent studies indicate that preactivation of phenyl 2-azido-2-deoxy-3- O -benzyl-4,6-benzylidene-1-thio-α- d -mannopyranoside 1 with the powerful DPS/Tf 2 O promoter system 11b offers an attractive approach for selective β-glycosylations. Thus, activation of donor 1 was achieved at low temperature (−60 °C) with DPS/Tf 2 O in the presence of 2,4,6-tri- tert -butylpyrimidine (TTBP) in CH 2 Cl 2 .…”