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Hyaluronicacid–properties,applicationandsynthesisofHAsubunits
25
24
1.LevOH,DlPC
DMAP,CH
2.TES,TFA
CH
2
Cl
2
2
Cl
2
25
2.NH
1.Ac
CH
2
CH
Cl
2
2
O,DMAP
NH
2
2
/MeOH
Cl
2
HOAc
2
26
Fig.17.Synthesisofglycosylacceptor26
Theorthogonallyprotectedanomericthioglucoside28wassynthe-
sizedfrom27.Thissynthesisinvolvedselectiveopeningoftheacetalring
followedbytreatmentwithlevulinicacid(Fig.18).
1.NaCNBH
3
,TFA
2.LevOH,DlPC
28
Fig.18.Theselectiveopeningoftheacetalringfollowedbytreatmentwithlevulinicacid
providingorthogonallyprotectedanomericthioglucoside28
27
28
26
CH
1.MeOTf,MS,
2.CAN,H
2
Cl
CH
2
,-30°C-RT
3
CN
2
O,
29
30
2.Mel,NaHCO
1.H
H
2
O,CH
5
lO
DMF
6
,CrO
3
CN
3
3
Fig.19.Synthesisofdisaccharide30
Thusobtainedthioglucosidedonor28wasreactedwiththeglucosa-
mineacceptor26usingMeOTfasanactivator.Then,thecrudereaction
mixturewastreatedwithCANtoremovethePMBether.Finally,oxida-
tionoftheresultingcompound29followedbytreatmentwithMeIinthe
presenceofNaHCO3afforded30inratherlowyield(39%),stillcontami-
natedwiththeunreacteddisaccharide29(Fig.19).Similarlytothedi-
