630
3
Chemical Glycosylation Reactions
⊡ Scheme 62
DISAL-Based intramolecular glycosylation approach to 1,4-linked disaccharides
The tethered glycoside 381 underwent intramolecular transglycosylation to form the 1,4-linked
mannoside 382 as an anomeric mixture (α/β = 3.7:1) in moderate yield ( > Scheme 62b).
4.4 Application of DISAL Donors to Oligosaccharide Synthesis
Jensen and co-workers reported the synthesis of hexasaccharide 383, a starch-related hexasaccharide ( > Scheme 63) [198]. Their approach was based on the use of DISAL disaccharides
384 and 385, readily obtained from the corresponding disaccharide hemiacetals, for sequential glycosylations. Glycosylation of phenyl 1-thio disaccharide 386 with DISAL donor 385
took place with good yield and excellent α-selectivity in CH 3 NO 2 in the presence LiClO 4 and
Li 2 CO 3 . The trityl group that have survived the coupling, was next removed and the ensuing tetrasaccharide glycosylated with DISAL donor 384 (LiClO 4 , Li 2 CO 3 , (CH 2 Cl 2 ) 2 , 35 °C,
38% yield, α/β = 3:2).
DISAL donors have also been used in the preparation of phenazine natural products and
analogs [199].
4.5 2-Deoxy-2-amino Derivatives as DISAL Donors
Jensen and co-workers evaluated the behavior of different glucosamine-derived DISAL donors
in glycosylation reactions [200]. N-tetrachlorophthaloyl (TCP), N-trifluoroacetyl (TFAc), and
N-trichloroethoxycarbonyl (Troc) DISAL donors 387, 388, and 389 and 390, respectively,
were prepared from the corresponding hemiacetals ( > Fig. 6). Glycosylation of cyclohexanol,
in NMP at 60 °C, with these donors took place with yields ranging from 35 to 76%. The N-TCP
protected donor 387, was the least reactive. N-Troc protected donors 389 and 390, gave the
highest glycosylation yields with monosaccharides (63–71% yield), although they displayed
3
Chemical Glycosylation Reactions
⊡ Scheme 62
DISAL-Based intramolecular glycosylation approach to 1,4-linked disaccharides
The tethered glycoside 381 underwent intramolecular transglycosylation to form the 1,4-linked
mannoside 382 as an anomeric mixture (α/β = 3.7:1) in moderate yield ( > Scheme 62b).
4.4 Application of DISAL Donors to Oligosaccharide Synthesis
Jensen and co-workers reported the synthesis of hexasaccharide 383, a starch-related hexasaccharide ( > Scheme 63) [198]. Their approach was based on the use of DISAL disaccharides
384 and 385, readily obtained from the corresponding disaccharide hemiacetals, for sequential glycosylations. Glycosylation of phenyl 1-thio disaccharide 386 with DISAL donor 385
took place with good yield and excellent α-selectivity in CH 3 NO 2 in the presence LiClO 4 and
Li 2 CO 3 . The trityl group that have survived the coupling, was next removed and the ensuing tetrasaccharide glycosylated with DISAL donor 384 (LiClO 4 , Li 2 CO 3 , (CH 2 Cl 2 ) 2 , 35 °C,
38% yield, α/β = 3:2).
DISAL donors have also been used in the preparation of phenazine natural products and
analogs [199].
4.5 2-Deoxy-2-amino Derivatives as DISAL Donors
Jensen and co-workers evaluated the behavior of different glucosamine-derived DISAL donors
in glycosylation reactions [200]. N-tetrachlorophthaloyl (TCP), N-trifluoroacetyl (TFAc), and
N-trichloroethoxycarbonyl (Troc) DISAL donors 387, 388, and 389 and 390, respectively,
were prepared from the corresponding hemiacetals ( > Fig. 6). Glycosylation of cyclohexanol,
in NMP at 60 °C, with these donors took place with yields ranging from 35 to 76%. The N-TCP
protected donor 387, was the least reactive. N-Troc protected donors 389 and 390, gave the
highest glycosylation yields with monosaccharides (63–71% yield), although they displayed