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OAc
OAc
O
O
DDQ (3eq)
DCM/MeOH
4h
AcO
AcO
HO
OAc
NAPO
OAc
OAc
OAc
87%
OPiv
OPiv
O
DDQ (3eq)
DCM/MeOH
3.5 h
HO
NAPO
O
HO
HO
OBn
OBn
NAPO
OH
88%
NAPO
OBn
OBn
OBn
OBn
O
DDQ (3eq)
DCM/MeOH
2h
O
NAPO
HO
OBn
OMe
OBn
OMe
80%
FIGURE 1.23
Selective removal of NAP groups in the presence of benzyl ethers using DDQ
according to Matta et al. [39].
[40]. Interestingly, the NAP group can be cleaved also at room temperature using
entirely different conditions than Spencer and coworkers. Matta et al. [39] developed
a method based on DDQ. Figure 1.23 shows the conditions and yields. Recently,
Boons et al. [41] took advantage of this approach when synthesizing an unusual
phosphoglycopeptide derived from
-dystroglycan. Yields were equally high.
Kovensky and coworkers [42] demonstrated quantitative yields of the allyl group
removal from the anomeric position of allyl galactopyranosiduronic acid derivatives.
The authors employ a two-step procedure consisting of DABCO and (Ph
3
P)
3
RhCl
followed by mercuric-assisted cleavage. Their work is an excellent example of diffi-
culties one often encounters when employing a specific reactant to a novel structure.
It turned out that standard literature procedures lead to mixtures consisting of the
starting material, the desired product, and a significant amount of the allyl group
oxidation product. Most alternatives did not offer any improvement. Eventually, the
researchers developed a very successful method as shown in Figure 1.24.
Recently, Finnish and Hungarian scientists [43] have shown the effectiveness of
utilizing flow chemistry to deprotection of benzyl/benzylidene protected carbohy-
drates. While the required conditions (that were not optimized) include a relatively
high pressure of hydrogen (40 bar) and elevated temperature (80
◦
C), the method
offers excellent yields and does not affect such protecting groups as acetates and
silyl ethers. Figure 1.25 shows the results. The presented yields are isolated yields.
Das and collaborators [44] developed a method enabling an effective and mild
removal of a trityl group in the presence of various protecting groups. The method
employs silica-supported sodium hydrogen sulfate. Figure 1.26 shows the results.
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