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O
OAc
N
N
3
O
O
+
OAc
O
O
O
cat. Cu(I)
quantitative
AcO
OAc
n
O
2
N
OAc
O
N
N
N
O
N
OAc
O
O
AcO
O
O
OAc
n
n = 1, 2, 3
NO
2
FIGURE 1.16
Maki and Ishida's [32] synthesis of compounds containing carbohydrate and
photocleavable parts.
1.5.2 Photocleavage
Maki and Ishida [32] designed and synthesized photocleavable molecules for laser
desorption ionization-mass spectrometry (LDI-MS). The authors envisaged that a
photocleavable molecule, which affords an MS-detectable ion upon irradiation with-
out matrix assistance, would simplify the ionization mechanism and be a reliable and
selective labeling device for LDI-MS. As expected, the connection takes advantage of
the click chemistry. The final step of the synthetic procedure is shown in Figure 1.16.
The cleavage takes place under the laser pulse at 337 nm.
Ju and coworkers [33] designed and synthesized a 3
-modified photocleavable flu-
orescent nucleotide, 3
-
O
-allyl-dUTP-PC-Bodipy-FL-510 (PC-Bodipy, photocleav-
able 4,4-difluoro-4-bora-3
-diaza-s-indacene), as a reversible terminator for DNA
sequencing by synthesis (SBS). Figure 1.17 shows the design and synthesis of the
product.
,4
1.5.3 Chemical Cleavage
Manabe, Ueki, and Ito [34] developed a very convenient method of deprotecting
propargyl ethers using the samarium-amine-water system. The method requires
little time (usually 15 minutes), reactions take place at room temperature, offer good
yields, and chemoselectivity (Fig. 1.18). The method was applied to the solid state
synthesis of oligosaccharides (Fig. 1.19).
At this point, it is impossible to say if the same decoupling can be applied to a
propargyl group in which one of the hydrogen atoms (in either of the two possible
positions) was replaced with a large (macromolecular) substituent.
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