Armed-disarmed approach

Another efficient strategy, the armed-disarmed approach, developed by Fraser-Reid is based on the chemoselectivity principle [193,202]. According to this... 

SCHEME 6.36 Mong s one-pot synthesis of trisaccharide 180 through combination of selective activation and armed-disarmed approach. 

Z. Li and J. C. Gildersleeve, An armed-disarmed approach for blocking aglycon transfer of thioglyco-sides, Tetrahedron Lett., 48 (2007) 559-562. 

The classic armed-disarmed approach, developed by Fraser-Reid, has created a solid basis for extensive studies and applications, and all strategies discussed in this section are related to (or derived from) this elegant concept. The key factor for the armed-disarmed activation to take place is the availability of a suitable promoter that differentiates between the armed and disarmed building blocks. While in most cases the differentiation of the reactivity between armed and disarmed species is maintained by the choice of promoter or temperature, the solvent effect observed by Oscarson may become a useful technique for future assemblies.160 Thus, it was demonstrated that highly reactive substrates could be activated in diethyl ether, whereas poorly reactive disarmed derivatives had to be activated in CH2CI2. 

SCHEME 33. Synthesis of cm—as-patterned oligosaccharide 170 via armed-disarmed approach. 

Sequential trisaccharide syntheses were carried out [48] with the use of the superarmed glycosyl donor 106, thus allowing to introduce a 1,2-trans linkage prior to other linkages. This is not possible in classic armed-disarmed approach. In the first sequence, a stepwise coupling of building blocks 106 and 129 and the... 

Troc Can be removed in the presence of acyl groups and acid/base labile groups, such as amino acids Armed-disarmed approach... 

Additionally, the arming and disarming properties of the STaz glycosides were evaluated. It was demonstrated that activated (benzylated) STaz derivatives could be activated over electronically disarmed (partially acylated) STaz glycosyl acceptors in die presence of either AgOTf or Cu(OTf)2 78). For example, a classic armed-disarmed approach (79) allowed chemoselective activation of 54 over disarmed acceptor 61 in the presence of Cu(OTf)2to afford... 

Selective activation utilising the armed/disarmed approach, where the glycosyl donor is preferentially activated under the reaction conditions glycosylation of (2 5,3 5) phenyl 6-<9-chloroacetyl-3,4-(9-(2, 3 -dimethoxybutane-2, 3 -diyl)-l-seleno-a-D-mannopyranoside with phenyl 2,3,4-tri-(9-benzyl-6-(9-ferf-butyldi-methylsilyl-1 -seleno-a-D-mannopyranoside [28]. 

Scheme 5 Synthesis of cis-cw-pattemed trisaccharide 10, via the modified armed-disarmed approach [34]...

It was also demonstrated that disarmed disaccharide 87 (obtained by classic armed-disarmed approach from building blocks 61 and 86, Scheme 17) could be further chemoselectively activated over superdisarmed building block 88. 

Smoot JT, Demchenko AV (2008) How the arming participating moieties can broaden the scope of chemoselective oligosaccharide synthesis by allowing the inverse armed-disarmed approach. J Org Chem 73 8838-8850... 

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