Eliminative cleavage

Another characteristic property of the products of /3-eliminative cleavage of pectic compounds is the reaction with thiobarbituric acid after previous cleavage with periodate, giving rise to red condensation products having229 an absorption maximum at 547-550 nm. Both properties are used for the identification of /3-eliminative cleavage of pectic substances. 

The periodate-thiobarbituric acid test developed by Waravdekar and Saslaw269 is used in the modification of Weissbach and Hur-witz229 for identification of the products of /3-eliminative cleavage. 

This enzyme [EC 4.2.2.3], also referred to as poly(j8-D-mannuronate) lyase and poly(mana) alginate lyase, catalyzes the eliminative cleavage of polysaccharides containing /3-D-mannuronate residues to give oligosaccharides with 4-deoxy-o -L-eryt/iro-hex-4-enopyranuro-nosyl groups at their ends. 

In a related study, Huang [34] has employed resin-bound selenosulfonate 202 in the radical cyclative-capture of 1,6-dienes such as 201 (Scheme 50). Oxidation and eliminative cleavage provided methylenetetrahydrofurans 204 in moderate yields. 

The radicals formed from this homolysis are unstable and each breaks down by cleavage of a C-C bond, generating CO2 and a radical phenyl radical. These homolytic bond elimination cleavages are elimination reactions and are the reverse of radical addition reactions. 

In the benzylidenated nitro glucoside181,185 139, and especially in the nitro galactoside186,187 176, the benzylidene group likewise is susceptible to eliminative cleavage in polar solvents, and this behavior may limit its usefulness as a protecting group. Nevertheless, acetals of this type have been found to survive carefully controlled... 

Eliminative cleavage of pectin to give oligosaccharides with terminal 4-deoxy-6-methyl-alpha-D-galact-4-enuronosyl groups. 

EC 4 Lyases Additions/Eliminations Cleavage of C-C-, C-O-, C-N-bonds one-substrate reactions two-substrate reactions - no co-factors required... 

An alternative to the -elimination cleavage uses a S-elimination mechanism by substituting the 2-cyanoethyl moiety by a 4-cyano-2-butenyl functionality, 9 [37]. This group is released conveniently with concentrated aqueous ammonium hydroxide for 2 h at room temperature. 

Strongly basic nonnucleophilic conditions such as 0.5 M DBU in di-oxane or pyridine were used by Eritja et al. [115] to effect the -elimination cleavage of a 4-ethyl-3-nitrobenzoyl carbonate linker, 44, allowing complete deprotection of oligonucleotides synthesized with p-nitrophenylethyl-based protecting groups under totally ammonia-free conditions [116]. 

V. Selective /3-Eliminative Cleavage of Natural Uronate-Sugar Conjugates.. . 238... 

The jS-eliminative cleavage of a molecular proportion of methane-sulfonic acid can be, carried out with alkali acetates nevertheless, the latter procedure needs more drastic conditions. In this way, compound 94 gave 95. 

On treatment of the terminally oxidized polynucleotides (ribo or 2 -de-oxyribo) with alkali, the / -eliminative cleavage of the pentofuranuronate residue was observed, resulting in the mononucleoside unit (144) having the characteristic 3,4-unsaturated 3-deoxypentofuranuronate residue. In addition, a shortened polynucleotide chain (145) was obtained, in... 

Figure 3. Eliminative cleavage mechanism for chondroitin lyase family.

A skeletal rearrangement of bicyclo[3.3.1]nonane-2,4,9-trione to the bicyclo[3.3.0] octane system is induced by an intramolecular Michael addition (Scheme 212). ° Anilines have been synthesised by a metal-free C-N bond formation accompanying eliminative cleavage through combined aryl C-O and amide C-N bond breakage (Scheme 213). ° ... 

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