Double cleavage

A moderate to strong peak at m/z 61 is present (see alkyl sulfide cleavage, above) in the spectrum of all except tertiary sulfides. When an a-methyl substituent is present, m/z 61 is the ion CH3CH=SH resulting from the double cleavage described above. Methyl primary sulfides cleave at the a,/3 bond to give the m/z 61 ion, CH3—s=ch2. 

After having shown that combination of two catalytic modules in one molecule results in twin ribozymes with double cleavage activity we wondered whether twin ribozymes can also catalyze RNA ligation and thus be used for catalysis of RNA fragment-exchange reactions. If all fragments (substrates and cleavage products)... 

Fragments derived from a double cleavage of the peptide main chain. 

The skeletal rearrangement of enynes proceeds through that kind of intermediates. Two basic types of products are obtained when an exo pathway is followed single cleavage and double cleavage, named owing to the fact that only the olefin or both the aUcene and the aUcyne are cleaved in the transformation. Some examples are depicted in equation (34-36). ... 

Any mechanism written for this preferential cleavage must take into account the double cleavage on both sides of the aspartyl residue that leads eventually to liberation of free aspartic acid (XXI). The nucleophilic concerted interactions (XVI-XVIII) pictured in the proposed mechanism may lead to a bicyclic orthoesteramide (XVII) which would collapse with the release of aspartic acid (XXI). Although the details of this tentative mechanism remain to be established, there is ample precedent for the formation of anhydride intermediates (XX) in intramolecular electro-... 

Reductive cleavage. Certain cyclic sulfonamides suffer double cleavage of C—S and N—S bonds, but an A -benzyl group is more labile. 

Carbonyl compounds can also act as the nucleophiles in intermolecular processes with 1,6-enynes. Thus, the gold (I)-catalyzed reaction between enynes and aldehydes or acetone gives stereoselectively tricyclic compounds (equation 71). The transformation is mechanistically intriguing, as it proceeds by a rearrangement of the initially formed cyclopropyl gold carbene (the intermediate in the double-cleavage mechanism), which is then trapped by the carbonyl compound to form the products. 

DCDC Double Cleavage Drilled Compression. See fracture... 

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