Sequence-controlled polymers ROMP

The investigations directed at the synthesis of thymine-substituted polymers demonstrate that the type of functional groups displayed by nucleic acid bases are compatible with ROMP. Moreover, the application of MALDI-TOF mass spectrometry to the analysis of these polymers adds to the battery of tools available for the characterization of ROMP and its products. The utility of this approach for the creation of molecules with the desired biological properties, however, is still undetermined. It is unknown whether these thymine-substituted polymers can hybridize with nucleic acids. Moreover, ROMP does not provide a simple solution to the controlled synthesis of materials that display specific sequences composed of all five common nucleic acid bases. Nevertheless, the demonstration that metathesis reactions can be conducted with such substrates suggests that perhaps neobiopolymers that function as nucleic acid analogs can be synthesized by such processes. 

Grubbs has investigated the stereochemistry of ROMP using titanocene—metallacyclobutane complexes. These complexes offer little control over olefin stereochemistry or tacticity in the polymerization of norbornene. ° However polymerization of rac-1-methylnorbornene yielded a polymer with 90—95% trans-olefins and a partially regioregular (head—tail) sequence of monomers (the tacticity of the polymer was not determined). Using a related CpzTi—metallacyclobutane complex, a polymer of anti-7-methyl-norbornene was formed that was 80% trans in configuration and was partially syndiotactic ([r] =... 

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