Template, transient effect

Although the experimental data summarized above provide convincing evidence that a subtle and transient template effect resulting from a finely tuned Lewis-acid/Lewis-base interaction is operative in productive RCM-based macrocyclizations, it should be emphasized that a detailed spectroscopic characterization of the key intermediates involved has not yet been achieved. Therefore structure A represents just a mnemotic device indicating that polarity, distance, and affinity are key issues in such transformations but does not imply any structural information [32]. 

One of the more interesting hole size effects arises when the metal ion successfully acts as a template, but is labilised in the macrocyclic complex that is formed. The consequence of this is that the metal ion acts as a transient template. The metal ion may be viewed as pre-organising the reactants to form the macrocyclic products, but then finding itself in an unfavourable environment after the cyclisation. The effect is best observed when a small metal ion is used as a template for a reaction that can only give one product (or at least, only one likely product). What happens to the metal ion when it finds itself in an environment that does not match up to its co-ordination requirements The most useful consequence would be labilisation of the metal ion, with resultant demetallation and formation of the metal-free macrocycle. This would overcome one of the major disad-... 

In the polymerase-dependent mode (i.e., in the presence of dNTPs), the specificity of HIV-1 RTase/RNase H is defined by the binding of the polymerase active site to the primer 3 terminus. The RNase H active site is then positioned 18—19 nt from the primer 3 terminus. In this coupled mode, RTase/RNase H needs to be positioned only transiently at a site along the elongating primer to effect hydrolysis of the RNA template, generating oligoribonucleotide products 2—30 bases long. 

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