Inoue and Orgel

Inoue and Orgel (1981) found that the oligomerisation of guanosine-5 -phosphoimidazolide on a poly(C) matrix can take place in the absence of Pb2+ or Zn2+, if guanosine-5 -phospho-2-methylimidazolide is used for the oligo-G synthesis. 

A further unusual feature of the matrix-dependent polycondensation lies in the character of the nucleobases themselves. Purine mononucleotides undergo polycondensation, in good yields, at complementary matrices consisting of pyrimidine polymers. However, the synthesis of pyrimidine oligonucleotides from their mononucleotides at purine matrices is not effective. This important fact means that a pyrimidine-rich matrix leads to a purine-rich nucleic acid, which is itself not suitable to act as a matrix. This phenomenon also occurs when matrices are used which contain both basic species, i.e., purines and pyrimidines. An increase in the amount of purine in a matrix leads to a clear decrease in its effectiveness (Inoue and Orgel, 1983). However, the authors note self-critically that the condensation agent used cannot be considered to be prebiotic in nature. 

This scheme can indeed be implemented by chemistry thus, the pen-tamer pGGCGG, for example, was obtained from a mixture of 5 -(2-methyl)-phosphorimidazolide derivatives of guanosine and cytidine in the presence of the complementary CCGCC as a template (Inoue and Orgel, 1983) see Scheme 4.1. Later, even longer templates were successfully used (Orgel, 1992) for a review of these, and other work, see Orgel, 1995. 

Catalytic systems based on polymerized purines and pyrimidines have been reported (a) T. Inoue and L. E. Orgel Science (Washington D.C.) 219, 859 (1983) R. Naylor and P. T. Gilham Biochemistry 5, 2722 (1966). 

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