Oligomerization reactions of deoxyribonucleotides on montmorillonite clay: The effect of mononucleotide structure, phosphate activation and montmorillonite composition on phosphodiester bond formation

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Abstract
2′-d-5′-GMP and 2′-d-5′-AMP bind 2 times more strongly to montmorillonite 22A than do 2′-d-5′-CMP and 5′-TMP. The dinucleotide d(pG)2 forms in 9.2% yield and the cyclic dinucleotide c(dpG)2 in 5.4% yield in the reaction of 2′-d-5′-GMP with EDAC in the presence of montmorillonite 22A. The yield of d(pC)2 (2.0%) is significantly lower but comparable to that obtained from 5′-TMP. The yield of dimers which contain the phosphodiester bond decreases as the reaction medium is changed from 0.2 M NaCl to a mixture of 0.2 M NaCl and 0.075 M MgCl2. A low yield of d(pA)2 was observed in the condensation reaction of 5′-ImdpA on montmorillonite 22A. The cyclic nucleotide (3′,5′-cdAMP) was obtained in 14% yield from 3′-ImdpA. The yield of d(pA)2 obtained when EDAC is used as the condensing agent increases with increasing iron content of the Na+-montmorillonite used as catalyst. Evidence is presented which shows that the acidity of the Na+-montmorillonite is a necessary but not sufficient factor for the montmorillonite catalysis of phosphodiester bond formation.