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Complementary short-strand DNA homooligomers and guanidinium-linked homonucleosides associate and form triplexes in solution. The melting temperatures, T m , the association and dissociation kinetic and thermodynamic parameters, and activation energies were determined by UV thermal analysis for the triplexes of short strand DNA homooligomers {d(pA) 5 -d(pA) 12-18 } and poly(dA) with the guanidinium-linked nucleoside d(Tg) 4 -T-azido {DNG 5 }. The melting and cooling curves exhibit hysteresis behavior in the temperature range of 5-95°C at 0.2 deg/min thermal rate. From these curves the rate constants and the energies of activation for association (k on , E on ) and dissociation (k off , E off ) processes were obtained. The T m decreases with the ionic strength and increases slightly with increase in concentration of the monomers. A greater increase in the T m results from an increase in the length of the DNA strand d(pA) x . In the case of d(pA) 5 and d(pA) 6 , triplexes are formed, with T m ) 34 and 39°C, respectively, only above 0.063 mM/(adenine base) concentration when ionic strength is 0.08. The rate constants k on and k off at a reference temperature (288 K) are dependent on the DNA strand length and also decrease and increase respectively with the ionic strength. The energies of activation for the association and dissociation processes are in the range of -10 to -50 and 17 to 44 kcal/mol, respectively. The equilibrium for the formation of the triplexes {(d(Tg) 4 -T-azido) 2 ‚d(pA) x , x ) 5-10)} is favored by several orders of magnitude when compared to the triplexes of DNA. The standard molar enthalpies for triplex formation have larger negative values at low ionic strength than at high ionic strength indicating that at lower µ values the formation of triplexes of d(Tg) 4 -T-azido with d(pA) x is more favored. The values of ∆H°(288) calculated from the activation parameters are between -30 and -60 kcal/ (mol base) and the values of ∆G°(288) are between -8 and -13 kcal/(mol base) for short-strand DNA. There is a linear relationship in the enthalpy-entropy compensation for the triplex-melting thermodynamics.

Adenosine 3‘-O(PO2 -)OCH2R phosphate esters have been synthesized with R = 8-hydroxyquinol-2-yl (1a) and 8-(hydroxyquinolyl)-2-methylene (1b). The adenosine 3‘-O(PO2 -)OCH2R structure has the essential features of an RNA dinucleotide. Equilibrium binding studies with metal ions Mg2+, Zn2+, Cu2+, and La3+ have been carried out with 1a, 1b, HOCH2R (7a and 7b), and 8-hydroxyquinoline (8), and equilibrium constants (K as) have been determined for the formation of 1:1 (L)M n + complexes. The hydrolysis of 1a and 1b as well as (1a)M n + and (1b)M n + species are first order in HO-. The rate enhancement for hydrolysis of 1a by complexation with metal ions is as follows:  ∼105 with Zn2+, ∼103 with Mg2+, ∼105 with Cu2+, and ∼109 with La3+. Molecular modeling indicates that metal ions ligated to the 8-hydroxyquinoline moiety in the complexes (1a)M n + and (1b)M n + catalyze 1a and 1b hydrolysis by interacting as Lewis acid catalysts with the negatively charged oxygen atom of the phosphate group. In the instance of La3+ complexes, the ligated metal ion is within an interactive distance with both the negative phosphate oxygen and the leaving oxygen. This bimodal assistance by La3+ to the displacement reaction at phosphorus by the 2‘-hydroxyl anion results in remarkable rate accelerations for the hydrolysis of (1a)La3+ and (1b)La3+ complexes. The complexes (1a)M n + and (1b)M n + are themselves hydrolyzed by metal ion catalysis in a reaction that is first order in HO-, an observation consistent with a transition state composition of [(1a,b)M n +][M n +][HO-]. We assume the kinetic equivalent [(1a,b)M n +][M n +OH] to represent the reacting species. In this catalysis the M n +OH is proposed to play the role of general base to deprotonate the 2‘-OH while the metal in the complexes (1a,b)M n + is coordinated to a negative oxygen of the −(PO2 -)− moiety. This double metal ion catalysis mimics a mechanism proposed for the ribozyme self-cleavage of RNA.

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The basic strategy is described for the connection of nucleosides by guanidinium (g) linkers to provide the positively charged deoxynucleic guanidine putative antigene agents. The synthetic procedures are provided for d(gT)". MATERIALS AND METHODS Synthesis. General procedures. All TLC was run with Merck silica gel 60 (F254) plates. High-resolution mass spectra were obtained from the mass spectrometry laboratory of the University of California at Los Angeles.S'-t-Butylcarbamoyl-S'-deoxythymidine (2; Scheme I). To a suspension of 5'-amino-5'-deoxythymidine (2) (4.0 g, 16.6 mmol) in 100 ml of dry NN-dimethylformamide (DMF) was added triethylamine (TEA, 4.4 ml, 18.2 mmol) followed by dropwise addition of di-t-butyl dicarbonate (4.2 ml, 31.6 mmol). The resulting solution was stirred at room temperature for 30 min and then evaporated to dryness. The residue was crystallized from water: yield, 5.5 g (97%); m.p. 1640C; TLC (5% methanol in ethyl acetate) Rf = 0.43; IR (KBr) 3381,