Naslov
Transacylation in Ferrocenoyl-Purines. NMR and Computational Study of the Isomerization Mechanism

Autori
Toma, Mateja ; Božičević, Lucija ; Lapić, Jasmina ; Djaković, Senka ; Šakić, Davor ; Tandarić, Tana ; Vianello, Robert ; Vrček, Valerije

Izvornik
Journal of organic chemistry (0022-3263) 84 (2019), 19; 12471-12480

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
ferrocene ; purine ; acyl migration ; NMR ; DFT ; MD

Sažetak
In the reaction of purines with ferrocenoyl chloride in dimethylformamide (DMF), a regioselective acylation occurred. The two products have been isolated and, according to detailed NMR analysis, identified as N7- and N9-ferrocenoylated isomers. In more polar solvent, e.g. in dimethylsulfoxide (DMSO), the two isomers interconvert to each other. The N7/N9 isomerization was followed by 1H NMR spectroscopy, until dynamic equilibrium was reached. Both kinetics and thermodynamics of the transacylation process are governed by C6-substituent on the purine ring (R = NH2, Me, NHBz, OBz). The observed rate constant for the N7/N9-isomerization in the adenine system (R = NH2) is kobs = 0.3668 h-1, whereas the corresponding process in the C6-benzyloxypurine is 56 times slower. By use of DFT calculations and MD simulations, several reaction pathways were considered and explored. Only the reaction mechanism involving DMSO as nucleophilic reactant, is in harmony with the experimental kinetic data. The calculated barrier (ΔG‡ = 107.9 kJ/mol ; at the M06L/6-311+G(d, p)/SDD level of theory) for this SN2-like reaction in the adenine system agrees well with the experimental value of 102.7 kJ/mol. No isomerization was detected in other organic solvents, e.g. acetonitrile, N, N-dimethylformamide, or acetone, which indicated the exceptional nucleophilicity of DMSO. Our results raise a warning when treating or dissolving acylated purines in DMSO as they are prone to isomerization. We observed that the N7/N9-group transfer was specific not only for the organometallic moiety only, but for other acyl groups in purines as well. The relevance of this isomerization may be expected for a series of nucleobases and heterocyclic systems in general.

Izvorni jezik
Engleski

Znanstvena područja
Kemija, Farmacija

POVEZANOST RADA