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Acyloxymethyl as a Drug Protecting Group. Part 3. Tertiary O-Amidomethyl Esters of Penicillin G: Chemical Hydrolysis and Anti-Bacterial Activity


Purpose. O-(N-alkylamido)methyl esters of penicillin G were studied as a new class of prodrugs.

Methods. Their hydrolysis in aqueous buffers containing 20 % (v/v) of acetonitrile was investigated by HPLC.

Results. A U-shaped pH-rate profile was seen with a pH-independent process extending from pH ca. 2 to pH ca. 10. This pathway is characterised by kinetic data that are consistent with a uni-molecular mechanism involving rate-limiting iminium ion formation and penicillinoate expulsion. Penicillin G and the corresponding amide are the ultimate products detected and isolated, indicating that β-lactam ring opening is much slower than ester hydrolysis. The O-(N-alkylamido)methyl esters of penicillin G displayed similar in vitro antibacterial activity to penicillin G itself.

Conclusions. Compared to the penicillin G derivatives, the much higher stability of the O-(N-methylbenzamido)methyl benzoate, acetate and valproate esters (which gave rise to a Bronsted βlg value of ca. -1) suggests that tertiary N-acyloxymethylamides may be useful prodrugs for carboxylic acid drugs with pKa >4.

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  1. H. Bundgaard. Design of Bioreversible Drug Derivatives and the Utility of the Double Prodrug Concept. In E.B. Roche (Ed.), Bioreversible Carriers in Drug Design: Theory and Application; Pergamon Press, New York, 1987; pp. 13–94.

    Google Scholar 

  2. J.N. Iley, R. Moreira, and E. Rosa. Triazene drug metabolites. 4. Kinetics and mechanism of the decomposition of 1-aryl-3-benzoyloxymethyl-3-methyltriazenes in mixed aqueous-organic solvents. J. Chem. Soc. Perkin Trans. 2: 1503–1508 (1987).

    Google Scholar 

  3. M. Johansen and H. Bundgaard. Pro-drugs as drug delivery systems. XVI. Novel water-soluble pro-drugs types for chlorzoxazone by esterification of the N-hydroxymethyl derivative. Arch. Pharm. Chemi, Sci. Ed. 9: 43–54 (1981).

    Google Scholar 

  4. H. Bundgaard and G.J. Rasmussen. Prodrugs of peptides. 11. Chemical and enzymatic hydrolysis kinetics of N-acyloxymethyl derivatives of a peptide-like bond. Pharm. Res. 8: 1238–1242 (1991).

    Google Scholar 

  5. S.A. Varia; S. Schuller; K.B. Sloan, and V.J., Stella. Phenytoin prodrugs. III. Water-soluble prodrugs for oral and parenteral use. J. Pharm. Sci. 73: 1068–1073 (1984).

    Google Scholar 

  6. A. Buur, H. Bundgaard, and E. Falch. Prodrugs of 5-fluorouracil. IV. Hydrolysis kinetics, bioactivation and physicochemical properties of various N-acyloxymethyl derivatives of 5-fluorouracil. Int. J. Pharm. 24: 43–60 (1985).

    Google Scholar 

  7. H. Bundgaard and N.M. Nielsen. Prodrugs as drug delivery systems. 74. Facile hydrolysis of N-(acyloxymethyl)amide derivatives and implications for the design of prodrugs of NH-acidic compounds and of carboxylic acids. Acta Pharm. Suec. 24: 233–246 (1987).

    Google Scholar 

  8. J. Iley, R. Moreira, and E. Rosa. Acyloxymethyl as a drug protecting group. Kinetics and mechanism of the hydrolysis of N-acyloxymethylbenzamides. J. Chem. Soc. Perkin Trans. 2: 563–570 (1991).

    Google Scholar 

  9. W.J. Wheeler, P.A. Preston, W.E. Wright, G.W. Huffman, H.E. Osborn, and D.P. Howard. Orally active esters of cephalosporin antibiotics. 3. Synthesis and biological properties of amino-acyloxymethyl esters of [D-(−)-mandelamido]-3-[[(1-methyl-1H-tetrazol-5-yl)thio]methyl]-3-cephem-4-carboxylic acid. J. Med. Chem. 22: 657–661 (1979).

    Google Scholar 

  10. M.I. Page. The mechanisms of reactions of β-lactam antibiotics. Adv. Phys. Org. Chem. 23: 165–270 (1987).

    Google Scholar 

  11. R. Moreira, E. Mendes, T. Calheiros, M.J. Bacelo, and J. Iley. A new direct synthesis of tertiary N-acyloxymethylamide prodrugs of carboxylic acid drugs. Tetrahedron Lett. 35: 7107–7110 (1994).

    Google Scholar 

  12. S. Winstein and A.H. Fainberg. Correlation of solvolysis rates. IV. Solvent effects on enthalpy and entropy of activation for solvolysis of t-butyl chloride. J. Am. Chem. Soc. 79: 5937–5950 (1957).

    Google Scholar 

  13. J.S. Lomas and J.-E. Dubois. Solvent effects in the solvolysis of aryl di-tert-butylcarbinyl p-nitrobenzoates in aqueous acetic acid. Substituent effects on transition state charge separation. J. Org. Chem. 40: 3303–3305 (1975).

    Google Scholar 

  14. N.-A.T. Nguyen, L.M. Mortada, and R.E. Notari. Potential improvement in the shelf life of parenterals using the prodrug approach: bacampicillin and talampicillin hydrolysis kinetics and utilization time. Pharm. Res. 5: 288–296 (1988).

    Google Scholar 

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Moreira, R., Calheiros, T., Cabrita, J. et al. Acyloxymethyl as a Drug Protecting Group. Part 3. Tertiary O-Amidomethyl Esters of Penicillin G: Chemical Hydrolysis and Anti-Bacterial Activity. Pharm Res 13, 70–75 (1996).

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  • O-amidomethylation
  • penicillin G
  • carboxylic acids
  • prodrugs
  • hydrolysis kinetics
  • mechanism of hydrolysis
  • antibacterial activity