T. Aboulfadl et Ea. Fouad, SYNTHESIS AND IN-VITRO INVESTIGATIONS OF NALIDIXIC-ACID AMIDES OF AMINO-ACID ESTERS AS PRODRUGS, Die Pharmazie, 51(1), 1996, pp. 30-33
For a new DDS of nalidixic acid (1) to overcome its therapeutic drawba
cks, amides of glycine ethyl ester and the methyl esters of alanine, p
henylalanine, leucine, isoleucine and valine, 2(a-f), were synthesized
as prodrugs, The stability of the prepared prodrugs in pH 1.2, 7.4 an
d 80% human plasma was investigated and showed higher stability in the
buffers than in the plasma. It was noticed that the reversion of the
parent drug from the synthesized prodrugs occurred through two steps,
the first was hydrolysis of the ester moiety with formation of nalidix
ic acid amides of the amino acids as intermediates. The second step wa
s the hydrolysis of these intermediates to 1 and the corresponding ami
no acid. The prodrugs showed an increase in the lipophilicity compared
with 1 as indicated from the log P values. The plasma protein binding
potency was studied in vitro using BSA and revealed a decrease in the
percentage bound in case of glycine and alanine derivatives (of low l
ipophilicity) and increase in the percentage bound of phenylalanine, l
eucine and isoleucine derivatives (of high lipophilicity). Lower bindi
ng potency and higher lipophilicity was observed in the case of valine
derivative, that was suggested to be owed to some steric hindrance wi
th the binding sites.