Synthesis, induced-fit docking investigations, and in vitro aldose reductase inhibitory activity of non-carboxylic acid containing 2,4-thiazolidinedione derivatives.

In continuation of our studies, we here report a series of non-carboxylic acid containing 2,4-thiazolidinedione derivatives, analogues of previously synthesized carboxylic acids which we had found to be very active in vitro aldose reductase (ALR2) inhibitors. Although the replacement of the carboxylic group with the carboxamide or N-hydroxycarboxamide one decreased the in vitro ALR2 inhibitory effect, this led to the identification of mainly non-ionized derivatives with micromolar ALR2 affinity. The 5-arylidene moiety deeply influenced the activity of these 2,4-thiazolidinediones. Our induced-fit docking studies suggested that 5-(4-hydroxybenzylidene)-substituted derivatives may bind the polar recognition region of the ALR2 active site by means of the deprotonated phenol group, while their acetic chain and carbonyl group at position 2 of the thiazolidinedione ring form a tight net of hydrogen bonds with amino acid residues of the lipophilic specificity pocket of the enzyme.

Evaluation of in vitro aldose redutase inhibitory activity of 5-arylidene-2,4-thiazolidinediones.

A number of 5-arylidene-2,4-thiazolidinediones containing a hydroxy or a carboxymethoxy group in their 5-benzylidene moiety have been synthesised and evaluated as in vitro aldose reductase (ALR2) inhibitors. Most of them exhibited strong inhibitory activity, with IC(50) values in the range between 0.20 and 0.70 microM. Molecular docking simulations into the ALR2 active site highlighted that the phenolic or carboxylic substituents of the 5-benzylidene moiety can favourably interact, in alternative poses, either with amino acid residues lining the lipophilic pocket of the enzyme, such as Leu300, or with the positively charged recognition region of the ALR2 active site.

Novel aldose reductase inhibitors derived from 6-[[(diphenylmethylene)amino]oxy]hexanoic acid.

Starting from the recently identified aldose reductase inhibitor 6-[[(diphenylmethylene)amino]oxy]hexanoic acid 1, the following systematic structural modifications were performed: (a) formal substitution of the phenyl rings, (b) isosteric replacement of the benzene core by the heteroarenes pyridine and thiophene, (c) formal reduction of the aromatic substructure and subsequent diminution of the cyclohexyl ring, (d) introduction of methylene spacer between C=N and the phenyl rings, and finally (e) formal ring closure in order to get derivatives of the tricycles fluorenone, xanthone, and thioxanthone, respectively. Out of these series, compounds 22-24 bearing disubstituted phenyl rings exhibit the highest inhibitory activity (IC(50 )value approx. 3 muM) which lie almost in the range of the reference sorbinil.

Synthesis and aldose reductase inhibitory activities of novel O-substituted hydroxyphenylacetic acid derivatives.

In continuation of our work aimed towards the preparation of novel aldose reductase inhibitors, several O-substituted hydroxyphenylacetic acid derivatives were investigated. The highest inhibitory activity was found for compounds 7b and 7c bearing a cyclohexylmethyl substituent. This result demonstrates that within these series, this moiety is a useful surrogate for the 4-bromo-2-fluorobenzyl residue which can be often found in potent aldose reductase inhibitors.

Discovery of novel aldose reductase inhibitors characterized by an alkoxy-substituted phenylacetic acid core.

In continuation of our effort aimed towards the development of novel aldose reductase inhibitors, several phenylacetic acids bearing an alkoxy substituent in position 3 or 4, respectively, were prepared and screened. The latter represent formal ring opening products of the cyclohexylmethyloxyphenylacetic acids IIa and IIb, recently elaborated in our group. Out of these series, compounds 4aa and 4ba characterized by an n-heptyloxy subunit turned out to be the most potent inhibitors. Based on these unexpected results, we suggest that such an alkyl side chain acts as a useful surrogate for the 4-bromo-2-fluorobenzyl residue often found in potent aldose reductase inhibitors.

In vitro aldose reductase inhibitory activity of 5-benzyl-2,4-thiazolidinediones.

Several 5-benzyl-2,4-thiazolidinediones (5-7) were synthesised and tested as in vitro aldose reductase (ALR2) inhibitors. Most of them, particularly N-unsubstituted 5-benzyl-2,4-thiazolidinediones 5 and (5-benzyl-2,4-dioxothiazolidin-3-yl)acetic acids 7, displayed moderate to high inhibitory activity levels. In detail, the insertion of an acetic chain on N-3 significantly enhanced ALR2 inhibitory potency, leading to acids 7 which proved to be the most effective among the tested compounds. In addition, in N-unsubstituted derivatives 5 the presence of an additional aromatic ring on the 5-benzyl moiety was generally beneficial. In fact, the ALR2 inhibition results of compounds 5-7, compared to those of the previously assayed corresponding 5-arylidene-2,4-thiazolidinediones, indicated that N-unsubstituted derivatives 5b, c and d, which bore an additional aromatic group in the para position of the 5-benzyl residue, were significantly more effective than their 5-arylidene counterparts; in all other cases, the saturation of the exocyclic double bond CC in 5 brought about a moderate decrease in activity.

Synthesis of novel phenylacetic acid derivatives with halogenated benzyl subunit and evaluation as aldose reductase inhibitors.

In the course of our ongoing studies several substituted benzyloxyphenylacetic acids were prepared. Comparison of their aldose reductase inhibition with the biological activity obtained for recently evaluated benzoic acid analogues revealed the critical role of a methylene spacer between the aromatic core and the acidic function. Starting from the most potent derivative (i.e. 5d, IC50 = 20.9 microM) further structural modifications were performed and their influence on the inhibitory effect was established.

Synthesis of novel benzoic acid derivatives with benzothiazolyl subunit and evaluation as aldose reductase inhibitors.

Several methyl benzothiazolyloxybenzoates, S-isosters, and the corresponding benzoic acids were synthesized and tested as aldose reductase inhibitors (ARIs). Out of this series, the ester derivative 2a-7 was found to exhibit the highest enzyme-inhibitoric activity. In order to investigate this unexpected result, further modifications were carried out which allowed us to explain this finding and to open a path to a novel class of ARIs.

On the synthesis of bioisosters of o-benzothiazolyloxybenzoic acids and evaluation as aldose reductase inhibitors.

In continuation of our attempts to develop novel aldose reductase inhibitors (ARIs), a number of compounds characterized by bioisosteric replacement of pharmacophors were prepared. On the one hand, the acidic function was formally replaced by an oxime or a nitro group and on the other hand the lipophilic substituent was modified. The results of the biological evaluation of these derivatives enabled us to gain insight into structural features critical for the aldose reductase inhibition.

Structure-activity relationships and molecular modelling of 5-arylidene-2,4-thiazolidinediones active as aldose reductase inhibitors.

The structure-activity relationships (SARs) of 5-arylidene-2,4-thiazolidinediones active as aldose reductase inhibitors (ARIs) were extended by varying the substitution pattern on the 5-arylidene moiety and on N-3. In particular, the introduction of an additional aromatic ring or an H-bond donor group on the 5-benzylidene ring enhanced ALR2 inhibitory potency. Moreover, the presence of a carboxylic anionic chain on N-3 was shown to be an important, although not essential, structural requisite to produce high levels of ALR2 inhibition. The length of this carboxylic chain was critical and acetic acids 4 were the most effective inhibitors among the tested derivatives. Molecular docking simulations into the ALR2 active site accorded with the in vitro inhibition data. They allowed the rationalization of the observed SARs and provided a pharmacophoric model for this class of ARIs.

On the prodrug potential of novel aldose reductase inhibitors with diphenylmethyleneaminooxycarboxylic acid structure.

Diphenylmethyleneaminooxycarboxylic acids were found to represent novel type inhibitors of the enzyme aldose reductase. Ester derivatives of the most active compound (3c) (IC(50)=33 microM) were prepared as potential prodrugs and the rate of degradation was studied by treatment with buffers, plasma, and various hydrolytic enzymes. Whereas all compounds were not hydrolysed at physiological pH, incubation in the presence of enzyme led to hydrolysis. The rate of enzymatic degradation, however, depended on the nature of the ester function. Whereas the isopropyl ester (4) turned out to be the most stable compound, the ethyl ester (2c) could be cleaved in the presence of esterase and lipase, respectively. The benzylic and aromatic esters were found to be hydrolysed rapidly in the presence of lipase (benzyl ester, 7), or in plasma, by cholinesterase and esterase (phenyl ester, 6), respectively.