Which is basic pyrrole or imidazole

New imidazole and indole derivatives -
Synthesis and in vitro biological tests

URN to cite this document:
urn: nbn: de: bvb: 355-epub-162660
Date of publication of this full text: 16 Aug 2012 09:10
Document Type:Thesis of the University of Regensburg (dissertation)
Date:16 August 2012
Reviewer (first reviewer):Prof. Dr. Siavosh Mahboobi
Examination day:July 27, 2010
Institutions:Chemistry and Pharmacy> Institute for Pharmacy> Chair of Pharmaceutical / Medicinal Chemistry I (Prof. Elz)
Thematic group:Not selected
Keywords / Keywords:Key words for part I: 1H-Imidazol-2-ylamine, pyrimidine, bioisosterism, receptor tyrosine kinases, imatinib, PDGF Key words for part II: SAR study, antibacterial compounds, indole derivatives, resistant Staphylococcus aureus, inflamation, NSAIDs
Dewey decimal classification:500 natural sciences and mathematics> 540 chemistry
Status:Released
Examined:Yes, this version has been reviewed
Developed at the University of Regensburg:Yes
Document ID:16266

Summary (German)

This work consists of 2 parts. In the first part a number of new N (3- (4- (pyridin-3yl) -1H-imidazol-2-ylamino) phenyl) amide derivatives should be synthesized. These derivatives should be tested for their inhibitory effect on PDGF and FLT3 receptor tyrosine kinase. The well-known tyrosine kinase inhibitor imatinib, which is a group of ...

Summary (German)

This work consists of 2 parts. In the first part a number of new N (3- (4- (pyridin-3yl) -1H-imidazol-2-ylamino) phenyl) amide derivatives should be synthesized. These derivatives should be tested for their inhibitory effect on PDGF and FLT3 receptor tyrosine kinase. The well-known tyrosine kinase inhibitor imatinib, which inhibits a group of tyrosine kinases, served as the lead structure for this synthesis. Particular mention should be made of PDGF-R, BCR-ABL and c-Kit.
Chemically, Imatinib is a phenylaminopyrimidine derivative that is substituted in the 4-position with a pyridine ring. The phenylamino partial structure is also substituted by a methyl group in the 6-position and a benzamide structural unit with a free NH group in the 3-position. The benzamide substituent is preferably equipped with a lipophilic substituent in the 4 position. To improve solubility and bioavailability, this lipophilic substituent is linked to a 1-methylpiperazine substituent. In this thesis, the synthesis of new imidazole derivatives as potential tyrosine kinase inhibitors based on the basic structure of imatinib was therefore the aim. Modifications should be made while maintaining the basic structure of Imatinib. To improve the selectivity and to investigate the structure-activity relationships in order to find structural requirements for the selective inhibition of the PDGF receptor. The central pyrimidine ring of imatinib was replaced by a bioisosteric imidazole ring. In addition to the 3 pyridyl substituents in position 4 (5) of the imidazolyl structure, derivatives with 4-pyridyl and phenyl substituents were also synthesized. The "flag methyl group" has been replaced by H and ethyl. An important modification was the replacement of the benzamide structure in position 3 with acetamide, arylamides and various substituted benzamides. The new 2-N-arylamino-4 (5) arylimidazole derivatives could be based on the synthesis route of phenylaminopyrimidine, which was first published by Zimmermann et al. synthesized. The synthesis was carried out by ring closure of various 2-bromo-1-aryl-ethanones with the appropriately substituted guanidinium nitrates. The corresponding amines could then be obtained by catalytic reduction of the nitro group with ammonium formate on Pd / C. These were reacted with the corresponding carboxylic acid chlorides in order to finally arrive at the target structures.
All newly presented imidazole derivatives were examined for their selectivity towards the FLT3 receptor. None of the investigated compounds influenced the FLT3 receptor up to a concentration of 10 µg / ml, a result that was also found for the lead structure imatinib. It can be deduced from this that the selectivity was conserved. In return, some of the imidazole derivatives, depending on their structural modifications, showed strong inhibitory effects on PDGF receptor phosphorylation (IC50 value of 0.2 μM). In comparison, imatinib has an IC50 value of 0.3 µM.
The examination of the structural changes on the inhibitory effects of the newly synthesized imidazole derivatives showed that the replacement of the pyrimidine by an imidazole system is well tolerated, the amide structure and the substitution with 3-pyridyl substituents are essential for the activity the introduction of the methyl group has little effect on the activity. In contrast to imatinib and independent of other structural modifications, the substitution of the imidazolyl analogs by a substituent in the para position of the benzamide substructure (usually 1-methylpiperazine) significantly weakened the activity. It was thus achieved to produce potent PDGF receptor inhibitors. The inhibitors of this class, like imatinib, show no inhibitory effect on the FLT3 receptor.
The aim of the second part of this work was to synthesize new indole derivatives and to investigate their antimicrobial activity against numerous bacterial and fungal strains, especially against multi-resistant epidemic strains, as well as their anti-inflammatory effect. Furthermore, some of these compounds were examined for their antiproliferative effects and their cytotoxicity.
Based on the lead structure 3-bromo-4- (1H-indol-3-yl) -2,5-dihydro-1H-2,5-pyrroldione, which was developed based on the structural framework and the biological effectiveness of acyriarubin, we were able to synthesize further indole derivatives. The idea was essentially to replace an indolyl substituent on the basic structure of the bisindolylmaleimide (Arcyriarubin A) with bromine, with the second indolyl substituent being retained. The starting point of our structure development is the lead structure of 3-bromo-4- (1H-indol-3-yl) -2,5-dihydro-1H-2,5-pyrroldione. The synthesized derivatives differ in chemical modifications. The indole skeleton was substituted in position 2, substituted and unsubstituted compounds on the imide nitrogen were synthesized and the bromine was replaced by nitrogen and sulfur substituents. The indole, which has the 4-methoxyphenyl substituent in the 2-position, was synthesized according to Bischler-Möhlau. The silyl-protected indolyl-maleimides were accessible by condensation of the indoles metallized in the 3 position by lithium hexamethyldisilylamide with silyl-protected dibromo-maleimide. The derivatives unsubstituted on the imide nitrogen were obtained after cleavage of the silyl protective group with tetrabutylammonium fluoride and reacted with various nitrogen and sulfur nucleophiles in Et3N and pyridine in order to exchange the bromine. For further investigations, the silyl-protected indolyl maleimides were each substituted on the imide nitrogen by reaction with an excess of alkylating agents (alkyl bromide, bromoethanol and 2-bromoethyl acetate) and TBAF. With regard to antimicrobial activity, it was generally found that the newly produced indole derivatives show no effects against gram-negative bacteria and against fungi and have a narrower spectrum of activity compared to ciprofloxacin. One reason for this could be that they have a different mechanism of action. On the one hand, there was selectivity against Gram-positive, multi-resistant epidemic bacterial strains S. aureus 134/49 (MRSA), which are resistant to the antibiotic ciprofloxacin, both among the series of derivatives unsubstituted on the imide nitrogen and the substituted derivatives. On the other hand, replacing bromine with nitrogen or sulfur nucleophiles causes a significant decrease in effectiveness. It can be stated that the effectiveness decreased with increasing length of the alkyl side chains. In contrast, the imide NH shows positive effects on the effectiveness. Furthermore, the substitution with the hydrophilic substituent on the imide nitrogen shows a stronger influence. These results are consistent with the results obtained when testing for anti-inflammatory activity. All of these effects require the presence of bromine on the maleimide backbone, but are independent of structural changes in position 2 of the indole backbone. The newly synthesized indole derivatives are notably cytotoxic for the HeLa cancer cell line and thus appear to be relatively toxic. With regard to their antiproliferative effect, the indole derivatives selectively inhibit the K-562 cell line, with GI50 values ​​of up to 0.5-0.8 µg / ml.
With regard to their anti-inflammatory activity, the new idol derivatives, whose bromine has been replaced by nitrogen or sulfur substituents, have good anti-inflammatory activity. In some cases, they provide good results that are comparable with the standards N-acetylcysteine ​​and indomethacin with regard to horseradish peroxidase and 3α-hydroxysteroid dehydrogenase. The activity against 3α-hydroxysteroid dehydrogenase could be due to a certain structural similarity with the standard indomethacin. In particular, the derivatives with CH3 at the 2-position of the indole are most effective and selective with regard to horseradish peroxidase. Based on these results, some substances were selected as lead structures for the further development of new derivatives by our working group.

Translation of the summary (English)

The thesis is divided into two parts. The first part deals with the synthesis of a series of new N- (3- (4- (pyridine-3yl) -1H-imidazole-2-ylamino) phenyl) amide derivatives. These derivatives were tested for their inhibitory effect on receptor tyrosine kinases. The lead compound for this synthesis was the well known tyrosine kinase inhibitor imatinib, which inhibits a group of tyrosine kinases. In ...

Translation of the summary (English)

The thesis is divided into two parts. The first part deals with the synthesis of a series of new N- (3- (4- (pyridine-3yl) -1H-imidazole-2-ylamino) phenyl) amide derivatives. These derivatives were tested for their inhibitory effect on receptor tyrosine kinases.
The lead compound for this synthesis was the well known tyrosine kinase inhibitor imatinib, which inhibits a group of tyrosine kinases. In particular, they are PDGF-R, BCR-ABL and c-Kit.
Chemically, Imatinib is a phenylaminopyrimidine derivative, which is substituted in the 4-position with a pyridine ring. The phenylamino partial structure is also substituted by a methyl group in 6-position “flag methyl group” and a benzamide moiety with a free NH group in position 3. The benzamide substituent is preferably equipped with a lipophilic substituent in position 4. This lipophilic substituent is linked with a 1-methylpiperazine substitute to improve the solubility and bioavailability.
The aim of the first part of this thesis was the synthesis of novel imidazole derivatives as potential inhibitors of tyrosine kinase based on the basic structure of imatinib. Modifications under maintaining the basic structure of imatinib have been made to improve the selectivity and to study the structure activity relationships in order to find structural conditions for the selective inhibition of the PDGF receptor. Here, the central pyrimidine ring of imatinib was replaced with a bioisosteric imidazole ring. Furthermore, derivatives with 4-pyridyl and phenyl substituent have also been synthesized in addition to the 3-pyridyl substituent in position 4 (5) of the imidazolyl scaffold. The “flag methyl group” was replaced by H and ethyl. The important modification was the replacement of the benzamide structure in position 3 by acetamide, arylamides, and various substituted benzamides. The synthesis of new 2-N-arylamino-4 (5) arylimidazole derivatives was based on the synthetic route of the phenylaminopyrimidins, which was synthesized for the first time by Zimmermann et al. The synthesis was carried out by cyclization of various 2-bromo-1-aryl-ethanones with the suitable substituted guanidine nitrates. The corresponding amines were subsequently accessible by catalytic reduction of a nitro group with ammonium formats. These were implemented with the corresponding acid chlorides, to finally reach the targeted structures. All newly synthesized imidazole derivatives were investigated for their selectivity against the FLT3 receptor.
Thereby, none of the investigated compounds influenced the FLT3 receptor up to a concentration of 10 µg / ml, this result as well found for the lead compound Imatinib.
This suggests that the selectivity was conserved. In turn, a few of the imidazole derivatives, depending on their structural modifications, showed strong inhibitory effect on the PDGF receptor phosphorylation (IC50 value of 0.2 µM). Imatinib by comparison has an IC50 value of 0.3 µM.
The examination of structural changes on the inhibitory effects of the newly synthesized imidazole derivatives showed that the replacement of pyrimidine by imidazole system is well tolerated, the amide structure and the substitution of 3-pyridyl substituent are essential for the activity and the introduction of the methyl group affects activity only slightly. In contrast to imatinib, and independent on other structural modifications the substitution in para position of the benzamide substructure (usually 1-methyl-piperazine) in the imidazolyl analogues weakened the activity significantly. It was, therefore, reached to produce potent PDGF receptor inhibitors, which show like imatinib, no inhibitory effect on the FLT3 receptor.
The aim of the second part of this thesis was to synthesize new indole derivatives, and investigate their antimicrobial activity against numerous bacterial and fungal strains, especially against multidrug-resistant epidemic strain (MRSA) as well as for their anti-inflammatory effect. Furthermore, some of these compounds were tested for their cytotoxicity and antiproliferative effects.
Based on the lead compound 3-bromo-4- (1H-indole-3-yl) -2,5-dihydro-1H-2,5-pyrroldions, which was developed based on the basic structural scaffold and biological activity of the Arcyriarubin A framework, so we could synthesize other indole derivatives. Essentially the idea was to replace the indolyl substituent in bisindolyl maleimide (Arcyriarubin A) by bromine; so that the second indolyl substitute was retained. The starting point of our structural development is the lead compound 3-bromo-4- (1H-indole-3-yl) -2,5-dihydro-1H-2,5-pyrroldione.
The synthesized derivatives differ in chemical modifications. The indole skeleton was substituted in position 2, substituted and non substituted derivatives at imide nitrogen were synthesized and the bromine replaced by nitrogen and sulfur substitents.
The indole with 4-methoxyphenyl substituent in the 2-position was synthesized according to Bischler-Möhlau. The silyl-protected indolyl maleimid were accessible by condensation at position 3 by lithiumhexamethyldisilylamid metallated indoles with silyl-protected dibromomaleimid. The unsubstituted derivatives of imid nitrogen were obtained after cleavage of the silyl protecting group with tetra-butylammonium fluoride and implemented with different nitrogen and sulfur nucleophiles in Et3N and pyridine to replace the bromine. For further investigations, the silyl-protected indolyl maleimides were substituted on imide nitrogen by reaction with an excess of alkylating agents (alkyl bromide, 2-bromoethanol and ethyl 2-bromoacetate) and TBAF. In view of the antimicrobial activity found in general that the newly produced indole derivatives show no effects against Gram-negative bacteria and fungi, and in comparison to ciprofloxacin they have a narrow spectrum of activity. The reason could be that they have a different mechanism of action. On the one hand, selectivity against Gram-positive multidrug-resistant epidemic strains S. aureus 134/49 (MRSA), which are resistant against antibiotic ciprofloxacin was observed, both within the series of the unsubstituted imide nitrogen and the substituted derivatives. On the other hand the replacement of bromine by nitrogen or sulfur nucleophiles causes a significant decrease in effectiveness. It can be stated that with increasing the length of alkyl side chains, the effectiveness decline gradually. In contrast, the imide NH shows positive effects on effectiveness. Furthermore, the substitution with the hydrophilic substitute on imide nitrogen shows a stronger influence.
These findings are consistent with the results when testing for anti-inflammatory activity. All of these effects presuppose the presence of bromine on maleimide backbone, but are independent on structural changes in position 2 of the indole skeleton. The newly synthesized indole derivatives are significantly cytotoxic for the HeLa cancer cell line and thus appear to be relatively toxic. In respect of its antiproliferative effect, the indole derivatives inhibit selectively the cell line K-562, with GI50 values ​​of up to 0.5-0.8 µg / ml. Regarding their anti-inflammatory activity, the new indole derivatives in which bromine replaced by nitrogen or sulfur substitents produce good anti-inflammatory activity. Partly they provide with the standards N-acetylcysteine ​​and indomethacin good comparable results regarding of horseradish peroxidase and 3α-hydroxysteroid dehydrogenase respectively. The activity against 3α-hydroxysteroid dehydrogenase may be due to a certain structural similarity with the standard indomethacin. In particular, indole derivatives with CH3 on 2-position regarding horseradish peroxidase are the most effective and selective.
Based on these results, some substances were selected as lead compounds for further development of new derivatives by our group.