Synthesis of novel acridine bis-sulfonamides with effective inhibitory activity against the carbonic anhydrase isoforms I, II, IX and XII.

TL;DR: By using a multi component reaction system (MCR), nitro acridine sulfonamides were obtained from cyclic-1,3-diketones, 4-aminobenzene sulfonamide and aromatic aldehydes and showed low micromolar inhibition against the medically relevant isoforms hCA I, II, IX, and XII.

About: This article is published in Bioorganic & Medicinal Chemistry.The article was published on 2015-10-15 and is currently open access. It has received 25 citations till now. The article focuses on the topics: Carbonic anhydrase II & Carbonic Anhydrase I.

Summary

1. Introduction

• Acridines are planar tricyclic aromatic compounds which contain nitrogen in the heterocyclic ring.
• 14 The sulfonamides and their isosteres such as the sulfamates and sulfamides, are established CAIs and are in clinical use for almost Chart 1.
• The large use of CAIs for pharmaceutical applications relies on the wide distribution of the 15 human (h) CA isoforms within different tissues as well as on their implication in many physiological/pathological conditions.
• 13,14 In vivo experiments showed that silencing of hCA IX reduces xenograft tumors to 40% of the volume along with up-regulation response of the gene encoding for hCA XII.

2.1. Chemistry

• The general synthetic method, three steps reaction shown in Scheme 1, was used to prepare the nitro acridine derivatives (4a and 4b), novel amino acridine compounds (5a and 5b) and novel acridine bis-sulfonamide compounds (6a–l).
• For the second step, new amino acridine derivatives (5a and b) were synthesized by using excessive reduction reactive—aqueous sodium poly-sulfide—from nitro acridine compounds (4a and 4b) at reflux temperature with high yields (respectively, 87% and 82%).
• For the compounds 6b, 6e, 6h and 6k singlet peaks were observed in between 2.18 and 2.52 ppm belong to protons of the methyl group.
• Standard errors were in the range of ±5–10% of the reported values (data not shown).

2.2. Carbonic anhydrase inhibition

• The new compounds reported here and the standard drug acetazolamide were assayed as inhibitors of four cytosolic human isoforms, hCA I, II, IX and XII (Table 1).
• It was observed that increasing of the bulkiness of the tails for the compound series 4a, 4b, and 6a–f (Chart 2) resulted with slight increasing of KI values, that is, decreasing on inhibitory effect, in the range of 0.69–6.92 lM.
• For the dominant cytosolic isoform hCA II, as for isoform CA I, it was observed that the new derivatives were rather ineffective inhibitors, showing a limited range of inhibitory power, with a variation of KI between 0.10 and 0.96 lM.

3. Conclusion

• There are still many important drug design aspect to be addressed for obtaining isoform-selective and more effective sulfonamide CAIs.
• Considering their interest in sulfonamides, herein the authors investigate a new series of acridine bis-sulfonamides which have been obtained by using multicomponent reaction techniques.
• The compounds were characterized by physicochemical methods and tested for their in vitro inhibition activity against the CA isoforms I, II, IX and XII.
• Several compounds showed low micromolar inhibition against the pharmacologically relevant isoforms hCA I, II, IX, and XII.
• The prepared compounds containing both acridine ring and sulfonamide group are thought to be of interest because sulfonamides are used in the treatment of many diseases, possessing antimicrobial, antimalarial, antiglaucoma, and anticancer properties.

Figures

Table 1 CA inhibition data for compounds (4a, 4b), (5a, 5b), (6a-l) and standard inhibitors against human isozymes hCA I, II, IX and XII by a stopped flow CO2 hydrase assay32

Frequently asked questions

Q1. What have the authors contributed in "Synthesis of novel acridine bis-sulfonamides with effective inhibitory activity against the carbonic anhydrase isoforms i, ii, ix and xii" ?

In this paper, a multi component reaction system ( MCRS ) was used to synthesize acridine sulfonamides from cyclic-1,3-diketones, 4-aminobenzene sulfonamide and aromatic aldehydes. 

Q2. What is the effect of hCA IX on tumor growth?

In vivo experiments showed that silencing of hCA IX reduces xenograft tumors to 40% of the volume along with up-regulation response of the gene encoding for hCA XII. 

Q3. What group of protons were observed in the compounds 6b, 6e, 6h and?

For the compounds 6b, 6e, 6h and 6k singlet peaks were observed in between 2.18 and 2.52 ppm belong to protons of the methyl group. 

Q4. What is the effect of the compounds on the sulfonamides?

The prepared compounds containing both acridine ring and sulfonamide group are thought to be of interest because sulfonamides are used in the treatment of many diseases, possessing antimicrobial, antimalarial, antiglaucoma, and anticancer properties. 

Q5. What is the effect of the hCA IX on the cytosolic iso?

The small range of inhibitory power of these compounds against the two transmembrane isoforms may be due to the fact that the variations in the structure are at rather distant parts of the tail from the primary sulfonamide, and the authors hypothesize that these parts of the molecules lay outside the active site, affording thus for less specific interactions with amino acid residues crucial for the binding of inhibitors. 

Q6. What is the role of acridine in the treatment of glaucoma?

12,13 Furthermore, many acridine sulfonamides are known as strong carbonic anhydrase (CA, EC 4.2.1.1) inhibitors (CAIs), potentially useful for the treatment glaucoma9,10 or other conditions, which the activity of the CA isoforms are deregulated. 

Q7. What is the main drawback of CAIs for pharmaceutical applications?

The large use of CAIs for pharmaceutical applications relies on the wide distribution of the 15 human (h) CA isoforms within different tissues as well as on their implication in many physiological/pathological conditions. 

Q8. What is the KI of the new derivatives?

For the dominant cytosolic isoform hCA II, as for isoform CA I, it was observed that the new derivatives were rather ineffective inhibitors, showing a limited range of inhibitory power, with a variation of KI between 0.10 and 0.96 lM. 

Q9. What is the main drawback associated with the use of CAIs?

The main drawback associated to the use of CAIs is represented by the lack of selectivity in inhibiting various isoforms by many of the first and second generation CAIs, thus resulting in a plethora of side effects. 

Q10. What is the structure of the new compounds?

20–22 Moreover novel CAIs classes such as the polyamines,23 phenols,24 dithiocarbamates,25 xanthates,26 coumarins, thiocoumarins, 2-thioxo-coumarins and coumarin oximes16,27–29were identified and their inhibition mechanisms of many of these compounds were determined by means of X-ray crystallography CA II adducts. 

Q11. What is the main drawback associated with the use of CAIs for pharmaceutical applications?

It should be stressed that currently a sulfonamide CA IX inhibitor (SLC0111) entered in Phase The authorclinical studies for the treatment of hypoxic, advanced stage metastatic solid tumors. 

Q12. What are the common acridine derivatives?

Well-known drugs containing the acridine moiety include Amsacrine, Asulacrine, Acronycine, Acridine carboxamide (DACA), Proflavine and Ascididemin (Chart 1), and they have been used as anti-cancer or anti-bacterial agents. 

Q13. What is the effect of the hCA The authoron the inhibition of the tails?

It was observed that increasing of the bulkiness of the tails for the compound series 4a, 4b, and 6a–f (Chart 2) resulted with slight increasing of KI values, that is, decreasing on inhibitory effect, in the range of 0.69–6.92 lM. 

Q14. What is the effect of the tails on the active site?

It is suggested that due to the fact hCA II has a wide entrance to active site, probably the hydrophobic and hydrophilic interactions of these tails with the active site were not highly effective, and leading in fact to the flat SAR mentioned above also for isoform hCA I. 

Q15. What is the effect of the bulky scaffold on the enzyme?

It is thus probable that the bulky scaffold of these sulfonamides does not make a lot of favorable contacts with the enzyme active site, whereas the secondary sulfonamide moiety is too far away for assuring the right interactions with the residues at the entrance of the cavity, which would lead to isoform-selective CAIs (Charts 4 and 5). 

Q16. What are the structure–activity relationships of the compounds?

The structure–activity relationships (SAR) for the inhibition of these isoforms with the acridine bis-sulfonamides are also discussed. 

Q17. What is the effect of the compounds on the cytosolic isoforms?

The compounds were characterized by physicochemical methods and tested for their in vitro inhibition activity against the CA isoforms I, II, IX and XII. 

Q18. What are the signals of the aromatic protons?

Also the signals of the CH protons were observed at 4.90 and 4.98 ppm and the signals for the aromatic protons were observed between 6.30 and 8.36 ppm. 

Q19. What is the inhibitory activity of hCA IX?

The transmembrane isoform hCA IX was inhibited better than the cytosolic ones, with KIs ranging between 90 nM and 1.12 lM (Table 1).