Rational modification of a lead molecule: Improving the antifungal activity of indole – triazole – amino acid conjugates

Article abstract of DOI:10.1016/j.ejmech.2018.06.039

The modification of a molecule that was identified as highly efficacious in the previous studies could considerably improve the biological activity of the resulting compounds. While targeting lanosterol 14-α demethylase, the molecular modelling studies convinced that the extension of the phenyl ring of compound 1 deep into the hydrophobic pocket of the enzyme may increase the enzyme – ligand interactions and hence improve the anti-fungal profile of the molecules. As a result, the newly designed compounds 2 were synthesized and screened for their anti-microbial properties and these compounds were found to exhibit considerably better activity than the previous molecule 1. Some of the compounds in this series exhibited MIC₉₀ 16 μg mL^?1 and 32 μg mL^?1 against Candida albicans and Aspergillus niger, respectively as against 312 μg mL^?1 for compound 1.

Full text of DOI:10.1016/j.ejmech.2018.06.039

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Accepted Manuscript
Rational modification of a lead molecule: Improving the antifungal activity of indole –
triazole – amino acid conjugates
Sahil Mishra, Manpreet Kaur, Subhash Chander, Sankaranarayanan Murugesan,
Lovedeep Nim, D.S. Arora, Palwinder Singh
PII:
S0223-5234(18)30530-0
10.1016/j.ejmech.2018.06.039
EJMECH 10509
DOI:
Reference:
To appear in: European Journal of Medicinal Chemistry
Received Date: 28 February 2018
Revised Date: 23 April 2018
Accepted Date: 14 June 2018
Please cite this article as: S. Mishra, M. Kaur, S. Chander, S. Murugesan, L. Nim, D.S. Arora, P. Singh,
Rational modification of a lead molecule: Improving the antifungal activity of indole – triazole – amino
acid conjugates, European Journal of Medicinal Chemistry (2018), doi: 10.1016/j.ejmech.2018.06.039.
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ACCEPTED MANUSCRIPT
Rational Modification of a Lead Molecule: Improving the
Antifungal Activity of Indole – Triazole – Amino Acid Conjugates
Sahil Mishra,a Manpreet Kaur,a Subhash Chander,b Murugesan Sankaranarayanan,b Lovedeep
Nim,c D. S. Arora,c Palwinder Singha*
aUGC Sponsored Centre for Advanced Studies, Department of Chemistry Guru Nanak
Dev University, Amritsar-143005
bDepartment of Pharmacy, Birla Institute of Technology and Science Pilani Campus, Vidya
Vihar, Pilani - 333031.
cDepartment of Microbiology, Guru Nanak Dev University, Amritsar-143005
Abstract. The modification of a molecule that was identified as highly efficacious in the
previous studies could considerably improve the biological activity of the resulting
compounds. While targeting lanosterol 14-α demethylase, the molecular modelling studies
convinced that the extension of the phenyl ring of compound 1 deep into the hydrophobic
pocket of the enzyme may increase the enzyme – ligand interactions and hence improve the
anti-fungal profile of the molecules. As a result, the newly designed compounds 2 were
synthesized and screened for their anti-microbial properties and these compounds were found
to exhibit considerably better activity than the previous molecule 1. Some of the compounds
in this series exhibited MIC90 16 µg mL-1 and 32 µg mL-1 against Candida albicans and
Aspergillus niger, respectively as against 312 µg mL-1 for compound 1.
1

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Introduction
The use of antineoplastic and immunosupressive agents along with the broad spectrum of
antibiotics, cancer treatment and AIDS [1-5] is responsible for the increasing incidences of
suprafacial and invasive fungal infections [6-7]. The pathogenic microbes including Candida
sp, Cryptococcus sp and Aspergillus sp are the most common causative agents of invasive
fungal diseases [8-10]. Besides the lack of complete understanding of the bio-mechanistic
pathways of the fungal cells, the similarity in the fungal cell structure and the human host has
made the invention of new antifungal agents quite problematic [11-12]. Thus a limited
number of chemotherapeutic agents for fungal infections are available and among the existing
antifungal agents, most of them act as fungistatic rather than fungicidal [13]. Furthermore, the
over use of the present antifungals, prevalence of mutations and development of biofilms by
the fungus are certain factors contributing for developing resistance to the antifungal drugs in
the pathogenic fungi [14-17].
Out of the available antifungals; the polyenes (amphotericin-B) and 5-fluorocytosine do
not impact on the synthesis of ergosterol. Allylamines (terbinafine) act upstream of the
ergosterol biosynthesis pathway whereas azoles, along with the other classes such as
morpholines and ployenes, act downstream while binding to ergosterol [18-23]. For the azole
class of antifungals (the imidazoles and triazoles); the imidazoels were the first one to be
used but with their poor bioavailability and high toxicity they had only limited formulations
and could not be used systemically [24]. Improved over the imidazoles, recently, 1,3-
thiazolidin-4-one derivatives have been reported with high anti-fungal potency and low
toxicity [25]. Owing to the favourable pharmacokinetics and safety profile, the triazoles have
been used frequently in treating invasive infections [26-28]. Triazoles act by deactivating the
cytochrome P450 dependent enzyme lanosterol 14-α demethylase, consequently minimizing
the synthesis of ergosterol. The depletion of ergosterol and accumulation of toxic methyl
2

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sterols alters the cell membrane fluidity, thereby disrupting the activity of membrane bound
enzymes and leading to the inhibition in the growth and replication of fungal cells [29-31].
Out of the recently reported series of indole – azole conjugates, compound 1 (chart 1) was
the most potent anti-fungal agent with MIC80 312.5 µg mL-1 [32]. Mechanistically, compound
1 was found to target lanosterol 14-α demethylase. Motivated by these findings, and in
continuation of our efforts endowed with the discovery of amino acid appended indole
conjugates with potential chemotherapeutic properties; it was planned to modify compound 1
so that its anti-fungal activity gets improved.
Chart 1
Results and Discussion
Since the computational techniques have made it possible to investigate the crystal
coordinates of the enzyme as well as the enzyme substrate complexes and thence helping in
the design of new chemical entities, the molecular docking studies of compound 1 in the
active site pocket of lanosterol 14-α demethylase were performed. The enzyme – compound
interactions were compared with the enzyme – fluconazole interactions. Significantly more
contacts of compound 1 in the active site of the enzyme were observed (Figure 1 A, 1B). In
addition to parallel with fluconazole for interacting with R96 and F83; compound 1 also
exhibited interactions with F255, F78, Y76, R326 and H392. Since a large part of the enzyme
pocket is hydrophobic (Figure 1C) and these interactions play critical role in the drug-enzyme
3