Skip to main content
NCBI home page
ACS Medicinal Chemistry Letters logoLink to ACS Medicinal Chemistry Letters
. 2015 Sep 22;6(11):1111–1116. doi: 10.1021/acsmedchemlett.5b00245

Silicon Incorporated Morpholine Antifungals: Design, Synthesis, and Biological Evaluation

Gorakhnath R Jachak †, Remya Ramesh †, Duhita G Sant ‡, Shweta U Jorwekar ‡, Manjusha R Jadhav §, Santosh G Tupe ‡,*, Mukund V Deshpande ‡,*, D Srinivasa Reddy †,*
PMCID: PMC4645241  PMID: 26617963

Abstract

graphic file with name ml-2015-002455_0005.jpg

Known morpholine class antifungals (fenpropimorph, fenpropidin, and amorolfine) were synthetically modified through silicon incorporation to have 15 sila-analogues. Twelve sila-analogues exhibited potent antifungal activity against different human fungal pathogens such as Candida albicans, Candida glabrata, Candida tropicalis, Cryptococcus neoformans, and Aspergillus niger. Sila-analogue 24 (fenpropimorph analogue) was the best in our hands, which showed superior fungicidal potential than fenpropidin, fenpropimorph, and amorolfine. The mode of action of sila-analogues was similar to morpholines, i.e., inhibition of sterol reductase and sterol isomerase enzymes of ergosterol synthesis pathway.

Keywords: Antifungal drugs, Candida albicans, ergosterol biosynthesis, morpholines, sila-analogues

Steep rise in invasive fungal infections (IFI) mainly in immunocompromised patients, change in epidemiology of IFI, emergence of fungal pathogens, which were previously insignificant, development of resistance against currently used antifungal drugs, and certain drawbacks (like less clinical efficacy, acute and chronic side effects) associated with them necessitate the development of new antifungal drugs.1,2 Similarly, in agriculture, fungal infections is a major cause for crop loss with consequential heavy economic burden worldwide. Though several groups of fungicides are available, development of resistance against most of them stresses on the need to explore new antifungal agents.3

An ideal antifungal agent is one that selectively interacts with a fungal target not found in other eukaryotic cells. The fungal cell wall and cell membrane are attractive therapeutic targets as cell wall constituents such as chitin and major membrane lipid ergosterol are not present in mammalian cells. For instance, from currently used antifungals, three classes of compounds inhibit ergosterol synthesis through selective inhibition of different enzymes involved in the biosynthesis pathway. Allylamines such as terbinafine and naftifine act on squalene epoxidase, and azoles inhibit cytochrome P450 enzyme lanosterol 14-α-demethylase, whereas morpholines act on two different enzymes of this pathway, viz., sterol Δ14 reductase and sterol Δ7-Δ8 isomerase (Figure 1).4 Thus, morpholines seem to be ideal antifungals, as acquiring resistance against them will be difficult for a pathogen because of the requirement to mutate two genes of these enzymes. However, only one drug, amorolfine, from this class is used clinically, and its use is restricted to topical application for nail infections, the reason is that though quite effective in vitro against different human pathogens, it is ineffective against IFI due to rapid metabolism inside the host.5 Nevertheless, in agriculture, aldimorph, fenpropimorph, fenpropidin, tridemorph, and dodemorph from this class are in use as fungicides (Figure 1). With this background, we synthesized modified morpholines by incorporating silicon to increase their efficacy and stability.

Figure 1.

Figure 1

Open in a new tab

Ergosterol synthesis pathway and known inhibitors of the pathway enzymes.

The introduction of bioisostere is a key strategy used by medicinal chemists during lead optimization process in order to improve the desired biological and physical properties of a potential compound without altering its structure significantly,6,7 which may lead to improvement in bioactivity and stability or reduction in toxicity of the compound. Chemists have used silicon as a classical bioisostere for carbon as it has similar steric and electronic features and has the same valency as carbon.8−12 The change in biological activities due to sila-substitution may be attributed to larger bond length, altered bond angles, and different ring conformations due to larger covalent radius of silicon over carbon and increased lipophilicity, which in turn will increase its tissue distribution, particularly uptake through membranes.13−15 In our group, we are interested in making silicon analogues of biologically active compounds so as to improve their drug-like properties.16−18 Acker et al. have previously reported the synthesis of siliconized antifungals in the patent literature, but their use was restricted to fungal plant pathogens.19 Specifically, we have reasoned our design around fenpropimorph and amorolfine, which are closely related antifungals. Generally metabolism of fenpropidin takes place through hydroxylation of the piperidine ring or hydroxylation and oxidation of the methyls of aromatic t-butyl group (Figure 2).20 Closely related amorolfine also undergoes oxidation at isopentyl group present at the p-position of the aromatic ring.21

Figure 2.

Figure 2

Open in a new tab

Metabolism of fenpropidin and rationale for our design.

We hypothesized that incorporation of silicon at these metabolic soft spots in morpholine antifungals will help to overcome their drawbacks and give more potent and stable compounds (Figure 2). In general, all the silicon analogues are expected to be more lipophilic compared with fenpropidin, fenpropimorph, and amorolfine. Based on calculated cLogP values, incorporation of one silicon atom showed only slight increase in lipophilicity, but two silicon atoms incorporation resulted in large increase in lipophilicity with respect to fenpropidin (see Table S2 in the Supporting Information). Incorporation of silicon in to heterocycle (piperidine ring) has more effect when compared to silicon incorporation in the aromatic ring. Sometimes, high lipophilicity can be detrimental to the druggable properties such as solubility. This undesired increase in lipohilicity can be counterbalanced by the addition of polar groups to the molecule, for example, morpholine containing silicon analogue showed lower cLogP values with respect to all three fungicides fenpropidin, amorolfine, and fenpropimorph.

To begin with, 4-(trimethylsilyl) benzaldehyde 1 was first prepared from 1,4-dibromobenzene as reported earlier.22 Treatment of 1 with ylide ethyl-2-(triphenyl phosphanylidene) propanoate in anhydrous toluene at 110 °C, afforded ethyl 2-methyl-3-(4-(trimethylsilyl)phenyl) acrylate, 2. Hydrogenation of 2 in the presence of 10% Pd/C in EtOH followed by ester hydrolysis using LiOH in THF-MeOH-H2O led to formation of carboxylic acid 3. Carboxylic acid 3 was then coupled with piperidine under standard conditions using EDC·HCl and HOBt in CH2Cl2 to give the amide 4. Reduction of amide 4 using LAH in THF afforded the sila-amine 5 (Scheme 1). The furnished carboxylic acid 3 was further exploited to synthesize a library of sila-amines 15–24 (Scheme 1, see details in the Supporting Information). The sulfone derivative 17 was prepared from 16 by m-CPBA oxidation. In a similar way, carboxylic acid 6(23,24) and 7(23,24) on coupling with 4,4-dimethyl-4-silapiperidine 8(17,18) using standard protocol followed by reduction of the resulting amide gave amines 11 and 12, respectively. Carboxylic acid 6 was coupled to (dimethyl(phenyl)silyl)methanamine 13 to give the amide 14. However, reduction of amide carbonyl of 14 to give corresponding amine was not successful. The structures of the compounds were confirmed by 1H NMR, 13C NMR, and HR-MS spectra.

Scheme 1. Synthesis of Silicon Incorporated Morpholines.

Scheme 1

Open in a new tab

All the synthesized sila-analogues were tested for antifungal activity against different human pathogenic yeasts and filamentous fungi by Clinical Laboratory Standards Institute’s (CLSI) broth microdilution assay (CLSI document M27-A3 and CLSI M38-A2).25,26 The results in terms of IC50, i.e., concentration causing 50% growth inhibition, minimum inhibitory concentration (MIC), and minimum fungicidal concentration (MFC) are given in Table 1. From the 15 sila-compounds synthesized, 12 compounds, namely, 5, 11, 12, 15, 16, and 18–24, exhibited potent antifungal activity against Candida albicans ATCC 24433, C. albicans ATCC 10231, Candida glabrata NCYC 388, Candida tropicalis ATCC 750, Cryptococcus neoformans ATCC 34664, and Aspergillus niger ATCC 10578 (Table 1). No antifungal effect was observed (MIC ≥ 256 μg/mL) for three compounds, viz., 9, 14, and 17 against all the pathogens tested. Compounds 9 and 14 are amides suggesting that the basic tertiary nitrogen is essential for the activity. In the case of compound 17, presence of polar sulfone moiety on heterocycle was found to be detrimental for the activity. The sila fenpropimorph analogue 24 was most effective followed by sila fenpropidin analogues 5 and 15. It is worth highlighting that silicon incorporation on aromatic ring seems to be more effective compared to silicon incorporation in heterocycle. Compound 24 exhibited better antifungal activity than fluconazole and morpholine fungicides fenpropimorph and fenpropidin against all the pathogens. Further, the MIC values of 24 were comparable or better than amorolfine with more potent fungicidal effect (MFC) against all the tested strains.

Table 1. Antifungal Activity of the Sila-Morpholine Analogues against Different Human Pathogenic Fungi.

  Candida albicans ATCC 24433
 Candia albicans ATCC 10231
 Cryptococcus neoformans ATCC 34664
 Candida glabrata NCYC 388
 Candida tropicalis ATCC 750
 Aspergillus niger ATCC 10578
compd IC50a MICb MFCc IC50 MIC MFC IC50 MIC MFC IC50 MIC MFC IC50 MIC MFC IC50 MIC MFC
5 0.12 0.25 2 0.11 0.25 32 0.0625 0.125 8 0.035 0.125 8 1 4 64 41.24 64 128
11 1.85 4 8 0.31 0.5 0.5 0.875 2 4 1.52 4 8 16 64 64 13.82 32 64
12 1.68 4 16 0.28 0.5 64 1.4 2 4 1.47 4 4 13.8 64 256 0.16 0.5 64
15 0.74 1 8 0.26 0.5 8 0.125 0.5 2 0.144 0.5 16 0.5 8 16 105.93 128 >256
16 0.245 1 8 0.5 1 2 0.80 2 64 0.25 0.5 8 0.25 2 >256 1 2 >256
18 1.25 4 8 0.45 1 4 1.98 8 64 1.75 8 16 44.8 64 >256 0.5 2 >256
19 0.396 1 2 0.19 0.25 4 0.93 2 16 0.196 0.5 8 0.198 4 256 0.25 0.5 256
20 1.55 4 8 1 2 2 3.77 8 8 1.63 2 4 5.87 16 16 1.25 2 64
21 5.13 8 8 1.59 2 2 6.9 16 16 5.92 8 16 1.50 64 256 4.5 8 >256
22 3.75 8 32 0.57 2 4 1.5 4 32 1.85 4 >256 4.85 16 256 64 256 >256
23 0.97 2 8 0.31 0.5 2 0.25 1 4 0.319 1 32 2.76 16 128 50.08 64 256
24 0.043 0.125 0.5 0.25 0.5 1 0.079 0.125 2 0.017 0.125 2 0.164 0.5 64 0.5 2 256
9, 14, 17    ≥256  ≥256    ≥256  ≥256    ≥256  ≥256    ≥256  ≥256    ≥256  ≥256    ≥256  ≥256
fenpropidin 0.19 0.25 0.5 0.27 1 2 0.22 1 32 0.1 0.5 16 0.125 4 256 16 32 128
fenpropimorph 0.21 0.5 4 0.833 2 2 0.25 1 64 0.25 1 128 0.125 2 >256 1 4 >256
amorolfine 0.028 1 8 0.1 0.25 32 0.031 0.125 64 0.038 0.125 32 0.173 0.5 >256 0.125 0.5 >256
fluconazole 0. 73 2 4 4.21 8 16 4.6 32 >256 16 128 >256 64 >256 >256 >256 >256 >256
Open in a new tab
a

IC50, concentration causing 50% growth inhibition. All the values are in μg/mL. The assay was done twice in triplicate.

b

MIC, minimum inhibitory concentration. All the values are in μg/mL. The assay was done twice in triplicate.

c

MFC, minimum fungicidal concentration. All the values are in μg/mL. The assay was done twice in triplicate.

Morpholine class of antifungals act on two enzymes of ergosterol biosynthesis pathway, viz., sterol Δ14 reductase and sterol Δ7-Δ8 isomerase, leading to ergosterol depletion and accumulation of intermediates ignosterol (Figure 1) and lichesterol.27,28 To check whether the present sila-analogues act in a similar way, C. albicans ATCC 24433 cells were grown in the presence of different subinhibitory (<MIC) concentrations of 5, 19, 24, and amorolfine and the cellular sterols were extracted and measured spectrophotometrically.29 Ergosterol and the late sterol intermediate 24(28) dehydroergosterol (24(28)DHE) in a sample shows characteristic four-peaked curve in a spectrometric scan between wavelengths 230–300 nm.29 In the presence of compounds 5, 19, and 24, a dose-dependent decrease in the height of the absorbance peaks was observed indicating decrease in the ergosterol content in Candida cells (Figure S1 in Supporting Information). Accumulation of specific intermediates was checked by GC–MS quantification of cellular sterols in samples of 24 and amorolfine treatment. Results confirmed decrease in ergosterol content and also showed concomitant increase in the concentration of ignosterol and/or lichesterol (Table 2). The accumulation of these intermediates was like amorolfine treated cells implying the same mode of action, i.e., inhibition of sterol reductase and sterol isomerase. More accumulation of lichesterol (32.13%) than ignosterol (11.11%) for amorolfine indicated stronger action on isomerase enzyme than reductase (Table 2), whereas, in the case of 24, accumulation of ignosterol (42.29%) can be attributed to the major effect on sterol reductase at higher concentration. Depletion of ergosterol compromises membrane integrity, affects membrane proteins functions due to membrane instability, and leads to cessation of growth.

Table 2. Effect of 24 and Amorolfine Treatment on the Sterol Profile of Candida albicans ATCC 24433a.

  control compound 24 0.125 μg/mL compound 24 0.25 μg/mL amorolfine 0.125 μg/mL amorolfine 0.25 μg/mL
squalene 07.17 ± 0.35 21.52 ± 1.37 13.82 ± 0.81 22.04 ± 1.07 17.08 ± 1.31
ergosterol 73.34 ± 2.53 15.52 ± 0.8 11.12 ± 0.54 30.16 ± 1.48 06.13 ± 0.29
cholesta-8,24-dien-3-ol, 4-methyl-(3a′,4a′)-, 07.19 ± 0.65 05.36 ± 0.61 27.78 ± 1.2 12.26 ± 0.73 12.03 ± 0.67
ergosta-5,8-dien-3-ol, (3a′) 05.15 ± 0.44 NDb ND ND ND
cholesta-5,24-dien-3-ol 03.58 ± 0.52 15.34 ± 0.86 0.87 ± 0.18 0.44 ± 0.1 ND
ergosta-8,14-dien-3-ol (ignosterol) ND 07.23 ± 0.68 42.29 ± 2.35 ND 11.11 ± 0.78
ergosta-5,8,22-trien-3-ol,(3a′,22E)- (Lichesterol) ND 29.84 ± 1.33 ND 08.26 ± 0.33 32.13 ± 1.95
ergostenol ND 05.19 ± 0.33 04.12 ± 0.38 11.56 ± 0.41 05.71 ± 0.42
ergosta-7,22-dien-3-ol,(3a′,22E)- ND ND ND 15.28 ± 0.3 15.81 ± 1.1
unidentified/other sterols 03.57 ± 0.57 ND ND ND ND
Open in a new tab
a

All the values mentioned here are average % determined from two experiments with standard error of the mean.

b

ND, Not detected.

The % microsomal stability of selected compounds was evaluated after 30 min incubation with mouse as well as human liver microsomes. All the tested compounds did not show good stability in mouse liver microsomes. However, three compounds with silicon incorporation (15, 18, and 24) showed relatively better stability than fenpropidin (Table 3). In case of human liver microsomes, metabolic stability was improved including for fenpropidin. Compound 18 showed better stability in human liver microsomes than fenpropidin, whereas compound 24 was found to be slightly inferior to fenpropidin. Thus, incorporation of silicon in the piperidine ring seems to be beneficial toward improving the metabolic stability.

Table 3. % Metabolic Stability of the Compounds in Liver Microsomes (after 30 min).

  metabolic stability
compds mouse human
15 5.1 26.0
18 17.3 44.5
24 6.2 27.3
fenpropidin 1.1 34.4
Open in a new tab

To determine that the compounds are selectively toxic to the fungal cells and not to mammalian cells, hemolysis assay30 using RBCs and MTT assay30 using HEK293 cells were carried out. RBC hemolysis was not observed for any of the tested compounds up to 128 μg/mL, whereas partial hemolysis was observed for 19, 20, and 21 at 256 μg/mL (Supporting Information Table S1). As this concentration was many folds higher than the MICs of the compounds against different pathogens, they may be considered safe. In the case of lead compound 24, only negligible hemolysis (∼7%) was observed at 512 μg/mL. The concentrations of the compounds required for 50% reduction in growth of HEK293 cells were also far higher than the MICs against fungi. Among the tested compounds, only compound 20 was found to be toxic to some extent against HEK293 cells with IC50 of 9.81 μg/mL (Supporting Information Table S1).

In conclusion, total 15 silicon analogues of morpholine antifungals were designed and synthesized. Twelve compounds, viz., 5, 11, 12, 15, 16, and 18–24, exhibited potent antifungal activity against different fungal pathogens. The compounds act similar to morpholines by targeting sterol reductase and sterol isomerase of ergosterol synthesis pathway and cause depletion of ergosterol. Compound 24 showed better antifungal activity than fenpropidin, fenpropimorph, and amorolfine against different yeast and filamentous human pathogens and was identified as the lead. Further optimization of this series is in progress.

Acknowledgments

We thank Sridhar Veeraraghavan, Incozen Therapeutics Pvt. Ltd., for metabolic stability analysis.

Glossary

ABBREVIATIONS

RBCs

red blood cells

HEK293

Human Embryonic Kidney 293 cells

Supporting Information Available

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsmedchemlett.5b00245.

  • Spectrophotometric sterol analysis, details of biological assays including cytotoxicity and metabolic stability, and experimental procedures and characterization data for all the new compounds (PDF)

The antifungal program at CSIR-NCL, Pune, is funded by Department of Biotechnology, India (grant BT/PR7442/MED/29/680/2012). Financial support from CSIR, New Delhi under XII Five Year Plan SMILE (CSC0111) program is acknowledged. G.R.J., R.R., and S.G.T. thank CSIR, India for Research fellowship.

The authors declare no competing financial interest.

Supplementary Material

ml5b00245_si_001.pdf (5.1MB, pdf)

References

  1. Chaudhary P. M.; Tupe S. G.; Deshpande M. V. Chitin synthase inhibitors as antifungal agents. Mini-Rev. Med. Chem. 2013, 13, 222–236. 10.2174/1389557511313020005. [DOI] [PubMed] [Google Scholar]
  2. Tupe S. G.; Deshpande M. V.. Current Status and New Directions in Antifungal Drug Development. In Biotechnology: Beyond Borders; Deshpande M. V., Ruiz-Herrera J., Eds.; National Chemical Laboratory: Pune, India, 2014; pp 241–252. [Google Scholar]
  3. Fungicide Resistance Action Committee. FRAC Code List: Fungicides sorted by mode of action (including FRAC Code numbering), 2011; pp 1–10.
  4. Gauwerky K.; Borelli C.; Korting H. C. Targeting virulence: a new paradigm for antifungals. Drug Discovery Today 2009, 14, 214–222. 10.1016/j.drudis.2008.11.013. [DOI] [PubMed] [Google Scholar]
  5. Hartman P. G.; Sanglard D. Inhibitors of ergosterol biosynthesis as antifungal agents. Curr. Pharm. Design 1997, 3, 177–208. [Google Scholar]
  6. Lima L. M.; Barreiro E. J. Bioisosterism: A useful strategy for molecular modification and drug design. Curr. Med. Chem. 2005, 12, 23–49. 10.2174/0929867053363540. [DOI] [PubMed] [Google Scholar]
  7. Meanwell N. A. Synopsis of some recent tactical application of bioisosteres in drug design. J. Med. Chem. 2011, 54, 2529–2591. 10.1021/jm1013693. [DOI] [PubMed] [Google Scholar]
  8. Geyer M.; Wellner E.; Jurva U.; Saloman S.; Armstrong D.; Tacke R. Can silicon make an excellent drug even better? An in vitro and in vivo head-to-head comparison between loperamide and its silicon analogue sila-loperamide. ChemMedChem 2015, 10, 911–924. 10.1002/cmdc.201500040. [DOI] [PubMed] [Google Scholar]
  9. Tacke R.; Popp F.; Müller B.; Theis B.; Burschka C.; Hamacher A.; Kassack M. U.; Schepmann D.; Wünsch B.; Jurva U.; Wellner E. Sila-haloperidol, a silicon analogue of the dopamine (D2) receptor antagonist haloperidol: synthesis, pharmacological properties, and metabolic fate. ChemMedChem 2008, 3, 152–64. 10.1002/cmdc.200700205. [DOI] [PubMed] [Google Scholar]
  10. Johansson T.; Weidolf L.; Popp F.; Tacke R.; Jurva U. In vitro metabolism of haloperidol and sila-haloperidol: new metabolic pathways resulting from carbon/silicon exchange. Drug Metab. Dispos. 2010, 38, 73–83. 10.1124/dmd.109.028449. [DOI] [PubMed] [Google Scholar]
  11. Geyer M.; Karlsson O.; Baus J. A.; Wellner E.; Tacke R. Si- and C- Functional organosilicon building blocks for synthesis based on 4-silacyclohexan-1-ones containing the silicon protecting groups MOP (4-methoxyphenyl), DMOP (2,6-dimethoxyphenyl), or TMOP (2,4,6-trimethoxyphenyl). J. Org. Chem. 2015, 80, 5804–5811. 10.1021/acs.joc.5b00774. [DOI] [PubMed] [Google Scholar]
  12. Nakamura M.; Kajita D.; Matsumoto Y.; Hashimoto Y. Design and synthesis of silicon-containing tubulin polymerization inhibitors: replacement of the ethylene moiety of combretastatin A-4 with a silicon linker. Bioorg. Med. Chem. 2013, 21, 7381–7391. 10.1016/j.bmc.2013.09.046. [DOI] [PubMed] [Google Scholar]
  13. Franz A. K.; Wilson S. O. Organosilicon molecules with medicinal applications. J. Med. Chem. 2013, 56, 388–405. 10.1021/jm3010114. [DOI] [PubMed] [Google Scholar]
  14. Mills J. S.; Showell G. A. Exploitation of silicon medicinal chemistry in drug discovery. Expert Opin. Invest. Drugs 2004, 13, 1149–1157. 10.1517/13543784.13.9.1149. [DOI] [PubMed] [Google Scholar]
  15. Gately S.; West R. Novel therapeutics with enhanced biological activity generated by the strategic introduction of silicon isosteres into known drug scaffolds. Drug Dev. Res. 2007, 68, 156–163. 10.1002/ddr.20177. [DOI] [Google Scholar]
  16. Ramesh R.; Reddy D. S. Zinc mediated allylations of chlorosilanes promoted by ultrasound: Synthesis of novel constrained sila amino acids. Org. Biomol. Chem. 2014, 12, 4093–4097. 10.1039/c4ob00294f. [DOI] [PubMed] [Google Scholar]
  17. Balamkundu S. S.; Ramesh R.; Dange S. S.; Khairnar P. V.; Singhal S.; Upadhyay D.; Veeraraghavan S.; Viswanadha S.; Vakkalanka S.; Reddy D. S.. Design, Synthesis and Identification of Silicon Incorporated Oxazolidinone Antibiotics with Improved Brain Exposure. Unpublished results; communicated. [DOI] [PMC free article] [PubMed]
  18. Reddy D. S.; Balamkundu S.; Ramesh R. Sila analogs of oxazolidinone derivatives and synthesis thereof. Patent WO2013054275, 2013.
  19. Acker R.-D.; Buschmann E.; Pommer E. H.; Ammermann E. Organosilyl compounds and their use as fungicides. Patent US4579842A.
  20. Roberts T. R.; Hutson D. H.. Morpholines. In Metabolic Pathways of Agrochemicals: Insecticides and Fungicides; Roberts T. R., Hutson D. H., Eds.; Royal Society of Chemistry: London, UK, 1998; pp 1225–1238. [Google Scholar]
  21. Polak A. Mode of action of morpholine derivatives. Ann. N. Y. Acad. Sci. 1988, 544, 221–228. 10.1111/j.1749-6632.1988.tb40406.x. [DOI] [PubMed] [Google Scholar]
  22. Brenzovich W. E.; Brazeau J.-F. Jr.; Toste F. D. Gold-catalyzed oxidative coupling reactions with aryltrimethylsilane. Org. Lett. 2010, 12, 4728–4731. 10.1021/ol102194c. [DOI] [PMC free article] [PubMed] [Google Scholar]
  23. Doherty E. M.; Fotsch C.; Bo Y.; Chakrabarti P. P.; Chen N.; Gavva N.; Han N.; Kelly M. G.; Kincaid J.; Klionsky L.; Liu Q.; Ognyanov V. I.; Tamir R.; Wang X.; Zhu J.; Norman M. H.; Treanor J. J. S. Discovery of potent, orally available vanilloid receptor-1 antagonists. Structure-activity relationship of N-aryl cinnamides. J. Med. Chem. 2005, 48, 71–90. 10.1021/jm049485i. [DOI] [PubMed] [Google Scholar]
  24. Kim H. D.; Suh Y. G.; Park H. G.; Oh U. T.; Park S. R.; Kim J. H.; Jang M. J.; Park Y. H.; Shin S. S.; Kim S. Y.. Novel compounds, isomer thereof, or pharmaceutically acceptable salts thereof as vanilloid receptor antagonist; and pharmaceutical compositions containing the same. Patent WO 2006101318A1, 2006.
  25. Clinical and Laboratory Standards Institute. CLSI document M27-A3, Reference method for broth dilution antifungal susceptibility testing of yeasts: approved standard, 3rd ed., Wayne, PA, 2008.
  26. Clinical and Laboratory Standards Institute. CLSI document M38-A2, Reference method for broth dilution antifungal susceptibility testing of filamentous fungi. Approved Standard, 2nd ed., Wayne, PA, 2008.
  27. Liang R.-M.; Cao Y.-B.; Fan K.-H.; Xu Y.; Gao P.-H.; Zhou Y.-J.; Dai B.-D.; Tan Y.-H.; Wang S.-H.; Tang H.; Liu H.-T.; Jiang Y.-Y. 2-Amino-nonyl-6-methoxyl-tetralin muriate inhibits sterol C-14 reductase in the ergosterol biosynthetic pathway. Acta Pharmacol. Sin. 2009, 30, 1709–1716. 10.1038/aps.2009.157. [DOI] [PMC free article] [PubMed] [Google Scholar]
  28. Müller C.; Staudacher V.; Krauss J.; Giera M.; Bracher F. A convenient cellular assay for the identification of the molecular target of ergosterol biosynthesis inhibitors and quantification of their effects on total ergosterol biosynthesis. Steroids 2013, 78, 483–493. 10.1016/j.steroids.2013.02.006. [DOI] [PubMed] [Google Scholar]
  29. Arthington-Skaggs B. A.; Jradi H.; Desai T.; Morrison C. J. Quantitation of ergosterol content: Novel method for determination of fluconazole susceptibility of Candida albicans. J. Clin. Microbiol. 1999, 37, 3332–3337. [DOI] [PMC free article] [PubMed] [Google Scholar]
  30. Maurya I. K.; Thota C. K.; Sharma J.; Tupe S. G.; Chaudhary P.; Deshpande M. V.; Prasad R.; Chauhan V. S. Mechanism of action of novel synthetic dodecapeptides against Candida albicans.. Biochim. Biophys. Acta, Gen. Subj. 2013, 1830, 5193–5203. 10.1016/j.bbagen.2013.07.016. [DOI] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

ml5b00245_si_001.pdf (5.1MB, pdf)

Articles from ACS Medicinal Chemistry Letters are provided here courtesy of American Chemical Society

RESOURCES