BusinessLaw

Organic & Biomolecular Chemistry Synthesis and identification of heteroaromatic N-benzyl sulfonamides as potential anticancer agents

Description
Sulfonamides are a crucial class of bioisosteres that are prevalent in a wide range of pharmaceuticals, however, the available methods for their production directly from heteroaryl aldehyde reagents remains surprisingly limited. A new approach for
Categories
Published
of 12
All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
Share
Transcript
  Organic &Biomolecular Chemistry PAPER Cite this:  Org. Biomol. Chem. , 2019, 17 , 8391Received 31st July 2019,Accepted 22nd August 2019DOI: 10.1039/c9ob01694e rsc.li/obc Synthesis and identi 󿬁 cation of heteroaromatic N -benzyl sulfonamides as potential anticanceragents † Megan D. Hopkins, Felagot A. Abebe, Kristina A. Scott, Garett L. Ozmer,Alec A. Sheir, Lucas J. Schroeder, Robert J. Shea ff * and Angus A. Lamar * Sulfonamides are a crucial class of bioisosteres that are prevalent in a wide range of pharmaceuticals,however, the available methods for their production directly from heteroaryl aldehyde reagents remainssurprisingly limited. A new approach for regioselective incorporation of a sulfonamide unit to heteroarenesca ff olds has been developed and is reported within. As a result, a variety of primary benzylic N -alkylsulfonamides have been prepared  via  a two-step (one pot) formation from the  in situ  reduction ofan intermediate  N -sulfonyl imine under mild, practical conditions. The compounds have been screenedagainst a variety of cell lines for cytotoxicity e ff ects using a Cell Titer Blue assay. The cell viability investi-gation identi 󿬁 es a subset of  N -benzylic sulfonamides derived from the indole sca ff old to be targeted forfurther development into novel molecules with potential therapeutic value. The most cytotoxic of thecompounds prepared, AAL-030, exhibited higher potency than other well-known anticancer agentsIndisulam and ABT-751. Introduction Cancer research has made significant advances over the past few decades in the development of new chemotherapeutics.However, cancer remains the second leading cause of death worldwide, and is projected to steadily grow due to the growthand aging of the population. 1 The desire for more e ff  ectivechemotherapeutics to combat cancer has led to intenseresearch e ff  orts which have been largely focused upon addres-sing the current shortcomings of available anticancer drugs,such as limitations that arise from undesirable side e ff  ectscaused by a lack of selectivity between cancerous and normalcell types as well as the occurrence of drug-resistant tumors. 2 In this context, the development of new synthetic organicapproaches and novel molecules with anticancer activity is ahigh priority when targeted towards addressing issues that include tumor specificity and/or insensitivity to chemo-resistance.Sulfonamide is a privileged moiety found within a broadrange of bioactive and/or medicinally relevant molecules. 3 Molecules that feature a sulfonamide unit have displayedbroad pharmacological profiles which have included anti-inflammatory, antiparasitic, antibacterial, antithyroid, anti- viral, hypoglycemic, and diuretic activities. 4 Of particular inter-est, sulfonamides have also recently shown substantial  in vitro and  in vivo  anticancer activity. 5  A structural similarity of many of these molecules lies within the direct attachment of a sulfo-namide (N) or sulfonyl (S) to an aromatic core (such as indisu-lam 6 and ABT-751; 7 Fig. 1). A structural class of sulfonamidesthat have received less attention from the synthetic community are sulfonamides attached to benzylic carbons of heteroarenes,such as the examples shown in Fig. 1. 8 Despite the potentialfor bioactivity among these  N  -benzylic sulfonamides,approaches toward the installation of a sulfonamide unit tothe benzylic position of a heteroaraomatic sca ff  old are surpris-ingly limited. Therefore, we envisioned the direct incorpor-ation of a sulfonamide unit to a heteroarene sca ff  old as ameans to access a relatively untapped pool of low molecular- weight bioactive molecules.In general, a sulfonamide is most frequently incorporatedinto a molecular sca ff  old by the reaction of a pre-installedamine with a sulfonyl chloride under basic conditions(Scheme 1, Path A). 9 However, the lack of commercially avail-able heterocyclic benzyl amines reduces the appeal of such anapproach with regard to the generation of a library of hetero-aromatic  N  -benzyl sulfonamides for bioactivity screening pur-poses. The use of benzylic alcohols as starting materials forincorporation of sulfonamide has gained attention recently from the synthetic community (Scheme 1, Path B). 10 – 12 † Electronic supplementary information (ESI) available. See DOI: 10.1039/c9ob01694e  Department of Chemistry and Biochemistry, The University of Tulsa, 800 SouthTucker Drive, Tulsa, Oklahoma, 74104, USA. E-mail: angus-lamar@utulsa.edu This journal is © The Royal Societyof Chemistry 2019  Org. Biomol. Chem. , 2019,  17 , 8391 – 8402 |  8391    P  u   b   l   i  s   h  e   d  o  n   2   2   A  u  g  u  s   t   2   0   1   9 .   D  o  w  n   l  o  a   d  e   d   b  y   M  c   F  a  r   l   i  n   L   i   b  r  a  r  y ,   T   h  e   U  n   i  v  e  r  s   i   t  y  o   f   T  u   l  s  a  o  n   0   9   /   2   1   /   2   0   1   9   2   3  :   3   6  :   2   1 . View Article Online View Journal | View Issue   Approaches that employ hydrogen autotransfer, 10 aerobic relay race, 11 or acid activation 12 strategies often require high tem-peratures, expensive catalysts, or acidic conditions that areincompatible with substrates containing basic sites capable of coordinating Lewis or Brønsted acids (such as N-heteroarenesor heterocycles). To our knowledge, the reported systems that have included N-heteroaryl benzylic alcohol substrates in theproduction of   N  -benzyl sulfonamides have only includedthiazole 10  g  ,12 c and/or pyridine 10 a , c ,   f   – h ,11 b – d  ,13 heteroarene cores.Lastly, the incorporation of a sulfonamide functional groupthrough the conversion of an aldehyde to an intermediate  N  -sulfonyl imine, which can serve as a highly versatile acti- vated (electron-deficient) imine in a number of organic trans-formations, 14 has also drawn attention from the synthetic com-munity in recent years (Scheme 1, Path C). Current methodsfor the production of activated imines from aldehydes arelargely limited to substituted benzaldehyde substrates that require the use of harsh Brønsted or Lewis acids to enhancethe electrophilicity of the aldehydic carbonyl. 15 In addition,high temperatures and/or the chemical or mechanical removalof water are also frequently necessary in order for a conden-sation reaction to occur. 15 Examples of methods to produceactivated imines that employ heteroaryl carboxaldehydes assubstrates are exceedingly rare, likely due to the potential forcoordination of the Brønsted or Lewis acid by the heteroatom within the aromatic unit. To our knowledge, the only report that has utilized aldehydes attached to heteroarene cores (suchas indole, pyrrole, and pyridine) to produce  N  -sulfonyl iminesemploys either Si(OEt) 4  at 140 – 160 °C, 15 d  or an air-sensitivecatalyst such as TiCl 4  with azeotropic removal of water. 15 d   As a result of our interest  16 in the preparation and appli-cation of N-centered radical (NCR) reactive species, 17 ourresearch group has recently developed a novel, non-traditionalcarbonyl activation of benzaldehyde substrates using I 2  and animinoiodinane reagent (PhI v NZ) to form  N  -sulfonyl iminesunder non-acidic conditions. 18  We envisioned the PhI v NZ/I 2 system as a valuable alternative method for the production of intermediate deactivated imines for the production of   N  -benzyl sulfonamides from heteroaromatic substrates that contain basic sites that would prevent traditional, acid-depen-dent reactive pathways from occurring.The direct installation of sulfonamide functionality to hetero-arene sca ff  olds is a highly desirable goal, and new methods that seek to provide complementary or alternative approaches tosulfonamide incorporation are needed. To this end, we report herein the production and cell viability studies of a wide rangeof   N  -benzyl sulfonamides  via  the one-pot reduction of intermedi-ate N-heteroarene-containing   N  -sulfonyl imines generated fromcommercially available aldehydes under mild conditions. Results and discussion Synthesis of initial library compounds 1 – 15 To begin our investigation, indole-3-carboxaldehyde wasselected to serve as a representative N-heteroaryl aldehyde sub-strate. The optimization of reaction conditions (see ESI,Table S1 † ) resulted in the most e ffi cient product formation when employing the following conditions: 2 equiv. PhI(OAc) 2 ,1 equiv. I 2 , 1 equiv. sulfonamide, 3 – 5 equiv. indole-3-carbox-aldehyde, 50 °C, 24 h, in chloroform. In addition, a series of control reactions and mechanistic experiments (see ESI,Table S2 † ) were conducted to confirm that the reaction wasproceeding through an  N  -sulfonyl imine intermediate similarto our previous work (a plausible mechanism is shown in ESI,Scheme S1 † ). Scheme 1  Current methods and limitations of  N -benzyl sulfonamideformation from benzylic amines, benzylic alcohols, or aldehydes. Fig. 1  Aromatic sulfonamides as anticancer agents and examples ofbioactive  N -benzylic sulfonamide (shown in red) pharmacores contain-ing heteroarene units (shown in blue). Paper Organic & Biomolecular Chemistry 8392  |  Org. Biomol. Chem. , 2019, 17 , 8391 – 8402 This journal is © The Royal Societyof Chemistry 2019    P  u   b   l   i  s   h  e   d  o  n   2   2   A  u  g  u  s   t   2   0   1   9 .   D  o  w  n   l  o  a   d  e   d   b  y   M  c   F  a  r   l   i  n   L   i   b  r  a  r  y ,   T   h  e   U  n   i  v  e  r  s   i   t  y  o   f   T  u   l  s  a  o  n   0   9   /   2   1   /   2   0   1   9   2   3  :   3   6  :   2   1 . View Article Online   With an optimized set of reaction conditions in hand, weturned our attention toward exploring the scope of heteroarylaldehyde substrates (Table 1) using a two-step (one pot)reduction method to form and isolate  N  -benzyl sulfonamideproducts. To begin our expansion, indole substrates werechosen as representative examples, and moderate to good yields were obtained of products  1 – 4 . Carboxaldehydes withindazole and pyrazole cores (Table 1,  5 – 7 ) also resulted ine ffi cient formation of   N  -benzyl sulfonamide products withrelatively electron-rich sulfonamide reacting partners. Next, weinvestigated aldehyde substrates that contain 6-memberedN-heteroarenes such as pyridine, quinoline, pyrimidine, andpyrazine. These substrates resulted in moderate yields of   N  -benzyl sulfonamides  8 – 11 . The use of thiazole, oxazole, andfuran sca ff  olds as substrates resulted in good product yields( 12 – 15 ). In general, a variety of heteroarene sca ff  olds that areknown within the drug discovery and medicinal chemistry communities as privileged pharmacophores 19 serve as e ff  ectivealdehyde substrates. An assortment of additional functional-ities (including aryl halide, amide, sulfonamide, aryl ether,benzylic C – H bonds, and C – H bonds adjacent to carbonylsand heteroatoms) are tolerated by the two-step production of   N  -benzyl sulfonamides. It is noteworthy that, despite the simi-larity of the reaction conditions to those reported for benzylicamidation  via  C – H activation, 20 no byproducts of benzylic sul-fonamidation were observed during our investigation (pro-ducts  3 ,  4 , and  15 ).  In vitro  cytotoxicity screening   An initial cytotoxicity screening of library compounds (500  μ M)using H293 cells ( ∼ 20000 in 20  μ L PBS) was conducted using Cell Titer Blue Cell Viability (Promega) assay, which is basedupon the conversion of resazurin to the fluorescent resorufinby living cells, 21 and several compounds were active relative toDMSO background (Fig. 2). The library compound concen-tration was reduced to 100  μ M in order to identify compounds with higher potency (Fig. 2). A screening of additional celllines (diploid fibroblast   –  HDF; prostate  –  PC3; pancreatic  – BxPC3; cervical  –  HeLa; lung   –  NCI-H196 and DMS-114-NSCLC; breast   –  MCF10A, MCF7, T47D, SkBr3, and MDA-MB) was then conducted at 100  μ M (Table 2). A number of interesting examples of selectivity betweenspecific cell lines by the library compounds can be observed inTable 2. For example, compound  2  displays a pronounced cyto-toxic e ff  ect on kidney (H293) and cervical (HeLa) cancer cells, but is fairly ine ff  ective against prostate (PC3) cancer cells. As seen inTable 2, compounds  1 – 15  consistently display an increased e ff  ect on the H293 (transformed kidney) cell line in comparison to thenon-transformed HDF (diploid fibroblast) cell line. Selectivity between strains of lung cancer cell lines (NCI-H196 andDMS-114) was observed with compounds  1 – 3 . Of the heteroarenesca ff  olds investigated in the initial screening, those containing an indole core were consistently the most active (compounds 1 – 4 ). Therefore, an investigation of the indole framework wasinitiated in an attempt to determine whether or not the cores would be amenable to structural optimization. Synthesis and evaluation of benzylic  N  -sulfonyl indole analogs Indole-3-carboxaldehyde was chosen as a representative indolealdehyde in order to investigate the role of the sulfonamideunit. A variety of indole sulfonamides  16 – 21  were prepared inaddition to compound  1  (Table 3). A cell viability study of H293 cells conducted at 100  μ M of library compounds verifiedthat 4-chlorobenzenesulfonyl was the most e ff  ective of the Fig. 2  Initial cell viability (H293) screening of compounds  1 – 15  per-formed at 500  μ M (yellow) and 100  μ M (blue). Table 1  Two-step formation of primary  N -benzyl sulfonamides a  All yields are isolated. Reaction conditions: Aldehyde(0.375 – 0.625 mmol), sulfonamide (0.125 mmol), PhI(OAc) 2 (0.25 mmol) and I 2  (0.125 mmol) in CHCl 3  (1.5 mL), 50 °C, 24 h.Solvent is then removed, crude is dissolved in 3 mL of 1:1 MeOH/DCM and NaBH 4  (2.0 mmol) is added at 0 °C. Organic & Biomolecular Chemistry Paper This journal is © The Royal Societyof Chemistry 2019  Org. Biomol. Chem. , 2019, 17 , 8391 – 8402 |  8393    P  u   b   l   i  s   h  e   d  o  n   2   2   A  u  g  u  s   t   2   0   1   9 .   D  o  w  n   l  o  a   d  e   d   b  y   M  c   F  a  r   l   i  n   L   i   b  r  a  r  y ,   T   h  e   U  n   i  v  e  r  s   i   t  y  o   f   T  u   l  s  a  o  n   0   9   /   2   1   /   2   0   1   9   2   3  :   3   6  :   2   1 . View Article Online   N  -sulfonyl units (POC values, Table 3). Aryl sulfonamides( 1 ,  16 – 19 ,  21 ) consistently displayed higher cytotoxic e ff  ectsthan the alkyl sulfonamide ( 20 ) that was tested. Electronice ff  ects of the sulfonamide R group appear to be negligible.Next, the 1-position (N) of the indole sca ff  old was examined(Table 4, entries 1 – 3). When protected with either an acetyl ormethyl group (compounds  22  and  23 ), cytotoxicity of H293cells was substantially decreased, indicating an important roleof the 1-position of the indole sca ff  old (see Table S3 in ESI † ).Compounds  1 – 3  exhibited higher cytotoxicity during the initialscreening (Fig. 2) than compound  4  despite structural simi-larities. The 4-chlorobenzenesulfonyl analog of   4  was prepared(Table 4, entry 7; compound  24 ), and an increase in activity  was observed as demonstrated by the reduced IC 50  values(Table 4, entries 6 and 7) and cell viability (Fig. 3). Theimprovement to  4  indicates that additional modifications tothe indole sca ff  old will potentially result in further improvede ffi cacy. To this end, e ff  orts to explore the  N  -benzylsulfonamide sca ff  old through further modificationsof a more diverse library of indole sca ff  olds are currently underway in our laboratories and will be reported in duecourse.Compound  24  (referred to as AAL-030) consistently exhibi-ted the highest cytotoxic e ff  ect of the indole analogs preparedin this study. In fact,  24  displayed lower IC 50  values thanknown anticancer agents Indisulam and ABT-751 in our cell viability assays using H293, HeLa, and NCI-H196 cells(Table 4). To further investigate  24 , cell viability of 12 cell lines was then determined using a 50  μ M dose of   24  (Fig. 4) and theresults demonstrate the potential for selectivity amongst di ff  erent cancer cell lines and subtypes (kidney, prostate, cervi-cal, lung, and breast). As shown in Fig. 4, cell viability assay of the non-small celllung cancer cell lines (NCI-H196 and DMS-114) revealed asubtype selectivity for compound  24 , as DMS-114 cells weremore adversely a ff  ected (32% of control) compared to theNCI-H196 cells (57% of control). A similar disparity wasobserved between the breast cell lines. Non-transformed cells(MCF10A) were least a ff  ected by compound  24 , with 70% of cells remaining intact compared to DMSO control. MCF7,SkBr3, and MDA-MB cell lines all remained above 50% of control after 24 hours exposure to compound  24  (50  μ M),however, the viability of subtype T47D cells was more signifi-cantly impacted (39% of DMSO control). Table 2  Cytotoxicity screening using compounds  1 – 15 POC a of various cell linesCompound HDF H293 PC3 BxPC3 HeLa NCI-H196 DMS-114 MCF10A MCF7 T47D SkBr3 MDA-MB 1  57.7  32.9  65.1  45.6  64.3  48.8  84.3  46.5 40.8  60.9  45.8  50.6 2 42.1 33.5  75.1  47.7 25.1 18.2  51.0  25.1 48.2  69.2  40.2  53.6 3 42.2 23.3 49.1  51.4  42.2 12.4  72.2  27.2  55.2 51.3  43.6 43.94  69.3 50.2 65.2 67.3 82.4 56.5 81.1 80.2 65.4 91.0 60.4 55.6 5  78.1 66.1 74.9 81.8 89.1 70.1 82.0 112.5 87.4 91.2 75.1 72.1 6  76.7 68.7 79.9 69.7 87.9 80.8 87.9 99.8 69.3 88.4 60.2 68.2 7  90.8 87.7 87.3 85.2 95.3 73.7 94.6 116.7 95.5 95.1 87.1 72.7 8  82.5 66.9 69.3 52.4 84.8 70.7 77.2 120.6 69.6 85.5 65.0 58.1 9  54.2 61.4 79.1 77.4 77.7 73.6 69.4 83.4 68.3 62.8 76.5 79.5 10  91.2 91.7 85.5 72.4 94.5 77.1 85.9 126.5 88.5 93.7 88.4 65.6 11  87.6 82.2 77.9 66.7 90.1 78.9 91.9 138.5 82.3 92.6 77.0 58.8 12  94.8 93.7 77.2 61.6 103.3 85.0 86.8 122.2 86.9 90.7 77.7 59.6 13  88.9 81.5 66.4 57.2 87.5 83.5 84.4 130.4 83.0 88.1 75.8 54.6 14  94.9 94.6 82.6 54.8 89.2 82.2 76.4 119.6 81.0 88.0 71.4 55.9 15  98.5 99.2 68.3 60.3 102 87.7 87.1 121.9 90.5 89.6 82.7 68.5 a  All values against 12 cell lines were obtained as an average of duplicate measurements  via  the Cell Titer Blue (Promega) assay at 100  μ M (24 h).Lower values of POC (percent of control) indicate stronger hits. POC values below 50% are highlighted in bold. Table 3  Variation of  N -sulfonyl unit Entry R  1 Product % Yld a POC b 1 4-CIC 6 H 4  1  60  32.90% ± 0.06% 2 4-CH 3 C 6 H 4  16  61 65.32% ± 8.20%3 C 6 H 5  17  60 53.25% ± 0.15%4 4-OCH 3 C 6 H 4  18  63 49.80% ± 3.40%5 3-NO 2 C 6 H 4  19  19 61.60% ± 6.20%6 CH 3  20  34 92.03% ± 6.58%7 4-CF 3 C 6 H 4  21  41 79.50% ± 6.03% a Isolated yields.  b Cell viability of compounds performed at 100  μ M with H293 cells. Strong hit values of POC (percent of DMSO control) shownin bold. Paper Organic & Biomolecular Chemistry 8394  |  Org. Biomol. Chem. , 2019, 17 , 8391 – 8402 This journal is © The Royal Societyof Chemistry 2019    P  u   b   l   i  s   h  e   d  o  n   2   2   A  u  g  u  s   t   2   0   1   9 .   D  o  w  n   l  o  a   d  e   d   b  y   M  c   F  a  r   l   i  n   L   i   b  r  a  r  y ,   T   h  e   U  n   i  v  e  r  s   i   t  y  o   f   T  u   l  s  a  o  n   0   9   /   2   1   /   2   0   1   9   2   3  :   3   6  :   2   1 . View Article Online  Sulfonamides have been reported as antibacterialagents. 4 a ,22 Therefore, synthesized compounds  1 – 24  werescreened against overnight cultures of yeast ( Saccharomyces cer-evisiae ) as well as bacteria (  E. coli   –  XL1-Blue strain) in the pres-ence of DMSO control or at 100  μ M concentration of library compound (Fig. 5 and 6). Viability was determined using BacTiter-Glo (Promega), which is an assay that measures celldeath by indirectly measuring a protease released by dying cells that cleaves a peptide conjugated to firefly luciferin. Thereleased luciferin is oxidized to luciferase, releasing light  which can be correlated with the number of dead cells. In sep-arate control reactions performed in which exogenous ATP wasadded to media in the absence of cells, it was confirmed that compounds  1 – 24  do not inhibit the BacTiter-Glo luciferaseassay itself (see ESI, Table S4 † ). Compound  24  (AAL-030) dis- Table 4  Preliminary structural modi 󿬁 cation of the indole sca ff old and comparison to established anticancer sulfonamides IC 50 b (µM)Entry R  1 R  2 R  3 R  4 Product % Yld a H293 HeLa NCI-H1961 H H Ac 4-ClC 6 H 4  22  642 H H CH 3  4-ClC 6 H 4  23  323 H H H 4-ClC 6 H 4  1  60 56.9 83.2 57.34 Br H H 4-CH 3 C 6 H 4  2  34 60.5 67.3 44.55 H CH 3  H 4-CH 3 C 6 H 4  3  58 50.5 60.6 47.36 CH 3  H H C 6 H 5  4  63 95.6 96.3 95.97 CH 3  H H 4-ClC 6 H 4  24  37 47.8 53.5 43.58 ABT-751 209.1 117.5 139.79 Indisulam 229.1 100.6 155.8 a Isolated yields.  b IC 50  values were established by Cell-Titer Blue assay and determined using non-linear regression analysis in Graph-Prismsoftware. Fig. 3  Cell viability screening of compounds  1 – 4  and  24  from Table 4performed at 50  μ M with H293, HeLa, and NCI-H196 cell lines. Valuesare shown as POC (percent of control). Fig. 5  Yeast cell ( S. cerevisiae ) viability assay using compounds  1 – 24  at100  μ M (BacTiter-Glo, Promega) at 3 h exposure. Values are shown asPOC with DMSO serving as control. Values below 50% (stronger activity)are highlighted in red. Fig. 4  Cell viability assays using compound  24  (AAL-030) at 50  μ M.Values are shown as POC with DMSO serving as control for each separ-ate cell line. Values below 50% (stronger activity) are highlighted in red. Organic & Biomolecular Chemistry Paper This journal is © The Royal Societyof Chemistry 2019  Org. Biomol. Chem. , 2019, 17 , 8391 – 8402 |  8395    P  u   b   l   i  s   h  e   d  o  n   2   2   A  u  g  u  s   t   2   0   1   9 .   D  o  w  n   l  o  a   d  e   d   b  y   M  c   F  a  r   l   i  n   L   i   b  r  a  r  y ,   T   h  e   U  n   i  v  e  r  s   i   t  y  o   f   T  u   l  s  a  o  n   0   9   /   2   1   /   2   0   1   9   2   3  :   3   6  :   2   1 . View Article Online
Search
Similar documents
View more...
Related Search
We Need Your Support
Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

Thanks to everyone for your continued support.

No, Thanks
SAVE OUR EARTH

We need your sign to support Project to invent "SMART AND CONTROLLABLE REFLECTIVE BALLOONS" to cover the Sun and Save Our Earth.

More details...

Sign Now!

We are very appreciated for your Prompt Action!

x