From its beginnings, organic chemistry has been a partner to biology, often crossing the artificial boundary between the sciences to the benefit of both disciplines. As the field has matured, it has continued to address matters of structure and synthesis to increasingly encompass the grand challenge of designing and preparing molecules having a particular function. All three of these come together in the pursuit of new chemical probes for use in chemical biology. This Thematic Series highlights some of the numerous ways that molecular tools inform biological research. The structural diversity of molecules that function as probes is broad indeed, some of them complex enough that even the most discerning practitioner of organic synthesis may consider them as worthy of their efforts.
Graphical Abstract
Figure 1: Biologically active imidazo[1,2,4]triazine scaffolds 1–4.
Scheme 1: Retrosynthetic approaches towards novel 7,8-dihydroimidazo-[5,1-c][1,2,4]-triazine-3,6-diones IV an...
Scheme 2: Synthesis of N3-unsubstituted, N1-substituted hydantoin 19 by using a protection strategy.
Scheme 3: Synthesis of 7,8-dihydroimidazo[5,1-c][1,2,4]triazine-3,6-diones 23–29. Reagents and conditions: (i...
Scheme 4: Proposed regioselective two-step cyclization pathway to form 24 from 14.
Figure 2: Optimized structure (MMFF95) and key HMBC correlations of imidazo[5,1-c][1,2,4]triazine-3,6(2H,4H)-...
Figure 3: ORTEP diagram of 24 showing the atomic numbering. The thermal ellipsoids are drawn at the 50% proba...
Graphical Abstract
Figure 1: Structures of well-known serotonin 5-HT2A agonists 1a,b, 2, and 3, and compounds 4 and 5 reported i...
Scheme 1: Synthesis of arylcyclopropane carboxylic acids from the corresponding cinnamic acids, followed by h...
Scheme 2: Conversion of arylcyclopropane carboxylic acids 10a,b to the amines 4 and 5, and chemical resolutio...
Scheme 3: Chemical resolution of arylcyclopropane carboxylic acid 9 followed by bromination.
Graphical Abstract
Figure 1: Structures of known fluorophores (1–8) and novel hydrophobic analogues of rhodamine (HRB, 9, and HR...
Scheme 1: Synthesis of the HRB 9 and HR101 10 fluorophores.
Figure 2: Normalized absorbance (Panel A) and fluorescence emission (Panel B) spectra. Fluorophores were anal...
Figure 3: Linear regression used to determine spectroscopic parameters of HRB 9 and HR101 10 in MeOH. Panels ...
Figure 4: Differential interference contrast (DIC, left panels) and confocal laser scanning (right panels) mi...
Figure 5: Panels A–D: High magnification confocal (top panels) and DIC micrographs (bottom panels, 60× object...
Figure 6: Images of mitochondrial motility, fusion, and fission in the germline of C. elegans extracted from ...
Graphical Abstract
Figure 1: Chemical structures of vinylsulfone-based cruzain inhibitors 1–4, known TcCYP51 inhibitor 5, dihydr...
Figure 2: Computational docking models. (A) Predicted binding modes of 4 and (R)-5 bound to TcCYP51. For 4, t...
Figure 3: Synthesis of the additional control compound 6–8, the reduced forms of analogues 1, 3, and 4 respec...
Figure 4: GC/MS analysis of lipid extracts from T. cruzi parasites treated with test compounds. DMSO and K777...
Figure 5: Chemical structures of compound 9, a “clickable” activity-based probe based on 1 and complementary ...
Figure 6: Competitive labeling of host cell (C2C12) proteins. Intact cells were labeled with probe 9 followin...
Figure 7: MS/MS spectrum of the tryptic peptide S264-R281 from mouse cathepsin B, identified in pull-down exp...
Graphical Abstract
Figure 1: FDA approved HDAC inhibitors for the treatment of CTCL.
Scheme 1: SAR of psammaplin A against zinc-dependant HDACs. Adapted from Baud et al. [20].
Scheme 2: Synthesis of 7–9. Conditions: (i) HCl·H2NOMe, pyridine, rt, 12 h; (ii) EDC, NHS, dioxane, rt, 3 h; ...
Scheme 3: Top: Generation of the fluorescent adduct 11 after reaction of probe 10 with thiols. Bottom left: F...
Figure 2: rHDAC1 was incubated with a predetermined IC50 concentration of 7 (left) and 9 (right) for 1–60 min...
Graphical Abstract
Figure 1: Structure of FP–PEG–biotin 1.
Scheme 1: Synthetic scheme to FP–PEG–biotin probe 1.
Figure 2: Labeling and affinity isolation of serine hydrolases by FP–PEG–biotin 1. (A) Lane 1: Protein standa...
Figure 3: Kinetic study on FP labelling reactions. Caco-2 cell homogenates (1 mg/mL) were treated at room tem...
Figure 4: Competition assay between FP–PEG–biotin and enzyme hydrolysis reactions. (A) Enalapril at the indic...
Graphical Abstract
Figure 1: Structure of first-generation lead compound 1.
Scheme 1: Synthesis of anilino nitrobenzene 7a.
Scheme 2: Preparation of morpholinyl-o-nitroanilines.
Scheme 3: Asymmetric synthesis of (R)- and (S)-isomers by using two different approaches.
Scheme 4: Preparation of chiral propionamides by HATU-mediated coupling (a) or thionyl chloride-mediated coup...
Figure 2: Renderings of crystal structures of (S)- (left, magenta) and (R)- (right, cyan) enantiomers of 1.
Figure 3: L-Tartaric acid salt (18f-tartrate) and benzenesulfonic acid salt (18f-benzenesulfonate) of 18f.
Graphical Abstract
Figure 1: PLG peptidomimetic design approach. The Φ2, ψ2, Φ3, and ψ3 torsion angles define the postulated β-t...
Figure 2: Lactam-based PLG peptidomimetics.
Figure 3: Lactam-based photoaffinity ligands of the PLG modulatory site.
Figure 4: Bicyclic PLG peptidomimetics.
Figure 5: Spiro-bicyclic PLG peptidomimetics.
Scheme 1: Synthesis of α-alkylaldehyde proline derivatives by Seebach's “self-regeneration of chirality” meth...
Scheme 2: Synthetic approaches to the spiro-bicyclic scaffolds.
Figure 6: Prolyl PLG analogues.
Figure 7: (A) Type VI β-turn mimics. An ethylene bridge connection in 43 and 45 between the α-carbon of the s...
Scheme 3: Synthesis of spiro-bicyclic type VI β-turn mimic 48.
Scheme 4: Biproline formation from Seebach’s oxazolidinone.
Figure 8: Positive and negative allosteric modulators of the D2 dopamine receptor based on the 5.6.5 spiro-bi...
Graphical Abstract
Figure 1: The chemical structure of a series of fluorescent amino acids. (1a) α-(2-(7-hydroxycoumarin-4-yl)et...
Scheme 1: Synthetic route to fluorescent amino acids 1a, 1b and 1c.
Figure 2: Coomassie-stained SDS-PAGE (left) of TAG38 mutant thioredoxin (indicated by the black arrow) expres...
Figure 3: Absorbance of compounds 1b and 1c at 360 nm as a function of pH value. (A) Absorption spectrum of 5...
Figure 4: Effect of the pH value of the solution on the fluorescence emission spectra of compounds 1b and 1c....
Graphical Abstract
Figure 1: p21 determines the fate of DNA-damaged [13] cells.
Figure 2: Retrosynthetic analysis of LLW62 (1) from acid 7 (A) or aldehyde 11 (B).
Scheme 1: Attempted synthesis of aldehyde 4 from nitrile 6.
Scheme 2: (A) Synthesis of 4 from acid 7 and (B) attempted β-amino acid-forming 3CRs.
Scheme 3: Synthesis of LLW62 by using an early stage 3CR.
Graphical Abstract
Figure 1: Design of the biotinylated Hsp90 probes based on PU-H71 (1a).
Scheme 1: Reagents and conditions: (a) D-biotin, DCC, DMAP, CH2Cl2, sonicate; (b) EZ-Link® NHS-LC-Biotin, DIE...
Scheme 2: Reagents and conditions: (a) 6-Boc-aminocaproic acid, DCC, DMAP, CH2Cl2, rt; (b) TFA, CH2Cl2, rt; (...
Figure 2: Analysis of the affinity and selectivity of the biotinylated probes for Hsp90. (a) K562 cancer cell...
Figure 3: Use of probe 2g to detect oncogenic Hsp90 by flow cytometry (a) and (b) and by microscopy (c). For ...
Graphical Abstract
Figure 1: FDA-approved riluzole (1) and other ALS drugs currently in phase III clinical trials (2–6).
Figure 2: Riluzole (left) and prodrugs developed by McDonnell et al. [11].
Figure 3: Neurotransmitters N-acetyl-aspartyl glutamate (NAAG, top) and D-serine (bottom).
Figure 4: Thiopyridazines developed to increase EAAT2 protein levels.
Figure 5: Compounds shown to reduce SOD1 expression.
Figure 6: Families of compounds (named in italics) capable of reducing SOD1-induced cellular toxicity and mut...
Figure 7: Compounds identified by Nowak and co-workers [37] in silico that selectively bind SOD1 over human plasm...
Figure 8: 4-Aminoquinolines developed by Cassel and co-workers [43] for disruption of oligonucleotide/TDP-43 bind...
Figure 9: Cu(II)(atsm), an example of a Cu(II)(btsc) copper complex.
Figure 10: Pharmacological inducers of autophagy.
Figure 11: Compounds used to evaluate the effects of trophic factors on ALS disease progression.
Figure 12: Compounds identified as neuroprotective.
Figure 13: Compounds developed to reduce oxidative stress and inflammation.
Figure 14: Probes used to elucidate the roles of distinct gene-expression profiles in ALS patients.
Figure 15: Targets of potential therapeutics: This diagram illustrates the physiological targets of each compo...
Graphical Abstract
Scheme 1: Synthesis of ML029 (4).
Scheme 2: Synthesis of ML236 (8).
Scheme 3: Synthesis of ML237 (12).
Scheme 4: Synthesis of ML130 (13).
Scheme 5: Synthesis of ML146 (17).
Graphical Abstract
Figure 1: Roseobacter clade metabolites.
Scheme 1: Degradation of DMSP via (A) demethylation pathway and (B) cleavage pathways. FH4: tetrahydrofolate.
Scheme 2: Sulfate reduction pathway and incorporation of sulfur into the amino acid pool. PAP: adenosine 3’,5...
Figure 2: Volatiles from P. gallaeciensis DSM 17395 and R. pomeroyi DSS-3. Feeding of [2H6]DMSP results in de...
Figure 3: Chromatograms of headspace extracts from P. gallaeciensis DSM 17395 after feeding of DMTeP by the u...
Figure 4: Chromatograms of headspace extracts obtained after feeding of [2H6]DMSP by the use of SPME from (A) ...
Figure 5: Chromatograms of headspace extracts from (A) R. pomeroyi DSS-3 wild type, (B) R. pomeroyi DSS-3 dmdA...
Scheme 3: Synthesis of 34S-labeled thiosulfate and sulfate.
Figure 6: Volatiles from P. gallaeciensis after feeding of selenate and selenite.
Figure 7: Chromatograms of headspace extracts from P. gallaeciensis grown on (A) 50% MB2216, (B) 50% MB2216 +...
Figure 8: Additional sulfur volatiles.
Graphical Abstract
Figure 1: Structures of lead Rho/MKL1/SRF inhibitor 1 and conformationally restricted analogue 2.
Figure 2: Strategy for tag-free photolabeling in whole cells (PG = photoactivatable group, TAG = fluorescent ...
Scheme 1: General synthesis of model benzophenone probes.
Scheme 2: Synthesis of aryl azide model probe 14.
Scheme 3: Synthesis of benzophenone photoaffinity probe 19.
Scheme 4: Synthesis of benzophenone photoaffinity probe 24.
Scheme 5: Synthesis of aryl azide photoaffinity probes.
Figure 3: Photoprobe 24 (CCG-206559) retains biological activity to block prostate cancer migration. A. Cellu...
Figure 4: Structure of the competitor used in the photolabeling experiment.
Figure 5: SDS-PAGE gel of photolabeling experiment in whole PC-3 cells. Lane 1 contains 0.3 µM 24 after 30 mi...
Graphical Abstract
Scheme 1: Synthesis of hexaethyl dialkylaminomethylidynetrisphosphonates 1 from dichloromethylene dialkylammo...
Scheme 2: Synthesis and some transformations of trisphosphonate 2.
Scheme 3: Attempt to synthesize trisphosphonates by the combination of Arbuzov reaction and dialkyl phosphite...
Scheme 4: Synthesis of hexaethylmethylidynetrisphosphonate 6 via phosphinylation of tetraethyl methylenebisph...
Scheme 5: Synthetic approach to methylidynetrisphosphonate ester 9.
Scheme 6: Synthesis of alkylidyne-1,1,1-trisphosphonate esters 12.
Scheme 7: Two-step one-pot synthesis of propargyl-substituted trisphosphonate 15.
Scheme 8: Synthetic route to trisphosphonate 18 via 7,7-bisphosphonyl-3,5-di-tert-butylquinone methide 17.
Scheme 9: Synthesis of trisphosphonate 18 starting from 2,6-di-tert-butyl-4-(dichloromethyl)phenol.
Scheme 10: Synthesis of triphosphorus derivatives 20 via quinone methides 17 and 19.
Scheme 11: Unexpected phosphonylation of the aromatic nucleus in reactions of quinone methides 19 and 21.
Scheme 12: Multistep synthesis of trisphosphonate 18 starting from quinone methide 25.
Scheme 13: Synthesis of hexaethyl methylidynetrisphosphonate (6) via metal-carbenoid-mediated P–H insertion re...
Scheme 14: Reaction between tert-butylphosphaethyne and diethyl phosphite in the presence of sodium metal.
Scheme 15: Cross metathesis of trisphosphonates 12 with 2-methyl-2-butene and the Grubbs second-generation cat...
Scheme 16: Hydroboration–oxidation of trisphosphonates 12b,e.
Scheme 17: Reaction of 3-butyn-1-ylidenetrisphosphonate 15 with benzyl azide.
Scheme 18: The use of the transsilylation reaction for the synthesis of trisphosphonate salts 37.
Scheme 19: Synthesis of the sodium salt of the acid-labile trisphosphonic acid 38.
Scheme 20: Acidic hydrolysis of trisphosphonate ester 1a.
Scheme 21: Methylation of trisphosphonate 1a.
Scheme 22: Synthesis of the free methylidynetrisphosphonic acid via trisphosphonate salt 38.
Scheme 23: Synthesis of halomethylidynetrisphosphonate salts 43 and 44 by modified Gross’s procedure.
Scheme 24: Synthesis of trisphosphonate modified nucleotides. Reagents: i, 5'-O-tosyl adenosine, MeCN; ii, AMP...
Figure 1: Bond angles and bond distances in pyrophosphate, methylene-1,1-bisphosphonate and fluoromethylidyne...
Graphical Abstract
Figure 1: Selection of prosthetic agents for 18F-labelling via acylation.
Scheme 1: Synthesis of radiofluorination precursors 3 and 4. Reagents and conditions: (a) KSCN, CH3OH, reflux...
Scheme 2: Synthesis of 3-fluoropropanesulfonamide 11 via intermediary 3-fluoropropanesulfonyl chloride (10). ...
Scheme 3: Synthesis of 3-fluoropropanesulfonamides 12–18. Reagents and conditions: (a) triethylamine (TEA), CH...
Figure 2: (A) View of the molecular structure of sulfonamide 18 with atom labelling scheme. Displacement elli...
Figure 3: Dependence of the labelling yields of [18F]9 on the precursor amount. Reactions of tosylate 3 and n...
Figure 4: Time course of the distillation of 3-[18F]fluoropropyl thiocyanate ([18F]9) in the argon stream. Fo...
Scheme 4: Radiosynthesis of 3-[18F]fluoropropanesulfonamides [18F]11–[18F]18. Reagents and conditions: (a) [18...
Figure 5: Radio-HPLC chromatograms for the reaction of [18F]10 with (A) 4-fluoroaniline in the absence and pr...
Figure 6: Time course of the carboxylesterase-catalysed degradation of 3-fluoropropansulfonamide 17 (red) and...
Graphical Abstract
Figure 1: Structures of A. dyes originally used to stain Aβ and B. newer scaffolds explored for the developme...
Scheme 1: General synthetic strategies (Gs) used to introduce A. 18F, B. 11C, C. 99mTc/Re, and D. 123I and 125...
Scheme 2: A. Structures of radiolabeled chalcone analogues discussed. B.–D. Synthetic schemes for the prepara...
Scheme 3: A. Structures of the radiolabeled flavone and aurone analogues discussed. B. Synthetic scheme for t...
Scheme 4: A. Structures of the radiolabeled stilbene analogues discussed. B. Synthetic scheme for the prepara...
Scheme 5: A. Structures of the diphenyl-1,3,4- and diphenyl-1,2,4-oxadiazoles discussed. B.,C. Synthetic sche...
Figure 2: Structures of the radiolabeled benzothiazole analogues discussed.
Scheme 6: A.–F. Synthetic schemes for the preparation of [11C]56b, [11C]56c, 57, 58a,b, 61, and [18F]65a–d.
Scheme 7: A. Structures of the [Re]- and [99mTc]-labeled benzothiazole analogues discussed. B.,C. Synthetic s...
Figure 3: Structures of the radiolabeled benzoxazole analogues discussed.
Scheme 8: A.–E. Synthetic schemes for the preparation of 94, [123I]95e, 96–98.
Figure 4: Structures of the radiolabeled benzofuran analogues discussed.
Scheme 9: A.–E. Synthetic schemes for the preparation of 121, [125I]122a, 123a,b, 125a,b, and 126.
Scheme 10: A. Structures of the radiolabeled imidazopyridine analogues discussed. B. Synthetic scheme for the ...
Scheme 11: Synthetic scheme for the preparation of the benzimidazole 146.
Figure 5: Structures of the quinolines discussed.
Scheme 12: Synthetic scheme for the preparation of the naphthalene analogues 152 and 160a,b.
Scheme 13: A. Structures of the radiolabeled analogues resulting from the combination of various scaffolds. B.,...
Scheme 14: A.–C. Synthetic schemes for the preparation of radiolabeled probes with unique scaffolds.
Scheme 15: A. Structures of the oxazine-derived fluorescence probes discussed. B. Synthetic scheme for the pre...
Figure 6: Structure of THK-265 (190).
Scheme 16: Synthetic scheme for the preparation of quinoxaline analogue 191.
Graphical Abstract
Figure 1: Assay pipeline for triaging hits. Individual assay cut-offs are given in italics.
Figure 2: Hit compounds selected for further optimization.
Scheme 1: Preparation of substituted methyl 2-(1H-indazol-1-yl)acetates. Reagents and conditions: (a) Et3N, B...