Kinase inhibitors can be divided into monoclonal antibodies (mAbs) and small molecule kinase inhibitors (SMKIs) based on their structure and size. Monoclonal antibodies have achieved great success in the development of cancer therapeutics. For example, as early as 1998, the United States approved the first monoclonal antibody, trastuzumab, to treat HER2-positive breast cancer. However, due to the inherent disadvantages of monoclonal antibodies such as production costs, stability, and immunogenicity, low molecular weight SMKIs have become an active research area for discovering kinase inhibitors. This article shares a total of 63 SMKIs approved by the US FDA as of 2020.

2001

Imatinib (STI571, CGP057148B, ST-1571) is a multitarget tyrosine kinase inhibitor, with IC50 values of 0.6, 0.1, and 0.1 μM for v-Abl, c-Kit, and PDGFR, respectively. Imatinib (STI571) can induce autophagy.

Synthetic route:

(i) Aldol condensation, NaOMe, PhMe, 25°C, 16 h;

(ii) Schiff base formation, HNMe2, AcOH, PhMe, reflux, 1 h;

(iii) Nucleophilic addition, NH2CN, HNO3, EtOH, reflux, 21 h;

(iv) Cyclization, NaOH, isopropanol, reflux, 12 h;

(v) Reduction, Pd/C, H2, THF, rt, 21 h;

(vi) Acylation, pyridine, rt, 24 h.

2003

Gefitinib (ZD1839) is an EGFR inhibitor that acts on Tyr1173, Tyr992, Tyr1173, and Tyr992 in NR6wtEGFR and NR6W cells, with IC50 values of 37 nM, 37 nM, 26 nM, and 57 nM, respectively. Gefitinib can promote autophagy and cell apoptosis in lung cancer cells by blocking the PI3K/AKT/mTOR signaling pathway.

Synthetic route:

(i) Demethylation of methionine, MeSO3H, L-methionine, 100 °C;

(ii) Acetylation, Ac2O/pyridine;

(iii) Formation of internal amide chloride, SOCl2;

(iv) SNAr reaction, 3-chloro-4-fluoroaniline;

(v) Deacetylation, NH4OH in MeOH;

(vi) Alkylation, N-morpholinopropyl bromide, K2CO3.

2004

Erlotinib (CP358774, NSC 718781) is an EGFR inhibitor with an IC50 of 2 nM. It is over 1000 times more sensitive to EGFR compared to human c-Src or v-Ab. Erlotinib can induce autophagy.

Synthetic route:

(i) Esterification, H2SO4, EtOH;

(ii) Alkylation, 2-bromoethylmethyl ether, K2CO3, TBAI in acetone;

(iii) Nitration, HNO3, 5 °C in AcOH;

(iv) Reduction, H2, PtO2, HCl in EtOH;

(v) Cyclization, HCONH4/HCONH2, 165 °C;

(vi) Intramolecular acyl chloride formation, (COCl)2, DCM/DMF;

(vii) SNAr reaction, 3-ethynylaniline in i-PrOH.

2005

Sorafenib (BAY 43-9006) is a multi-kinase inhibitor of Raf-1 and B-Raf, with IC50 values of 6 nM and 22 nM in cell-free assays. Sorafenib also inhibits VEGFR-2, VEGFR-3, PDGFR-β, Flt-3, and c-KIT, with corresponding IC50 values of 90 nM, 20 nM, 57 nM, 59 nM, and 68 nM, respectively. Sorafenib can induce autophagy and apoptosis as well as activate ferroptosis.

Synthetic route:

(i) Chlorination, SOCl2, DMF, 72 °C, 16h;

(ii) Acylation, MeNH2, THF, MeOH, 0-3 °C, 5 h;

(iii) SNAr reaction, 4-aminophenol, t-BuOK, DMF, rt, 2 h; then V, K2CO3, 80 °C, 8 h;

(iv) Preparation of urea with isocyanate, 4-chloro-3-(trifluoromethyl)phenylisocyanate, DCM, 0 °C to rt, 22 h.

2006

Dasatinib (BMS-354825) is a novel and effective multi-targeted inhibitor that targets Abl, Src, and c-Kit. It exhibits an IC50 of in vitro assays, respectively. Dasatinib can induce autophagy and apoptosis and has anti-tumor activity.

Synthetic route:

(i) Acylation: Acyl chloride (COCl)2, DMFcat, DCM, 0 °C−rt, 1.5h.

(ii) Acylation: 2-chloro-6-methylaniline, DCM, DIPEA, rt, 24 h.

(iii) Boc deprotection: TFA.

(iv) Dehydrogenation: NaH, THF, rt, 30 min.

(v) SNAr reaction: 4,6-dichloro-2-methylpyrimidine.

(vi) SNAr reaction: 2-(piperazin-1-yl)ethan-1-ol, 80 °C, 2 h.

Sunitinib (SU11248) is a multitarget RTK inhibitor that targets VEGFR2 (Flk-1) and PDGFRβ with IC50 values of 80 nM and 2 nM, respectively. It also has inhibitory effects on c-Kit. Sunitinib is a dose-dependent inhibitor of the autophosphorylation activity of IRE1α. Sunitinib can induce autophagy and cell apoptosis.

Synthetic route:

(i) Ring-opening, NH2NH2 H2O, 110 °C, 4 h;

(ii) Hydrolysis and ring closure, 12 N HCl, H2O, room temperature, 12 h;

(iii) Oxime formation, NaNO2, AcOH, room temperature, 1 h;

(iv) Pyrroline formation, ethyl-3-oxobutyrate, Zn, HOAc;

(v) Hydrolysis, 10 N HCl, EtOH, 54 °C, 1 h;

(vi) Formylation, POCl3, DMF/DCM, 4 °C to reflux, 1 h;

(vii) Hydrolysis, KOH, H2O/MeOH, reflux, 2 h;

(viii) Acid amine condensation, HOBt, Et3N, EDC, NH2(CH2)N(C2H5)2, DMF, room temperature, 20 h;

(ix) Methylation of VIIa and aldehyde condensation, pyrrolidine, EtOH, 78 °C, 3 h.

2007

Nilotinib (AMN-107) is a specific BCR-ABL inhibitor with an IC50 below 30 nM in mouse bone marrow progenitor cells. Nilotinib (AMN-107) can induce autophagy by activating AMPK.

Synthetic route:

(i) SNAr reaction, DMF, 145 °C, 19 h;

(ii) Hydrolysis, aq. NaOH, 1,4-dioxane, H2O, 95 °C, 18 h;

(iii) Curtius rearrangement, Et3N, DPPA, t-BuOH, 80 °C, 16 h;

(iv) Boc deprotection, HCl, i-PrOH, 60 °C, 5 h;

(v) Addition, H2NCN, HCl, EtOH, 90 °C, 15 h;

(vi) Salt formation, NH4NO3, H2O;

(vii) Closure of the Imatinib fragment, NaOH, EtOH, reflux, 68 h;

(viii) Hydrolysis, NaOH, H2O/EtOH, 45 °C, 2.5 h;

(ix) Acidification, HCl, 1.5 h;

(x) Acid-amine condensation, diethyl phosphorocyanidate, Et3N, DMF, 60 °C, 12 h.

Lapatinib (GSK572016), used in the form of Lapatinib Ditosylate, is an effective inhibitor of EGFR and ErbB2 with IC50 values of 10.2 and 9.8 nM in cell-free assays, respectively. Lapatinib can induce ferroptosis and cell autophagy.

Synthetic route:

(i) Alkylation, K2CO3, MeCN;

(ii) Reduction of nitro group, H2, Pt/C, EtOH, THF;

(iii) Reduction of cyanide group, BH3Me2S, THF;

(iv) SNAr reaction, VIIIa, i-PrOH, 70 °C;

(v) Suzuki reaction, (5-formylfuran-2-yl)boronic acid Pd(OAc)2, PPh3, Et3N, DMF;

(vi) Reductive amination, VIIIb, Na(OAc)3BH, DCM, HOAc.

2009

Pazopanib (GW786034) is a novel multitarget inhibitor of VEGFR1, VEGFR2, VEGFR3, PDGFR, FGFR, c-Kit, and c-Fms/CSF1R. Its IC50 values in cell assays are 10 nM, 30 nM, 47 nM, 84 nM, 74 nM, 140 nM, and 146 nM, respectively. Pazopanib can induce activation of cathepsin B and autophagy.

Synthetic route:

(i) Nitration, HNO3, H2SO4, 0−5 °C;

(ii) Nitrosoylation closure, isoamyl nitrite dropwise, AcOH, rt, 0.5 h;

(iii) Methylation, Me3OBF4, acetone, rt, 3 h;

(iv) Reduction, SnCl2, conc HCl, diglyme, 0 °C to rt, 0.5 h;

(v) SNAr reaction, 2,4-dichloropyrimidine, NaHCO3, EtOH, THF, 85 °C, 4 h;

(vi) Methylation, MeI, Cs2CO3, DMF, rt, overnight (on);

(vii) SNAr reaction, 5-amino-2-methylbenzenesulfonamide, conc HCl, i-PrOH, reflux, on.

2011

Vemurafenib (PLX4032, RG7204) is a novel and effective B-RafV600E inhibitor with an IC50 of 31 nM. Vemurafenib is 10 times more selective towards B-RafV600E compared to wild-type B-Raf and can be more than 100 times selective in cell experiments. Vemurafenib (PLX4032, RG7204) can induce autophagy.

Synthetic route:

(i) Sulfonylation, Propane 1-sulfonyl chloride chloride, Et3N, THF, N2 atm, rt, overnight (on);

(ii) Formylation, lithium diisoproylamide, THF, −78°C, DMF (dropwise), −78 °C−rt, 40 min;

(iii) Suzuki reaction, K2CO3, H2O, CH3CN, tetrakis(triphenylphosphine)palladium(0), N2 atm, 170 °C, on;

(iv) Dehydrogenation, intermediate XVIa, KOH, MeOH, rt, 72 h;

(v) Nucleophilic addition, hydrobromic acid (8%), rt, on;

(vi) Oxidation, DDQ, 1,4-dioxane, H2O(4.8%), rt, 2 h.

Vandetanib (ZD6474) is an effective VEGFR2 inhibitor with an IC50 of 40 nM in cell-free assays. It also inhibits VEGFR3 and EGFR with IC50s of 110 nM and 500 nM, respectively. It has little effect on PDGFRβ, Flt-1, Tie-2, and FGFR1, with IC50s ranging from 1.1 to 3.6 μM. It has almost no effect on MEK, CDK2, c-Kit, erbB2, FAK, PDK1, Akt, and IGF-1R, with IC50s greater than 10 μM. Vandetanib (ZD6474) can induce apoptosis and autophagy by increasing the levels of reactive oxygen species (ROS).

Ruxolitinib (INCB018424) is the first clinically effective selective JAK1/2 inhibitor. Its IC50 values in cell-free assays are 3.3 nM for JAK1 and 2.8 nM for JAK2. Compared to its activity on JAK3, it exhibits 130-fold higher selectivity. Ruxolitinib kills tumor cells through toxic mitophagy. It induces autophagy and enhances cell apoptosis.

Synthesis route:

(i) Protection group, SEM-Cl, DMAC, NaH, 0-5 °C, 35 min;

(ii.1) Suzuki reaction with 1-(1-ethoxyethyl)-1H-pyrazole-4-boronic acid pinacol ester, K2CO3, Pd(PPh3)4, n-BuOH/H2O, reflux, 4 h; (ii.2) HCl, THF, room temperature;

(iii.1) Michael addition with 3-cyclopentylacrylonitrile (racemic mixture), DBU, MeCN, room temperature, overnight; (iii.2) Chiral separation;

(iv) Deprotection of the SEM group, TFA, DCM, room temperature, 6 h.

Crizotinib (PF-02341066) is an effective c-Met and ALK inhibitor, with IC50 values of 11 nM and 24 nM, respectively, in cell assays. It is also a potent ROS1 inhibitor, with a Ki value of less than 0.025 nM. Crizotinib can induce autophagy in various lung cancer cell lines by inhibiting the STAT3 pathway.

Synthetic route:

(i) Sulfonylation, MsCl, Et3N, DCM;

(ii) Alkylation, NaH, DMF, 100 °C;

(iii) Boronic ester bis(pinacolate)diboron, Pd(Ph3P)2Cl2, KOAc, DMSO, 80 °C;

(iv) Mitsunobu reaction, Ph3P, DEAD, THF, 0 °C;

(v) Reduction, Fe, AcOH/EtOH, reflux;

(vi) Bromination, NBS, MeCN, 0 °C;

(vii) Suzuki coupling, XIIIa, Pd(dppf)Cl2, Cs2CO3, DME/H2O, 90 °C;

(viii) Boc deprotection, 4 N HCl in 1,4-dioxane, DCM, 0 °C.

2012

Tofacitinib is a novel JAK3 inhibitor, with an IC50 of 1 nM in cell-free experiments. It exhibits low selectivity for JAK2 and JAK1, around 20 to 100 times lower. Tofacitinib can inhibit anti-apoptotic BCL-A1 and BCL-XL in human plasma dendritic cells (PDC) and induce PDC apoptosis.

Synthesis route:

(i) SNAr reaction, (3R,4R)-1-benzyl-N,4-dimethylpiperidin-3-amine, Et3N, 100 °C;

(ii) Hydrogenation and debenzylation, Pd(OH)2/C, H2, EtOH, room temperature;

(iii.1) Acid amine condensation, cyanoacetic acid 2,5-dioxopyrrolidin-1-yl ester, EtOH, room temperature, 1 hour;

(iii.2) Salt formation, citric acid, acetone, 40 °C to room temperature, 2 hours.

Regorafenib (BAY 73-4506, Fluoro-Sorafenib, Resihance, Stivarga) is a multi-target inhibitor that acts on VEGFR1, VEGFR2, VEGFR3, PDGFR-β, Kit (c-Kit), RET (c-RET), and Raf-1. In cell-free assays, the IC50 values of Regorafenib are 13 nM, 4.2 nM, 46 nM, 22 nM, 7 nM, 1.5 nM, and 2.5 nM for VEGFR1, VEGFR2, VEGFR3, PDGFR-β, Kit (c-Kit), RET (c-RET), and Raf-1, respectively. Regorafenib can induce autophagy.

Synthesis route:

(i) Reduction of nitro group, 10% Pd/C, ethyl acetate, H2 atmosphere, room temperature, 4 hours;

(ii) Dehydrogenation for SNAr reaction, potassium t-butoxide, 0 °C, 25 minutes, intermediate V, DMA, 100 °C, 16 hours;

(iii) Preparation of urea using isocyanate, 4-chloro-3-(trifluoromethyl)phenyl isocyanate, toluene, room temperature, 72 hours.

Ponatinib (AP24534) is a new and effective multi-target inhibitor that acts on Abl, PDGFRα, VEGFR2, FGFR1, and Src in in vitro assays, with IC50 values of 0.37 nM, 1.1 nM, 1.5 nM, 2.2 nM, and 5.4 nM, respectively. Ponatinib (AP24534) can inhibit autophagy.

Synthesis route:

(i) Sonogashira coupling with trimethylsilylacetylene, Pd(PPh3)2Cl2, CuI, (i-Pr)2NEt, DMF, 80 °C;

(ii) Deprotection with TBAF, THF, at room temperature;

(iii) Alkylation with 1-methylpiperazine, Et3N, DCM, at room temperature;

(iv) Reduction of nitro group with Na2S2O4, acetone/H2O, reflux;

(v) Acylation with 3-iodo-4-methylbenzoyl chloride, (i-Pr)2NEt, THF, at room temperature;

(vi) Sonogashira coupling with intermediate XX, Pd(PPh3)4, CuI, (i-Pr)2NEt, DMF, at room temperature.

Cabozantinib (XL184, BMS-907351) is an effective VEGFR2 inhibitor, with an IC50 of 0.035 nM in cellular assays. It can also effectively inhibit c-Met, Ret, Kit, Flt-1/3/4, Tie2, and AXL, with IC50 values of 1.3 nM, 4 nM, 4.6 nM, 12 nM/11.3 nM/6 nM, 14.3 nM, and 7 nM, respectively. Cabozantinib can induce PUMA-dependent apoptosis through the AKT/GSK-3β/NF-κB signaling pathway in colon cancer cells.

Bosutinib (SKI-606) is a novel dual Src/Abl inhibitor, with IC50 values of 1.2 nM and 1 nM in cellular assays. Bosutinib can effectively reduce the activity of the PI3K/AKT/mTOR, MAPK/ERK, and JAK/STAT3 signaling pathways by blocking the phosphorylation of p-ERK, p-S6, and p-STAT3. Bosutinib can also promote autophagy.

Axitinib (AG 013736) is a multi-target inhibitor that acts on VEGFR1, VEGFR2, VEGFR3, PDGFRβ, and c-Kit, with IC50 values of 0.1 nM, 0.2 nM, 0.1-0.3 nM, 1.6 nM, and 1.7 nM, respectively, in porcine aortic endothelial cells.

2013

Trametinib (GSK1120212, JTP-74057, Mekinist) is a highly specific and effective MEK1/2 inhibitor with an IC50 of 0.92 nM/1.8 nM in cell assays. It does not inhibit c-Raf, B-Raf, or ERK1/2. Trametinib can activate autophagy and induce apoptosis.

Ibrutinib (PCI-32765) is a potent and highly selective Brutons tyrosine kinase (Btk) inhibitor with an IC50 of 0.5 nM in cell assays. It moderately inhibits Bmx, CSK, FGR, BRK, and HCK, but has weaker effects on EGFR, Yes, ErbB2, JAK3, and others. Ibrutinib can be used as a Btk ligand for the synthesis of various PROTACs, including P13I.

Synthetic route:

(i) iodination, NIS, DMF, heat;

(ii) Suzuki reaction, 4-phenoxyphenylboronic acid pinacol ester, Pd(dppf)Cl2·DCM, aq. K2CO3/1,4-dioxane, 180°C, 10 min;

(iii) Mitsunobu reaction, N-Boc-3-hydroxypiperidine, diisopropyl azodicarboxylate, polymer-bound PPh3, THF, rt, overnight;

(iv) deprotection, 4 M HCl/1,4-dioxane, rt, 1 h;

(v) acylation, acryloyl chloride, Et3N, DCM, rt, 2 h.