Total Synthesis of Resorcinol Amide Hsp90 Inhibitor AT13387
Bhavesh H. Patel and Anthony G. M. Barrett*
Department of Chemistry, Imperial College, London SW7 2AZ, England
S* Supporting Information

ABSTRACT: The synthesis of C-5-substituted resorcinol amide AT13387, a known Hsp90 inhibitor currently in clinical trials, is reported without the use of phenolic protection in an overall yield of 13.4%. Biomimetic aromatization and Suzuki-Miyaura cross coupling approach were employed to synthesize the resorcinol and iso-indoline units, respectively, which were efficiently coupled using Grignard-mediated amidation.

■ INTRODUCTION
Molecular chaperones are responsible for the correct folding, stabilization and function of other cellular proteins.1 The most extensively studied of these is heat shock protein 90 (Hsp90), which is a highly abundant 90-kDa protein and regulates the conformation, activation, function and stability of client proteins.2 Over recent years, Hsp90 has gained considerable interest due to the recognition of its importance to cancer cell survival.3 Over the past decade a substantial number of Hsp90 inhibitors have been discovered with one of the earliest being the resorcylate natural product radicicol (1) (Figure 1).2 The

research programs on Hsp90. Their efforts have led to lead structures 4 and 5, differing by the C-5 resorcinol substituent (Figure 2). The study by Pfi zer scientists led to the

Figure 1. Structures of resorcinol-containing Hsp90 inhibitors.

Figure 2. Structures of Pfi zer and Astex Hsp90 inhibitors.

resorcinol-diarylpyrazole CCT018159 (2) was identified as a Hsp90 inhibitor through HTS, and computer-aided design resulted in the discovery of the more potent resorcinylic isoxazole amide VER-50589 (3). Moreover, further semi- synthetic structure activity relationship (SAR) studies have been reported on radicicol (1) and its analogues.4
It became evident that the resorcinol anchor unit was critical for binding, especially in the effectiveness of radicicol as an Hsp90 inhibitor.2 Several pharmaceutical companies, including Pfi zer5 and Astex Therapeutics6 undertook medicinal chemistry

identification of diamide 6, which was potent (Ki < 1 nM, cell IC50 = 0.3 μM) and also displayed good clearance and acceptable oral bioavailability.7 Astex used fragment-based drug discovery (FBDD) and focused SAR studies of their lead resorcylate 5 to develop AT13387 (7) (Kd = 0.71 nM, HCT116 cell IC50 = 48 nM, hERG % inhibition: 7% at 3 μM),8 which

Received: October 31, 2012 Published: November 27, 2012

© 2012 American Chemical Society 11296 dx.doi.org/10.1021/jo302406w | J. Org. Chem. 2012, 77, 11296-11301

Scheme 1. Projected Retrosynthetic Strategy

has progressed through preclinical development, and is now in clinical trials for the treatment of refractory gastrointestinal stomal tumors.
The resorcylate unit of these molecules has previously been synthesized from substituted benzoic acid precursors with lengthy sequences of transformations including aromatic substitution, palladium catalyzed coupling reactions and protection-deprotection steps. For example, the reported total synthesis of AT13387 is 13 steps with an overall yield of 2.6%.9 We sought to circumvent these issues by the use of our biomimetic approach10 to generate the resorcylate ring thereby developing a flexible synthesis much more suitable for analogue generation as well as for the scale up synthesis of lead compounds. We considered that AT13387 (7) should be available from dioxinone-resorcylate 8 and amine 9 via transacylative ring-opening (Scheme 1). The C-5 iso-propyl dioxinone-resorcylate 8 should in turn be prepared from dioxinone 10 utilizing a base-mediated cyclization-aromatiza- tion process. Intermediate 10 should be accessible from the C- formylation of the dilithium enolate of 11 with esters, activated amides or mixed anhydrides 12. Finally, iso-indoline 9 should be available using Molander’s methodology,11 from potassium 4-methylpiperazinomethyltrifluoroborate (13) and bromo-iso- indoline 14.
■ RESULTS AND DISCUSSION
iso-Valeric acid (15) was converted to the imidazolide 16 using carbonyl diimidazole (98% yield), which was allowed to react with the lithium enolate, generated from dioxinone 17 with lithium bis-trimethylsilylamide in the presence of diethylzinc, to give keto-dioxinone 11 in 73% yield on a multigram scale (Scheme 2).12 The zinc enolate dianion, derived from keto- dioxinone 11 with lithium di-iso-propylamide and diethylzinc, was allowed to react with ethyl formate (2 equiv) to give crude adduct 10, which was directly aromatized with aqueous sodium hydroxide followed by acidification with hydrochloric acid to give dioxinone-resorcylate 8 (73% yield), without the need for chromatographic purifi cation.13
We sought to extend this resorcylate synthesis to the equivalent Pfi zer intermediate 21. Chloroacetyl chloride (18) was allowed to react with the lithium enolate from dioxinone 17 to give chloro-dioxinone 19,14 with the best albeit modest yield (38%) being obtained with addition of chloroacetyl chloride at -100 °C (Scheme 3).15 Chloro-dioxinone 19 was subsequently subjected to the formylation-cyclization-aromati- zation sequence, which gave rise to enol 20. Without isolation, final reaction with triethylamine gave the dioxinone-resorcylate 21 in 44% yield over the two steps.16
Scheme 2. Synthesis of Key Resorcylate 8 using a Formylation-Cyclization-Aromatization Sequence

Scheme 3. Synthesis of Key Resorcylate 21 from Chloroacetyl Chloride

At this stage, we examined the synthesis of the iso-indoline unit (Scheme 4). Commercially available 5-bromophthalimide (22) was allowed to react with sodium borohydride and boron trifl uoride etherate in THF to give 5-bromo-iso-indoline 23 (76%), which was subsequently protected as the corresponding

Scheme 4. Synthesis of N-Boc Protected 5-Bromo-iso-inoline 14
resorcylate 8 and amine 25 at -40 °C and warming up to 0 °C, gave amide 5 (75%). Similarly, chlororesorcylate 4 was obtained, albeit in lower yield (44%), presumably due to side reactions of the Grignard reagent with the aryl chloride.
The N-Boc protected 5-N-methylpiperazine iso-indoline 24 was allowed to react with methanolic HCl to aff ord trihydrochloride salt 26 in 96% yield.18 Subsequently, salt 26 was allowed to react with dioxinone-resorcylate 8 and iso- propylmagnesium chloride (6.0 equiv) at -20 °C, gradually warming up to 0 °C and subsequently at room temperature, to give AT13387 (7) in 70% yield (Scheme 7).

Scheme 7. Completion of the Synthesis of Hsp90 Inhibitor AT13387 (7)
Boc-derivative 14 (89%) with di-tert-butyl dicarbonate in DMF.17
Following the excellent Molander protocol, potassium bromomethyltrifl uoroborate was allowed to react with N- methylpiperazine under reflux in THF to provide potassium 4- methylpiperazinomethyl-trifl uoroborate (13) in 78% yield (Scheme 5). Much to our delight, subsequent Suzuki-Miyaura

Scheme 5. Synthesis of Piperazino-iso-indoline 24 using a Suzuki-Miyaura Coupling Reaction

cross coupling with N-Boc-5-bromo-iso-indoline 14 using palladium acetate, dicyclohexyl-2-(2,4,6-triiso-propylphenyl)- phenylphosphine (XPhos) and cesium carbonate gave the piperazino-iso-indoline 24 in 72% yield.11
Iso-indoline 25 was initially used as a model amine to investigate the resorcinol amide formation from dioxinone- resorcylates 8 and 21 (Scheme 6). To our delight, addition of iso-propylmagnesium chloride (2.2 equiv) to a mixture of
In conclusion, we have completed a total synthesis of AT13387 (7), with 9 synthetic manipulations and an overall yield of 13% using our biomimetic aromatization, a key Suzuki- Miyaura palladium cross coupling for the iso-indoline unit, and an iso-propylmagnesium chloride mediated amine dioxinone transacylation reaction. Further studies highlighting the applicability of this methodology to other bioactive resorcylates will be reported in due course.
■ EXPERIMENTAL SECTION
General Methods. All reactions were carried out in oven-dried glassware under N2, using commercially supplied solvents and reagents unless otherwise stated. Reaction temperatures other than room temperature were recorded as the external bath temperature unless otherwise stated. THF, CH2Cl2, Et3N, and MeOH were redistilled from Na-Ph2CO, CaH2, CaH2, and Mg turnings-I2, respectively. Petroleum spirits bp 40-60 °C was used. Column chromatography was carried out on silica gel, using flash techniques (eluants are given in parentheses). Analytical thin layer chromatography was performed on precoated silica gel F254 aluminum plates with visualization under UV light or by staining using acidic vanillin, anisaldehyde, potassium permanganate or ninhydrin spray reagents. Mps were obtained using a

Scheme 6. Synthesis of Hsp90 Inhibitor Lead Resorcylamides 5 and 4
melting point apparatus and are uncorrected. Infrared data were carried out neat unless otherwise stated. Indicative features of each
-1
spectrum are given with adsorptions reported in wavenumbers (cm ). 1H NMR spectra were recorded at 400 or 500 MHz with chemical shifts (δ) quoted in parts per million (ppm) and coupling constants (J) recorded in Hertz (Hz). 13C NMR spectra were recorded at 101 or 126 MHz with chemical shifts (δ) quoted in ppm. High resolution mass spectra (electrospray ionization, ESI-TOF) were recorded by Imperial College Mass Spectrometry Service.
1-(3-Methylbutanoyl)-imidazole (16). Carbonyl diimidazole (90%; 9.1 g, 50.6 mmol) was added portionwise with stirring over 15 min to iso-valeric acid (5.08 mL, 46 mmol) in THF (90 mL) at 0 °C. After 2 h, the mixture was diluted with Et2O (250 mL), H2O (100 mL) was

added carefully and the layers separated. The organic layer was washed with H2O (2 × 80 mL) and brine (100 mL), dried (MgSO4) and rotary evaporated to give the imidazolide 16 (6.82 g, 98%) as a colorless oil: Rf 0.15 (petroleum spirits/EtOAc 1:1); 1H NMR (acetone-d6, 400 MHz) δ 8.30 (s, 1H), 7.64 (br m, 1H), 7.03 (br m, 1H), 2.94 (d, J = 6.8 Hz, 2H), 2.26 (m, 1H), 1.03 (d, J = 6.4 Hz, 6H); 13C NMR (acetone-d6, 101 MHz) δ 171.3, 138.4, 132.3, 118.0, 45.0, 26.9, 23.5 (2C);19 used in the next step without further purification.
2,2-Dimethyl-6-(4-methyl-2-oxopentyl)-4H-1,3-dioxin-4-one (11). n-BuLi in hexanes (2.5 M; 20.5 mL, 51.3 mmol) was added dropwise with stirring to HN(SiMe3)2 (10.8 mL, 51.3 mmol) in THF (105 mL) at -78 °C. After 20 min and a further 1 h, respectively, dioxinone 17 (5.21 g, 36.7 mmol) in THF (12 mL) and Et2Zn in hexanes (1.0 M; 51.3 mL, 51.3 mmol) were added slowly, and after a further 20 min, the mixture was allowed to warm up to -20 °C. Imidazolide 16 (6.69 g, 44 mmol) in THF (50 mL) was added and the reaction mixture immediately warmed to -10 °C. After 3.5 h, the reaction was quenched with 1.0 M aqueous HCl (100 mL), and the aqueous layer acidified to pH 1-2 using 1.0 M aqueous HCl. The product was extracted with EtOAc (2 × 100 mL) and the combined organic extracts dried (MgSO4), the solvent evaporated under vacuum and the residue chromatographed (petroleum spirits/Et2O 6:1 to 4:1 to 1:1) to give iso-butyl-keto-dioxinone 11 (6.07 g, 73%) as a yellow oil: Rf
-1
0.55 (petroleum spirits:Et2O 1:1); IR 1719, 1635 cm ; 1H NMR (acetone-d6, 400 MHz) δ 5.39 (s, 1H), 3.54 (s, 2H), 2.48 (d, J = 6.8 Hz, 2H), 2.14 (m, 1H), 1.69 (s, 6H), 0.93 (d, J = 6.8 Hz, 6H); 13C NMR (acetone-d6, 101 MHz) δ 204.8, 167.3, 161.6, 108.4, 98.1, 53.1, 48.7, 26.1 (2C), 25.9, 23.6 (2C); HRMS (ESI-TOF) m/z: [M + H]+ Calcd for C12H18O4 227.1283; Found 227.1276.20
6-(3-Chloro-2-oxopropyl)-2,2-dimethyl-4H-1,3-dioxin-4-one (19). n-BuLi in hexanes (2.5 M; 5.6 mL, 14.0 mmol) was added dropwise with stirring to (Me3Si)2NH (2.95 mL, 14.0 mmol) in THF (35 mL) at -78 °C. After 20 min and a further 1 h respectively, dioxinone 17 (1.42 g, 10.0 mmol) in THF (5 mL) and Et2Zn in hexanes (1.0 M; 14.0 mL, 14.0 mmol) were added dropwise, and after a further 20 min, the mixture was cooled down to -100 °C. Chloroacetyl chloride (18) (0.96 mL, 12.0 mmol) was added dropwise and the reaction mixture stirred at -100 °C. After 2 h, the reaction was quenched with 1.0 M aqueous HCl (20 mL), and the aqueous layer acidified to pH 1-2 using 1.0 M aqueous HCl. The product was extracted with EtOAc (2 × 50 mL) and the combined organic extracts dried (MgSO4), the solvent evaporated under vacuum and the residue chromatographed (petroleum spirits/Et2O 4:1 to 2:1 to 1:1) to give chloro-keto- dioxinone 19 (0.82 g, 38%) as a yellow gum: Rf 0.32 (petroleum
-1
spirits:Et2O 1:1); IR 1721, 1638 cm ; 1H NMR (acetone-d6, 400 MHz) δ 5.42 (s, 1H), 4.53 (s, 2H), 3.74 (s, 2H), 1.68 (s, 6H); HRMS (ESI-TOF) m/z: [M + NH4]+ Calcd for C9H11ClO4 236.0690; Found 236.0696.14
5-Bromo-iso-indoline (23). Sodium borohydride (3.48 g, 92.0 mmol) was added with stirring to 5-bromopthalamide 22 (2.0 g, 8.8 mmol) in THF (87 mL) and the resultant suspension cooled to -10 °C. BF3.Et2O (12.7 mL, 102.6 mmol) was added slowly and once the addition was completed, the reaction mixture was heated at 70 °C. After 16 h, the reaction mixture was allowed to cool to 0 °C, quenched slowly with cold water (18 mL), diluted with EtOAc (140 mL) and made alkaline to pH 10 using 6.0 M aqueous NaOH. The organic layer was separated, washed with brine (4 × 70 mL), dried (Na2SO4) and rotary evaporated. The residual gray oil was diluted with Et2O (50 mL) and acidified to pH 2 using 6.0 M aqueous HCl with stirring. The aqueous layer was separated, made alkaline to pH 10 using 6.0 M aqueous NaOH and extracted with EtOAc (70 mL). The organic layer was separated, washed with brine (3 × 70 mL), dried (Na2SO4) and rotary evaporated to give the 5-bromo-iso-indoline 23 (1.33g, 76%) as
-1 a pale green oil: Rf 0.10 (petroleum spirits/EtOAc 1:1); IR 1604 cm ; 1H NMR (CDCl3, 400 MHz) δ 7.38 (s, 1H), 7.32 (d, J = 7.6 Hz, 1H), 7.11 (d, J = 8.0 Hz, 1H), 4.20 (s, 2H), 4.17 (s, 2H), 2.11 (br s, 1H); 13C NMR (CDCl3, 101 MHz) δ 144.3, 140.9, 129.6, 125.5, 123.7, 120.4, 52.8, 52.6; HRMS (ESI-TOF) m/z: [M(79Br) + H]+ Calcd for C8H879BrN 197.9918; Found 197.9926; m/z: [M(81Br) + H]+ Calcd for C8H881BrN 199.9898; Found 199.9908.17
tert-Butyl 5-Bromo-iso-indoline-2-carboxylate (14). (Boc)2O (1.1 g, 5.04 mmol) was added to iso-indoline 23 (0.83 g, 4.2 mmol) in DMF (11.8 mL) at room temperature, followed by a few crystals of DMAP. After 16 h, the reaction mixture was diluted with EtOAc (50 mL), washed with brine (4 × 30 mL), dried (Na2SO4), the solvent evaporated under vacuum and the residue chromatographed (petroleum spirits/Et2O 4:1 to 3:1) to give the N-Boc-protected product 14 (1.05 g, 84%) as a pale yellow solid: mp 54-56 °C (petroleum spirits/Et2O 3:1); Rf 0.80 (petroleum spirits/Et2O 1:1); IR
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1697 cm ; 1H NMR (CDCl3, 400 MHz) δ 7.37 (m, 2H), 7.13 (d, J = 8.0 Hz, 0.5H, rotamer 1), 7.08 (d, J = 8.0 Hz, 0.5H, rotamer 2), 4.61 (m, 4H), 1.50 (s, 9H); 13C NMR (CDCl3, 101 MHz) δ (mixture of rotamers) 154.3, 139.6, 139.2, 136.3, 136.0, 130.4 (2C), 126.0, 125.7, 124.3, 124.0, 121.1, 79.9, 51.9, 51.6, 28.5 (3C) HRMS (ESI-TOF) m/
z: [M(79Br) - tBu + H]+ Calcd for C13H1679BrNO2 241.9817; Found 241.9820; [M(81Br) - tBu + H]+ Calcd for C13H1681BrNO2 243.9801; Found 243.9796; [M(79Br) - tBu + MeCN + H]+ Calcd for C13H1679BrNO2 283.0082; Found 283.0081; [M(81Br) - tBu + MeCN + H]+ Calcd for C13H1681BrNO2 285.0062; Found 283.0062.17
Potassium 1-Methyl-4-trifluoroboratomethylpiperazine (13). K- (F3BCH2Br) (1.0 g, 5.00 mmol) was added to a solution of 1- methylpiperazine (0.59 g, 5.25 mmol) in THF (7 mL) at room temperature. After 3.5 h, the resulting mixture was the solvent evaporated under vacuum and the residue dissolved in a solution of dry acetone (150 mL) and K2CO3 (0.69 g, 5.0 mmol) and stirred for 30 min. The solution was filtered through a pad of Celite to remove the insoluble salts, and the fi ltrate was rotary evaporated. The solid product was dried under vacuum overnight to give the desired compound 13 (0.76 g, 70%) as a yellow solid: mp 117-120 °C; Rf 0.05 (petroleum spirits/EtOAc 1:1); IR 1457 cm-1; 1H NMR (acetone-d6, 400 MHz) δ 3.58 (br m, 2H), 3.07 (br m, 2H), 2.91 (br m, 2H), 2.47 (br s, 2H), 2.29 (s, 3H), 2.13 (br s, 2H); HRMS (ESI-TOF) m/z: [M - K]- Calcd for C6H13BF3KN2 181.1124; Found 181.1121.11
tert-Butyl 5-((4-Methylpiperazin-1-yl)methyl)-iso-indoline-2-car- boxylate (24). Pd(OAc)2 (5 mg, 0.022 mmol), 2-(2,4,6-iso-Pr3C6H2)- P(c-hexyl)2 (XPhos) (21 mg, 0.045 mmol), the piperazine derivative 13 (0.16 g, 0.74 mmol), and Cs2CO3 (0.72 g, 2.2 mmol). The tube was sealed with a septum and purged with N2. A solution of compound 14 (0.22 g, 0.74 mmol) in THF and H2O (10:1) (0.25 M, 3.0 mL) was added and the mixture was stirred at 80 °C. After 24 h, the reaction mixture was cooled to room temperature, diluted with H2O (3 mL)
and extracted with EtOAc (2 × 15 mL). The organic layer was dried (Na2SO4), the solvent evaporated under vacuum and the residue chromatographed (petroleum spirits/EtOAc:Et3N 2:1:0.1) to yield the carbamate 24 (177 mg, 72%) as a pale yellow gum: Rf 0.15 (petroleum
-1
spirits/EtOAc:Et3N 2:1:0.1); IR 1697 cm ; 1H NMR (CDCl3, 400 MHz) δ 7.24-7.14 (m, 3H), 4.67 (s, 2H), 4.62 (s, 2H), 3.50 (s, 2H), 2.80-2.28 (br s, 8H), 2.18 (s, 3H), 1.51 (s, 9H); 13C NMR (CDCl3, 101 MHz) δ (mixture of rotamers) 154.6, 137.7, 137.6, 137.5, 137.1, 136.2, 135.8, 128.4, 123.5, 123.2, 122.5, 122.2, 79.6, 62.9, 55.1 (2C), 53.1 (2C), 52.2, 52.1, 51.9, 51.8, 46.0, 28.5 (3C); HRMS (ESI-TOF) m/z: [M + H]+ Calcd for C19H29N3O2 332.2338; Found 332.2334.
5-((4-Methylpiperazin-1-yl)methyl)iso-indoline trihydrochloride (26). HCl in MeOH (2.0 M; 1.95 mL, 3.90 mmol) was added to carbamate 24 (0.13 g, 0.39 mmol) in MeOH (5.85 mL) at room temperature. After 16 h, the solvent was evaporated to give trihydrochloride salt 26 (0.13 mg, 96%) as an off-white solid: mp > 300 °C; IR 1402, 1365 cm-1; 1H NMR (DMSO-d6, 400 MHz) δ 12.89-10.91 (br m, 2H), 10.03 (br m, 2H), 7.60 (br m, 2H), 7.47- 7.46 (br d, J = 6.0 Hz, 1H), 4.51 (br s, 4H), 4.42-4.03 (br s, 2H), 3.47 (s, 8H), 2.78 (s, 3H); 13C NMR (DMSO-d6, 101 MHz) δ 135.5, 131.6, 131.0, 125.5, 125.5, 123.2, 58.6, 49.7 (2C), 49.7 (2C), 48.0, 47.9, 42.1; HRMS (ESI-TOF) m/z: [M - 3HCl + H]+ Calcd for C14H24Cl3N3 232.1814; Found 232.1804; Anal. Calcd. for C14H24Cl3N3: C, 49.35; H, 7.10; N, 12.33. Found: C, 49.22; H, 6.98; N, 12.24.
7-Hydroxy-6-iso-propyl-2,2-dimethyl-4H-benzo[d][1,3]dioxin-4- one (8). n-BuLi in hexanes (2.5 M; 4.4 mL, 11 mmol) was added dropwise with stirring to iso-Pr2NH (1.55 mL, 11 mmol) in THF (40 mL) at -78 °C. After 20 min and a further 50 min respectively, keto-

dioxinone 11 (1.13 g, 5.0 mmol) in THF (10 mL) and Et2Zn in hexanes (1.0 M; 11 mL, 11 mmol) were added dropwise with stirring at -78 °C. After 30 min, ethyl formate (0.81 mL, 10 mmol) was added slowly and the reaction mixture stirred for 2 h at -78 °C. The reaction was quenched with saturated 1.0 M aqueous NaOH (35 mL), and the reaction mixture allowed to warm up to room temperature and stirred for 10 min. The aqueous layer was acidified to pH 1-2 using 1.0 M aqueous HCl. The product was extracted with EtOAc (300 mL), washed with brine (100 mL), dried (MgSO4), the solvent evaporated under vacuum and the residue triturated with Et2O/petroleum spirits (1:9; 20 mL) and then CH2Cl2/petroleum spirits (1:9; 20 mL) to give dioxinone-resorcylate 8 (0.86 g, 73%) as a pale yellow solid: mp 136- 138 °C (petroleum spirits/Et2O 2:1); Rf 0.52 (petroleum spirits/Et2O
-1
1:1); IR 3361, 1708, 1611, 1505 cm ; 1H NMR (acetone-d6, 400 MHz) δ 9.61 (br s, 1H), 7.65 (s, 1H), 6.46 (s, 1H), 3.24 (sep, J = 6.8 Hz, 1H), 1.66 (s, 6H), 1.23 (d, J = 6.8 Hz, 6H); 13C NMR (acetone-d6, 101 MHz) δ 163.8, 162.0, 157.7, 132.7, 128.8, 107.6, 107.1, 104.1, 28.3, 26.8 (2C), 23.7 (2C); HRMS (ESI-TOF) m/z: [M + H]+ Calcd for C13H16O4: 237.1127; Found 237.1116; Anal. Calcd. for C13H16O4: C, 66.09; H, 6.83. Found: C, 66.16; H, 6.87.
6-Chloro-7-hydroxy-2,2-dimethyl-4H-benzo[d][1,3]dioxin-4-one (21). n-BuLi in hexanes (2.5 M; 0.88 mL, 2.2 mmol) was added dropwise with stirring to iso-Pr2NH (0.31 mL, 2.2 mmol) in THF (7 mL) at -78 °C. After 20 min and a further 50 min respectively, keto- dioxinone 19 (0.22 g, 1.0 mmol) in THF (1.5 mL) and Et2Zn in hexanes (1.0 M; 2.2 mL, 2.2 mmol) were added dropwise with stirring at -78 °C. After 30 min, EtOCHO (0.16 mL, 2.0 mmol) was added slowly and the mixture stirred for 2 h at -78 °C. The reaction was quenched with saturated 1.0 M aqueous HCl (25 mL), and the aqueous layer acidified to pH 1-2 using 1.0 M aqueous HCl. The product was extracted with EtOAc (50 mL), washed with brine (20 mL), dried (MgSO4) and rotary evaporated to give the crude formyl- keto-dioxinone 20, which was dissolved in CH2Cl2 (22 mL), Et3N (2 mL) added, and the mixture stirred at room temperature. After 16 h, 1.0 M aqueous HCl (40 mL) and EtOAc (75 mL) were added and the layers separated. The aqueous layer was further extracted with EtOAc (25 mL) and the combined organic extracts dried (MgSO4), the solvent evaporated under vacuum and the residue chromatographed (petroleum spirits/EtOAc 5:1 to 1:1) to give dioxinone-resorcylate 21 (100 mg, 44%) as a pale yellow solid; mp 138-140 °C (petroleum spirits/Et2O 2:1); Rf 0.40 (petroleum spirits/Et2O 1:1); IR 3300,
-1
1684, 1604 cm ; 1H NMR (acetone-d6, 400 MHz) δ 10.19 (br s, 1H), 7.82 (s, 1H), 6.66 (s, 1H), 1.71 (s, 6H); 13C NMR (acetone-d6, 101 MHz) δ 161.8, 160.9, 158.2, 132.1, 117.5, 108.4, 106.0 (2C), 26.8 (2C); HRMS (ESI-TOF) m/z: [M + H]+ Calcd for C10H8ClO4 228.0189; Found 228.0182.
General Procedure for the Amine Dioxinone Ring Opening. The dioxinone-resorcylate (0.25 mmol) in THF (1.5 mL) was cooled to -40 °C, when amine 25 (0.25 mmol) in THF (0.2 mL), and after 10 min, iPrMgCl in THF (2.0 M; 0.28 mL, 0.55 mmol) were added dropwise. The mixture was warmed up to -10 °C, and after 1 h, the temperature was increased to 0 °C. After 0.5-1.5 h, the reaction mixture was quenched with saturated aqueous NH4Cl (5 mL), the aqueous layer acidified to pH 1-2 using aqueous HCl (1.0 M) and extracted with EtOAc (25 mL). The organic layer was washed with brine (20 mL), dried (MgSO4), the solvent evaporated under vacuum and the residue triturated with Et2O (25 mL) to give the desired resorcylamide.
(2,4-Dihydroxy-5-iso-propylbenzoyl)-iso-indoline (5). Yield 75%; white solid; mp 104-106 °C (petroleum spirits/Et2O 2:1); Rf 0.48
-1
(petroleum spirits/Et2O 1:1); IR 3255, 1627, 1562 cm ; 1H NMR (DMSO-d6, 400 MHz) δ 10.03 (s, 1H), 9.60 (s, 1H), 7.33 (br m, 4H), 7.04 (s, 1H), 6.40 (s, 1H), 4.77 (br s, 4H), 3.09 (sep, J = 6.8 Hz, 1H), 1.13 (d, J = 6.8 Hz, 6H); 13C NMR (DMSO-d6, 101 MHz) δ 168.7, 156.7, 153.7, 136.8, 136.0, 127.2 (2C), 125.5, 125.3, 122.7 (2C), 113.9, 102.4, 52.9, 51.7, 25.8, 22.6 (2C); HRMS (ESI-TOF) m/z: [M + H]+ Calcd for C18H19NO3 298.1443; Found 298.1438; Anal. Calcd. for C18H19NO3: C, 72.71; H, 6.44; N, 4.71. Found: C, 72.82; H, 6.38; N, 4.81.9
(5-Chloro-2,4-dihydroxybenzoyl)-iso-indoline (4). Yield 44%; white solid; mp 210-212 °C (petroleum spirits/Et2O 2:1); Rf 0.38
-1
(petroleum spirits/Et2O 1:1); IR 3265, 1599, 1564 cm ; 1H NMR (DMSO-d6, 400 MHz) δ 10.42 (s, 1H), 10.33 (s, 1H), 7.36 (br m, 4H), 7.22 (s, 1H), 6.60 (s, 1H), 4.74 (app 2s, 2H + 2H); 13C NMR (DMSO-d6, 101 MHz) δ 166.7, 154.7, 154.1, 136.8, 135.9, 128.7 (2C), 127.2 (2C), 122.8, 116.3, 109.9, 103.8, 52.7, 51.7; HRMS (ESI-TOF) m/z: [M + H]+ Calcd for C15H12ClNO3 298.1443; Found 298.1438; Anal. Calcd. for C15H12ClNO3: C, 62.19; H, 4.17; N, 4.83. Found: C, 62.35; H, 4.10; N, 4.94.7
N-(2,4-Dihydroxy-5-iso-propylbenzoyl)(5-((4-methylpiperazin-1- yl)methyl)-iso-indoline (7). Resorcylate 8 (35 mg, 0.15 mmol) and iso- indoline trihydrochloride 26 (51 mg, 0.15 mmol) in THF (0.75 mL) were cooled to -20 °C, when iPrMgCl in THF (2.0 M; 0.45 mL, 0.90 mmol) was added dropwise with stirring. The mixture was warmed up to 0 °C over 3 h, and subsequently to room temperature over 12 h, when reaction was quenched with saturated aqueous NH4Cl (10 mL). The aqueous layer was acidified to pH 6-7 using aqueous HCl (1.0 M) and extracted with EtOAc and CH2Cl2 (1:1; 30 mL). The organic layer was washed with brine (15 mL), dried (MgSO4), the solvent evaporated under vacuum and the residue chromatographed (CH2Cl2/
MeOH 19:1 to 4:1) to give the desired amide 7 (36 mg, 70%) as a white solid: mp 93-94 °C (acetone/MeOH 3:1); Rf 0.20 (CH2Cl2/
-1
MeOH 4:1); IR 3134, 1700, 1610, 1564 cm ; 1H NMR (CDCl3, 400 MHz) δ 7.59 (s, 1H), 7.34-7.31 (m, 2H), 7.28-7.26 (m, 1H), 6.42 (s, 1H), 5.08 (br s, 4H), 3.49 (s, 2H), 3.26 (sep, J = 2.8 Hz, 1H), 2.44 (br s, 8H), 2.23 (s, 3H), 1.26 (s, 6H); 13C NMR (CDCl3, 101 MHz) δ 172.6, 162.1, 160.4, 140.2, 138.5, 137.0, 130.2, 128.4, 127.3, 124.9, 124.2, 110.8, 104.7, 64.2, 56.7 (3C), 54.5 (3C), 47.0, 28.4, 24.0 (2C); HRMS (ESI-TOF) m/z: [M + H]+ Calcd for C24H31N3O3 410.2444; Found 410.2434.9
■ ASSOCIATED CONTENT
S* Supporting Information
Copies of 1H and 13C NMR spectra corresponding to all reported compounds. This material is available free of charge via the Internet at http://pubs.acs.org.
■ AUTHOR INFORMATION
Corresponding Author *[email protected] Notes
The authors declare no competing financial interest.
■ ACKNOWLEDGMENTS
We thank GlaxoSmithKline for the generous endowment (to A.G.M.B.), the Engineering and Physical Sciences Research Council (EPSRC) Pharma Synthesis Programme and Glax- oSmithKline for grant support (to B.H.P.), and P.R. Haycock and R.N. Sheppard (Imperial College) for high-resolution NMR spectroscopy and David Rees (Astex) for helpful discussions.
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