90% |
With benzotriazol-1-ol; triethylamine; dicyclohexyl-carbodiimide In tetrahydrofuran at 0 - 25℃; |
|
85% |
Stage #1: <i>N</i>-<i>tert</i>-butoxycarbonyl-<i>L</i>-phenylalanine With benzotriazol-1-ol; 1-ethyl-(3-(3-dimethylamino)propyl)-carbodiimide hydrochloride In dichloromethane at 25℃; for 0.5h; Inert atmosphere;
Stage #2: glycine ethyl ester hydrochloride With N-ethyl-N,N-diisopropylamine at 25℃; for 14h; Inert atmosphere; |
|
84.7% |
With 4-methyl-morpholine; isobutyl chloroformate In tetrahydrofuran for 6h; |
4
General procedure: 2((tert-Butoxycarbonyl)amino)propanoic acid (9.45 g, 50 mmol)and NMM (2 equiv) were dissolved in 100 ml anhydrous THF. Tothis stirring solution was added IBCF (1.05 equiv) followed by compound8. After 6 h, the mixture was condensed, dissolved in EtOACand washed with saturated NaHCO3 solution, 1 M citric acid andbrine. Evaporation of EtOAc gave compound 9a. White solid: yield82.7%, |
78% |
Stage #1: <i>N</i>-<i>tert</i>-butoxycarbonyl-<i>L</i>-phenylalanine With benzotriazol-1-ol; dicyclohexyl-carbodiimide In dichloromethane at 0℃; for 1h; Inert atmosphere;
Stage #2: glycine ethyl ester hydrochloride With triethylamine In dichloromethane; N,N-dimethyl-formamide at 20℃; for 12h; Inert atmosphere; |
Synthesis of N-tert-butyloxycarbonyl-L-Phenylalanine-Glycine methyl ester (1)
A solution of compound N-tert-butyloxycarbonyl Phenylalanine (1.5 g, 5.6 mmol, 1eq.) in dry DCM (20 mL) was cooled to 0 oC and 1-hydroxybenzotriazole (0.84 g, 6.2 mmol, 1.1 eq) was added, followed by dicyclohexylcarbodi-imide (1.39 g, 6.8 mmol, 1.2 eq). After 1 h the mixture was allowed to warm to room temperature then compound glycine methyl ester hydrochloride salt (0.78 g, 6.2 mmol, 1.1 eq) dissolved in dimethyl formamide (10 mL) was added, followed by triethyl amine (0.94 mL, 6.8 mmol 1.2 eq.) The reaction mixture was stirred for 12 h. The precipitated dicyclohexylurea was filtered off and washed with little DCM. The filtrate was evaporated under high vacuuo, the crude compound was acidified under ice cold condition with 1N HCl to pH 2-3 and extracted with (3x10 mL) dichloromethane. The organic layer was washed with 10% NaHCO3 solution (3x10mL), and finally with saturated brine solution (2x10 mL), followed by drying of the organic layer overanhydrous sodium sulphate. Dichloromethanewas evaporated to get the crude compound (2.3 g), which was further purified with a silica gel column (0.5 - 4 % CH3OH gradient in CH2Cl2) to give protected compound phenyalnine glycine methyl ester (1) as a yellow solid, M.P. 64-66 °C Rf value is 0.8 (10 % methanol in dichloromethane, ~1.5 g, 78% yield). |
70% |
With benzotriazol-1-ol; triethylamine; dicyclohexyl-carbodiimide In N,N-dimethyl-formamide |
|
63% |
With dmap; benzotriazol-1-ol; 1-ethyl-(3-(3-dimethylamino)propyl)-carbodiimide hydrochloride; N-ethyl-N,N-diisopropylamine In dichloromethane at 20℃; for 3h; Inert atmosphere; |
(S)-methyl 2-(2-(tert-butoxycarbonylamino)-3-phenylpropanamido)acetate (6)
To a stirred solution of Boc-L-phenylalanine 5 (500 mg, 1.88 mmol) in anhydrous CH2Cl2 (100 mL) were added Glycine methyl ester hydrochloride (236 mg, 1.88 mmol), 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDCI, 541 mg, 2.82 mmol), 1-Hydroxybenzotriazole (HOBT, 381 mg, 2.82 mmol), 4-dimethylaminopyridine (DMAP, 23 mg, 0.19 mmol) and N,N-Diisopropylethylamine (DIEA, 1.0 mL, 5.64 mmol) at r.t. under N2 atmosphere. After 3 h, the reaction solution was washed with 1 N hydrochloric acid (20 mL), saturated NaHCO3 solution (20 mL) and saturated brine (20 mL), subsequently, dried over by anhydrous Na2SO4. The concentrated residue was purified by flash silica gel column chromatography [petroleum/ether-EtOAc = (4:1), V/V] to obtain the corresponding target product as a white solid (400 mg, 63%). HPLC analysis: 100%. 1H-NMR (400 MHz, d6-DMSO): 1.29 (s, 9H), 2.72-2.78 (m, 1H), 3.01 (d, J = 13.2 Hz, 1H), 3.65 (s, 3H), 3.83-3.97 (m, 2H), 4.24 (s, 1H), 6.93 (d, J = 8.6 Hz, 1H), 7.24 (d, J = 31.9 Hz, 5H), 8.38 (s, 3H). 13C-NMR (100 MHz, d6-DMSO): 172.8, 170.7, 155.7, 138.7, 129.6, 128.4, 126.6, 78.4, 56.0, 52.1, 37.9, 28.6. ESI-MS m/z: 337.1 (M+H)+. |
57% |
With dmap; diphenylsilane; N-ethyl-N,N-diisopropylamine In acetonitrile at 80℃; for 42h; Inert atmosphere; Sealed tube; Green chemistry; |
|
43% |
Stage #1: <i>N</i>-<i>tert</i>-butoxycarbonyl-<i>L</i>-phenylalanine With phosphorus pentoxide In tetrahydrofuran at 20℃; Inert atmosphere;
Stage #2: glycine ethyl ester hydrochloride With dmap; N-ethyl-N,N-diisopropylamine In tetrahydrofuran at 20℃; for 13h; Inert atmosphere; |
General procedure for amide bond formation
General procedure: A solution of acid (1.2 equiv) in THF (10 mL) in a 50 mL reaction tube was added to phosphorus pentoxide (4 equiv). The resulting mixture was allowed to stir at room temperature for 20-30 min. Subsequently, the amine (1 equiv), diisopropyl ethylamine (3 equiv) and DMAP (0.2 equiv) were added. After 14 h, the solvent was removed in vacuo and the mixture was quenched with water (10 mL). The mixture was extracted with EtOAc (15 mL) and sequentially washed with saturated bicarbonate solution (3 × 15 mL), 10% HCl solution (3 × 15 mL) and saturated NaCl (2 × 10 mL) solution. The organic layer was dried over Na2SO4, filtered and concentrated in vacuo. Purification by column chromatography afforded the desired amide. |
|
(i) N-ethylmorpholine, ClCO2iBu, (ii) /BRN= 3593644/; Multistep reaction; |
|
|
Multistep reaction; |
|
|
With benzotriazol-1-ol; 1-ethyl-(3-(3-dimethylamino)propyl)-carbodiimide hydrochloride; triethylamine In dichloromethane for 4h; Ambient temperature; |
|
|
With (benzotriazo-1-yloxy)tris(dimethylamino)phosphonium hexafluorophosphate; triethylamine In N,N-dimethyl-formamide at 20℃; for 2.5h; |
|
|
With 1-ethyl-(3-(3-dimethylamino)propyl)-carbodiimide hydrochloride; N-ethyl-N,N-diisopropylamine In tetrahydrofuran at 20℃; for 24h; |
20a.1
20a.1 Preparation of methyl (2-tert-butoxycarbonylamino-3-phenylpropionylamino)-acetate At 0° C., ethyldiisopropylamine (259 g, 2.0 mol), N-tert-butoxycarbonyl-L-phenylalanine (212 g, 0.8 mol) and 1-ethyl-3-(3'-dimethylaminopropyl)carbodiimide (EDAC, 230 g, 1.2 mol) were added to a solution of glycine methyl ester hydrochloride (100 g, 0.8 mol) in tetrahydrofuran (THF, 1000 ml). The reaction mixture was then stirred at room temperature for 24 h. The reaction mixture obtained was freed from volatile components under reduced pressure, and the residue obtained in this manner was taken up in water (1000 ml). The aqueous phase was extracted repeatedly with CH2Cl2. The organic phases obtained in this manner were combined, washed with water, dried over Na2SO4, filtered and freed from the solvent under reduced pressure. Methyl (2-tert-butoxycarbonylamino-3-phenylpropionylamino)acetate was obtained as a yellow oil in an amount of 300 g. The crude product obtained was reacted further without further purification. |
|
With N-ethyl-N,N-diisopropylamine; N-[(dimethylamino)-3-oxo-1H-1,2,3-triazolo[4,5-b]pyridin-1-yl-methylene]-N-methylmethanaminium hexafluorophosphate In N,N-dimethyl-formamide at 0 - 23℃; for 3h; |
General procedure for diketopipierazines 7, 9-16:
General procedure: A 250 mL round bottom flask was charged with N-Boc amino acid (10.0 mmol, 1.00 equiv),glycine methyl ester hydrochloride (1.256 g, 10.0 mmol, 1.00 equiv), DMF (50mL), and DIPEA (3.50 mL, 20.5 mmol, 2.05 equiv.) and the temperature was cooledto 0 °C.HATU (3.802 g, 10.0 mmol, 1 equiv) was added and the reaction stirred for 3hours while warming to room temperature. EtOAc (150 mL) was added and theorganic layer was washed with 75 mL each of 0.5 N hydrochloric acid, saturatedaqueous sodium bicarbonate, water, and brine, dried with MgSO4,filtered and concentrated. The crude material was dissolved in CH2Cl2(33 mL) and TFA (17 mL) and stirred for 2 h at room temperature. The mixturewas then concentrated and azeotroped with toluene (2 × 40 mL). To this crudematerial was added 2N NH3 in methanol (40 mL). The reaction timeand workup procedure for the cyclization are specified for each compound. Enantiomericexcesses were determined by making the racemate and finding conditions thatseparated the enantiomers by SFC. In general a Chiralpak ADH column(4.6 x 150 mm) was used, eluting with 15-25% ethanol or methanol insupercritical CO2 (total flow was 4 mL/min). |
|
Stage #1: glycine ethyl ester hydrochloride With triethylamine In chloroform at 0℃; for 0.25h;
Stage #2: <i>N</i>-<i>tert</i>-butoxycarbonyl-<i>L</i>-phenylalanine With dicyclohexyl-carbodiimide In chloroform at 0 - 20℃; for 12h; |
Preparation of dipeptides14
General procedure: Amino acid methyl ester hydrochloride (10 mmol) was dissolved in chloroform (CHCl3) (20 ml). To this, triethylamine (TEA) (4 ml, 28.7 mmol) was added at 0°C and the reaction mixture was stirred for 15 mins. Boc-amino acid (10 mmol) in CHCl3 (20 mL) and DCC (10 mmol) were added with stirring. After 12 hrs, the reaction mixture was filtered and the residue was washed with CHCl3 (30 mL) and added to the filtrate. The filtrate was washed with 5% NaHCO3 (20 mL) and saturated NaCl (20 mL) solutions. The organic layer was filtered and evaporated in vacuum. To remove the traces of the dicyclohexylurea (DCU), the product was dissolved in minimum amount of CHCl3 and cooled to 0°C. The crystallized DCU was removed by filtration. Petroleum ether was added to the filtrate at 0°C to recrystallize the pure product. Boc-Phe-Trp-OMe and Boc-Phe-Gly-OMe were prepared in this manner (Scheme-1). |
|
Stage #1: <i>N</i>-<i>tert</i>-butoxycarbonyl-<i>L</i>-phenylalanine With benzotriazol-1-ol In N,N-dimethyl-formamide at 0℃; for 0.25h;
Stage #2: glycine ethyl ester hydrochloride With 1-ethyl-(3-(3-dimethylamino)propyl)-carbodiimide hydrochloride In N,N-dimethyl-formamide for 0.0833333h;
Stage #3: With triethylamine In N,N-dimethyl-formamide at 20℃; for 24h; |
|