Structure of PPA
CAS No.: 452072-22-9
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| CAS No. : | 452072-22-9 |
| Formula : | C10H13NO2S2 |
| M.W : | 243.35 |
| SMILES Code : | CC(SSC1=NC=CC=C1)CCC(O)=O |
| English Name : | 4-(Pyridin-2-yldisulfanyl)pentanoic acid |
| MDL No. : | MFCD21332845 |
* All experimental methods are cited from the reference, please refer to the original source for details. We do not guarantee the accuracy of the content in the reference.

| Yield | Reaction Conditions | Operation in experiment |
|---|---|---|
| 45% | With 1-ethyl-(3-(3-dimethylamino)propyl)-carbodiimide hydrochloride In dichloromethane for 2h; | |
| 45% | With 1-ethyl-(3-(3-dimethylamino)propyl)-carbodiimide hydrochloride In dichloromethane at 20℃; for 2h; | 2b Preparation of N-succinimidyl ester of 4-(2-pyridyldithio)-pentanoic acid (SPP, 7): A solution of 4-(2-pyridyldithio)-pentanoic acid (5, 30 g, 123 mmol) in methylene chloride (525 mL) was treated with N-hydroxysuccinimide(14.3 g, 124 mmol) and 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide.HCl (31.8 g, 165 mmol). The contents werestirred at room temperature for 2 hours after which 750 mL of ethyl acetate was added. The solution was washed with0.5% aqueous acetic acid (3 x 350 mL) and once with 150 mL of saturated aqueous sodium chloride. The organic layerwas dried over anhydrous sodium sulfate, filtered, and the solvent was removed under vacuum by rotary evaporation.The residue was taken up in a minimum volume of ethyl acetate and loaded on a 6.25 x 20 cm silica column, slurrypacked in 1:1 hexanes:ethyl acetate. The column was eluted with 1:1 hexanes:ethyl acetate. Fractions containing theproduct were combined and solvent was removed by rotary evaporation. The resulting oil (31 g) was taken up in a minimum volume of warm reagent grade ethanol and magnetically stirred as 350 mL of ethyl ether was added, followedby 100 mL of hexanes. The resulting precipitate was collected by vacuum filtration and dried in a vacuum oven at 30degrees C for 12 hours, giving 18.7 g of SPP (7) as a white solid(18.7 g, 45 % yield). 1H NMR (CDCL3) δ 1.39 (d, 3 H),2.0 (t, 3H), 2.56-3.4 (m, 7 H), 6.8-7.2 (m, 1 H), 7.6-7.8 (m, 2H), 8.4-8.6 (d, 1H). Elemental analysis: Calculated: %C 49.4,%H 4.70, %N 8.20, %S 18.80. Found: %C 49.3 %H 4.68, %N 8.18, %S 18.94. |
| 23.5% | With 1-ethyl-(3-(3-dimethylamino)propyl)-carbodiimide hydrochloride In N,N-dimethyl acetamide at 20℃; | 5 [00344] Synthesis of 2,5-dioxopyrrolidin-l-yl 4-(pyridin-2-yldisulfaneyl)pentanoate (linker I) To a solution of 4-(pyridin-2-yldisulfaneyl) pentanoic acid (24 mg, 0.1 mmol) and NHS (14 mg, 0.12 mmol) in DMA is added EDC (HC1 salt, 61 mg, 0.32 mmol). The solution is stirred at room temperature overnight. After filtration, the filtrate is concentrated and purified by column (MeOH/DCM = 0% to 10%) to obtain 2,5-dioxopyrrolidin-l-yl 4- (pyridin-2-yldisulfaneyl)pentanoate as white solid (8 mg, 23.5%). (MS: [M+l]+ 341.1). |
| With 1-ethyl-(3-(3-dimethylamino)propyl)-carbodiimide hydrochloride In N,N-dimethyl acetamide at 25℃; for 1h; | 23.1.1 Procedure for preparation of compound 3 To a solution of compound 1 (0.025 g, 102.73 umol, 1 eq.) in DMA (1 mL) was added EDCI (21.66 mg, 113.01 umol, 1.1 eq.) and compound 2 (13.01 mg, 113.01 umol, 1.1 eq.). The reaction mixture was stirred at 25 °C for 1 h. LC-MS showed a peak with desired m/z (341 [M+H+]) and the crude product was used directly in the next step without further purification. |

| Yield | Reaction Conditions | Operation in experiment |
|---|---|---|
| 60.3% | With acetic acid In ethanol; ethyl acetate at 14.9℃; for 2.66h; | 3 Successful Separation of PPA from the Undesired Dicarboxylic Acid Dimer Without Acetic Acid in the Silica Gel Column Mobile Phase 2,2'-dithiodipyridine (Aldrithiol, 100 g, 454 mmol) was dissolved in ethanol ( 700 mL) to which acetic acid (280mL) was added and the solution was magnetically stirred in an ice/water bath until it reached 14.9 °C. A solution of 4-mercapto-pentanoic acid (30 g, 220 mmol) in ethyl acetate (140 mL) was then added over 15 min with stirring. After addition the cooling bath was removed and the reaction was stirred for 2 h and 25 min. Solvent was evaporated under vacuum to give a yellow gum residue. The residue was taken up in dichloromethane (60 mL). A dry packed silica column (1.46 Kg silica, 60 A pore size, 230 - 400 mesh) was equilibrated with 4: 1 heptane:ethyl acetate (3.4 L). The residue in dichloromethane was then loaded on the column and the column was eluted with 4: 1 heptane:ethyl acetate. Unreacted 2,2'-dithiodipyridine eluted first followed by desired PPA. Fractions containing PPA were combined and solvent was removed under vacuum to give 43 g (60.3% yield) of desired product which had no detectable the dicarboxylic dimer. A repeat of this experiment again gave desired product that was not contaminated with undesired dicarboxylic acid dimer. |
| 60.7% | In methanol at 20℃; | 12 To a solution of compound 33 (5 g, 37.3 mmol) in MeOH (70 mL) was added 1 ,2- di(pyridin-2-yl)disulfane (12.3 g, 56 mmol). The mixture was stirred at room temperature overnight. The pH of the mixture was adjusted to 4- . The mixture was extracted with ethyl acetate, washed with water and brine, dried over anhydrous Na2S04, and concentrated to give a crude product, which purified by a column chromatography to give compound 34 (5.5 g, 60.7%). 'HNMR (CDCb, 300 MHz) δ: 1.3-1.4 (d, 2 H), 1.8-2.05 (m, 2 H), 2.5-2.6 (m, 2 H), 3.0-3.1 (m, 1 H), 7.0-7.2 (m, 1 H), 7.6-7.7 (m, 1 H), 7.7-7.8 (d, 1 H), 8.4-8.5 (d, 1 H). |
| 47% | In ethanol at 20℃; for 16h; Inert atmosphere; | 7.a (a) (+-)-4-(pyridin-2-yldisulfanyl)pentanoic acid (35) (a) (+-)-4-(pyridin-2-yldisulfanyl)pentanoic acid (35) Adrithiol-2 (176 m, 0.86 mmol) was added to a stirred solution of (+-)-4-mercaptopentanoic acid 34 (107 mg, 0.80 mmol, Aurora Fine Chemicals LLC) in EtOH (2 mL) at room temperature. The reaction mixture was allowed to stir for 16 hours under an argon atmosphere at which point analysis by LC/MS revealed substantial product formation at retention time 1.32 minutes (ES+) m/z 244 ([M+H]+, ˜95% relative intensity). The solvent was removed by evaporation in vacuo and the resulting residue purified by flash chromatography (gradient elution: 90:10 v/v hexane/EtOAc to 80:20 v/v hexane/EtOAc) to give 35 as a white solid (92 mg, 47% yield). |
| 23% | With acetic acid In ethanol; ethyl acetate for 2.25h; Inert atmosphere; | 2a Synthesis of the maytansinoid derivative (2) that bears a reactive N-succinimidyl ester A 2 L flask containing a stir bar was charged with 2-2'-dithiodipyridine (300 g, 1.36 mol), reagent grade ethanol (1 L) and glacial acetic acid (42 mL). A solution of the crude 4-mercapto pentanoic acid in ethyl acetate (400 mL) was added dropwise over 15 minutes and the reaction was stirred under argon for an additional 2 hours. The solvent was removed by rotary evaporation and the residue was taken up in a minimum of ethyl acetate and purified by column chromatography using a silica gel column (6.25 x 27 cm). The column was eluted with 4:1 hexanes:ethyl acetate until all of the unreacted 2,2'-dithiopyridine (Aldrithiol-2) was removed. The column was then eluted with 4:1 hexanes:ethyl acetate containing 2% acetic acid. The elution was monitored by TLC and fractions were combined. The solvent was then removed by rotary evaporation under reduced pressure to give pure 4-(2-pyridyldithio)-pentanoic acid (PPA, 5) as a white solid (40 g, 23% overall yield). 1H NMR (CDCl3) δ 1.39 (d, 3H), 2.0 (t, 2H). 2.56 (t, 2H), 2.8-3.3 (m, 1H), 6.8-7.2 (m, 1H), 7.6-7.8 (m, 2H), 8.4-8.6 (m, 1H), 11.68 (s, 1H). Preparation of N2'-deacatyl-N2'-[3-(3-carboxy-1-methyl-propyldithio)-1-oxopropyl]-maytansine (L-DM1-TPA, 6): |
| 21.4% | With acetic acid In ethanol; ethyl acetate for 2h; | |
| 1 g | In ethanol at 20℃; for 16h; | 4-(Pyridin-2-yldisulfanyl)pentanoic acid (1-6). A 0.67 g (5.00 mmol) aliquot of 1-3 was dissolved in 25 mL absolute ethanol. To the solution was added 6.61 g (30.0 mmol) of 1-5 dissolved in 150 mL. The reaction was allowed to stir at room temperature and monitored via TLC (Rf = 0.296; developed on 1:1 hexanes: ethyl acetate). After 16 h, the reaction solution was evaporated. The resulting yellow oil was dissolved in CH2Cl2 at purified via silica gel column chromatography to obtain unreacted 1-3 and desired 1-6 (hexanes: ethyl acetate 3:1), and to obtain dimmers and reaction side products (hexanes: ethyl acetate 1:1). 1 g of 1-6 was obtained (82.4 %) as a yellow oil. 1H NMR (300 MHz, CDCl3) δ 1.311 (d, J = 3.3 Hz, 3 H), 1.875-2.003 (m, 2 H), 2.525 (t, J = 3.9 Hz, 2 H), 2.981-3.026 (m, 1H), 7.060-7.101 (m, 1 H), 7.604-7.661 (dt, 1 H), 7.721-7.748 (m, 1 H), 8.456 (m, 1 H). [M1+] 244.0. |
| In ethanol at 80℃; for 2h; | ||
| In ethanol at 80℃; for 2h; |

| Yield | Reaction Conditions | Operation in experiment |
|---|---|---|
| 23% | In ethanol; acetic acid; ethyl acetate | 2.a Synthesis of the Maytansinoid Derivative (2) that Bears a Reactive N-succinimidyl Ester A 2 L flask containing a stir bar was charged with 2-2'-dithiodipyridine (300 g, 1.36 mol), reagent grade ethanol (1 L) and glacial acetic acid (42 mL). A solution of the crude 4-mercapto pentanoic acid in ethyl acetate (400 mL) was added dropwise over 15 minutes and the reaction was stirred under argon for an additional 2 hours. The solvent was removed by rotary evaporation and the residue was taken up in a minimum of ethyl acetate and purified by column chromatography using a silica gel column (6.25*27 cm). The column was eluted with 4:1 hexanes: ethyl acetate until all of the unreacted 2,2'-dithiopyridine (Aldrithiol-2) was removed. The column was then eluted with 4:1 hexanes:ethyl acetate containing 2% acetic acid. The elution was monitored by TLC and fractions were combined. The solvent was then removed by rotary evaporation under reduced pressure to give pure 4-(2-pyridyldithio)-pentanoic acid (PPA, 5) as a white solid (40 g, 23% overall yield). 1H NMR (CDCl3) δ1.39 (d, 3H), 2.0 (t, 2H). 2.56 (t, 2H), 2.8-3.3 (m, 1H), 6.8-7.2 (m, 1H), 7.6-7.8 (m, 2H), 8.4-8.6 (m, 1H), 11.68 (s, 1H). Preparation of N2'-deacetyl-N2'-[3-(3-carboxy-1-methyl-propyldithio)-1-oxopropyl]-maytansine (L-DM1-TPA, 6): |
| Yield | Reaction Conditions | Operation in experiment |
|---|---|---|
| In ethanol; acetic acid | 3 Briefly, 1,3-Dibromobutane (15 g, 0.069 mol) was dissolved in DMSO. NaCN (3.75 g, 0.076 mol) was dissolved in 8 mL of water and 1 mL was added immediately. The rest of the cyanide solution was added over 0.5 hour. The reaction mixture was then stirred overnight. The reaction mixture was diluted with 70 mL of water and the aqueous mixture extracted with 2 x 125 mL of 1:1 heptane:ethyl acetate. The combined organic layers were then washed with 70 mL water, and 70 mL of brine. The organic layer was concentrated and dissolved in 21 mL of ethanol. Thiourea (6.64 g, 0.087 mol) was added along with 21 mL of water and the homogenous reaction mixture was heated to reflux for 4 hours. At this point 50 mL of 1OM NaOH solution was added and the reaction mixture heated to reflux overnight. The reaction mixture was cooled to room temperature and diluted with 50 mL EtOAc. The EtOAc was separated and the organic layer washed with another portion of EtOAc. The combined organic layers were combined and concentrated to yield a slightly yellow liquid (6.48 g, 70%). 2, 2'~Dithiopyridine (25 g) was dissolved in ethanol (100 mL) and acetic acid (4.2 mL). The thiol-acid was added over 15 minutes and the reaction stirred for 2 hours at room temperature. The reaction was concentrated to yield a solution that was purified on a Biotage 4OM cartridge eluting with 3:1 toluene:EtOAc to 1:3 toluene:EtOAc to give a while solid, SPP, 13 g (79%). |
| Yield | Reaction Conditions | Operation in experiment |
|---|---|---|
| 91% | With triethylamine In dichloromethane at 0 - 20℃; Inert atmosphere; | Triisopropylsilyl 4-(pyridin-2-yldisulfanyl)pentanoate (1-7). A 1.00 g (4.1 mmol) aliquot of 1-6 and 0.83 g of TEA was dissolved in 20 mL of CH2Cl2 and cooled to 0 °C under inert conditions. To the mixture, 1.05 mL of TIPSCl was added dropwise. The mixture was stirred at room temperature and monitored via TLC (Rf = 0.93; developed on 3:1 hexanes: ethyl acetate). The reaction was quenched with NH4Cl and extracted with CH2Cl2. The organic layer was dried over MgSO4 and concentrated in vacuo. Purification was done via column chromatography on silica gel with increasing amounts of eluent (hexanes: ethyl acetate) to yield 1.49 g of light yellow oil, 1-7 (91 %): 1H NMR (300 MHz, CDCl3) δ 8.421 - 8.396 (dq, 1 H), 7.721 - 7.688 (dt, 1 H), 7.621 - 7.563 (m, 1H), 7.619 (t, J = 7.6, 1 H), 7.058 (t, J = 5.2 Hz, 1 H), 3.011 - 2.960 (m, 1 H), 2.253 - 2.468 (m, 2 H), 2.004 - 1.866 (m, 2 H), 1.300 (m, 3 H), 1.007 (m, 21 H). |
| 2.71 g | With triethylamine In dichloromethane at 0 - 25℃; for 24h; | |
| With triethylamine In dichloromethane at 0 - 25℃; for 24h; |
| Yield | Reaction Conditions | Operation in experiment |
|---|---|---|
| With 1-ethyl-(3-(3-dimethylamino)propyl)-carbodiimide hydrochloride In dichloromethane at 20℃; for 20h; Inert atmosphere; | 7.b (b) (±)-Di-tert-butyl 8,8′-(((5-(5,21-dioxo-24-(pyridin-2-yldisulfanyl)-8,11,14,17-tetraoxa-4,20-diazapentacos-1-yn-1-yl)-1,3-phenylene)bis(methylene))bis(oxy)) (11S,11aS,11′S, 11a′S)-bis(7-methoxy-2-methylene-5-oxo-11-((tetrahydro-2H-pyran-2-yl)oxy)-2,3,11,11a-tetrahydro-1H-pyrrolo[2,1-c][1,4]benzodiazepine-10(5H)-carboxylate) (36) (b) (±)-Di-tert-butyl 8,8′-(((5-(5,21-dioxo-24-(pyridin-2-yldisulfanyl)-8,11,14,17-tetraoxa-4,20-diazapentacos-1-yn-1-yl)-1,3-phenylene)bis(methylene))bis(oxy)) (11S,11aS,11′S, 11a′S)-bis(7-methoxy-2-methylene-5-oxo-11-((tetrahydro-2H-pyran-2-yl)oxy)-2,3,11,11a-tetrahydro-1H-pyrrolo[2,1-c][1,4]benzodiazepine-10(5H)-carboxylate) (36) EDCI (22 mg, 0.12 mmol) was added to a stirred solution of (+-)-4-(pyridin-2-yldisulfanyl)pentanoic acid (35) (26 mg, 0.10 mmol) and amine 29 (˜139 mg, 0.1 mmol) in dry DCM (2 mL) at room temperature. The reaction mixture was stirred under an argon atmosphere for 20 hours at which point analysis by LC/MS showed a substantial amount of desired product (split peak) at retention time 1.88 minutes (ES+) m/z 1548 ([M+H]+, ˜40% relative intensity) along with product corresponding to 1 N10Boc/1 THP cleaved at retention time 1.67 minutes (ES+) m/z 1346 ([M+H]+, ˜20% relative intensity), 1138 ([M+H2O]+, ˜20% relative intensity) and product corresponding to 2 N10 Boc/2 THP cleaved at retention time 1.43 minutes (ES+ M+ not observed). The reaction mixture was diluted with DCM (30 mL) and washed with H2O (15 mL), brine (20 mL), dried (MgSO4), filtered and evaporated in vacuo to provide the crude product 36 as a foam. |
| Yield | Reaction Conditions | Operation in experiment |
|---|---|---|
| With acetic acid In ethanol; ethyl acetate at 14.9℃; for 2.66h; | 1 Reaction of 4-Mercapto-Pentanoic Acid with 2,2’-Dithiopyridine 2,2'-dithiodipyridine (Aldrithiol, 100 g, 454 mmol) was dissolved in ethanol ( 700 mL) to which acetic acid (280mL) was added and the solution was magnetically stirred in an ice/water bath until it reached 14.9 °C. A solution of 4-mercapto-pentanoic acid (30 g, 220 mmol) in ethyl acetate (140 mL) was then added over 15 min with stirring. After addition the cooling bath was removed and the reaction was stirred for 2 h and 25 min. Solvent was evaporated under vacuum to give a yellow gum residue. |
| Yield | Reaction Conditions | Operation in experiment |
|---|---|---|
| 2.8 g | With dmap; 1-ethyl-(3-(3-dimethylamino)propyl)-carbodiimide hydrochloride In N,N-dimethyl-formamide at 0 - 20℃; | 12 To a solution of compound 34 (5.5 g, 22.6 mmol) and compound 35 (5.8 g, 22.6 mmol) in 50 mL of DMF at 0° C, EDCI (6.8 g, 35.3 mmol) and DMAP (828 mg, 6.8 mmol) were added. Then the reaction was stirred at room temperature overnight. Water was added and extracted with ethyl acetate. The organic layer was washed with water and brine, dried over anhydrous a2S04, and concentrated to give a crude product, which was purified by column chromatography to give 2.8 g of compound 36. 1HNMR (CDCb, 300 MHz) δ: 1.3-1.4 (m, 3 H), 1.4-1.6 (s, 9 H), 1.9-2.1 (m, 2 H), 2.3-2.5 (m, 2 H), 3.1-3.2.2 (m, 2 H), 4.7-4.9 (m, 1 H), 6.0-6.1 (m, 1 H), 7.0-7.1 (m, 1 H), 7.1-7.2 (m, 2 H), 7.3-7.5 (m, 3 H), 7.6-7.8 (m, 2 H), 8.5 (m, 1 H). |
| Yield | Reaction Conditions | Operation in experiment |
|---|---|---|
| With 1-ethyl-(3-(3-dimethylamino)propyl)-carbodiimide hydrochloride In dichloromethane at 20℃; for 2h; | 3b Synthesis of sodium salt of sulfoSPP (N-sulfosuccinimidylester of 4-(2-pyridyldithio)-pentanoic acid, 8 [0080] Maytansinoid 3a can also be prepared directly by reaction of DM1 (1) with the sodium salt of sulfoSPP (N-sulfosuccinimidylester of 4-(2-pyridyldithio)-pentanoic acid, 8). The sodium salt of sulfoSPP (8a) can be prepared bycoupling of PPA (5) with the sodium salt of N-hydroxysulfosuccinimde in the presence of EDC.HCl, by the methoddescribed for SPP (7) (see Example 2a above). Reaction of DM1 with a 20-fold molar excess of 8a in dimethylacetamideand potassium phosphate buffer pH 6 containing 2 mM EDTA at ambient temperature gives maytansinoid 3a, whichcan be purified by HPLC as described in Example 3a. |