Pictet-Spengler route to Praziquantel

 

*Wrong user ID used for original post, can no longer edit it

Attempts to improve promising results of MW56-3





Hazard and Risk Assessment:
As for MNR11-3

Procedure

MNR11-4
MNR8-2(50 mg, 0.11 mmol) and 1,1’-Binaphthalene-2,2’-disulfonic acid, MW54-3 (10 mg, 0.01 mmol) DCM (1 mL) was heated at reflux overnight

MNR11-5
MNR8-2(50 mg, 0.11 mmol) and 1,1’-Binaphthalene-2,2’-disulfonic acid, MW54-3 (10 mg, 0.01 mmol) chloroform (1 mL) was heated at reflux overnight

MNR11-6
MNR8-2(50 mg, 0.11 mmol) and 1,1’-Binaphthalene-2,2’-disulfonic acid, MW54-3 (10 mg, 0.01 mmol) DCM (1 mL) was stirred at room temperature overnight

MNR11-7
MNR8-2(50 mg, 0.11 mmol) and 1,1’-Binaphthalene-2,2’-disulfonic acid, MW54-3 (10 mg, 0.01 mmol) chloroform (1 mL) was stirred at room temperature overnight

MNR11-8
MNR8-2(100 mg, 0.22 mmol) and 1,1’-Binaphthalene-2,2’-disulfonic acid, MW54-3 (20 mg, 0.02 mmol) toluene (2 mL) was stirred at room temperature overnight

TLC of all 5 reactions after 16 hours showed very little reaction. MNR11-5 (refluxing chloroform) showed signs of possible product. After 20 hours a sample of MNR11-5 was removed from the reaction and filtered through a pipette of silica and ran through the LCMS.

All 5 reactions were left at their original temperatures for 44 hours then at room temperature over the weekend.

After 2.5 days at room temperature a small aliquot from each reaction was removed and filtered through a small silca column (pipette) and submitted for LCMS

MNR11-4

LCMS MNR11-4
Ret. Time 16.100 373.2 [M+H]
20.167 487.3 [SM+Na]

*Showing signs of cyclisation


MNR11-5

LCMS MNR11-5

Ret. Time 16.192 373.2 [M+H]
20.658 487.3 [SM+Na]


More significant peak for unwanted hemiaminal at 19.167

MNR11-6

LCMS MNR11-6
Ret. Time 16.183 373.2 [M+H]
19.983 487.3 [SM+Na]
419.3 [Hemiaminal+H]
20.5 481.1 Unknown
21.025 556 Unknown

No peak at 19.1 (good) but side reactions going on (?)

MNR11-7

LCMS MNR11-7
Ret. Time 14.167 373.2 [M+H]
19.217 487.3 [SM+Na]
419.3 [Hemiaminal+H]

Mainly starting material.

MNR11-8

LCMS MNR11-8
Ret. Time 16.067 373.2 [M+H]
19.917 487.3 [SM+Na]
419.3 [Hemiaminal+H]
20.442 481.1 Unknown
21.025 556 Unknown
No peak at 19.1 (good) but side reactions going on (?)

Next step: Repeat DCM at reflux and try toluene at reflux for longer reaction time?