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21st February 2012 @ 02:16
PS = Pictet-Spengler

***Experiment still in progress with regular updates. Last updated 22/02/12.

START: 21/02/12
FINISH:

Background

Scheme%20KAB8-14.png
Table%20KAB8-14.jpg

Hazard and Risk Assessment
As for KAB8-11 and KAB1-3.
Hazard and Risk Assessment KAB8-11
Hazard and Risk Assessment KAB1-3


Previous Related Experiments


Following Experiments


Procedure

21/02/12
General procedure. The peptide acetal Ugi-intermediate was dissolved in toluene before the addition of triflic acid at rt. The reaction vessel was immediately fitted with a condensing tube and placed in a pre-heated oil bath at 90 °C. The reaction mixture was reflux heated and the progress monitored by TLC against the relevant starting material and the expected product.

KAB8-14. Peptide acetal MNR10-2 (302.4 mg, 0.659 mmol), toluene (30 mL), TfOH (2.92 μL, 0.033 mmol, 5 mol%).

KAB1-5. Peptide acetal MNR8-3 (381.6 mg, 0.821 mmol), toluene (38 mL), TfOH (3.64 μL, 0.041 mmol, 5 mol%).


Monitoring the Reaction Progress by TLC
All TLCs were eluted with EtOAc/hexane, 5:3, v/v and stained with KMnO4. Time noted is the amount elapsed since the addition of acid.

Workup Procedure
After 3.5 hours the reaction mixture was allowed to cool. After the mixture was diluted with EtOAc (50 mL) then quenched with saturated sodium bicarbonate solution (50 mL), the organic layer was separated. The aqueous fraction was extracted with EtOAc (3 × 30 mL) before the organic layers were combined then dried over magnesium sulfate and filtered.
The pale yellow KAB8-14 and the yellow KAB1-5 solutions were concentrated under reduced pressure to give the crude products. KAB8-14 as a orangish semi-solid (249.8 mg, 103%) and KAB1-5 as a reddish semi-solid (312.0 mg, 102%).

Purification
Both crude KAB8-14 and KAB1-5 residues were dissolved in EtOAc. The solutions were passed through silica pads then concentrated under reduced pressure.
KAB8-14 (233 mg, 96%).

Summary and Conclusion


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NOTES 21/02/12
- KAB8-14 Flask: 49.1531 g
- Forgot to weigh out KAB1-5 flask. Will weigh it out after the filtration step tomorrow.

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Linked Posts
Attached Files
Scheme KAB8-14 & KAB1-5
Table KAB8-14 & KAB1-5
TLC of KAB8-14 reaction mixture (5 min)
TLC of KAB1-5 reaction mixture (5 min)
Reaction mixtures (5 min)
TLC of KAB8-14 reaction mixture (15 min)
TLC of KAB1-5 reaction mixture (15 min)
Reaction mixtures (15 min)
TLC of KAB8-14 reaction mixture (30 min)
TLC of KAB1-5 reaction mixture (30 min)
Reaction mixtures (30 min)
TLC of KAB8-14 reaction mixture (1 h)
TLC of KAB1-5 reaction mixture (1 h)
Reaction mixtures (1 h)