Wednesday, March 29, 2006

Exp 006

Objective:
To test out the Ugi Synthesis and cyclization to a diketopiperazine using phenylacetaldehyde, 5-methylfurfurylamine, N-(tert) butoxycarbonyl)L-methionine, and benzylisocyanide using the protocol described here. The target diketopiperazine is not predicted to be active but is a close analog of the product that we wish to make once the catechol aldehyde is obtained.
As pointed in one of the comments posted to exp 003, the complete reaction was carried out at a higher concentration for each of the component involved. Also, the reaction mixture was heated to 80C for 30 min in 1,2-dichloroethane and TFA at the uncyclized stage.

Procedure:
To a 50 ml Erlenmeyer flask was added methanol (20 ml), phenyl acetaldehyde (55µl, 0.49 mmol) , 5-methylfurfurylamine (55µl, 0.49 mmol) , benzylisocyanide 60µl, 0.49mmol) and N-tert-butoxycarbonyl L-methionine (124.7 mg, 0.50 mmol). The mixture was stirred for 24 h, evaporated, refluxed for 30 min in 1,2-dichloroethane (9 ml) and trifluoroacetic acid (1 ml) then evaporated again to a dark oil. The crude product was taken up in dichloromethane (5 mL), washed with 5% HCl, dried over anhydrous MgSO4 and evaporated to yield a dark red oil.

H-NMR of the crude product in CDCl3:


TLC after extraction using 1:1 5%HCl/DCM

Discussion

The H-NMR of the crude product does not show an aldehyde peak in the 9-10 ppm region, indicating that at least one starting material is consumed. The crude product may contain both cyclized a diketopiperazine and deprotected uncyclized amine but the NMR of the mixture cannot distinguish between these. For a possible mechanism of the Ugi reaction, click here.

Conclusion

This experiment will have to be aborted if the HNMR obtained is to be trusted. It can be seen that the furan peaks at 5.9 ppm are not strong enough to advocate an isolation and purification.

This experiment helped me acquaint with the chromatotron, NMR and refreshed other experimental techniques .
Log

  1. 8:38 pm (03/28/2006): In a 50ml Erlenmeyer flask, 20ml of methanol placed. To it 55µl (0.49mmol) of phenyl acetaldehyde, 55µl (0.49mmol) of 5-methylfurfurylamine, 60µl (0.49mmol) of benzylisocyanide and 0.12468 gms (0.50mmol) of N-(tert) butoxycarbonyl) L-methionine was added. An FTIR spectrum was obtained at t=0.
  2. The reaction was stirred at room temperature with a teflon coated stir bar on a stir plate.
  3. 8:38pm (03/29/2006): Stirring was stopped.
  4. 8:45pm (03/29/2006): Methanol was evaporated from the sample using a rotovap (75 C).
  5. 10:30pm (03/29/2006) Added 9ml of 1,2-dichloroethane and 1ml of trifluoro acetic acid to the methanol void sample in a round bottom flask. Heated the reaction mixture for about 5 mins before the vapors got intense and had to attach a reflux condenser, the heating was turned off after 30 mins..; the boiling points of the solvents are, TFA= 72.4 ° C and 1,2-DCE = 83 °C
  6. 11:10pm (03/29/2006) After 30 mins the solvents were evaporated using a rotovap, at 85C.
  7. 11:40pm (03/29/2006) The residue is a dark brown liquid.
  8. 12:10am (03/29/2006) A TLC of the product was run in a mixture of 10ml 1,2-dichloroethane and 10ml of hexanes.
  9. H-NMR of the crude final product was also obtained. (Varian 300Mz Instrument)
  10. 2:30pm (04/02/2006) Extraction: Added 5ml of 5% HCl and 5 ml methylenechloride to the round bottom flask containg the crude product and transferred it to a separatory funnel. Separated the bottom methylenechloride layer from the top aqueous layer. Washed the aquoues acid layer twice with 5mls of methylenechloride and collected the bottom methylenechloride layer each time. Combined the organic layers and dried it over anhydrous magnesium sulfate (MgSO4). Evaporated the dichloromethane using a rotovap and collected the extracted product. A TLC of the product was obtained (Shown above).
  11. 11:30 am (05/10/2006) Separation using a Chromatotron : The compound was dissolved in 10 ml of methylene chloride, applied to the rotating plate on the chromatotron.The round bottom flask was rinsed with 1ml of methylene chloride, the residue was poured over the rotating plate of the chromatotron. A mix of 1:1 hexanes and methylene chloride was used initially as the mobile phase. (60mls).
    In the mean time fractions were collected. To speed-up the movement of the compound a more polar solvent mix was used. The composition of the mobile phase was changed from 1:1 hexanes, methylene chloride to 1:1 methylene chloride, methanol (gradually), and finally to methanol.



Tuesday, March 28, 2006

Exp 005



Purpose: To synthesize 3,4-dihydroxyphenylacetaldehyde from adrenaline. How this fits into the synthesis of anti-malarials is explained here. In a prior attempt using glacial acetic acid as the main solvent, monitoring by TLC and IR was problematic. In this attempt benzene will be added and samples drawn from the top benzene layer should be easier to chromatograph and follow by IR. Also since benzene boils near 80C it will be convenient to reflux at a lower temperature.

Procedure: Benzene (12 mL), glacial acetic acid (12mL), 6M sulfuric acid (1.5mL) and adrenaline (51.7 mg, 0.282mmol) are stirred and refluxed in a 50mL flask under nitrogen.

ABORT
Discussion and Conclusion

The video after 60 minutes shows that a small brown layer separates at the bottom of the flask, suggesting that it contains only the aqueous sulfuric acid dissolving the adrenaline. Since the point of adding the benzene was to extract out the resulting aldehyde from the acetic and sulfuric acids, this didn't work. The acetic acid is clearly favoring the benzene layer. The heavy streaks in the TLCs are consistent with this.

Log

2006-03-28

12:15) Mixed chemicals and turned on heating mantle at 80 degrees C. A sample of 1mL, t=0 (5A) was taken and as expected there was some separation. The bottom layer was brownish in color while top layer was clear.

12:46) Sample 5B or t= 30 min was taken. Still under N2, the flask was allowed to cool to take the sample. The solution did not separate in the amount of time lotted in any visible way. Sample does not separate. TLC of 5A(t0) vs 5B (30 min) with methylene chloride (MC) as eluent was put in iodine chamber.

13:15) Sample 5C (t=60 min) was taken. Still no clear separation in the solution, although the solution itself is clear except for the adrenaline which has not dissolved. Video at this time shows that a small brown layer settles at the bottom of the flask when stirring stops.

13:35) Sample 5D (t=80min) was taken. Reflux solution remains the same, samples turn somewhat cloudy in atmosphere. After a while cloudiness dissipates and sample is clear. Pic of TLC 5A (t0) vs 5C (60min) and 5D(80min) (5D plate is on the left and on each plate 5A is on the left).

14:20) TLC of 5A vs 5B, 5C and 5D was made in 1:1 (MC/hexanes) and is similar to pure MC

14:45) Sample 5E taken t=2.5hrs. Refluxed stopped and solution saved. UV lamp is needed. TLC's reveal after several minutes in iodine chamber what would be a moving streak surrounded by the iodine coating. Streaks of 5B-E against 5A are higher.

Thursday, March 16, 2006

Exp 004


Purpose: To convert adrenaline to a catechol aldehyde using acid catalysis. How this fits into the synthesis of anti-malarials is described here

Procedure: In a round-bottomed flask, 25ml of acetic acid, 58.47mg (0.319mM) of epinephrine, 2ml of 6M Sulfuric Acid, and 3 ml of water was added. The solution had a slightly dark tint. The solution was then refluxed in a nitrogen gas environment.

LOG
Samples were taken at the following times:
1230: t=0 (20A)
1300: t=1/2 hour (20B)
1330: t=1 hour (20C)
1430: t=2 hours (20D)


Next steps:
1) Add ether and water to each sample vial
2) Spot each reaction on a TLC plate using the upper ether layer
3) Determine from TLC if the reaction took place.