ugi_reaction01.jpg

Objective

To accomplish the Ugi reaction 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.

Procedure

To a 50 ml Erlenmeyer flask added methanol (20 ml), phenylacetaldehyde, (623 µl , 5.59mmol) ,5-methylfurfurylamine (555µl, 4.97mmol ) benzylisocyanide(608µl, 4.99mmol ) and N-(tert)-butoxycarbonyl)-L-methionine (1.24604 g, 4.99mmol). The mixture was stirred for 15 h, evaporated, refluxed for 45 min in 1,2-dichloroethane (27 ml) and trifluoroacetic acid (3 ml) then evaporated again to a dark oil. The crude product was taken up in dichloromethane (30 ml), washed with water, dried over anhydrous MgSO4 and evaporated again. A dark, reddish oil was obtained.

Results

The main fast moving fractions HNMR of 14B, 14EF-1 , 14EF-3, 14EF-4 lack significant peaks at 5.8 and 5.9 ppm.
The NMR of Boc-Met-OH (Varian Inova 300MHz) indicates the presence of impurities at 7.3 ppm, 6.85ppm, and 5.3 ppm.

Discussion

The key NMR peaks expected of the diketopiperazine are:
Furan aromatic H's at 5.8 and 5.9 ppm, and methyl on furan ring at 2.2 ppm, based on the NMR of 5-methylfurfurylamine.
L-methionine CH3 at 2.1 ppm and S-CH2 at 2.6 ppm , based on the NMR of Boc-Met (and the nmr of unprotected L-methionine).
Since the main fast moving fractions lack key furan peaks, the desired diketopiperazine is not present there.
The impurities in the Boc-Met-OH complicate the analysis of this experiment.

Conclusion

This experiment is aborted and will be revisited after a successful synthesis of a simpler diketopiperazine.

Log

2006-05-30

1. 21:00 mixed chemicals and started stirring

2006-05-31

2.12:00 The reaction was stirred at room temperature for 15 hours (Videos of the reaction being stirred).
3.Evaporated methanol on rotovap set at 100C, obtained 14A (3.239 g) the crude product.
4.Added 27ml of 1,2-dichloroethane and 3ml of trifluoroacetic acid to crude product, refluxed for 45 mins then rotovaped (was not put on high vac)
5. Added 70mls of water and 60mls of methylene chloride to the crude product, separated the organic layer using a separatory funnel. A second wash was carried out similarly with 30mls of water and dried over anhydrous Magnesium Sulfate and filtered. and evaporated on rotovap to14B.
6. 16:00 HNMR of 14B obtained (Varian 300MHz).

2006-06-01

7.14:30 Crude product 14B was further dried under high vacuum until it foamed and settled for one and half hours to 14C (3.5174 g)
8.Applied 1.3051 g of 14C on a 4mm Chromatotron. Initially a 2:1 mix of hexanes and methylene chloride was used (about 400ml), 19 of 20mls portions were accumulated. Based on the TLC they were combined to just three fractions, 14C-F1 (77.3mg),14C-F2 (74.4mg), 14C-F3 (80.2mg) TLC
9. Most of the compound still remained on the rotor disc. The compound was left to dry overnight on the rotor.

2006-06-02

11.Remaining compound removed from the rotor using methanol and evaporated to 14D. and introduced back on chromatotron and eluted with 1:1 hexanes and methylene chloride (100 mL mix)
The eluent composition was changed gradually from 1:1 hexanes, methylene chloride to just methylene chloride (100mls), then it was further changed to 0.5% methanol in methylene chloride. Polarity of the solvent was changed regularly. 0.5% methanol, 1% methanol, 2% methanol, 3% methanol, 4% methanol, 6% methanol, and 8% methanol in methylene chloride.
12. 16 fractions were collected. A TLC was run in 1:1 Hexanes and methylene chloride, the fractions were combined based on TLC.The following fractions were obtained 14D-F1 (49mg), 14D-F2 (90.3mg), 14D-F3 (132.1mg), 14D-F4 (169.6mg), 14D-F5 (103mg), 14D-F6 (119mg) . TLCs of these fractions vs. 14D . (why does 14D not have all the spots of the fractions in it?) .The low concentration 14D (and 14C) on the TLC plates may be an apparent reason for the absence of all the spots of the fractions. This is evident from the TLC of 14C2-F4which is run against a strongly spotted 14C.
13.The remaining crude 14C (3.5 g - 1.3g = 2.2g) was subjected to flash chromatography, using methylene chloride.
(65 g of Silica gel 60, 0.040-0.063mm (230-400 mesh)
14.Three fractions were collected, before a final methanol run was carried out and the remaining crude product that had not moved by methylene chloride was collected as a fourth component. The fractions are called 14C2-F1 (199mg), 14C2-F2 (85 mg), 14C2-F3 (152.2 mg) and 14C2-F4 (1.56g)
15 A TLC of the 14C2-F1,014C2-F2 and 014C2-F3 was obtained using methylene chloride.
16. HNMRs were also obtained for 014C2-F1, 014C2-F2, 014C2-F3(is this fractions.
17. At this stage 14C-Fractions, 14C2-Fractions and 14D-Fractions are to be processed.
From the TLCs it might be of interest to combine fractions 14C-F3, 14C2-F1,14C2-F2,14D-F1,14D-F2 and 14D-F3 and run a flash chromatograph to separate the fast moving spots with 3:1 methylene chloride,hexanes as mobile phase.
18. Fractions 14C-F3, 14C2-F1, 14C2-F2, 14D-F1, 14D-F2 and14D-F3 were combined to get 14E (247mg ). Expected amount of fraction 14E was approximately 650 mgs; however some of the fraction got lost (splattered into the vac), being vacuum dried, only 247 mgs of could be salvaged.
A TLC(14E is massively overloaded - redone in 1:1 and 1:2 hex/MC) of 14C,14D and 14E in methylene chloride indicates that MeCl2 is not best suited for a good separation of 14E.
19. A flash chromatography column was run on 23.5gms of Silica gel (-230+400 Mesh, S.A. 500-600m2/g) was used. The column was run initally with 3:1 hexanes-MeCl2 (100mls), 2:1 hexanes-MeCl2 (100mls), 1:1 hexanes-MeCl2 (300mls), 1:2 hexanes-MeCl2 (100mls), 1:3 hexanes-MeCl2 (100mls), then pure MeCl2 (300mls), 0.5% MeOH in MeCl2 (100mls), 1%MeOH in MeCl2 (100ml), 2% MeOH in MeCl2 (100ml), 5%MeOH in MeCl2, apparently most of the compound had been pushed out of the column at this time. Therefore pure MeOH (50mls) was used to rinse the column out completely.
20.180 fractions were collected. These fractions will be combined based on there TLCs.
21.The fractions from 1 to 113 were combined based on TLC to 6 fractions, namely 14EF-1(19.2 mg), 14EF-2(7 mg), 14EF-3(15.6 mg), 14EF-4(13.3 mg), 14EF-5(7.5 mg), and 14EF-6(7.2 mg), the remaining fractions had base line stuff which was assumed as unworthy of analysis (Assumption: diketopiperazine is a fast moving spot) A TLC of these fractions against 14E was obtained.The remaining fractions did not show enough movement considered worthwhile. Did any of the other fractions have one of the two major fast moving spots in 14E? In essence the answer to the question posed is, No.
22.NMRs of fractions 14EF-1 , 14EF-3, 14EF-4 (blow-up) was obtained.

Tags

Benzylisocyanide InChI=1/C8H7N/c1-9-7-8-5-3-2-4-6-8/h2-6H,7H2
Phenylacetaldehyde, InChI=1/C8H8O/c9-7-6-8-4-2-1-3-5-8/h1-5,7H,6H2
Boc-Methionine InChI=1/C10H19NO4S/c1-10(2,3)15-9(14)11-7(8(12)13)5-6-16-4/h7H,5-6H2,1-4H3,(H,11,14)(H,12,13)
5-methylfurfurylamineInChI=1/C6H9NO/c1-5-2-3-6(4-7)8-5/h2-3H,4,7H2,1H3
DKP014 InChI=1/C20H24N2O3S/c1-14-8-9-16(25-14)13-22-18(12-15-6-4-3-5-7-15)19(23)21-17(20(22)24)10-11-26-2/h3-9,17-18H,10-13H2,1-2H3,(H,21,23)