Index

• 2009 roefractine Synthesis Home Page Students working on this project
• Table of Reagents and Amounts Available
• Notes on Step 1
• Notes on Step 2
• Notes on Step 3
• Notes on Step 4

Project TA: Wilson Bailey (wbailey@ups.edu)

Dopamine is an important neurotransmitter. For example, cocaine acts by blocking dopamine uptake, while a deficiency of dopamine is associated with Parkinson’s disease. As part of a series of studies aimed at better understanding the binding of alkaloids to dopamine receptors, (R)-(+)-nor-Roefractine was recently synthesized and its binding to dopamine receptors was studied. The synthesis starts with isovanillin which is protected as the benzyl ether before condensation with nitromethane to give the b-nitrostyrene derivative. Reduction to the amine, followed by reaction with 4-methoxyphenylacetyl chloride gives a compound that can be cyclized using POCl₃. Stereoselective reduction of the resulting cyclic imine followed by deprotection of the benzyl ether gives the desired (R)-(+)-nor-Roefractine.

The table below lists the chemicals that we will have available for this project. If you need something that is not on this list, consult with the mentor for your project. Also note the "Amount/group" column. This is the total amount of material available for each group to use on the project.

Reagent	Source	Amount/group	Location	Comments
3-hydroxy-4-methoxybenzaldehyde (isovanillin)	Aldrich Cat. # 14,368-5	5 g	TA room
Benzyl chloride	Aldrich Cat. # 18,555-8	25 mL	TA room	This material is a cancer suspect agent. It must be disposed of in a special container.
Nitromethane	Aldrich Cat. #36,055-4	50 mL	TA Room
4-Methoxyphenylacetic acid	Aldrich Cat. # M1,920-1	10 g	TA Room
Phosphorus oxychloride	Aldrich Cat # 20,117-0	10 g	TA Room

Notes Step 1

Preparation of 3-benzoxy-4-methoxybenzaldehyde.

(O-Benzylation of iso-Vanillin (3-hydroxy-4-methoxy benzaldehyde)

The cited literature source references the following paper for directions on the benzylation reaction. In that paper they benzylate vanillin but this should be the same for isovanillin. Meyers, A.I.; Gulles, J.. Heterocycles 1989, 28, 295-301.

• To a stirred solution of iso-vanillin (39.0 g, 0.258 mol) in ethanol (200 mL) was added K₂CO₃ (38.9 g, 0.292 mol), and benzyl bromide (44.11 g, 0.258 mol), and the mixture was maintained under an nitrogen atmosphere overnight. The solution was filtered through celite, the celite rinsed with dichloromethane (2 x 200 mL), and the solvent removed in vacuo . The residue is dissolved in 250 mL dichloromethane and washed with 5% NaOH, concentrated and crystallized from ethanol (55.4 g, 88% yield), m.p. 62-63 °C.

(1) We will use benzyl chloride in place of the bromide. Benzyl chloride is a lachrymator so do this reaction and workup in the hood. We will set-up a rotoevaporator in one of the hoods as well.

(2) You will need to adjust the amounts used to reflect your scale of reaction. Try using about 2.5 grams of isovanillin.

(3) Note that Cortes, et.al. refluxed for 5 hours whereas the cited paper stirred overnight at ambient. You can probably use a combination of reflux and stirring overnight at room termperature.

(4) Filtering through a bed of Celite will remove very small particles which would otherwise pass through the filter.

(5) After removing the reaction solvent you may have unreacted benzyl chloride in your mix. One trick to get rid of it and ease the purification process is to cover the oil (or crude solid) with cold hexane. This will draw up the benzyl chloride but not dissove your product. In may take a bit for the oil to crystallize. Once solid, three rinses with cold hexane should remove any unreacted benzyl chloride. You will need to pump on your sample (or rotovap) to remove traces of remaining hexane before you take an NMR. Check the purity by GC/MS to decide if you need to crystallize or not. Also, once solid, a melting point is a good indicator of purity.

(6) For GC/MS of the benzylated isovanillin use method 251high; your product will elute around 7-8 minutes. There was a trace amount impurity that came later with a molecular weight of 328. Note that the CH₂ in benzyl chloride comes at 4.45 ppm.


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Step 2 Notes



Preparation of 3-benzoxy-4-methoxyphenylnitrostyrene.

The main reference has little detail on this reaction but descriptions are given in footnotes 8 and 9. Here is one procedure you can use which will need to be scaled to about 1 gram of starting aldehyde.



• 3-benzyoxy-4-methoxybenzaldehyde (1 g) is combined with 3 equivalents of nitromethane, 0.9 gram of ammonium acetate and dissolved in about 20 mL acetic acid. This was refluxed for 3-4 hours. After cooling the solution is added to about 30 mL ice-water which is then transfered to a separatory funnel (use your glass funnel to keep the ice out) and the aqueous solution extracted with 5 x 20 mL dichloromethane. The combined organic extracts is washed with water, 5% bicarbonate then saturated NaCl solution, dried and the solvent removed to yield a gold colored solid, m.p. 126 - 128 degree C. If neccessary recrystallize from ethanol.

(1) We need to extract many times with dichloromethane to get all of our product. As long as your extract is deeply colored you know there is more to remove from the water layer.

(2) We wash with water first to remove most of the acetic acid. The bicarbonate extract removes the rest.


(3) After drying and removing the solvent obtain a good NMR and maybe GC/MS, (Use method 251high) and melting point to know if recrystallization is needed.


(4) Condensation with nitromethane will give both the cis and trans isomers so expect two peaks in your GC/MS.


(3) In addition to the two product isomers you will see some starting material and a peak just after that which has a m/z of 239. My guess is that it is a methoxy benzyloxy cyanobenzene. How that can be I do not know. Also I've noted that on some crystallization one of the product isomers is lost as well as the impurities. You might GC/MS your crystallization elutant to see what it contains. We could be losing a significant amount of product there.


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Step 3 Notes







Preparation of 3-benzoxy-4-methoxyphenylnitrostyrene.

(LAH reduction of the nitrostyrene.)

This procedure is adapted from the Chen article on synthesis of a related compound. You will need to scale this to your amount. Chen, Chi-Ming, et. al. , Jr. of Natural Products , 1995, 58, 1767.

• A solution of the nitrostyrene (22.5 mmol) in 80 mL anhydrous THF was added dropwise to a well-stirred suspension of LiAlH₄ in 120 mL anydrous THF, and the mixture refluxed for 4 hours. Excess LAH was destroyed by dropwise addition of 3 mL water then 3 mL 10% NaOH. Filter through a bed of Celite, and remove solvent to give the oily amine.

(1) You should try this on a 250-400 mg scale for the first time. Don't scale you solvents down directly. For example, you can add the LAH to about 15 mL THF and add your nitrostyrene in 5 mL THF or diethyl ether.

(2) Flame dry your setup and use a proper sized RB. You can add the initial THF and LiAlH₄ directly into the RB, then attach the reflux condenser. But, be sure to rinse any LiAlH₄ off the ground glass joint with a little THF. Add your nitrostyrene using a long stemmed pipet dropwise directly through the condenser. Rinse with dry THF if needed and then put a nitrogen balloon on top. A 2 hour reflux is probably enough for this scale reaction.

(3) Once the solvent is removed, to get rid of water, we should take up our amine in dichloromethane and extract with water 2x, dry, then remove solvent. Get a good NMR and we'll see if a GC/MS is feasible.





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1. Formation of Amide.

   We have a new method to try here using molecular sieves. Check with Wiz for information. The following procedure from the lit. article seems to be a sound procedure. We will have some groups doing this method while one or two groups will use the carbodiimide procedure. We will then compare the results.

   Have any procedure checked before starting.

   

   Preparation of amide using Molecular sieve.

   A mixture of Oleic Acid (5.65g, 20.0 mmol) and N-benzylamine (2.14g, 20.0 mmol) was placed in a flame-dried 20-mL headspace vial. Highly activated molecular sieve (3Å, 1.80g) was added in one portion and the mixture was heated to 160°C. After completion of reaction (2h, monitored by TLC*) mixture was cooled, diluted with 150 mL of MeOH, filtered through a thin pad of celite, washed with iced MeOH(50 mL) and concentrated in vacuo to afford 7.41g (99%) of amide.

   *Silica gel (EtOAc:Hex, 1:1), Rf= 0.8.

   Preparation of amide using Diisopropylcarbodiimide, DIC.

   (The procedure was adapted from general instructions for the amide formation using Diisopropylcarbodiimide, DIC.)

   These instructions are from the procedure from Wilson Bailey last year and you will need to scale your procedure after you calculate MW and #mmoles, etc. When you have determined the amount of product from the previous reaction then scale this reaction as follows:

   HAZARDS: Carbodiimides are strong sensitizers. Wear gloves.

   N-(3-(benzyloxy)-4-methoxyphenylethyl)-4′-methoxyphenacetamide (5). The amine product from the previous reaction (0.251g, 0.971 mmol) was added with a one equivalence of 4-methoxyphenylacetic acid (0.1608g, 0.971 mmol). One equivalence of N,N-diisopropylcarbodimide (0.151 ml) and dichloromethane (3.6 ml) was added to a 25ml round bottom flask. The reaction was left to stir overnight. The solution was then diluted with dichloromethane (10 ml) and washed with 0.5M hydrochloric acid (15 ml), 0.5M sodium hydroxide (15 ml) and with Brine (15 ml). The solution was dried, vacuum filtered and run through a flash column*. The white chalky solid (0.1872g, .462mmol, 47.6%) characterized by H-NMR, IR, MP. 1H-NMR (400 MHz, CDCL3) δ 2.61 (3H, t, J = 6.71 Hz) 3.38 (2H, q) 3.43 (2H, s) 3.78 (3H, s) 3.86 (3H, s) 5.08 (2H, s) 6.55 (1H, d, J = 7.32Hz) 6.63 (1H, s) 6.73 (1H, d, J = 7.93 Hz) 6.83 (2H, d, J = 7.93 Hz) 7.05 (2H, d, J = 8.54 Hz) 7.25-7.43 (5H, m). IR (KBr) 3297, 3159, 3123, 2963, 2927, 1732, 1638, 1609, 1577, 1548, 1512, 1244 cm-1. MP 104.4-108.5 °C. *The Flash column was collected in three different fractions: the first eluent was 70/30 hexane/ethyl acetate, second was 60/40 hexane/ethyl acetate and the final was 100 % ethyl acetate.

   Get your procedure checked off.

   We will investigate solvent systems for the TLCs and the flash column as the week progresses.)