Synthesis of Caffeic Acid Phenethyl Ester (CAPE): A Laboratory Report

Abstract

Caffeic-Acid Phenethyl Ester (Cape) is a bioactive polyphenol element which is acquired from propolis naturally found in the hives of the honeybee and occurs in many plants. It’s a resin-sealant like substance used by the honey-bee. Studies have shown that its a powerful enzyme inhibitor of nuclear-transcription factor (NF-kB) and 5-lipoxygenase 5-LO, which is an enzyme - arachidonic-acid and leukotriene-LTA4. There are therapeutic effects and benefits which include anti-oxidant, anti-inflammatory, anti-microbial, immunomodulatory and cytotoxic properties. CAPE has further medicinal benefits which include the prevention and growth of certain cancer forming cells, a measured amount of CAPE contained the growth of prostate cancer cells (PC-3, DU-145, LNCap) (2).

CAPE inhibits NF-kappa -beta which is vital factor in the initiation of cancer.

Introduction

The report will look at the various steps of the sythesis of Caffeic Acid Phenethyl Ester in extracting CAPE. Even though CAPE is provided by nature it is in short supply. Our experiment is to extract CAPE by its synthesis in the lab.

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We will synthesise CAPE in a 3-step process. Firstly, Caffeic-acid will be acetylated with acetic anhydride. The result of conversion is a reactive acid, (carboxylic-chloride) under dimethylformamide activation. Secondly: it progresses with alcoholysis, here the acid-chloride intermediate and 2-phenylethanol are reacted. Thus resulting in acetylated-ester (intermediate) form of (CAPE). Thirdly and final, the reaction progresses to the final base-induced de-oacetylation. Potassium-carbonate in methanol and dichloromethane will eliminate the acetyl groups and reintroduces alcohol. The process includes IR-spectroscopy, establishing the melting point and chromatography.

Materials and Methods

The synthesis was conducted in three main steps, with safety precautions due to the use of flammable and toxic chemicals.

Diacetylcaffeic acid and oxalyl chloride were used in the initial step, followed by alcoholysis and final de-acetylation using potassium carbonate.

Reaction Scheme

1. Acetylation of Caffeic Acid: Diacetylcaffeic acid reacted with oxalyl chloride.
2. Alcoholysis: The acetylated product reacted with 2-phenylethanol.
3. De-acetylation: The ester underwent de-acetylation to yield CAPE.

Ethyl acetate/methanol/pyridine/petroleum-ether & toluene must always be kept away from any heat, flames or ignitable items as these are highly flammable. Methanol, oxalyl-chloride & petroleum-ether are highly toxic if ingested and extremely toxic to the environment. They should be strictly only disposed of in the (non halogenated organic) waste bin. Any solution which contains oxalyl-chloride should be disposed of in the (halogenated) waste bin, oxalyl-chloride is highly reactive to water. All reagents must and strictly be used within the fume-hood, including all reactions.

Table 1: Synthesis Steps and Chemicals

We weighed 2.0110 g of diacetylcaffeic acid and transferred this in to a pre-weighed 100 cm3 round-bottom flask (60.19g). We then measured (20 cm3) of di-chloromethane and added it to the flask. The flask was clamped into an ice-bath on a hotplate and set to stir with a magnetic stirrer within the flask. The heater was then switched off, The amount of diacetylcaffeic acid was then calculated:

We then added 1.297 mL of Oxalyl-chloride. As the material started to dissolved, the solution reaches (0 0C), 2-drops of di-methylformamide was added and a silica-gel drying tube was placed at the neck of the round bottomed flask. The mixture was then stirred for 2 hrs.

Esterification-Process

At this stage any excess di-chloromethane & oxalyl-chloride were evaporated using a rotary evaporator. The result was a creamy substance at the bottom of the flask. The flask was then weighed for a second time (62.63 g) with a result that the residue weighed: (62.6295g — 60.1890g = 2.4405g). This material was then re-dissolved in 20cm3 of (dry toluene) & 1cm3 of (pyridine) was added. The result was a thick (cloudy yellow/golden) solution. After this, 0.930 mL of 2-phenylethanol was added.

Moles of residue: 8.631818712 x10-3

Moles of 2-Phenyl-ethanol: = moles of residue x 0.9

= 8.631818712 x10-3 x 0.9 = 7.768636841 x10-3 moles

Mass of 2-Phenylethanol = 7.768636841 x10-3 x 122.16 (Mr) = 0.9490166765g

Volume of 2-Phenylethanol = 0.9490166765 / 1.02 g/cm3 used (density) = 0.9304085064 (L)

Volume (ml); Mass/Density = 0.9304085064 x 1000 = 930.4085064 (ml)

Table 2: Synthesis Yields and Observations

We started by removing the solvents via rotary evaporation, the crude esterified product was a milky golden/yellow solid at the bottom. We added 20cm3 of ethyl-acetate to the round bottom flask for the material to redissolve. The solution was then transferred to a 250cm3 separating funnel & 10cm3 more of ethyl-acetate was added to our original round bottom flask, this was to dissolve any remaining material left in the flask. The solution from the original flask was then added to the separating funnel & rinsed with 2x 50cm3 of distilled-water & 2x 50cm3 of brine. This was then dried with magnesium sulphate, the magnesium sulphate was filtered using fluted filter paper. A rotary evaporator was then used to remove the ethyl acetate from the solution. 1.9626g mass of crude material was obtained after drying, and the appearance was a crystallised cream solid.

We carried out a T.L.C of our crude ester with a free-acid, using a 50/50 ethyl-acetate. We calculated the free-acid by the Rf-values from the 2cm T.L.C plate. Prior to our (deacetylation reaction) we had to prime a 5cm T.L.C plate with 5 equally spaced markers to represent the various time in (Mins) starting at: 0:15:30:45:60 mins. We used this plate in tracking the actual reaction. Using a 50cm3 round bottomed flask we added;

The solid material was then dissolved, we spotted the T.L.C at (0 min) and then introduced Potassium-Carbonate K2CO3 to our solution. We continued to add in a magnetic stirrer and stir the solution for 60-mins. We took a sample spot (x5) from our reaction at each of the times and spotted the markers on the 5cm T.L.C plate. Our solution progressively changed appearance from yellow to caramel to a dark brown/coffee colour.

Next we removed any solvents by the rotary evaporator resulting in a solid dark-coloured material left in the flask. We then added 20cm3 (ethyl acetate), swirled it and poured this into a separating funnel. Next, we washed our material twice with 20cm3 water and twice with 20cm3 brine, finally adding magnesium sulphate to dry it out. We prepared a new pre-weighed flask (62.93g) & flute with filter-paper to filter the solution removing the magnesium sulphate. We then placed this solution back onto the rotary evaporator to remove any ethyl-acetate. In the afternoon we placed our material in the Vacuum desiccator for 20mins.

We re-weighed the flask (63.39g), we then calculated the final-product (63.39g-62.93g) = 0.457g. The appearance was a Dark Brown Cape power. Our next step was to perform a the IR (infrared) & MP (Melting Point).

Results Acetylated-CAPE

(Pre) weight of flask = 62.93g

Weight of flask INC Cape3 = 63.39g

Mass (CAPE3) = (63.39 - 62.93) = 0.46g

Results Mass & Moles CAPE-4

Mr of Acetylated CAPE = 284.311

(Pre) weight of flask = 62.93g

Weight of flask INC Cape4 = 63.1344g

Mass (CAPE4) = (63.1344 - 62.93) = 0.2044g

Moles (CAPE4) = Mass/Mr 0.2044/284.311 = 0.00071893 Moles

% Yield (CAPE4) = Moles (CAPE4) / Moles (CAPE3) x100

= 0.00071893/0.0053 x100 = 13.6 %

OVERALL % Yield = Moles (CAPE4) / Moles (CAPE3) x100

= 0.00071893/0.008631818712 x100 = 8.33 %

MP (Melting-Point) Analysis

Our product: CAPE4 =121 0C

The IR was a precise method of examining the Cape and its purities.

T.L.C 2CM Plate & RF Results

Solvent Front = 3.8CM

Rf of Acetylated (CAPE) = 2.2cm RF: 0.579

Rf of Acetylated (CAPE) & Free Acid = 2.1cm RF: 0.553

Rf of Free Acid = 0.1cm RF: 0.0263

Our Rf values showed us there is no free-acid left in our reaction product. We placed the TLC plate to a (short-wavelength) UV-light. All spotting was clearly visible.

Table 3: TLC Results for Reaction Monitoring

T.L.C 5CM Plate & RF Results

Solvent Front = 3.6CM

We can see that 0 (zero) point has greater distance but the measured points thereafter are of similar distance. As our reaction continues over 60 minutes the acetylated-cape dissipates, with just more Cape remaining.

Discussion

Once we had our full results, we can see that our yield was 8.33%. This could have been caused by numerous factors. We were governed by time restraints and limited apparatus, we also only experimented with one route of reaction over others with could improve the yield.

The lab results showed that from starting to finish our yield was reduced consistently through each step. This again could be that material was lost through the steps as we transferred the material from flask to flask. We could limit this by practice of lower volume sized vessels and limiting transfers. Our actual reactions were done over a time that was conducted to comply with learning rather than earning us the best yield of material. If conducting again, we may alter these factors to focus on the most effective time needed to achieve a better yield.

We also did not maintain the most strict conditions in our apparatus and vessels (glassware) as these too could have contributed to impurities being introduced. Water was something again which could have impaired the reaction if not been kept away or vessels were not dried fully.

We observed that we had on conducting rotary evaporation, a magnetic stirrer had been left in the round bottom flask, once removed this would have had material on which was then taken from our reactions effecting our final yield. Another error we noted was that our Stirrer plate was replaced 3 times over our reaction due to infective working equipment. On the last hotplate stirrer we the noticed at the end that the temperature had been raised substantially over the room temperature. This again could have led to increased evaporation and loss of material.

Conclusion

We can conclude that we have successfully carried out the synthesis of Cape. The yield was low due to factors which of some were in our control such as errors of contamination, faulty equipment and there were those which were of environment and time. When we propose any synthesis we cannot discount factors such as efficiency and cost, reaction rate vs time. The skills and knowledge that have been gained by us will only improve us for future experiments and help us to improve our accuracy and quality.

References

1. Sigma-Aldrich. Caffeic Acid Phenethyl Ester.
2. PubMed. Therapeutic Effects of CAPE.