Active constituents of Saussurea lappa as protein tyrosine phosphatase 1B inhibitors

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>> Tuesday, November 24, 2009

Protein-tyrosine phosphatases (PTPases) are enzymes that remove phosphate groups from phosphorylated tyrosine on proteins. Among many PTPases, PTP1B plays an important role in inhibition of insulin signaling. These enzymes bind with insulin receptor (IR) and dephosphorylate the beta subunit leading to the inactivation of IR and termination of insulin signal. They are viewed as potent target for the design of various agents in treating type II diabetes and obesity.

Recently, it has been reported that betulinic acid (1), its methyl ester (2) and guaiane sesquiterpenoids: mokko lactone (3) and dehydrocostuslactone (4) from the roots of Saussurea lappa C.B. Clarke have significant PTP1B inhibitory activity. (Molecules, 2009, 14, 266-272; doi:10.3390/molecules14010266).

In this study total 13 compounds were isolated by bioassay-guided fractionation of a MeOH extract of S. lappa root. PTP1B inhibitory activity was performed for all 13 compounds and among them only above mentioned compounds showed the significant PTP1B inhibition ratio as compared to ursolic acid.

1. Dadke, S.; Kusari, J.; Chernoff, J. J. Biol. Chem. 2000, 275, 23642.
2. Johnson, T. O.; Ermolieff, J.; Jirousek, M. R. Nat. Rev. Drug Discov. 2002, 1, 696.

Hydrogenation demonstration

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>> Wednesday, November 18, 2009

Before going to an experimental section, let’s have a brief introduction about hydrogenation. Hydrogenation,  addition of hydrogen atoms to molecules, is used to reduce or saturate various organic compounds. Hydrogen gas is the common source of hydrogen and palladium on activated charcoal (Pd/C), platinum (Adam’s catalyst) and raney nickel are the most common catalyst. Reduction of alkene to saturated alkane is the simplest hydrogenation. Hydrogenation can also be used to reduce alkyne to alkene and finally to alkane. Use of Pd/C results complete reduction of alkyne to alkane whereas less active catalyst like Lindlar catalyst gives alkene.
#Lindlar catalyst: finely divided palladium, precipitated onto calcium carbonate and then deactivated by lead acetate and quinoline.
General mechanism of hydrogenation (of alkene) starts with the adsorption of H2 on the catalyst surface. After that alkene forms the complex with catalyst. Insertion of hydrogen into carbon-carbon double bond occurs and finally saturated alkane releases from the catalyst.
I think I shall stop on introduction part and rather come to the main aim of this post. Actually, I want to show how to setup the hydrogenation reaction using hydrogen balloon and Pd/C catalyst.At first, reagents, solvent and catalyst are kept in the RBF. Before adding catalyst to the solvent be sure to remove the air by flushing with inert gas like nitrogen. Thereafter, one end of the connector is joined to the RBF and another end (opposite to RBF) to the hydrogen balloon. Third outlet is for evacuating the RBF by connecting to the vacuum. Evacuation is repeated for few times and finally the hydrogen gas is passed by opening the upper valve. Evacuation should be done carefully. During my early days, I had bad experience of evacuating the reaction mixture and loosing the compound. The reaction was kept until the completion of starting material (TLC checking). On completion of reaction, Pd/C was removed by filtration through celite, residue washed with appropriate solvent and the filtrate was concentrated to get the desired compound. If necessary, further purification is performed.

Simple but useful laboratory tool: safety disposal can

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>> Saturday, November 14, 2009

It’s been a while since I have posted on this blog. These days I am quite busy concentrating on my lab work and not getting much time to prepare for blog post. However, I am sharing the information about the simple but quite useful tool in the laboratory; SOLVENT DISPOSAL CAN.

I have been looking for good solvent disposal can for a long time. We were using normal galloon with funnel fitted on top. But because of lack of good airtight cap, unusual smell of organic solvents was surrounding the laboratory. Recently, we have new solvent disposal can with leak tight and airtight cap which eliminates this problem.
This is not the only reason we need the well-closed disposal can. Closed disposal can avoids lots of hazard that may occur in laboratory. For e.g. use of closed disposal can prevent escape of various flammable solvents and avoids accidental fire. Expose to organic solvents for long time is harmful for health. Choice of good solvent disposal can saves from these harmful solvent vapors.
Besides, the new disposal can has wire mesh within which stops solid materials entering into it (check out the video).

Fun with chemistry

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>> Sunday, November 08, 2009

I have heard many people complaining chemistry as a boring subject. Hey! just wait, it can be a fun too. Check out the video to find out how it can be so funny? Too hilarious, especially when oxygen was carried away by Hydrogen and water molecule interact with potassium. Even though I got this video long time back, I was not able to share with you guys. So today I am going to share the funny chemistry through this post.

Always going through serious topic? Result: tired.Solution: Let's check out the video and refresh the mind!

PS. It will be great if you leave a comment regarding the funniest part of the video.

Easy way to clean NMR tube

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>> Tuesday, November 03, 2009

Clean NMR tube is one of the factors that determine the fineness of NMR spectra. To clean so many NMR tubes is quite boring. Simple NMR tube solvent jet washer has made the job easy, convenient and fast. Though it looks simple, one can’t ignore it.
The NMR tube solvent jet cleaner is mounted in solvent reservoir. The solvent reservoir is connected to the aspirator (tap water) for generating vacuum. As we can see in the picture, jet cleaner consist of two opening. One is used for putting NMR tube and washing solvent is run through another (image). Generally, tube is washed with distilled water followed by organic solvent (acetone, methylene chloride or chloroform). After washing, NMR tube is taken out, put in flat tray (aluminium foil) and kept in oven for drying (Wilmad-Lab glass recommends 125°C for only 30-45 min). Keeping NMR tube at elevated temperature damage and reshape the tube increasing the camber. It's better to avoid high temperature as much as possible.
Tubes left with samples in them for a long period of time results in more difficult cleaning method. Simple rinsing with water and organic solvent doesn't always remove the degraded or precipitated materials that has been stuck in the inner walls of tube.In such case strong mineral acids such a concentrated nitric acid should be used with precautions.
Check out the video for more understanding.

Process is quite simple but it’s very helpful for those, who are working in the field dealing with NMR. In the same way, I hope this post is helpful for you.

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