Best separation technique for natural products

[moumita]

This is my first post on this forum and in fact I am very new to the field of research so I might seem a little lost...my apologies for that.
well, I am working with crude plant extracts and plan to study their bioactive compounds in detail, for which the first step i suppose is to separate and isolate the various phytochemicals...so i am planning to initially go for analytical TLC followed by HPLC. However, I do not know on what basis I should select my solvent system for TLC. I am more interested in isolating the alkaloids, flavanoids and tannins from the crude extracts so kindly suggest the best solvent system for that. Also, because I am from a non chemistry background, i will be grateful if you can suggest some books/journals which i can refer to in regard to the chromatographic techniques used in separation of natural products in particular plant phytochemicals.

Thank You.

[Hollow]

there's no "best" system for plants. It depends on the plants constituents.
So you have to find the one that fits your purposes.


But some suggestions for Literature:

beside the generic basic books about chromatography these sources could be of special interest for you:

Preparative chromatography techniques - Applications in Natural Product Isolation
Kurt Hostettmann, 1997, 2nd Ed., Springer, ISBN-13: 9783540624592

and some Journals:
- Phytochemical analysis
- Journal of Agricultural and Food chemistry
- Phytochemistry

[Jack Silver]

Add Journal of Natural Products to Hollow's list.

For alkaloids, I used to partition the extract in dichloromethane/acidic water (1 N HCL). The alkaloids would be in the aqueous layer as a salt. I would make the water basic and partition again with dichloromethane, the alkaloids would move to the DCM which I evaporated and the compounds could be purified on C18.

Chromatographically, I've written an application note describing the isolation of alkaloids using a strong ion exchange column- found here: http://www.isco.com/WebProductFiles/App ... olumns.pdf

For flavanoids, a similar procedure could be followed with a strong anion exchange column; I've written an application where I've isolated flavones with this technique; it should be posted soon. Send an e-mail to jsilver teledyne.com and I'll send the word file to you. Here's an application note describing other flavanoid methods: http://www.isco.com/WebProductFiles/App ... pounds.pdf

I found tannins to be difficult to work with. I think the SAX column might work, using a diol column as aqueous normal phase might also work.

[MarkK]

I work with tannins on a daily basis. Diol will work for proanthocyanidins (a.k.a. condensed tannins). Run a gradient of acidified MeOH into ACN. Methinks retention is mostly based on H-bonding. As such, elution is dependent upon degree of polymerization or more correctly, degree of hydroxylation. Keep in mind that all diol phases are not created equally. Details of separation upon request.