Stoltz Lab

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As promised, here are the "recipes" for the chromatography solvents
I told you about, useful for silica gel chromatography of polar
materials. I got them originally from Silvano DeBernardo, a
medicinal chemist in our department here at Wyeth - I don't know
whether he developed them himself or not.

EtOAc : MeCN : MeOH : water (relative volumes, not percentages)

60 : 20 : 20 : 20
60 : 15 : 15 : 15
60 : 10 : 10 : 10
70 : 10 : 5 : 5
70 : 5 : 2.5 : 2.5
70 : 2.5 : 1.25 : 1.25

If streaking occurs, or if you are trying to purify an acid with
limited solubility in these systems, it sometimes helps to add 0.5%
triethylamine.

Silvano feels that one gets better separations doing these columns
under gravity, with a pretty slow flow rate (1-2 drops per second).
I've found this to be true for some compounds, but not for all, and
usually I just do flash chromatography. Either way, it's important
to wash the silica gel well with the solvent (2-4 column volumes),
and throw out the washings.

To pack the column, we make a slurry of silica gel (230-400 mesh) in
the desired solvent, then use this to pack the column under air
pressure. The washing of the column should also be done under
pressure. Then the column can be run either under gravity or air
pressure.

For flash chromatography, you can also use these solvents with the
pre-packed silica gel columns manufactured by Biotage or equivalent.

I don't know whether these solvent systems will work for your
compounds, but they've worked wonderfully for some of the stuff
we've made, including heterocyclic carboxylic acids, and
water-soluble compounds with as many as 2 carboxy and 3 hydroxy
groups. I hope you'll find them useful!