Separation of diastereomers

[kaha37]

Hello
I am working on a method to separate a pair of diasteromers with a view to using the method on a semi-prep scale and am struggling to obtain a separation. The diastereomers are eluted (as a single peak) right at the top of my scouting gradient (100% organic) with both MeOH and MeCN as the organic eluent and on both a C18 and C8 column. I do see some resolution running at Aqueous:Organic 1:1 but it takes about 40 minutes and the peaks are nowhere near well enough resolved. Is there something else I can try to improve things or do I need to use normal phase or a totally different column? Any advice would be very much appreciated.
Thanks.

[blackdrum]

If you don't have any chiral preparative column, you should start from normal phase column(silica, cyano) and non-polar mobile phase, for diasteromers separation, silica column sometimes gives good resolution.

[Mattias]

Diasteromers are usually not possible to separate by changing gradient or buffer (as you may have noticed). It is a matter of finding the right column!

I don't think it is possible to predict the behaviours of different columns, so it is an trial-and-error practise. I have had some luck in the past when using Hypercarb columns for this application, could be worth a try.

Anyone used additives in the mobile phase? I know cyclodextrines are sometimes used in CE.

[tom jupille]

The Hypercarb column as suggested by Mattias would probably be my first trial-and-error choice. Another possibility is the Cyclobond (cyclodextrin) column. This is normally sold for chiral, but can have good isomer and diastereomer selectivity as well.

[banala_b]

Hi,
Trial on chiral columns works out for most of diastereomers,I would suggest to try on chiral AG-P column,it worked out previously for me.
Primesep-D has lots os applications in separating positional isomers(diastereomers).Hope u can try on both columns.
Good luck

[AdrianF]

Another possibility is the Luna PFP (PentaFlourylPhenyl) phase which can separate many isomers.

[sfe-co2]

Just to throw in another suggestion: Carbon-clad Zirconia columns. The company is Zirchrom if my memory didn't fail me. Or look up Peter Carr's papers in the literature.

Good luck.

[Kelly Johnson]

We have been very successful with diastereomers and other closely related products on our ZirChrom-CARB product. I would be happy to supply more information directly. Please feel free to contact me directly with any questions.

Kelly Johnson

support@zirchrom.com

[adam]

There are some companies out there that make C30 phases. I have heard that these can also show good shape selectivity: allowing for separation of things like diastereomers.

Kelly: Have you ever done any comparison of how your ZirChrom-CARB works in comparison to these phases.

Anyone: Have any experience using C30 columns to separate compounds with very similar structures.