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Author Topic: diastereomeric excess & diastereomeric ratio definition and calculation  (Read 9561 times)

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excenen

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Hello!

Can you please help me with below definistions:
diastereomeric excess & diastereomeric ratio definition and calculation

And can you please make an example to explain: Diastereomeric purity: >99% de?
And what is the formula to calculate the value?

Thank you so much in advance!!!
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wayne

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Re: diastereomeric excess & diastereomeric ratio definition and calculation
« Reply #1 on: August 06, 2011, 01:41:40 AM »

I think you should know the defination of "diastereoisomers".
http://en.wikipedia.org/wiki/Diastereomer.

Those compouds usually have more than two chiral carbon center, so they have different configurations. They are not mirror images of each other.

diastereoisomers A and B:  A: 98%, B:2%  (mole or  weight percent).
So,
diastereomeric excess (de value):  (98-2)/(98+2) = 96%
diastereomeric ratio  (dr value): 98:2

Diastereomeric purity: >99% de,   
that means the de value:
(A-B)/(A+B)>99%,
maybe:  A:B>99.5:0.5


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excenen

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Re: diastereomeric excess & diastereomeric ratio definition and calculation
« Reply #2 on: August 07, 2011, 11:05:00 PM »

Thanks you very much for your kind *delete me*

What kind of apparatus/devices can be used to ananysis diastereomers?
e.g.:
(3S,4S)-tert-butyl 3-amino-4-hydroxypyrrolidine-1-carboxylate   190792-74-6
(3R,4R)-tert-butyl 3-amino-4-hydroxypyrrolidine-1-carboxylate   330681-18-0
We provided the above 2 compounds to our customers. They need us to provide compounds with [de>99%].
We usually only provide [ee] values(>99%). So is there any idea to get [de%] of the compound with CAS: 190792-74-6
?

Thanks!
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wayne

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Re: diastereomeric excess & diastereomeric ratio definition and calculation
« Reply #3 on: August 07, 2011, 11:37:23 PM »

Thanks you very much for your kind *delete me*

What kind of apparatus/devices can be used to ananysis diastereomers?
e.g.:
(3S,4S)-tert-butyl 3-amino-4-hydroxypyrrolidine-1-carboxylate   190792-74-6
(3R,4R)-tert-butyl 3-amino-4-hydroxypyrrolidine-1-carboxylate   330681-18-0
We provided the above 2 compounds to our customers. They need us to provide compounds with [de>99%].
We usually only provide [ee] values(>99%). So is there any idea to get [de%] of the compound with CAS: 190792-74-6
?

Thanks!
The diastereomers could be separated by silica colume chromatography, and for apparatus to analyse them, HPLC, GC or NMR can be used. It’s more easier to analyse the diastereomers (de value) than enantiomer (ee value).
The compound 190792-74-6 (3S 4S) and the 330681-18-0 (3R 4R) are enantiomers, but, for the comound 190792-74-6 (3S 4S), its diastereomers are (3S 4R) one or (3R 4S) one. If you want to get the relative de values, you can also use HPLC, GC or NMR.
What kind of method did you choose to determine the ee value? This method could also be used to analyse the de value.
Since you have got the high ee value, in most situations, I think the de value of 190792-74-6 is also high.

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