Due to the same polarity, it's very difficult to obtain optically pure 1 and 2, so 3 and 4 were designed and prepared to enhance the polarity difference of C24 epimers
. After isolation over silica gel (petroleum ether:ethyl acetate=10/1), suitable crystals of 3 and 4 were obtained from ethyl acetate and acetone, respectively.
Considering the 3[alpha]/[beta]-[[sup.18]F]FCA epimers
, it was found that 3[alpha]-[[sup.18]F]FCA shows a slight, yet significant decrease in time-to-peak of the liver TAC and excretion to gallbladder and intestines proceeded faster.
The ability of the Accucore Vanquish C18+ column to separate the two budesonide epimers
was further optimized by investigating the effect of separation temperature on peak resolution.
 developed a green chemistry method for extraction, chromatography, and derivatization of first-, second-, and third-generation tetracyclines and epimers
from feed samples.
However, pharmacokinetic studies of ginsenosides are challenging, especially for ginsenosides epimers
. Firstly, because of the UV end absorption of ginsenosides, HPLC-UV method detection performed at 200~205 nm usually caused high level of baseline noise.
25-OH Vitamin D is a challenging analyte to accurately measure in human blood due to the presence of 25-OH Vitamin D2, Vitamin D binding proteins, 25-OH Vitamin D metabolites such as 24, 25 (OH)2 Vitamin D, and C-3 epimers
of 25-OH Vitamin D.
Tyrakowska, "The influence of stereochemistry on the antioxidant properties of catechin epimers
," European Food Research and Technology, vol.
2002) and using the chemical shift difference of the diastereomeric protons at C-26 (Agrawal 2005) revealed that compound 1 was a 7:3 mixture of the 25R and 25S epimers
. Compound 1a/b was, therefore, identified as a mixture (7:3, 25R.25S epimers
) of 26-O-[beta]-D-glucopyranosyl-furost-5-ene-3,22,26-triol 3-O-[[alpha]-L-rhamnopyranosyl-(1[right arrow]-3)- [beta]-D-glucopyranosyl-(1[right arrow]2)]-[alpha]-Lrhamnopyranosyl-(1[right arrow]4)-[beta]-D-glucopyranoside (Fig.
For liquid chromatographic separation of the epimers
, different stationary-phase chemistries have been investigated.
Gotlinger, "Resolvins, docosatrienes, and neuroprotectins, novel omega-3-derived mediators, and their endogenous aspirin-triggered epimers
," Lipids, vol.
22R homohopanes are more abundant than 22S epimers
and the 22S/(22S + 22R) homohopane ratio of oil shale samples is very low (Table 6).