Abstract: A method of separating compounds, includes: a. tagging at least a first organic compound with a first tagging moiety to result in a first tagged compound; b. tagging at least a second organic compound with a second tagging moiety different from the first tagging moiety to result in a second tagged compound, the first tagging moiety and the second tagging moiety including at least one of a common repeat unit, but having a different number of the repeat units therein, the greater the number of repeat units, the greater the polarity of the tagging moiety; and c. separating the first tagged compound from a mixture including at least the second tagged compound using a chromatographic separation technique based upon differences in the number of repeat units between the first tagging moiety and the second tagging moiety.

Abstract: 17-Arylcarboxylate esters of 9,11-unsubstituted 4-pregnene-17.alpha.,21-diol-3,20-diones are prepared by reaction of the corresponding 17.alpha.-hydroxy derivative with alkyl lithium and an anhydride or acyl halide reagent in the presence of 4-(di-lower alkyl)aminopyridine at low temperatures. A preferred mode of the process is the preparation of 16.beta.-methyl-1,4-pregnadiene-17.alpha.,21-diol3,20-dione 17.alpha.-m-iodobenzoate 21-benzoate, a valuable intermediate in the manufacture of betamethasone.