Abstract: The invention provides a method for selectively extracting a compound of formula I: ##STR1## wherein: R is hydrogen or --NR.sub.3 R.sub.4 ; and when R=--NR.sub.3 R.sub.4, R.sub.3 and R.sub.4 may be the same or different and are selected from hydrogen and straight or branched (C.sub.1 -C.sub.4)alkyl; R.sub.1 and R.sub.2 may be the same or different and are selected from straight or branched (C.sub.1 -C.sub.6)alkyl; from an aqueous mixture containing a compound of Formula I, its C-4 epimer and its oxidative degradation by-products by adding methylene at a concentration of 2-4 ml of methylene chloride per gram of compound of Formula I and at a pH between pH 6.5-8.0; and obtaining an extract containing methylene chloride, a compound of Formula I, and its C-4 epimer, said epimer being present in an amount of less than 3% of the amount of the compound of Formula I.

Abstract: A process for producing the compound [2S-(2.alpha.,3.beta.,5.alpha.)]-3-methyl-7-oxo-3-(1H-1,2,3-triazol-1-yl-m ethyl)-4-thia-1-azabicyclo[3 2 0]-heptane-2-carboxylic acid, (4-nitrophenyl)methyl ester, 4,4-dioxide, which comprises reacting a solution of azidopenamsulfone, 4-methoxyphenol and vinylpropionate with a solution of bis(trimethylsilyl)acetamide and 4-methoxyphenol is toluene at 80.degree.-100.degree. C. for 18-30 hours followed by filtering the resulting solution and cooling the filtrate to 0.degree.-10.degree. C.