(3β,4α)-1-Benzyl-4-methylpyrazolidine-2,3-dicarboxylic acid 2-ethyl 3-methyl ester C??? ??, ??, ??

(3β,4α)-1-Benzyl-4-methylpyrazolidine-2,3-dicarboxylic acid 2-ethyl 3-methyl ester ?? ?? ? ???

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(3β,4α)-1-Benzyl-4-methylpyrazolidine-2,3-dicarboxylic acid 2-ethyl 3-methyl ester ?? ??