In acid solution, water can add to the double bond of 2-butenedioic acid to form 2-hydroxysuccinic acid. This reaction is also an important reaction of the tricarboxylic acid cycle in cells, wherein the reaction occurs in neutral solution, so the acid groups are both ionized to the carboxylate form. The reaction is catalyzed by the stereospecific enzyme fumarase that utilizes only the trans form of 2-butenedioate ion (also known as fumarate) and produces only the (S)-2-hydroxysuccinate enantiomer (also known as (S)-malate). Draw the correct stereochemical structures of these two compounds of the fumarase-catalyzed reaction. Be sure to include all hydrogen atoms and show the carboxylates as anions.
1. fumarate (trans-2-butenedioate)
2. (S)-malate ((S)-2-hydroxysuccinate)