The citric acid cycle is a series of biological reactions that plays a central role in cell metabolism. The cycle includes dehydration reactions of both malic and citric acids, yielding fumaric and aconitic acids, respectively (all common names). Both proceed strictly by enzyme-catalyzed anti-elimination mechanisms.
Malic Acid ----Fumarase-----> Fumaric Acid
Citric Acid -----Aconitase---> Aconitric Acid
Isocitric Acid: Image: http://upload.wikimedia.org/wikipedia/commons/3/3a/Threo-Ds-isocitrate_wpmp.png
(a)
In each dehydration only the hydrogen identified by an asterisk is removed together with the OH group on the carbon below. Write the structures for fumaric and aconitic acids as they are formed in these reactions. Make sure that the stereochemistry of each product is clearly indicated.
(b)
Specify the stereochemistry of each of these products, using either cis-trans or E,Z notation, as appropriate.
(c)
Isocitric acid (shown above) also is dehydrated by aconitase. How many stereoisomers can exist for isocitric acid? Remembering that this reaction proceeds through anti-elimination, write the structure of a stereoisomer of isocitric acid that will give, on dehydration, the same isomer of aconitic acid that is formed from citric acid. Label the chiral carbons in the isomer of isocitric acid, using R,S notation.
thanks so much for your help.
Sorry about the lack of pictures, in the homework, we were given 2 fischer projections of maleic acid and citric acid. In the maleic acid, the H on the right bonded to the CH has an asterrik next to it. In the citric acid, the H next to the CH has an asterik. Thanks in advance.
Malic Acid ----Fumarase-----> Fumaric Acid
Citric Acid -----Aconitase---> Aconitric Acid
Isocitric Acid: Image: http://upload.wikimedia.org/wikipedia/commons/3/3a/Threo-Ds-isocitrate_wpmp.png
(a)
In each dehydration only the hydrogen identified by an asterisk is removed together with the OH group on the carbon below. Write the structures for fumaric and aconitic acids as they are formed in these reactions. Make sure that the stereochemistry of each product is clearly indicated.
(b)
Specify the stereochemistry of each of these products, using either cis-trans or E,Z notation, as appropriate.
(c)
Isocitric acid (shown above) also is dehydrated by aconitase. How many stereoisomers can exist for isocitric acid? Remembering that this reaction proceeds through anti-elimination, write the structure of a stereoisomer of isocitric acid that will give, on dehydration, the same isomer of aconitic acid that is formed from citric acid. Label the chiral carbons in the isomer of isocitric acid, using R,S notation.
thanks so much for your help.
Sorry about the lack of pictures, in the homework, we were given 2 fischer projections of maleic acid and citric acid. In the maleic acid, the H on the right bonded to the CH has an asterrik next to it. In the citric acid, the H next to the CH has an asterik. Thanks in advance.