Investigating the role of the geminal dimethyl groups of coenzyme A: Synthesis and studies of a didemethyl analogue

An analogue 2 of coenzyme A (CoA) has been prepared in which the geminal me thyl groups are replaced with hydrogens. An NMR titration study was conduct ed and shifts in frequency of protons in the pantetheine portion of the mol ecule upon titration of the adenine base were observed as has been previous ly reported with CoA. These studies indicate that the geminal dimethyl grou ps are not essential for adoption of a partially folded conformation in sol ution. Based on H-1-H-1 coupling constants, the distribution of conformatio ns about the carbon-carbon bonds in the region of the methyl deletion were estimated. The results suggest that the conformer distribution is similar t o that of CoA, but with small increases in population of the anti conformer s. A simple model compound containing the didemethyl pantoamide moiety was prepared and subjected to similar conformational analysis. The coupling con stants and predicted conformer distribution were almost identical to that o f the CoA analogue, indicating that the conformer distribution is controlle d by local interactions and not influenced by interactions between distant parts of the CoA molecule. The acetyl derivative of 2 was a fairly good sub strate for the acetyl-CoA utilizing enzymes carnitine acetyltransferase, ch loramphenicol acetyltransferase, and citrate synthase, with 1.3- to 10-fold increased K-m values and 2.5- to 11-fold decreases in V-max. The combined results indicate that the geminal dimethyl groups of CoA have modest effect s on function and minimal effects on conformation. (C) 2000 Elsevier Scienc e Ltd. All rights reserved.