Trialkyl lock

Attachment of phosphopantetheine to proteins is catalyzed by a phosphotransferase that utilizes CoA as the donor. A phosphodiesterase removes the phosphopantetheine, providing a turnover cycle.15, 5b A variety of synthetic analogs have been made.4 16 The reactive center of CoA and phosphopantetheine is the SH group, which is carried on a flexible arm that consists in part of the (3-alanine portion of pantothenic acid. A mystery is why pantoic acid, a small odd-shaped molecule that the human body cannot make, is so essential for life. The hydroxyl group is a potential reactive site and the two methyl groups may enter into formation of a "trialkyl lock" (p. 485), part of a sophisticated "elbow" or shoulder for the SH-bearing arm. 

Reduction of quinone propionic esters or amides 129 bearing three Me groups in the so-called trialkyl lock positions (< -, 0-, P-positions) or hydrolysis of the corresponding phenolic esters 130 has been shown to undergo spontaneous lactonization with the release of alcohol or amine, respectively (Scheme 22).73-75 Several amides... 

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