A Study of the Substrate and Inhibitor Specificities of AMP Aminohydrolase, 5′-Nucleotidase, and Adenylate Kinase with Adenosine Carboxylates of Variable Chain Length

A series of AMP analogs in which a terminal carboxylate residue, linked to C4′ of the ribose moiety of adenosine by zero, one, or two methylene groups (1, 2 ,3) or by the unsaturated ethylidene link (4) replaces the phosphate anion, is tested for activity as substrates or effectors of three enzymes known to interact with AMP with a different degree of specificity. 2 - 4 are substrates of AMP aminohydrolase, 3 and 4 are competitive inhibitors of adenylate kinase, and all acids produce competitive inhibition of the least specific enzyme, 5′-nucleotidase. These activities can be cor­ related with the intramolecular flexibility of anionic substituent and adenine base which in turn is expressed in typical shifts of the proton magnetic resonance signal of purine H-8. The uronic acid 1, having a rigid molecular conformation, is inactive towards two AMP-dependent enzymes and little active with the third, indicating that this type of compound is not suitable as a nucleotide an­ tagonist whereas nucleoside carboxylates of type 2 and 3 have a higher potential as effectors of nucleotide metabolism.

Strong amide–halothane hydrogen-bonding observed by nuclear magnetic resonance

The widely-used halothane anaesthetic CF3CHBrCl exhibits a proton magnetic resonance signal in CCl4 solution which is strongly deshielded by addition of N-methylpyrrolidone. This is interpreted as a hydrogen-bonding interaction with halothane C—H as donor and carbonyl as acceptor. From the temperature dependence of the halothane C—H proton chemical shift in the presence of varying concentrations of N-methylpyrrolidone, thermodynamic parameters ΔH0 = −4.7 kcal mol−1 and ΔS0 = −14 cal mol−1deg−1 were obtained. The carbon magnetic resonance spectrum of the two components in CCl4 shows desheilding of the carbonyl carbon at higher concentrations of CF3CHBrCl the halocarbons (1-H) undecafluorobicycloheptane and (1-H,4-H)decafluorobicycloheptane show similar H-bonding behaviour which is comparable with that exhibited by CHCl3.These results are discussed in relation to their possible relevance to the mechanism of action of halocarbon anaesthetics.