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Inhibition of folylpolyglutamate synthetase by substrate analogues with an ornithine side chain
Author(s) -
Rosowsky Andre,
Forsch Ronald A.,
Moran Richard G.
Publication year - 1996
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570330457
Subject(s) - chemistry , ornithine , substrate (aquarium) , side chain , stereochemistry , substrate specificity , chain (unit) , biochemistry , combinatorial chemistry , enzyme , organic chemistry , amino acid , arginine , physics , oceanography , astronomy , geology , polymer
N α ‐[4‐[[(4‐Aminopteridin‐6‐yl)methyl]amino]benzoyl]‐L‐ornithine (dAPA‐Orn) was synthesized, and its ability to inhibit folylpolyglutamate synthetase from mouse liver was compared with that of the corresponding 2,4‐diamino analogue APA‐Orn. Also compared were the inhibitory activities of the deaza analogues 5‐deazaAPA‐Orn, 8‐deazaAPA‐Orn, and 5,8‐dideazaAPA‐Orn, as well as those of N α ‐pteroyl‐L‐ornithine (PteOrn) and its deaza analogues 5‐deazaPteOrn and 5,8‐dideazaPteOrn. The inhibition constant K i of dAPA‐Orn was 7‐fold greater than that of APA‐Orn, indicating that the 2‐amino group plays a role in binding to the active site. The binding affinity of the 2,4‐diamino compounds increased in the order 5‐deazaAPA < APA‐Orn <5,8‐dideazaAPA‐Orn < 8‐deazaAPA‐Orn, and that of the 2‐amino‐4(3 H )‐oxo compounds increased in the order 5‐deazaPteOrn < PteOrn < 5,8‐dideazaPteOrn. The most potent inhibitor of both groups was 8‐deazaAPA‐Orn, with a K i of 0.018 μ M , coresponding to an 8‐fold and 15‐fold increase in affinity relative to APA‐Orn and 5‐deazaAPA‐Orn, respectively. The results suggest (a) that the binding of Orn‐containing folylpolyglutamate synthetase inhibitors is affected to a greater degree by replacement of N 8 by a carbon atom than it is by the corresponding change at N 5 , (b) that the effect of carbon for nitrogen replacement is greater in the 2,4‐diamino derivatives than in the 2‐amino‐4(3 H )‐oxo compounds, and (c) that the 2,4‐diamines are the better inhibitors. Comparison of the K i values of the Orn‐containing inhibitors with the K m values of the corresponding glutamate‐containing substrates revealed that K m /K i ratio can vary as much as 100‐fold depending on the nature of the heterocyclic moiety, suggesting that caution should be exercised in using K m values of known substrates to predict K i values of putative inhibitors.