First Non-α-Amino Acid Guanidines Acting as Efficient NO Precursors upon Oxidation by NO-Synthase II or Activated Mouse Macrophages

Abstract

A study of the oxidation of a series of guanidines related to L-arginine (L-Arg) and of various alkyl- and arylguanidines, by recombinant NO-synthase II (NOS II), led us to the discovery of the first non-alpha-amino acid guanidine substrate of NOS, acting as an efficient NO precursor. This compound, 3-(trifluoromethyl)propylguanidine, 4, led to a rate of NO formation (k(cat) = 220 +/- 50 min(-1)) only 2 times lower than that of L-Arg. Formation of 1 mol of NO upon NOS II-catalyzed oxidation of 4 occurred with consumption of 2.9 mol of NADPH, which corresponds to a 52% coupling between electron transfer and oxygenation of its guanidine function. Its oxidation by activated mouse macrophages in an L-Arg-free medium resulted in NO(2)(-) formation that was inhibited by classical NOS inhibitors with a rate only 2-3 times lower than that observed with L-Arg itself. These results open the way toward the research of selective, stable guanidine substrates of NOS that could be interesting, new NO donors after in situ oxidation by a given NOS isoform.

Role of Arginine Guanidinium Moiety in Nitric-oxide Synthase Mechanism of Oxygen Activation

“…The hydrochloride salts of 4,4,4-trifluorobutylguanidine (CF 3 -(CH 2 ) 3 -Gua) 1, 4-fluorobutylguanidine (CH 2 F-(CH 2 ) 3 -Gua) 2, n-pentylguanidine (CH 3 -(CH 2 ) 4 -Gua) 3, cyclopropylguanidine (cyclopropyl-Gua) 4, 4-methoxyphenylguanidine (CH 3 OPh-Gua) 5, 4-fluorophenylguanidine (FPh-Gua) 6, 4-chlorophenylguanidine (ClPh-Gua) 7, 4-trifluoromethylphenylguanidine (CF 3 Ph-Gua) 8, and 4-nitrophenylguanidine (NO 2 Ph-Gua) 9 have been synthesized following general procedures from commercially available amines (46). Their physicochemical characteristics have been described previously (40). See Fig.…”

“…First, the stability and reactivity of the heme Fe II -O 2 species depend on the nature of the L-Arg analogue bound at the active site (41,43). Second, the NADPH/NO ratio was shown to dramatically increase in the presence of these guanidine analogues (40,43). Finally, the NOS catalytic products were extremely diverse, ranging from the specific and efficient release of NO to the predominant production of various ROS (40,43).…”

“…Second, the NADPH/NO ratio was shown to dramatically increase in the presence of these guanidine analogues (40,43). Finally, the NOS catalytic products were extremely diverse, ranging from the specific and efficient release of NO to the predominant production of various ROS (40,43). Consequently, the differences in the physicochemical properties of the guanidine analogues appeared to significantly modify and even alter the NOS catalytic mechanism (41,43).…”

“…In contrast, the loss of such a strong H-bond would decrease the stability of the Fe II -O 2 complex; this is observed with guanidines of families 2 and 3 for which the autoxidation rates increase by 100-fold (Table 2). Thus, the decrease of the guanidinium pK a value can be related to the decrease in NO production by the uncoupling of electron transfer and the associated release of high amounts of ROS (Table 2) (40,42,86).…”

Guanidines from ‘toxic substances’ to compounds with multiple biological applications – Detailed outlook on synthetic procedures employed for the synthesis of guanidines

“…These results opened the way towards the research of selective, stable guanidine substrates of NOS that could be interesting, new NO donors after in situ oxidation by a given NOS isoform. [223] 3.…”