Synthesis and in vitro/in vivo Evaluation of the Antitrypanosomal Activity of 3‐Bromoacivicin, a Potent CTP Synthetase Inhibitor

Abstract

The first convenient synthesis of enantiomerically pure (αS,5S)-α-amino-3-bromo-4,5-dihydroisoxazol-5-yl acetic acid (3-bromoacivicin) is described. We demonstrate that 3-bromoacivicin is a CTP synthetase inhibitor three times as potent as its 3-chloro analogue, the natural antibiotic acivicin. Because CTP synthetase was suggested to be a potential drug target in African trypanosomes, the in vitro/in vivo antitrypanosomal activity of 3-bromoacivicin was assessed in comparison with acivicin. Beyond expectation, we observed a 12-fold enhancement in the in vitro antitrypanosomal activity, while toxicity against mammalian cells remained unaffected. Despite its good in vitro activity and selectivity, 3-bromoacivicin proved to be trypanostatic and failed to completely eradicate the infection when tested in vivo at its maximum tolerable dose.

Exploring the Potent Inhibition of CTP Synthase by Gemcitabine‐5′‐Triphosphate

“…The glutamine amidotransferase cytidine-5'-triphosphate synthase [EC 6.3.4.2;U TP:ammonia ligase (ADP-forming);C TPS] catalyzes the ATP-dependentf ormation of CTP from UTP using either l-glutamine (Gln) or NH 3 as the nitrogen source (Scheme 1). [1] Because this is the sole route for the de novo biosynthesis of the cytosine base, and also in view of the central role of CTP in the biosynthesis of nucleic acids, [2] phospholipids via the Kennedy pathway, [3,4] and sialic acid, [5] CTPS is an attractive target for the development of antiviral, [6,7] antiprotozoal, [8][9][10][11][12][13][14] and antineoplastic agents. [2,15,16] CTPS is also ar ecognized target for immunosuppressivet herapy due to its importance in T-cell proliferation.…”

A Series of Novel Organically Templated Germanium Antimony Sulfides

“…A spacer connects the two moieties, and a hydroxymethyl side chain, linked at the C3 position of the benzodiazepine, is functionalized as a carbamate. For the warhead, we selected the 3‐bromoisoxazoline nucleus, which, as well as the 3‐chloroisoxazoline, was previously exploited for the covalent inhibition of enzymes containing a catalytic cysteine residue, for example, glutamine amidotransferases 17b–d. Derivatives 1 and 2 displayed a time‐independent inhibition of the target enzyme (inhibition constant ( K i ) values in the range of 0.96–4.64 μ M ) 17a…”

Inspired by Nature: The 3‐Halo‐4,5‐dihydroisoxazole Moiety as a Novel Molecular Warhead for the Design of Covalent Inhibitors

“…Acivicin binds to the glutaminase domain of CTPS, irreversibly inactivating the enzyme by mimicking l ‐Gln, the natural substrate. In accordance with such a mechanism of action, the replacement of the chloro with a bromo group to give 3‐bromo‐acivicin led to a threefold increase in the inhibitory potency against CTPS . Interestingly, this translated into a twelvefold increase in the in vitro antitrypanosomal activity, leaving unaffected the toxicity against mammalian cells, resulting in a selectivity index of about 300‐fold.…”

“…In accordance with such am echanism of action, the replacement of the chloro with ab romo group to give 3bromo-acivicin led to at hreefold increasei nt he inhibitory potency against CTPS. [19] Interestingly,t his translated into at welvefold increase in the in vitro antitrypanosomal activity,l eavingu naffected the toxicitya gainst mammalian cells, resultingi naselectivity index of about 300-fold. 3-Bromo-acivicin displayed no acute toxicity in mice at 50 mg kg À1 (intraperitoneal injection) and was also active in an in vivo model of HAT.…”