Improved synthesis of V-PYRRO/NO, a liver-selective nitric oxide prodrug, and analogues

Enzyme Mimics for the Catalytic Generation of Nitric Oxide from Endogenous Prodrugs

The highly diverse biological roles of nitric oxide (NO) in both physiological and pathophysiological processes have prompted great interest in the use of NO as a therapeutic agent in various biomedical applications. NO can exert either protective or deleterious effects depending on its concentration and the location where it is delivered or generated. This double-edged attribute, together with the short half-life of NO in biological systems, poses a major challenge to the realization of the full therapeutic potential of this molecule. Controlled release strategies show an admirable degree of precision with regard to the spatiotemporal dosing of NO but are disadvantaged by the finite NO deliverable payload. In turn, enzyme-prodrug therapy techniques afford enhanced deliverable payload but are troubled by the inherent low stability of natural enzymes, as well as the requirement to control pharmacokinetics for the exogenous prodrugs. The past decade has seen the advent of a new paradigm in controlled delivery of NO, namely localized bioconversion of the endogenous prodrugs of NO, specifically by enzyme mimics. These early developments are presented, successes of this strategy are highlighted, and possible future work on this avenue of research is critically discussed.

O2-functionalized methylamine diazeniumdiolates: evidence for E ⇄ Z equilibration in an acyclic system

Diazeniumdiolates that have the structure RHN-N(O)═NOR' are of interest as prodrug (caged) forms of the bioeffectors nitric oxide (NO) and nitroxyl (HNO). Previous work has focused on examples possessing α-branched R groups, with isopropylamine (IPA)/NO (R = isopropyl) being the smallest examined to date. To probe the effect of minimizing the alkyl-group size on the chemistry of IPA/NO, we prepared the corresponding methylamine derivative as a sodium salt that was highly unstable but could be trapped in very low overall yield as the stable O(2)-benzyl derivative. To prepare enough for efficient characterization, we devised an alternate synthesis involving a novel N-dealkylation route. CH(3)HN-N(O)═NOBn, synthesized in high yield and crystallized as the Z isomer as determined by X-ray crystallography, was observed to exist as a 11:1 mixture of two isomeric forms in dynamic equilibrium in solution. Similar results were seen for the O(2)-ethyl derivative, whose two equilibrium constituents were partially separated by HPLC to reveal essentially identical UV and mass spectra, indicating them to be Z and E isomers of CH(3)HN-N(O)═NOEt. The results could lead the way to a fuller understanding of the chemistry of the acyclic (E)-diazeniumdiolates.

Novel protection-deprotection strategies in diazeniumdiolate chemistry: synthesis of V-IPA/NO

Synthesis of previously inaccessible, potentially liver selective HNO donor V-IPA/NO ([iPrHN(3)-N(1)(O(1))=N(2)-O(2)-R], where R = vinyl) is reported here. A novel fluoride-labile TOM group at O-2 in conjunction with MOM protection at N-3 in IPA/NO is employed. The strategy developed is also extended to synthesis of other NO-releasing prodrugs and has applications in diversity-oriented synthesis of HNO- and NO-prodrugs.

The Nitric Oxide Prodrug V-PROLI/NO Inhibits Cellular Uptake of Proline

V-PYRRO/NO is a well studied nitric oxide (NO) prodrug which has been shown to protect human liver cells from arsenic, acetaminophen, and other toxic assaults in vivo. Its proline-based analogue, V-PROLI/NO, was designed to be a more biocompatible form that decomposes to the naturally occurring metabolites of proline, NO, and glycolaldehyde. Like V-PYRRO/NO, this cytochrome P450-activated prodrug was previously assumed to passively diffuse through the cellular membrane. Using (14)C-labeled proline in a competition assay, we show that V-PROLI/NO is transported through proline transporters into multiple cell lines. A fluorescent NO-sensitive dye (DAF-FM diacetate) and nitrite excretion indicated elevated intracellular NO release after metabolism over V-PYRRO/NO. These results also allowed us to predict and design a more permeable analogue, V-SARCO/NO. We report a proline transporter-based strategy for the selective transport of NO prodrugs that may have enhanced efficacy and aid in development of further NO prodrugs with increased permeability.

"Click" reaction in conjunction with diazeniumdiolate chemistry: developing high-load nitric oxide donors

The use of Cu(I)-catalyzed "click" reactions of alkyne-substituted diazeniumdiolate prodrugs with bis- and tetrakis-azido compounds is described. The "click" reaction for the bis-azide using CuSO(4)/Na-ascorbate predominantly gave the expected bis-triazole. However, CuI/diisopropylethylamine predominantly gave uncommon triazolo-triazole products as a result of oxidative coupling. Neither set of "click" conditions showed evidence of compromising the integrity of the diazeniumdiolate groups. The chemistry developed has applications in the synthesis of polyvalent and dendritic nitric oxide donors.