Oxidation prodrugs

Udupi, V., Yu, M., Malaviya, S., Saavedra, J.E., and Shami, P.J. (2006). Js-k, a nitric oxide prodrug, induces cytochrome c release and caspase activation in hl-60 myeloid leukemia cells. Leuk. Res. 30,1279-1283. 

Kitagaki, J., Yang, Y, Saavedra, JJi., Colburn, N.H., Keefer, L.K., and Perantoni, A.O. (2009). Nitric oxide prodrug JS-K inhibits nbiquitin El and kills tumor cells retaining wUd-type p53. Oncogene 28, 619-624. 

Viprostol (81) also incorporates a hydroxy group moved to C-16 and protects this from facile metabolic oxidation by vinylation. It is a potent hypotensive and vasodilatory agent both orally and transdermally. The methyl ester moiety is rapidly hydrolyzed in skin and in the liver so it is essentially a prodrug. It is synthesized from protected E-iodo olefin 78 (compare with 75) by conversion to the mixed organocuprate and this added in a 1,4-sense to olefin 79 to produce protected intermediate 80. The synthesis of viprostol concludes by deblocking with acetic acid and then reesterification with diazomethane to give 81 [19]. 

Nifurtimox, a nitrofuran, is a prodrug that is reduced to unstable nitroanion radicals, which react to produce highly toxic oxygen metabolites, such as superoxide and peroxide. Oxidative stress subsequently kills the parasite, which seems to lack effective enzymatic pathways to detoxify oxygen metabolites. 

Structure 139 represents a cephalosporin conjugate of SIN-1 13 that has been synthesized and evaluated as a /3-lactamase-dependent, nitric oxide-releasing conjugate with potential application in antibody-directed enzyme prodrug therapy (ADEPT) <2003BML1687>. 

Clorazepate, a prodrug, is converted to desmethyldiazepam in the stomach through a pH-dependent process that may be impaired by concurrent antacid use. Several other BZs are also converted to desmethyldiazepam, which has a long half-life and can accumulate, especially in the elderly and those with impaired oxidation. 

Syndonimine /— 0 N-N / + V° R2 p Spontaneous, enhanced by light, oxidants, pH >5 Prodrugs require enzymatic hydrolysis... 

The diazeniumdiolate anions react with electrophiles to produce stable covalent compounds (Fig. 3.9) [213, 216]. These compounds have the ability to act as prodrugs, releasing nitric oxide only when metabolically or enzymatically converted to the diazeniumdiolate anion [217-219]. Several compounds ofthis class have been synthesized by reaction of alkyl or aryl halides, sulfate esters, epoxides, etc. with the ionic diazeniumdiolates [220, 221]. 

The related derivative (79), obtained by thermal rearrangement of the /V-oxide of (78), also exhibits excellent prodrug properties [110], This compound, when administered orally to mice, liberates excellent levels of norfloxacin and is slightly more effective in mouse protection tests than (78) and significantly better than norfloxacin. 

AO is also effective in metabolizing a wide range of nitrogen-containing heterocycles such as purines, pyrimidines, pteridines, quinolines, and diazanaphthalenes (95). For example, phthalazine is rapidly converted to 1-phthalazinone by AO and the prodrug, 5-ethynyl-2-(l//)-pyrimidone, is oxidized to the dihydropyrimidine dehydrogenase mechanism-based inhibitor, 5-ethynyluracil, by AO (Fig. 4.40) (96). 

Metabolic pathways rarely lead to breaking a carbon-carbon bond however, there are exceptions such as the conversion of the prodrug nabumetone to an active nonsteroidal anti-inflammatory agent as shown in Figure 4.84 (153). Although the mechanism of this conversion is unknown, if oxidation leads to two adjacent carbonyl groups it weakens the carbon-carbon bond and further oxidation leads the rupture of this bond. 

There are few drugs that are thioesters, but you may recall that one of the intermediates in the oxidation of aldehydes by aldehyde dehydrogenase is a thioester involving the thiol of the enzyme (Fig. 30 in Chapter 4), which is readily hydrolyzed back to the native form of the enzyme, a thiol, and the carboxylic acid product. Some drugs that are carboxylic acids, such as enaloprilate, are administered as ester prodrugs (enalopril), which are more readily absorbed from the intestine than the carboxylic acid and are then readily hydrolyzed to the active drug by esterases as mentioned in Chapter 1 (Fig. 1 in Chapter 1). 

Based on the idea that pyrrolidines can be metabolized selectively to y-aminobutyric acid derivatives, Wall and Baker [189] developed a retro-metabolic approach with 3-(4-chlorophenyl)pyrrolidine (5.92, Fig. 5.25) as a prodrug for the GABA-ergic agent baclofen (5.93, Fig. 5.25). In vitro studies showed that metabolism of 5.92 yields a pair of isomeric lactam metabolites (5.94, 5.96) and a pair of isomeric amino acid metabolites (5.93, 5.95). The formation of the metabolites resulting from the oxidation... 

The oxidation of dihydropyridine-based chemical delivery systems (CDSs) pioneered by Bodor and co-workers [176] has been discussed in a previous book (Chapt. 13 in [81]). There, we examined the principles by which such compounds function to deliver drugs to the brain. Here, we focus our attention to the last step in the activation of these double prodrugs, namely hydrolysis to release the drug. 

A further condition for good brain delivery, one that is particularly relevant in the present context, is that e) direct hydrolysis of the dihydropyridine pro-prodrug (Fig. 8.14, Reaction c) does not compete with oxidation, especially in the periphery, since this would decrease the amount of CDS available for brain delivery. In fact, the pyridinium metabolite is more susceptible than the dihydropyridine pro-prodrug to alkaline and enzymatic hydrolysis, since the carbonyl C-atom of the pyridinium compound (B, Fig. 8.15) is much more electrophilic than that of the dihydropyridine (A, Fig. 8.15). 

The pharmacokinetic implications of these findings are not straightforward. One important factor that must also be considered is hepatic extraction, which is higher for lovastatin than for its hydroxy acid metabolite [188], Some lactones are useful prodrugs of HMG-CoA reductase inhibitors due to this organ selectivity coupled with the efficiency of enzymatic hydrolysis. However, other factors may also influence the therapeutic response, in particular the extent and rate of metabolic reactions that compete with or follow hydrolysis, e.g., cytochrome P450 catalyzed oxidations, /3-oxidation, and tau-... 

These compounds contain the fragment R as an alkyl or aryl moiety. In other words, they result from the esterification of an alcohol or a phenol with nitrous acid, nitric acid, phosphoric acid, sulfuric acid, or sulfamic acid, respectively. Many of the esters to be examined in this chapter must be activated prior to eliciting their effects, e.g., the organic nitrites and nitrates, which act as donors of nitric oxide or an analogous molecule, and phosphates, which are activated by hydrolysis or even by phosphorylation (antiviral agents). Sulfates are very seldom active or used as prodrugs, but they have significance as metabolites and as industrial xenobiotics. 

Whereas, in imidates, an O-atom is attached to the sp2 C-atom, in another class of imines, the amidines, a N-atom is attached to the sp2 C-atom. Oxidative cleavage of benzamidines has been discussed (Chapt. 5 in [50]). Here, we present studies in which formamidines were examined (N-CH=N-R) as potential prodrugs of anti-HIV cytidine analogues [103]. Specifically, the... 

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