Sulfur mustard derivatives

Bi- and poly-thioethers with aliphatic backbones are produced by attack of RS on the appropriate haloalkane. This is the method of choice for RS(CH2)raSR (R = Me or Ph),26 MeC(CH2SR)3,27,28 MeS(CH2)raS(CH2)raSMe (n = 2 or 3) and MeS(CH2)raS(CH2) S(CH2) SMe.28,29 [Caution Some of these syntheses involve sulfur mustard derivatives as intermediates - these are very powerful vesicants and should be handled only with extreme care.] The other tridentates RS(CH2)3S(CH2)3SR (R = Et, Pr or Ph) may be obtained from nucleophilic attack by RS on the ditosylate TsO(CH2)3S(CH2)3OTs.30 Tetra-dentate thioethers involving o-phenylene interdonor linkages are also known.31 More recently the preparation and coordination chemistry of the silicon-apex derivative MeSi(CH2SMe)3 has been described.32... 

Another interesting reaction is cyclization with halide elimination. The case of formation of aziridinium rings from A-(2-chloroethyl) derivatives (nitrogen mustards) has been reviewed in Sect. 11.4.2, as was sulfur mustard. The remainder of this subsection is devoted to comparable reactions in which the product is not a strongly electrophilic aziridinium ion, but another ring type. 

The nitrogen mustard analogues are nitrogen derivatives of sulfur mustard, used as poison gas in World War I. Agents include cyclophosphamide, mechlorethamine, chlorambucil, melphalan, ifos-famide, uramustine and estramustine. 

Mechlorethamine (nitrogen mustard Mustargen), a derivative of the war gas sulfur mustard, is considered to be the first modern anticancer drug. In the early 1940s it was discovered to be effective in the treatment of human lymphomas. 

T. A. Connors, "Mechanism of Action of 2-Chloroethyl Derivatives, Sulfur Mustards, Epoxides and Aziridines" in "Antineoplastic and Immunosuppresive Agents" Part II, A. C. Sartorelli and D. J. Johns Eds., Springer-Verlag Berlin-Heidelberg New York, 1975, p. 18. 

LC/MS/MS is an important technique for the analysis of free metabolites and covalent adducts of sulfur mustard in urine and blood. In the case of TDG and TDGO, LC/MS has not yet been able to achieve the LODs obtainable with GC/MS after derivatization. LC/MS/MS has, however, been used successfully to analyze the metabolites (20, 21) derived from an initial reaction of sulfur mustard with glutathione (see Chapter 16). The two metabolites (20), derived from the 3-lyase pathway, can be isolated from urine by SPE on a hydroxylated polystyrene-divinylbenzene polymeric cartridge. Using a sensitive triple sector quadrupole LC/MS/MS system, detection limits of O.lng/ml have been achieved using positive ESI and MRM (56). This provides a useful alternative to GC/MS/MS, which requires reduction of the sulfoxide functions with titanium trichloride. An LC/MS/MS method (detection limit lng/ml) has been developed for the analysis of the hisf N - ace ly I cysteine) metabolite (21) in urine (57). Concentration from acidified urine was achieved on... 

The N7-guanine adduct (22) is a urinary excretion product derived from the reaction of sulfur mustard with DNA. It can be isolated from urine by SPE on C18. GC/MS analysis of the derivatized adduct was problematic. A sensitive method was developed for the underivatized compound using LC/ESI/MS/MS, monitoring the fragmentation MH+, m/z 256 —> [CH2CH2SCH2CH2OH]+, m/z 105 on a triple-sector quadrupole instrument (60). LC separation was on a C18 column eluted with water-acetonitrile-formic acid. The detection limit was 8pg injected (S/N 5 1), 0.2 ng/ml in urine. Rao et al. (61) also reported characterization by LC/ESI/MS but using 25 mM NH4HC03 in 20 % MeOH as eluent. 

Sulfur mustard forms adducts with the blood proteins hemoglobin and albumin. Adducts with histidine residues are the most abundant after exposure of hemoglobin in vitro to sulfur mustard. Analysis of adducted histidine by GC/MS is hampered by poor thermal stability of volatile derivatives. A sensitive method was developed using LC/ESI/MS/MS after... 

Figure 3. Metabolites of sulfur mustard identified by mass spectrometry, derived from an initial reaction with glutathione and metabolized by divergent mercapturic acid and (1-lyase pathways (8)...

Figure 5. Urinary excretion profiles of metabolites derived from hydrolysis and the (5-lyase pathway in the rat following cutaneous application of sulfur mustard (dose = 2 p,mol/animal, data points mean of 4 animals dotted fine = hydrolysis products, solid fine = (5-lyase metabolites). (Reproduced from the Journal of Analytical Toxicology by permission of Preston Publications A Division of Preston Industries, Inc.)...

Figure 7. Scheme for the combined analysis of urine for sulfur mustard metabolites derived from hydrolysis and the... 

Figure 2. N7-Deoxyguanosine adduct of sulfur mustard and derived N7-(2-hydroxyethylthioethyl)guanine (N7-HETE-Gua). (Reprinted from Toxicology and Applied Pharmacology, Vol. 184, D. Noort, H.P. Benschop and R.M. Black, Biomonitoring of Exposure to Chemical Warfare Agents A Review, pages 116-126 (2002), with permission from Elsevier Science.)...

The Army s interim RfD of 7 x 10 mg/kg per day for sulfur mustard was based on an oral two-generation reproductive toxicity study in rats, in which thickening of the forestomach epithelium was observed. The subcommittee agrees that this study is the best available one from which to derive the RfD for sulfur mustard and concludes that the interim RfD for sulfur mustard is scientifically valid. However, the subcommittee recommends adjustments in two of the uncertainty factors used to derive that RfD. Although the adjustments do not change the RfD for sulfur mustard, the subcommittee believes that they are scientifically justified and should be reflected in the Army s supporting documentation for the RfD. 

The major gap in the available information on sulfur mustard is the lack of a chronic oral animal bioassay from which to derive the RfD and... 

THIS CHAPTER contains a brief description of the methods used by toxicologists at Oak Ridge National Laboratory (ORNL) to derive the U.S. Army s interim reference doses (RfDs) for GA, GB, GD, VX, sulfur mustard, and lewisite. Those methods were based on the procedures outlined by the U.S. Enviromnental Protection Agency for Superfund risk assessment guidelines (EPA 1989) and for reference concentrations (EPA 1994). An alternative method, the benchmark-dose (BD) approach (Crump 1984) is also described. Because uncertainty factors are integral to both approaches, further consideration is also given to the statistical distribution and confidence associated with them. 

Because sulfur mustard is the only agent identified in this report as a carcinogen, a description of the derivation of the carcinogenic slope factor is presented in the chapter on sulfur mustard (see Chapter 7). 

The critical study used by ORNL for deriving the RfD for sulfur mustard was a two-generation reproductive study (Sasser et al. 1989a) in which Sprague-Dawley rats (20 males and 27 females per group) were intragastrically intubated with sulfur mustard dissolved in sesame oil at concentrations of 0.03, 0.1, and 0.4 mg/ kg per day. Males and females were dosed for 5 days per week for 15 weeks, including 13 weeks before... 

The study by McNamara et al. (1975) was an inhalation study using rats, mice, rabbits, guinea pigs, and dogs therefore, equivalent oral doses could only be estimated from the data. Because of that, the subcommittee considered the study to be inappropriate for deriving the RfD for sulfur mustard. Furthermore, inhalation of sulfur mustard resulted in lesions to the skin and eyes, which would not be expected from oral exposure. The subcommittee also reviewed the Institute of Medicine s (lOM 1993) evaluation of the health effects of mustard gas and found no other relevant studies with respect to derivation of the RfD. 

Table 7-1 presents the values assigned to the uncertainty factors by ORNL and those recommended by the subcommittee. The product of the factors for deriving the RfD for sulfur mustard is 3,000 for both sets of values. Thus, the subcommittee recommends the same RfD as ORNL for sulfur mustard (7 x 10 mg/kg per day) but notes that slightly different uncertainty factors were used in the calculation. 

In the absence of a chronic bioassay for sulfur mustard, the two approaches described above for estimating an upper limit on the carcinogenic potency give remarkably similar results—1.6 and 5.3 per mg/kg per day for lifetime exposure. Those potency values are less than an order of magnitude lower than the 9.5 per mg/kg per day derived by ORNL (see Table 7-2). That would indicate that the potency estimate of 132 per mg/kg per day relative to BCME (described earlier) is too high... 

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