Document zQ3LjBOvo3gJRd5RgyRpD0EL6

rf` [(urgcnm, /Vat: jiical I'ubl. Nn. rdinvase. Sura i. jM., 63, 1115, I Die lung, Hr. J if [; liot vilallium in lIIitcI iican Lhevia [in conjiiiiciimi t l|iie tibia, Cancer 1. |9,95, 1963. 12. I|iLancet, 1, 807, Inn. N. Y- Acad |l Ifico/ Effects of |:,, lids., WHO ,,Publ. No. 8, | on Cancer, iis'oestos, 1ARC Inal Agency for 1)04, 106, 1968. |-oci;r leel disease Irell, V., Gilson, lin Components liianal Institutes I Rapid in vitro I'ornia, 1971. ly the organism, li, 173, 1972. I'mcrs for tissue |tt of lysosomal limore), 7, 10S, I methods, Food IDSomtil enzyme It ljr.\ 9, 59, 1970. i K **** /C i I * 7 CHEMICAL REACTIVITY, UIOTRANSEORM ATION, AND L-. >, M TOXICITY ON POLYCHLORINATED AUI'IIATIC C'OMl'OUNDS N Authors: C, House D. Henschlcr Institute of Toxicology University of Wur/burg Wurzburg, Germany KcftTcc: Horry J. Gohring Toxicology Kosonrcli Luhoraiory iJow Chcinkul Cmiipuny Midland, iMicIng.m INTRODUCTION Chlorinated aliphatic eoinpounds arc released, in increasing number and quantity, into the environment. They arc used on a large-scale basis as industrial solvents, in textile cleaning shops, and as plastic monomers, pesticides, and drugs. Some of the technically important products have long been known as hepatotoxie agents, and single members of the family (like vinyl chloride and vinylidene chloride) have recently been claimed to be carcinogenic; at present, trichloroethylene is also suspected as a potential carcinogen. In addition, several polychlorinated compounds possess a marked persistence in biological and abiotic systems and may accumulate to healththreatening concentrations. The means and degree of metabolic transforma tion of chloiinatcd compounds, which may vary considerably, are influenced to a great extent by the nature of the ehlotine substitution of differ ently hybridized C-atoms. The tendency of the behavior of the compounds under consideration with respect to metabolic and nonmetabolic reactivity can be particularly well demonstrated with poly- and pctchlotusubstiuitinns. Tins report desetibes some aspects of the interrelationship among polychlorinated aliphatics, chlorine substitulion, chemical reactivity, and metabolic fate in biological systems, as well as their toxic properties. The molecular context is emphasized, whereas details of enzyme mechanisms and pathophysio logical aspects of toxic reactions are not dealt with. CENTRAL CONSIDERATIONS ON CHLORINE SUBSTITUTION IN ALIBI!ATIC HYDROCARBONS In general, chlorine substitution provides a dccicasc in the electron density of the involved C-atoms by their electron-attracting inductive effect (-1 effect) which dominates the mesomeric donator effect. In unclear magnetic resonance spectroscopy, the frequency of the resonance of an atomic nucleus depends on the electron density of us environment. The diamagnetic protection by the electrons diminishes the effective magnetic Held at the nucleus. Thus, the shift of the resonance absorption may serve as a criterion for thp electronic influence of substituents.1 Recent publications''5 reveal the possibility of a linear correlation between ^C-NMR shifts and the total electron density of the corresponding C-atoms, f/crv ;3 u as <-o! October 1976 395 fi , -Zit R&S 026692 Thus, the position of the 1 'C'-SMR sip,mils is a measure of the electron-attracting cited of chlorine substitutions in organic molecules. "Ihe electronic shifts indicated in fable I dcaily illustrate that an increase m chlorine substitution induces a decicase in election density at the substituted C'-aioiii; this correlates with a shift ot resonance signals to lower fields. Substitution ol hydrogen by chlorine in alkenes results in a smaller shift of 13C-signuIs than it docs in alkanes. This is probably due to the interaction of the chlorine with the rr-bond. The inductive effect may he dominant in chlorinated alkanes, but m alkenes another effect (magnetic anisotropy, resonance effect) may conttibutc to the shift.3 The mesotneric substitution effect encountered with chlotinc substituents may also be demon strated separately by microwave and radiowave spectroscopy.5,10 One criterion of the mesomeric effect is the bond extension C-Cl which will be submitted in part to some kind of "double-bond character" and tints to a contraction by the participation of /.witter ionic structures. Tims, for example, the bond extension C - Cl is 1.76 A v.'itli alkanes, 1.69 A with alkenes (e.g., vinyl chloride), and 1.63 A with alkynes (e.g., ehloroacetylene). The proportion of the double-bond charactci ol the C-Ci bond, according to nuclear quadrupoie measurements, amounts to 5 to tn the case of vinyi chloride. An enforced electron-attracting effect in connection with steric factors resulting from polychloro- or pcrclilorosubstitution induces decisive changes in reactivity as compared to imsnb'.limted hydrocarbons. In the senes of alkanes, an increasing chlorine substitution with an elongation of the caibon chain results in an enhanced tendency toward destabilization. whiJi leads to C- C fissions or eliminations ol 11C! 01 chlorine with consequent fomiation o! alkenes. On the other hand, alkenes arc stabilized against electrophihe ageuis by increasing chlorine substitu tion: chlorinated olefines arc characterized by an elevated thermal stability. Alkynes, unlike alkenes. are considerably destabilized by chlorine substitu tion. alkanes Cl II --c--c -- The destabilizing effect in chlorinated alkanes is observed with an increase in the number of chlorine and carbon atonis. The steric hindrance of accumulated chlorine substituents, as well as their electron-attracting effect, favors C--C lissions (a. structure below) and eliminations of C). or HC! with the formation of more stable oleftnie com {rounds (b, structure belowj. TABU-. 1 1 ,C*NMI< Shitts of Chlorinated Aliphatic Hydrocarbons (ppm Referring to CSa = 0 ppm)"'11 C, c, c, c, Cll, CM, Cl Cll,Cl, cun, CCI. 194.9 167.7 13X.6 115.6 9G.fi Cll, -Cll, Cti,CI CIt, CIICI, Cll, C'CI,-Cll, CCI, -CCI, CII,-CJI, CIICI Cll, (TV C!t, tM-vCitn nici cis-c'nct cun cct, = nici CCI, - CCI, 186.9 152.9 123 6 96.9 87.3 70.0 66.7 64 : 71.7 7 3.5 67 8 72.1 186.9 174 1 160,3 1-16.5 87.3 70.0 75.4 77,3 7 1.7 7 3.5 75.3 72.1 yi(t < l\C C fllli ! lit ll,-l, \ ill luMml,,,-1 For example, thermal decomposition of dccachlorobutanc (lj renders, by C-C lission, thctiaehloroethylcnc (2) and hcxachlorocthane (3). Under dechlorinating conditions, bexacblorobuladicne (4} may easily be obtained from dccaelilorobutane (l).1 1 rev co, -C'CI. CC|. u) , ca, -~r et, * co, - co, 12) 12) 00,-00-00 cot, (-1) C--A Fission Up to now, investigations on metabolic comer- In the series of substitution with Jn .`nain results in an ^stabilization. which vitiations of IICI or ,:ation of alkcnes. Or. *e Stabilized against eng chlorine substtiucharacleii/cd by an .vnes, unlike alkcnes, nv chlorine substitu- i I t .vlorinatcd alkanes is :n the number of .e stcric hindrance of tents, as well as their ars C-C fissions (a, vons of Cl2 or MCI stable olcfinic Cl II -- C-C -- c =c /\ imposition of de. by C-C fission, -d hexachloroethane editions, hcxachlorobc obtained fioin cct.-cci, * rci,-eci, 12) <31 eei,=cct - cn-cci, to on metabolic conver sions of chlorinated aliphatic hydrocarbons have focused on C, and Cj compounds; higher homolognes of C., and C, units have occasionally been included Regarding the C'i senes (the chlorinated methanes), carbon tetrachloride is converted metabolically to eliloiofortn and CO;.15 eiiloiofoun to CO;,'5 and dtchlommetlianc to CO.'4 A deeper insight into the mechanism of the hcpaloioxicity of cathon tetrachloride was provid ed in 1901 by Butler's who suggested a homolytie C--Cl fission with the formation of trichloroincthyl and chlorine radicals. At present, the most probable subsequent pathoelicinical reaction mechanism is the interaction of the trieliloromethyl radical with unsaturated fatty acid chains, with the formation of chlotofotm and a fatly acid radical. The latter reacts with oxygen and forms peroxides and hydroperoxides which, in turn, induce the decomposition of the fatly acid chains.'6 At the same time, it was recently demonstrated that the hcpatoio.xie activity of Cl / Cl -- c \ Cl Cl / Cl-C \ Cl Carbon tetrachloride forms an enzymesubstrate complex with cytochrome P.,50 of liver rnicrosoincs20 in v.hieh the following sequence of reactions takes place.5 ` CC14 + c --. -CCl, + tCi CCl, +e-------.|CCl/ The complex cytochrome P4S0-iCCI3d may then decompose m the picsence of protons, releasing chloroform as the stable final product. The work of Heppel and Porterfield5 5 has well established that enzymes catalyze the oxidative C--Cl fission of chloimatcd organic compounds in the organism. According to Van Dyke 5i and Van Dyke and Chcnoweth.54 the enzyme system involved shares all relevant properties with mixed function oxidases. It is inducible by phennbarhuu! and benzo-a-pyrene and requires oxygen and NADPil.35 High rates of dechlorination have been found with this enzyme system in the series of chlorinated ethanes; I , 1 -dichloroetiianes ( C 11CI j - C II, ), I ,1 ,2 -1 r i c h I oroe t hane (C11CI; -CTUCI), and 1,1,2,2-letraehlnmeihane (ClIClj -ClIClj). hlltanes with a trichloromelhyi broinnwichlornmviliunc (BrCTl,) is consuleiahly greater than that of CCIj or CIlC'lj.'1 "Iliete is a cot relation between the cytotoxic eltecis produc ed in vitro and in vivo and the boml-dissociation energies for the fission of the three methane derivatives (CIICI3, CCl.,. and UiC'Olj): II -CCl,. 95.7 kcat/mol. Cl-CCl,, 73 keal/mol; Hr-CCl,. 54 keal/mol.16,1 'J a low dissociation energy corresponds to an increased tendency for a homolytie fission to the triehloromcthyl radical. Correspondingly, UrCCI, is considerably more effective than CCIj tn producing a peroxidative breakdown of the microsomal lipids in rat liver.'7 In principle, chlorine-substituted alkanes lend to have radical reaction mechanisms because chlorine substituents are capable of delocalizing the unpaired electron via empty d orbitals of low energy'. Consequently, the resonance energy of the CCl., radical amounts to 8.3 keal/mol (as compar ed to the Cl!j radical = 0). Possible resonance structures of the trichloromelhyi radical are shown below. Cl / Cl -- c \ Cl Cl / Cl. (CC13 - - 9 group [for example, 1,1,1 -trieliloroethane (CCl,--CI l3), 1,1,1,2-ictiachloroethane (CCIj - Cl U C'I), and 1.1,1,2,2-peniaehloroeihane (CCIj --ClIClj >] are characterized by a low ten dency towards oxidative dechlorination; the same is true for tctrachloroclhylene (CCl;-CCD). Accordingly, acute and chronic hcpaloioxicity are high in the fonner and low in the latter group of chlorinated aliphatics.26"58 Elimination of Chlorine The elimination of chlorine with formation of more stable alkcnes represents the second type of metabolic conversion ,sf chlorinated alkanes. This is the main pathway and the first step in the metabolic conversion of pentachloroethane (5y214 and hexachloroethane (fi),'"' leading to the formation of trichloroethylene (7) or tetrachlo/oethylenc (2), respectively, CIICI,- CCl, ~ rla-fr CIICI-CCI, (S) (7) cct,-rn, --iit-Kct.-cct, > (2) October 1976 397 R&S 026693 Ilowcvet, nil :m;i logons mechanism with 1,112.2*U,ii:idiliimclh:ini.' (S) wInch would yield 1,2-diclilonictli) lene (')) could 1101 he demonstrated up to now. The piedoininani pathway in the metabolism of 1.1,2.2-tetiachloroclh:ine (S) goes through the sequence dichloronccialdohydcdicliloroacetic acid ( 10-1 M. while tlie pioducl of nonen/ymaiie dehydtocholoi malion (hj is found only in minor propomon: this reaction is ulieady found in neutral phosphate buffer.'1 In addition, traces of oxidatively formed letrachloroelhyleue (2) are found. CIICI--diet ftv) )( cct.-cct, <-------- ciin.-cnn, ---------- |Ciici,-cho| (:) () tie) cnci-cci, cnci.-cooii CO, Eliirtination of HC1 The elimination of hydrogen chloride Iron) polychlorinated alkanes, leading to olefinic structtircs, tdso represents a major pathway m the metabolism of /;,;/-d iehiorodi phenyl t rich lorocthanc (DDT) (12), with /i./j'-diehlorodiphenylJichloroethylcne (DDT) (13) as the lirsi metabo lite.31 This conversion is additionally catalyzed by the enzyme "DDT-dehydrodtloimase" (h.C. 4.S.I.I.) in the presence of glutathione.33 Cl (12) Cl <c Dchydiochlorinatinns are also discussed as primary metabolic pathways of polychlorinated cyclic alkanes, for example as m the case of 1 ,2,3,4,5,6-he xaelilotocyclohexaiKV1'1 1152****3* *he 7-isomet of II,,Cl,, (14) is convened, by successive dehyrhochlonuatioit, via a 7-|icni:i- clth)loeyclohe.\ene to 1,2,-1-mehioroben/eite ( I 5), 398 ( `A'C` ( i t!u <;/ AVi fnn in //\/t which is then conjugated alter aromatic hydroxylalton.15 <i> AI.KIlNI-S rt (IS) Cl \/ c /\ Considerations on Stability Toly- and pcrchlomsubstitution at sp:-hybrid ized C-atoms in misatnratcd systems increases tiie thermal and chemical stability of these molecules. The -I effect dominates the +M cited ot the clihume substituents, thus resulting in a "depriva tion" of the election density of the double-bond system. This provides, in combination with a steric protective effect of the bulky chlorine substitu ents, an increased stability against electrophilic attack. A gor'd example of this effect is the reaction ol chlorinated eihylencs with ozone. The relative rates of ozom/ation in the series ethylene'vmylchlor;dc:lric-hioioelhylene:retiachloroethylene are 2500:1180:3.6: l.36 Cll, - CH-CH-CH, CCI, -CCI-CCT-CC1, (16) 07) Liquid butadiene (16) (bp^o -S.6C) poly merizes when left open to air for months after some period ol induction; light irradiation acceler ates the reaction. On the other hand, hexachlorubutadienc (17) (b|>7<,u 213C) is stable up to SOO'T and cannot be brought to polymerization by pressure up to 100 atm (17). in addition, is chaiaclcrized by a remarkable chemical stability, similar to the higher homologous stereoisomerie pcrehloiohe\.iiiienes.' ' They are Iaiti> stable against strong mineral acids and aqueous alkali even at high temperatures, hut aie converted to highly chlorinated vmyl ctheis by alcoholic alkali at 80'JC'.1,1 At least the action of turning nitric acid at 1.30J anil arlditional tieaiment with concentrated sulfuitc acid at 170' are nccess.ny to Tnalic hydroxyl- ci Cl (15) at sp*-hybrid 's increases the ::cse molecules, effect of the in a "deprivae double-bond n with a slerie nrinc substitu|J^etroplivlie the reaction of The relative .thylcnc.vinyloethylene are rci-cci=cct, (17) ; -S-b'C) poly months after nation acceler-i. hcxachlorostablc up to : '-ilymerization ,.;t addition, is - ucal stability, 3 .icrcoisoroerie ; fairly stable : ,uucous alkali converted to cohnlic alkali S turning nitric . Ament with necessary to rLJ convert he.vaehlorohiundiciie (17) to dichloromaleic acid anlmlude.'10 II II Cl II Cl Cl II n (IS) Cl II (I Vi n Cl COi Cyclooctotelrenc (IK) (bp7,,u 1-11C). a representative of cyclic polyolelines with alter nating double bonds, is sensitive against light and oxygen. After an extended stay, or acceleration by heating, it convetts ti) a mixture of diineis and resinous substances. The enormous reactivity of the molecule is again demonstrated by the rapid addition of halogens.1,11 1 Attack of oxidants (Oj, KMiiO*. and CrOj) easily results in products with ring contraction. The transition to pentachlorocylooetatetiene (19) and oviachloiocyclooctalctrcne (20) coincides with an increase in thermal and chemical stability. After heating in the pressure tube for 6 hr at 250C. pentachlorocyclooctaietrcne ( 19) can be isolated unchangcJ. With elemental bromine it reacts to a product of the composition C,,IIjCIj Br; .4: Octachlorocyclooctaietrene (20) does not react with ozone or aqueous JOlnO* and cannot be bromtnated under varying conditions. It remains thcrmically stable up to 180t'C.'13,4`' The reason lor this remarkable inertness of the double bonds should be determined in the protection by the accumu lated voluminous chlorine atoms which, per sc, render an electrophilic attack more difticuli due to their - I effect. The validity of the genetal principle of an extraordinary stabilization of nlcfinic systems by poly- and peichlorosubsiitutton may be further demonstrated by some paired examples (Table 2), Metabolism Chlorinated ethylcues are metabolically converted to predominantly C; alcohols and acids A .significant interrelationship has been demon strated between the enhanced stability associated with increasing tutmbets ofchloiine substitutions and the metabolic behavior in biologic systems with all chlorinated ethylenes in the isolated perlused rat livei piep.ii.ition.' 1 ': At a given piehcpatic voiKviili.ilnui ill the ethylenes, a significant use in llic ptopoilinn metabolized was found in the senes tetra-. in-, and cts-'l ,2-diclilomcthylene vinylulene ehloiide. T r.e metabohe changes of chlorinated ethylenes arc initialed with the oxidation to corresponding uxiranes5h In uionooxygenases. Up to now this class of compounds has only found limited interest. The principal reactions ol oxiranes in biological ss stems ate sumnun/cd in figure 1. The main toxic el feels, acme as well as chrome, have been associated with electrophilic reactions with essential eclhilur components I alkylation), whereas the other pathways (reduction, hydrolysis, and conjugation, both enzymatically and nonen/.ymalically) and rearrangements of cntbonylic com pounds jre tonsidcied to be detoxication mechanisms. The type ol' rearrangement in chlori nated ethylenes depends on the number and position of chlorine substuutionis). it goes to either chlorinated aldehydes or acyl chlorides. I c-- R \ c- c / /\ Cl R II. Cl ---- VA / c--c /\ Cl Cl \\ ^ c--c1 -- /I Cl R Further metabolic steps with the rearrangement products aie oxidations or reductions of aldehydes to catboxyiic acids of ethanol derivatives or hydrolyses of acyl chlorides to corresponding acids. With /"rzJll/l/o;^o(7/n'/|i.v, (2), the metabolic foimmion of tricliloioacetic acid (23) can plausibly be explained by the primary formation of an oxtrane (21) and subsequent rearrangement to trichloroacetyI chloride (22) and its hydroly sis.5 'SJ The transition of the oxirane to trichloroacety! ehloiide (2! to 22) is, m analogy, loom! with the tctrachloroetliyloue oxide (2) which can be synthesized by pholooxidalion and which rearranges in vitro in different solvents to iNchloruacelyl chloride.5' Ot tuber 1976 399 R&S 026696 TABI.K 2 Comparison of the Stability ol LmsubMituted and PcrchlorosubMitutcd Cyclic Polyolelines Cl (45) (46) jj Bicyclo-(4,2,0) ot tatrien-( 1,5,7); some hours Stable at room temperature, no tendency to stable at room temperature, rapid poly polymerization, rearranges to aromatic com $ merization at open air pounds at 80BC ?3l ^ 11 1 a (47) CJ V 4 --^ Cl --f Cl 1 ^Cl (48) 3,4`Dimelhylcnceyclnt>utene; rapid poly merization in the pioseme oi h>dn and air Stable in air up to 160C 400 CH(` Cnlu til AVn^u's m I'uxmtlu^y ,Mf, r,; *, -.<,r CCI, -- c \ on (23) ivfwcs ,icncy to _iic coni- TAHI.K 2 (continual) Compariinn of (he Stability of Uniubsiiiuicd and iVrclilormuhMMutaJ Cyclic Polyolefines 11 H Cl Cl 11 11 Hcptafulvcnc; polymerization in Miluiion already at -80DC Cl Cl Stable in air up to 340 (' reaction with cellular macromoleculcs (alkylation) conjugation (glutathione) \ c= c/ /\ oxidation reduction v"\ / c----- c /\ rearrangement I / -C --C `\ hydrolysis OH OH --C -- C -- I'lGURL 1. Synopsis of metabolic conversions and biuloi'ical consequences of to\ication (alkylation) and detoxication I conjugations, hydrolysis, and rearrangement) of alkcnes. Trichloroethylene (7) is metabolically convert ed to trichloroethylene oxide (24) and fnriher converted to chloral,53-5 5 ,5 5,59 In subsequent metabolic reactions, chloral (25) is in part reduced to trichloroethanol (26) or oxidized to trichloro acetic acid (23)/ The real occurrence of the oxiranc (24) as a metabolic intermediate could be substantiated by spectroscopic investigations with the catalytic hemoprotcin l'jS0 of the converting enzyme monooxygenase.61 After administration of 36Cl-labeled trichloro ethylene to cxpeiimental animals, the specific activity remains unchanged in the recovered metabolites trichloroethanol and trichloroacetic acid; no exchange of 36C1 with the chlorine pool of the organism is observed.53 Again, this is indicative of an intramolecular chlorine migration m the course of the transition of trichloroethylene oxide to chloral (24 to 25). Surprisingly, at first glance, the trichloroethylene oxide (24) which can be synthesized from trichloroethylene by photo chemical oxidation63 thermally rearranges (in vitro) mainly to dichloroacctyl chloride (27).63 In vivo, however, no dichloroacciic acid is found as a metabolite.5:'64 Tins remarkable dtlfetcnce has important practical implications. In principle, there arc three possible ways of rearranging the oxiranc of trichloroethylene (24). October 1976 401 SSwSSWS'lAiitVf'IY''1" 'iff J~'" 'f >'f. ... 1 v, ' " V *I 'Si Ilf I if & 1 R&S 026697 Regarding ihc two rearrangements leading to dichloroacetylehloiidc, the hydride shift (2) has low probability, according to investigations by McDonald and Schwab.65 If one postulates that a-ketoenrbonium ions or ton pairs06'68 are transi tion forms of the reairangemenl (a synchronous process cannot, however, positively be ruled out69), the carboniurn ion (which after C--0 hctcrolysis is solely destabilized by one direct, liganded Cl atom) should be indicative ufa favored rearrangement. Way (3) would involve a carboniurn ion with two direct liganded Cl atoms, conseqnently giving a lower dcgiee of probability. Experiments on the behavior of ihc oxirane aic in accordance with this assumption; rearrangement to dichlomacetyl chloride is accelerated by tertiary amines70 winch, after addition of methanol, render dichloioaccttc acid metlryl ester.71 Upon heating to 100 to I40C for 4 hr in a glass tube, the oxirane is converted in high yields (S8%) into diciiloruacctylchloridc, and only a small propor tion of chloral can be delected.6 3 Tile rearrangement of trichloroethylene oxirane to chloral in vino can only be elicited by Lewis acids such as AJCIj m LeClj .5 * Thus, it has been suggest ed that m the living organism ihe '`environment"at the site of I'oi mat ion of the oxirane (24) might poss ess electron acceptor properties and induce the re arrangement in the direction of chloral.51 ,s 2 The most plausible mechanism for the influence of Lewis acid O. -t- C -- CClj / Lewis adds is an interaction with the oxirane (24) at the site where there is a stene opening of the molecule with the oxirane oxygen, with the nearest chlorine atom, or with both, inducing the final rearrangement according tc> shift (3) to chloral (25). a 0 CO oro O) 05 (O 00 102 ( ' ( run o! K 4'171'U`s m `/ii.Vh uhni u VTT  -ri v--. grated by tertiary of methanol, i ester.71 Upon I-*' in a glass tube, I itlds (88%) into a small propor- -thylenc oxirane a by lewis acids ias beensuggest.nvironmcru"at 124)might poss J induce the re: chloral.51 >52 cue influence of o, inducing the shift (3) to / CIICI, -- 011,011 (32) (28) (30) cun, -- c \ (10) \ ettet, -- c (29) (31) C/s- and mins-!J-tUchlorncihvh'ncs (28 and 29) both form the metabolites dichloroethanul (32) and dichloroacetic acid (II) which have been identified in perfusates of the isolated rat liver preparation.51'52 Their foimation can be ex plained by the ptimary intermediate oxiranes (30 (33) (34) The isomeric 1,1-dichtoroeihylcnc (vmvlidcne chloride) (331 is metabolized to monoobloroaeciic acid (36).5'''72 If 1,1 -dichloroethylcru is oxidized with w-chloroperben/.oic acid, only chloroacetyl chloride (35) (the expected rearrangement product of the oxirane) can be isolated. The oxirane itself seems to be extremely unstable and resistive to Cl (11) and 31) and subsequent rearrangement to dichluroacelaldehyde (10), which is then oxidized to dichloroacetic acid (1 1) or reduced to dtchloroethanol (32). The thermal rearrangement of (he oxiranes that occurs with chlorine migration to dichloroacctaldchydc (10) has been demonsttated.66 O / CiLCT -- C \ Cl CII.CI _ c \ OH (35) (36) synthesis under varying conditions.73 However, from these findings it can be speculated that the oxirane (34) is formed as a metabolic intermediate and rearranges spontaneously to chloroacetyl chloride (35). which is subse quently hydrolv/cd to monochloroaceiic acid (36). \ Cl 0 It \/ \/ (38) y CII.CI -- C \ (39) CH.CI -- C (36) R&S 026699 ii -% 'if ! -1 (40) October 1976 403 Monocliloroaectic acid (36) is likewise funm-il as a metabolite ol inoiiinhloriH'ihyliiu: (vinyl cidoiide) (37).74',(l One possible explanation ol (he fomintiun of monocldoio.icelic acid (36) is die primary oxidation ol' nioiiochluroeihylvne (31) In vinyl chloride ox unite (3X), which rearranges id chloroacelaldehyde74 (33) foihmed hy Imlhei metabolic oxidation lo ddoroaceuc acid (36). In analogy, momichloroacelaldehydc (31) is Inmied as a rearrangement piodnct of the uxirane of vinyl cidoiide, which can he synthesized by chloiination of cihylenc oxide (40) in the gaseous phase.77,7" The further metabolic fate of vinyl cidoiide oxirane has been elucidated in [tart. A veiy small proportion of metabolized vinyl chloride is hound covalently to tissue components, as has been Shown in vitro79 and in vivo."0 Major metabolites in vivo arc d-liydroxyetbylcyslcine"1 (4 1), 2-hydioxyethyi-N-acetylcysteine"1 (42). car- box ymciliylcysteine*: (43), and tbiodiacetic acid81'"3 (44). The mechanism of the formation of these conjugates can easily be explained by the previous rearrangement of the oxiianc to chloroacetnldehyde (39) and oxidation to cltloroacetic acid (36) which reacts with glutathione; eatboxymethylgltitatitione is convened to carboxytnethylcysteine (43), and the latter, by further oxi dations, is converted to thindiacetic acid (4-1). Yllner lias identified carboxymcihylcystcinc (43) and thiodineciic acid (44) as the main meta bolites"3 in the urine of mice after dosing with chloroacettc acid. The formation of S-(2-cldoroctiiyl)-cysleine and its N-acetyl conjugate71' as products of simple addition reactions has been questioned;8 1 in fact, this hypothesis is incon sistent with an enzymatic mechanism postulated according to the results of experiments m vto with en/yme inhibitors.74'"0 The formation of a cyclic vinyl chloride peroxide, m equilibrium with an oxiranc-smglel oxygen complex, might account for the obsetved formation of formaldehyde as a decomposition product and oxidation to carbon dioxide, which has been identified in part.m vivo, after metabolic ineorpoiation into urea or methionine and serine.76 Another interesting hypothesis is the addition of vinyl chloride to hydrogen sulllde under formation of brs-(2-ehlorocthyl)-sulfide, which then might account for the formation of thiodiaeelic acid71' (-14); the alky lating intcinicdiaie could be suspected as one of the carcinogenic metabolites of vnnl cidoiide. However, funlier experiments, particularly in iso lated biological systems, are necessary to confirm or reject these assumptions. NH, yj ("it, on -- at,-- s--cti, -- at--c \ (41) on o / Nil --C ''CM, ai.oii--at, -- s --cn,--ni --c \ Oil (42) O Ml, q \ c -- oi, -- s-- at, --cI ii -- cS /\ 110 (43J OH \ c -- cii, -- s -- cn, -- c/ /\ HO (44) oil Mutagenicity and Carcinogenicity Three chlorinated elltylenes exert mutagenic o i Teels: vinyl chloride,4"86 vinyltdene chloride,86 4 7 and trichknuethyleae86 (see Figure 2). The common molecular feature of these compounds is the formation of unsynimctne oxiianes,86,68 the stability of which (as tested In non polar solvents) is far less63 ,73 '71 than that of the others which foim symmetric oxiranes67 ,66 and are not mutagenic. Oxiranes may react m vivo enzymatically or noncnzymatically with Sllcompounds to form nonaetive conjugates."9 On the other hand, the highly electrophilic oxiranes may react directly with nucleophilic constituents of the animal cell as a fust step in a genetoxic effect. If this mechanism is taken to be essential for the mutagenic effects (as has been elucidated in the case of vinyl chloride),65 the interre lationship between symmetry/asymmetry and stabihty/instability of the oxiranes might offer an important rule*" ami possibly a usolul criterion which may be used to measure chemical reactivity and picdict biologic activity (see Figure 3). Vinyl chloride has been demonstrated to be carcinogenic R&S 026700 40*1 CKC Cutnut A' (T/t'U \ 111 Jii\lt uioii V .'sssary to confirm ;n, :ti -- c Cl Cl y c N Cl Cl Cl Cl N/ c=c y Cl H Cl H s C=C s. Cl H HH sy C "C ys Cl Cl H Cl y C =c y Cl H H Cl v C= y H CG3 s I 200 D) F 5& C 100 .xert mutagenic 6 vinylidcnc .'.c86 (see figure .ulurc of tiiese j; unsynmictric ueh (as tested in 77 than that of v oxiranes57'116 .av react in vivo -ily with SI I.njugates.89 On .philic oxirjnes ..:ic constituents tn a gcnctoxic . to be essential ' ocen elucidated . the interrevminelry and might offer an useful criterion mical reactivity mure 3). Vinyl carcinogenic FIGURL 2, Mutagenicity of chlorinated ethylene1: in an m \itro test system. Incubation of the compounds in concentrations (aqueous phase) irom 0.9 to 10.9 ml/ in a metabolic activating microsomal system. Results as percent ol spontaneous (? lOO^) mutation rate m different operon* of the test germ t\ coli K,:: gal', galactose; nrg\ arginine; MIR', methyl tryptophane; nad', NAD.1 h tetrachloro* ethylene -7 -- ,0, trichloro ethylene RH \/\/ /\ cis-1,2dichloroothylene 1,1-dichloroethyleno =GH trans-1,2dichiorocthyicne vinyl chlorido symmetric ml. stablo not mutagonic asymmetric unstable mutagenic FIGURK 3, Moleeulai features of oxidative metabolic intermediates (o\ir,mes) of chlorinated eihylcnes in relation to liieir mutagenic potent til m vitro (see l igurr 2). October 1976 405 $' in humans 0 ami experimental animals.'*1 In high oial doses, iiiehloioethyleiie piodticcs malig nancies in mice.'*1 Vmylidene ehhuidc also has been icported as an animal carcinogen.'*3 ALKYNKS - C- C-ci In general, ehloiine subsliltilitm of sphybridi/.cd C-atoms in olioucs;ui<J acetylenes results in a destabilization of the molecules. Tin's lias been demonstrated with pcrchloioallcnc (45), svhtch is stable only below -SO^C and starls dinieri/.ation from -30'C upwind.94,9 s Sitntlar beltaviot is encountered wilh iiibtomoaUeue, petimmto.tUene, and irichloroallenes svitli electronegative substiItuents.Q t!-*)() 'c=c=c ci-cstc-ci chc-cci-cscn Cl XC1 (45) (46) (47) Oikliloi I'lit'dy lone (*1 "j > is also extiemely icaeuve (explosive) ansi decs'inposos immedi.ucly, in the presence of air, lo phosgene and carhsiti monoxide.1 00 Tin; destabilizing effect of cltlmine substitutions ai \p-liybridi/cii bonds lias also been dcmonsiraicd f(lioLiyrh in a loss intensity) wiili perchloiobutcnyno"11 (-17); tins thermally un stable.' coiiipimiid forms (slowly above iST) a dimer, (',,('!*. The metabolic falc of chlorinated acetyl enes and allcnes has not yet been investi gated- Dichloioacetylcnc which is formed fiom trichloioeihylonc, tetrachloroelhanc(s), or acetyl ene in some working environments produces n highly characteristic symptomatology of acute intoxication; irreversible damage to tltc cranial nerves (predominantly the nervus trigeminus) in humans10* as well as experi mental animals1c*3*10 s and tubular nephro toxicity in animals.104,105 Whether these toxic effects arc due to the reactive dichioroacetylene oi.to metabolites is open to furthei expetimeiuaiion. RIZI-HKUN'CRS 1. Dailey, B. P. and Shooh-ry, J. N., The electron sutluliuujl power of substituent groups,/. Am. Chon. Sue.. 77, 3977, 1955. 2. Tokuhiro, T. and Fraciikcl, G,, Ought of linearity of carbon-13 shift with ih-arge. Calculations lor the a/.ines, /. -4 m. Chon. Soc., 91.5005, 1969, 3. Bloor, J, h. and Breen, L,, Valence shell caieulations on polyatomic molecules. It. 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