Structure activity relationship of epoxides: different mutagenicity of the two diastereoisomeric 3-bromo-1,2-epoxycyclohexanes

The mutagenic activities in V79 Chinese hamster cells and the alkylating abilities towards nicotinamide of the two diastereisomeric cis and trans-3-bromo-1,2-epoxycyclohexanes were measured and compared with those of unsubstituted 1,2-epoxycyclohexane and bromocyclohexane. trans-3-Bromo-1,2-epoxycyclohexane exhibited a mutagenic activity 2.5 times higher than that of its cis diastereoisomer, but very similar to that of the parent unbrominated epoxide, whereas the electrophilic reactivities towards nicotinamide were very similar for the three epoxides tested. Bromocyclohexane showed the highest toxicity, but no alkylating ability. The presence of an epoxide hydrolase activity in the V79 Chinese hamster cells used in the mutagenesis tests has been demonstrated using safrole oxide as the substrate, cis-3-Bromo-1,2-epoxycyclohexane, but not its trans diastereoisomer, is hydrolyzed by the enzyme present in microsomal preparations from the V79 cells. The results indicate that for the cycloaliphatic compounds examined: (1) the introduction of a bromide substituent at the carbon adjacent to the oxirane ring does not cause an increase in mutagenicity, (2) the relative stereochemical configuration at the above carbon does affect the biological activity and (3) the significantly different mutagenicity of the two diastereoisomeric 3-bromo-1,2-epoxycyclohexanes is not attributable to a different electrophilic reactivity, but could be related to some specific interaction with detoxifying enzymes present in the V79 Chinese hamster cells used in the biological experiments.     

Bacterial mutagenicity investigation of epoxides: drugs,drug metabolites,steroids and pesticides

Although it has been observed that many epoxides are ultimate mutagens, surprisingly little is known about epoxides to which man may be extensively exposed, e.g., physiological compounds, drugs, drug metabolites and pesticides. We have now investigated 35 such and related epoxides for mutagenicity, using reversion of his^?Salmonella typhimurium TA98 and TA100 as biological end-point. None of the tested steroids (12 compounds), vitamin K epoxides (3 compounds) and pesticides (dieldrin, endrin, HEOM (1,2,3,4,9,9-hexachloro-6,7-epoxy-1,4,4a5,6,7,8,8a-octahydro-1,4-methanonaphthalene), heptachlor epoxide) showed any mutagenic activity. Negative results were also obtained with the antibiotics oleandomycin, anti-capsin and asperlin, the cardiotonic drug resibufogenin, the widely used parasympatholytic drugs butylscopolamine and scopolamine, the sedatives valtratum, didovaltratum and acevaltratum, the tranquilizer oxanamide as well as with the drug metabolites carbamazepine 10,11-oxide and diethylstilbestrol α,β-oxide. Three barbiturate epoxides, formed by metabolism of allobarbital, alphenal and secobarbital, caused weak but reproducible mutagenic effects at high concentrations. The cytostatic agent ethoglucide was the only drug having substantial mutagenic activity. Its mutagenic potency was similar to those of the control epoxides styrene 7,8-oxide, p-bromostyrene 7,8-oxide and m-bromostyrene 7,8-oxide, but much lower than those of benzo[a]pyrene 4,5-oxide, benzo[e]pyrene 4,5-oxide and 7,12-dimethylbenz[a]-anthracene 5,6-oxide.Some epoxides were also tested in other Salmonella typhimurium strains or in the presence of rat-liver S9 mix. Positive results were only obtained with compounds that had already been detected as mutagens in the direct test with strain TA100.     

Halogenated epoxides and related compounds as inhibitors of epoxide hydrase

A variety of chlorinated and fluorinated epoxides and related compounds were synthesized and evaluated as inhibitors of epoxide hydrase. The compounds were tested using chicken liver microsomes and a radiometric assay based on [³H]styrene oxide, and using partially purified chicken liver microsomal epoxide hydrase and a continuous photometric assay based on p-nitrostyrene oxide, whose hydration could be monitored at 310 nm. For the 16 compounds studied both assays gave similar patterns of inhibitory activity. As expected from the relative K_m values of the two substrates, all inhibitors were considerably more active against styrene oxide (K_m =1.0 mM) than against p-nitrostyrene oxide (K_m = 4.2 μM), and styrene oxide was a weak alternate-substrate inhibitor against p-nitrostyrene oxide. 1,1,1-Trichloropropene oxide, however, was a potent alternate-substrate inhibitor against p-nitrostyrene oxide. Addition of various substituents to the α-carbon of styrene oxide generated a series of compounds whose inhibitory potency toward p-nitrostyrene oxide increased in the order H ≈ CF₃ < CH₃ < CH₂Cl < CHCl₂ < CCl₃ ≈ 1,1,1-trichloropropene oxide. In contrast, addition of a CH₃ or CCl₃ group to the β-carbon of styrene oxide resulted in only a modest increase in inhibitory potency. 2-Phenyl- and 3-phenyloxetane showed no pronounced inhibitory activity toward either styrene oxide or p-nitrostyrene oxide, but pentafluorophenyl ethylene oxide and 1,1, 1-trichlorobutane-3,4-oxide were moderately active inhibitors, although significantly less potent than 1,1,1-trichloroproene oxide. These results show that electronegativity, steric effects, and hydrophobic effects are each important in governing the interaction of epoxide hydrase substrates with the enzyme, although it is not yet possible to analyze separately the effects of each of these parameters on K_m, V, and the catalytic mechanism.     

Biocatalysis of nitro substituted styrene oxides by non-conventional yeasts

Yeast strains (410) from more than 45 different genera were screened for the enantioselective hydrolysis of nitro substituted styrene oxides. These strains included 262 yeasts with known epoxides hydrolase activity for various other epoxides. Epoxide hydrolase activity for p-nitrostyrene oxide (pNSO) (177 strains) and m-nitrostyrene oxide (mNSO) (148 strains) was widespread in the yeasts, while activity for o-nitrostyrene oxide (oNSO) was less ubiquitous (22 strains). The strains that displayed enantioselectivity in the hydrolysis of one or more of the nitro substituted styrene oxides (35 strains) were also screened against styrene oxide (SO). Rhodosporidium toruloides UOFS Y-0471 displayed the highest enantioselectivity for pNSO (ee 55%, yield 35%) while Rhodotorula glutinis UOFS Y-0653 displayed the highest enantioselectivity for mNSO (ee >98%, yield 29%), oNSO (ee 39%, yield 19%) and SO (ee >98%, yield 19%). (R)-Styrene oxide was preferentially hydrolysed to the corresponding (R)-diol with retention of configuration at the stereogenic centre. In the case of the nitro substituted styrene oxides the absolute configurations of the remaining epoxides and the formed diols were not established.     

An approach based on liquid chromatography/electrospray ionization-mass spectrometry to detect diol metabolites as biomarkers of exposure to styrene and 1,3-butadiene

Styrene and 1,3-butadiene are important intermediates used extensively in the plastics industry. They are metabolized mainly through cytochrome P450-mediated oxidation to the corresponding epoxides, which are subsequently converted to diols by epoxide hydrolase or through spontaneous hydration. The resulting styrene glycol and 3-butene-1,2-diol have been suggested as biomarkers of exposure to styrene and 1,3-butadiene, respectively. Unfortunately, poor ionization of the diols within electrospray mass spectrometers becomes an obstacle to the detection of the two diols by liquid chromatography/electrospray ionization-mass spectrometry (LC/ESI-MS). We developed an LC/ESI-MS approach to analyze styrene glycol and 3-butene-1,2-diol by means of derivatization with 2-bromopyridine-5-boronic acid (BPBA), which not only dramatically increases the sensitivity of diol detection but also facilitates the identification of the diols. The analytical approach developed was simple, quick, and convincing without the need for complicated chemical derivatization. To evaluate the feasibility of BPBA as a derivatizing reagent of diols, we investigated the impact of diol configuration on the affinity of a selection of diols to BPBA using the established LC/ESI-MS approach. We found that both cis and trans diols can be derivatized by BPBA. In conclusion, BPBA may be used as a general derivatizing reagent for the detection of vicinal diols by LC/MS.     

Correlation of alkylating and mutagenic activities of allyl and allylic compounds: Standard alkylation test vs. kinetic investigation

Thirty-nine allylic and non-allylic compounds have been tested in the standard 4-(p-nitrobenzyl)pyridine (NBP) alkylating procedure and the Salmonella typhimurium mutagenicity assay. Fourteen of these were found directly mutagenic (without addition of S-9 mix activating enzyme system). With twelve of these compounds, a good correlation of alkylating and mutagenic potencies was established; the remaining two do not meet the chemical conditions of the NBP procedure on account of HCl elimination with these two compounds. The other 25 substances were inactive in both systems. The quantitative correlation proved to be almost linear in the lower activity ranges (E ～ 2; revertants/μmol ～ 600). The reasons for some deviations from the linear relationship have been analyzed and discussed on the basis of structural features. In addition to the standard alkylation test, a modified NBP-test was performed in order to obtain kinetic data and activation energy values. The results with 6 representative allylic compounds show that the overall correlation is not substantially improved above that of the standard procedure; nonetheless, additional information on reaction characteristics is obtained with some substances.     

Metabolism of Styrene Oxide and 2-Phenylethanol in the Styrene-Degrading Xanthobacter Strain 124X

Styrene oxide and 2-phenylethanol metabolism in the styrene-degrading Xanthobacter sp. strain 124X was shown to proceed via phenylacetaldehyde and phenylacetic acid. In cell extracts 2-phenylethanol was oxidized by a phenazine methosulfate-dependent enzyme, probably a pyrroloquinoline quinone enzyme. Xanthobacter sp. strain 124X also contains a novel enzymatic activity designated as styrene oxide isomerase. Styrene oxide isomerase catalyzes the isomerization of styrene oxide to phenylacetaldehyde. The enzyme was partially purified and shown to have a very high substrate specificity. Of the epoxides tested, styrene oxide was the only substrate transformed. The initial step in styrene metabolism in Xanthobacter sp. strain 124X is oxygen dependent and probably involves oxidation of the aromatic nucleus.     

Mutagenic effect of furocoumarin monoadducts and cross-links on bacteriophage lambda

The mutagenicities of 17 closely related oxiranes were determined in 4 tester strains (Salmonella typhimurium TA98, TA100, TA1535, TA1537). The test compounds comprised all possible oxides of benzene and its partially hydrogenated congeners. In TA100 and TA1535, 12 of the tested oxiranes were weak to moderate mutagens. 4 of these were also active in TA98. No mutagenicity was observed with the remaining 5 compounds in any of the 4 strains.The presence of a double bond in formal conjugation with the epoxide ring increased the mutagenicity relative to that of the saturated oxirane. Interestingly, additional epoxide rings within the same molecule did not markedly increase the mutagenic activity, and for the oxiranes that are not activated by a double bond, the relationship between mutagenic activity and the number of epoxide rings in the molecule was even inverse.The influence of bromo and hydroxyl substitution on oxirane mutagenicity is discussed. Most notably, a compound having a 4-hydroxyl group in syn position to a 1,2-epoxide ring fused to the cyclohexane ring, a structure which has been suggested to increase the electrophilic reactivity of dihydrodiol epoxides through hydrogen bonding, was almost inactive.     

Mutagenicity of styrene and styrene oxide

Incubation of S. typhimurium strain TA 1535 with styrene increased the number of his⁺ revertants/plate in presence of a fortified S9 rat-liver fraction. Styrene was also highly cytotoxic for Salmonella cells. Styrene oxide, the presumed first metabolite, had a mutagenic effect towards strains TA 1535 and TA 100 both with and without metabolic activation. Styrene is probably mutagenic because it is metabolized to styrene oxide.     

Cytogenetic and antineoplastic effects by newly synthesised steroidal alkylators in lymphocytic leukaemia P388 cells in vivo

Volatile organic compounds (VOCs) exert their carcinogenic activity through the production of epoxide metabolites. Because of their high reactivity some epoxides are also produced in the chemical industry for the synthesis of other compounds. Therefore, human exposure to VOCs epoxides does occur and may be an important human health concern. In this study, the in vitro genotoxic potential of epoxides originating from 1,3-butadiene (3,4-epoxy-1-butene: EB; 1,2:3,4-diepoxybutane: DEB), isoprene (3,4-epoxy-2-methyl-1-butene: IO), styrene (styrene-7,8-oxide: SO), propylene (propylene oxide: PO) and 1-butene (1,2-epoxy-butane: BO) in human peripheral blood mononuclear cells (PBMCs) and promyelocytic leukaemia cells (HL60) was measured with the comet assay (single-cell gel electrophoresis, SCGE). The effect of inclusion of foetal calf serum (FCS, 5%) in the cell-culture medium and different durations of exposure (2h, 24h) were also investigated. All epoxides tested produced DNA damage in a concentration range that did not reduce cell viability. HL60 cells were more resistant than PBMCs to the DNA damage induced by the different epoxides. With the exception of IO, the treatment for 24h resulted in an increase of DNA damage. FCS slightly protected PBMCs from the genotoxic effects induced by IO and BO, whilst no such effect was noted for the other compounds. Overall, the dose-dependent effects that were seen allowed us to define a genotoxicity scale for the different epoxides as follows: SO>EB>DEB>IO>PO>BO, which is in partial agreement with the International Agency for Research on Cancer (IARC) classification of the carcinogenic hazards.     

Mutagenicity of the phenacetin metabolites: N-hydroxy-p-phenetidine and nitrosophenetol in S. typhimurium TA100 and derivatives deficient in nitroreductase or O-acetylase: probes for testing intrabacterial metabolic activation

Two mutagenic metabolites of phenacetin, p-nitrosophenetol and N-hydroxy-p-phenetidine, were tested in S. typhimurium strains TA100, its nitroreductase-deficient derivative TA100NR, and O-acetylase-deficient strains TA100 Tn5-1-8-DNP1011 and -DNP1012 in the presence or absence of an exogenous metabolic activation system. The results indicate that bacterial nitroreductase(s) and O-acetylase(s), shown to be involved in the conversion of certain nitroarenes, are not required for the intrabacterial activation of the two phenacetin metabolites to bacterial mutagens. In view of the low reactivity of nitrosoarenes towards nucleophiles at neutrality, the mechanism by which they exert such a high mutagenic effect in S. typhimurium strains remains to be clarified, but is discussed.     

Studies on glutathione-S-arene oxidase transferase. A sensitive assay and partial purification of the enzyme from sheep liver

A sensitive assay has been devised for glutathione-S-arene oxidase transferase using as substrates naphthalene-1,2-oxide or styrene oxide along with [³⁵S]glutathione. Activity of the order of 2–3 nmoles of conjugate formed during a 5-min incubation can be detected. This yields about 2000 cpm above a blank of about 1500 cpm. Transferase activity was found mainly in liver and kidney but was also present in most other tissues of rats. Glutathione-S-arene oxide transferase has been purified 70- to 80-fold from sheep liver 100,000 g supernatants using the conventional procedures. After electrofocusing, enzyme activity separated into two major peaks and two or three minor peaks, ranging in isoelectric point from pH 6.5 to 7.5. Activities assayed with naphthalene-1,2-oxide or styrene oxide as substrates were found to almost parallel each other in all the peaks.The sheep liver transferase required neither metal ions nor cofactors such as FAD, pyridoxal-phosphate and thiamine pyrophosphate. The molecular weight of the transferase has been estimated to be about 40,000.K_m values for glutathione, naphthalene-1,2-oxide, and styrene oxide are 1.6, 0.11, and 0.13 mm, respectively. K_m values for glutathione decreased with increasing pH, whereas the K_m values for naphthalene-1,2-oxide were independent of pH in the range of 6.5–8.     

Induction, activation and inhibition of epoxide hydrase: an anomalous prevention of chlorobenzene-induced hepatotoxicity by an inhibitor of epoxide hydrase

Epoxide hydrase activity, measured with [³H]styrene oxide as substrate, is present in mammalian liver, kidney, lung, intestine and skin. The hepatic level of the enzyme, measured in vitro with [³H]styrene oxide, benzene oxide or naphthalene-1,2-oxide, is elevated substantially by pretreatment of rats with phenobarbital and to a lesser extent by pretreatment with 3-methylcholanthrene. Metyrapone and 1-(2-isopropylphenyl)-imidazole, two monooxygenase inhibitors, activate epoxide hydrase in vitro, but have no demonstrable effect on the enzyme in vivo. 3,3,3-Trichloropropene oxide, a potent in vitro inhibitor of epoxide hydrase, has no effect on monooxygenase activity measured in vitro with [³H]benzenesulfonanilide. Trichloropropene oxide is extremely toxic. In sub-lethal dosages, it does not significantly inhibit epoxide hydrase activity in vivo, although it and several other epoxides do react with and thereby reduce hepatic levels of glutathione. Cyclohexane oxide, another potent in vitro inhibitor of epoxide hydrase, reduces hepatic glutathione levels to 10% of control values. This relatively non-toxic substance should potentiate the hepatotoxicity of chlorobenzene by inhibiting further metabolism of the toxic chlorobenzene oxide intermediate through either hydration or conjugation with glutathione. Instead, co-administration of cyclohexene oxide and chlorobenzene significantly reduces the rate of metabolism of [¹⁴C]chlorobenzene and prevents the hepatic centrilobular necrosis caused by chlorobenzene in rats. Arene oxide-mediated hepatotoxicity apparently is dependent upon a variety of factors including both rates of formation and degradation of arene oxides in tissue. The presently known hydrase inhibitors are not sufficiently selective in their effects on liver cells to permit a quantitative assessment of the relative importance of these factors.     

Biosynthesis of (R)-phenyl-1,2-ethanediol from racemic styrene oxide by using bacterial and marine fish epoxide hydrolases

Enantio-convergent hydrolysis of racemic styrene oxides was achieved to prepare enantiopure (R)-phenyl-1,2-ethanediol by using two recombinant epoxide hydrolases (EHs) of a bacterium, Caulobacter crescentus, and a marine fish, Mugil cephalus. The recombinant C. crescentus EH primarily attacked the benzylic carbon of (S)-styrene oxide, while the M. cephalus EH preferentially attacked the terminal carbon of (R)-styrene oxide, thus leading to the formation of (R)-phenyl-1,2-ethanediol as the main product. (R)-Phenyl-1,2-ethanediol was obtained with 90% enantiomeric excess and yield as high as 94% from 50 mM racemic styrene oxides in a one-pot process.     

Cloning and characterization of a microsomal epoxide hydrolase from Heliothis virescens

Epoxide hydrolases (EHs) are α/β-hydrolase fold superfamily enzymes that convert epoxides to 1,2-trans diols. In insects EHs play critical roles in the metabolism of toxic compounds and allelochemicals found in the diet and for the regulation of endogenous juvenile hormones (JHs). In this study we obtained a full-length cDNA, hvmeh1, from the generalist feeder Heliothis virescens that encoded a highly active EH, Hv-mEH1. Of the 10 different EH substrates that were tested, Hv-mEH1 showed the highest specific activity (1180 nmol min^?1 mg^?1) for a 1,2-disubstituted epoxide-containing fluorescent substrate. This specific activity was more than 25- and 3900-fold higher than that for the general EH substrates cis-stilbene oxide and trans-stilbene oxide, respectively. Although phylogenetic analysis placed Hv-mEH1 in a clade with some lepidopteran JH metabolizing EHs (JHEHs), JH III was a relatively poor substrate for Hv-mEH1. Hv-mEH1 showed a unique substrate selectivity profile for the substrates tested in comparison to those of MsJHEH, a well-characterized JHEH from Manduca sexta, and hmEH, a human microsomal EH. Hv-mEH1 also showed unique enzyme inhibition profiles to JH-like urea, JH-like secondary amide, JH-like primary amide, and non-JH-like primary amide compounds in comparison to MsJHEH and hmEH. Although Hv-mEH1 is capable of metabolizing JH III, our findings suggest that this enzymatic activity does not play a significant role in the metabolism of JH in the caterpillar. The ability of Hv-mEH1 to rapidly hydrolyze 1,2-disubstituted epoxides suggests that it may play roles in the metabolism of fatty acid epoxides such as those that are commonly found in the diet of Heliothis.     

Substrate range and enantioselectivity of epoxidation reactions mediated by the ethene-oxidising Mycobacterium strain NBB4

Mycobacterium strain NBB4 is an ethene-oxidising micro-organism isolated from estuarine sediments. In pursuit of new systems for biocatalytic epoxidation, we report the capacity of strain NBB4 to convert a diverse range of alkene substrates to epoxides. A colorimetric assay based on 4-(4-nitrobenzyl)pyridine) has been developed to allow the rapid characterisation and quantification of biocatalytic epoxide synthesis. Using this assay, we have demonstrated that ethene-grown NBB4 cells epoxidise a wide range of alkenes, including terminal (propene, 1-butene, 1-hexene, 1-octene and 1-decene), cyclic (cyclopentene, cyclohexene), aromatic (styrene, indene) and functionalised substrates (allyl alcohol, dihydropyran and isoprene). Apparent specific activities have been determined and range from 2.5 to 12.0 nmol min^?1 per milligram of cell protein. The enantioselectivity of epoxidation by Mycobacterium strain NBB4 has been established using styrene as a test substrate; (R)-styrene oxide is produced in enantiomeric excesses greater than 95%. Thus, the ethene monooxygenase of Mycobacterium NBB4 has a broad substrate range and promising enantioselectivity, confirming its potential as a biocatalyst for alkene epoxidation.     

Synthesis and evaluation of nitric oxide-releasing derivatives of 3-n-butylphthalide as anti-platelet agents

Most ischemic stroke results from brain blood vessel blockage by platelet-mediated thrombus, and anti-platelet therapy has been demonstrated clinical benefits in the treatment of this disease. In the present work, novel nitric oxide (NO)-releasing derivatives of an anti-ischemic stroke drug 3-n-butylphthalide (NBP) were synthesized. Compounds 7a and 7c exhibited more potent anti-platelet activity than NBP and aspirin, and released a moderate amount of NO, which is beneficial in improving cardiovascular and cerebral circulation. These findings provide an alternative approach to the development of drugs more potent than NBP for the intervention of ischemic stroke.     

Nuclear metabolism. II. Further studies on epoxide hydrolase activity

Apparent K_m- and V_max-values of nuclear styrene 7,8-oxide hydrolase were determined at different protein concentrations. In the protein concentrations range used no significant differences in the apparent K_m-values were observed. The influence of the incubation with different modifiers (i.e. SKF-525A, metyrapone, 1,2-epoxy-3,3,3 trichloropropane, cyclohexene oxide) at two different concentrations on this enzyme activity was also determined. Cyclohexene oxide and 1,2-epoxy-3,3,3-trichloropropane, two well known inhibitors of the microsomal epoxide hydrolase(s) caused a marked inhibition, metyrapone had a strong activating effect whereas SKF-525A had no effect. In vivo pretreatment with phenobarbital significantly induced the nuclear epoxide hydrolase whereas β-naphthoflavone caused a lower degree of induction. This pattern is quantitatively different but qualitatively very similar to the microsomal one. Moreover a toxifying to detoxifying enzymatic activity balance is attempted for the metabolization of the alkenic double bond of styrene, taking into account the ratio between the styrene monooxygenase (toxifying enzyme) and the styrene 7,8-oxide hydrolase (detoxifying enzyme) after the above mentioned pretreatments, both in the microsomal and nuclear fractions.     

Production of Monoclonal Antibodies Specific for the i and 1,2 Flagellar Antigens of Salmonella typhimurium and Characterization of Their Respective Epitopes

Salmonella typhimurium expresses two antigenically distinct flagellins, each containing a different H antigen (i and 1,2), the combination of which is highly specific for this serotype. In this study, overlapping recombinant flagellin fragments were constructed from the fliC (H:i) and fljB (H:1,2) flagellin genes, and the expression products were tested for binding to H antigen-specific monoclonal and polyclonal antibodies. A minimal area, 86 amino acids for H:i and 102 amino acids for H:1,2, located in the central variable domain of each flagellin was required for the binding of serotype-specific antibodies, providing further evidence for the presence of a discontinuous H epitope. Two peptides comprising these areas were shown to be highly suitable for application as antigens in an enzyme-linked immunosorbent assay detecting S. typhimurium-specific antibody.     

2D Holodirected lead(II) bromide coordination polymers constructed of rigid and flexible ligands

Three new 2D Pb^II coordination polymers containing 4,4′-bipyridine (4,4′-bipy), 1,2-bis(4-pyridyl)ethane (bpa) and 1,2-bis(4-pyridyl)ethene (bpe) with bromide anions, [Pb(μ-4,4′-bipy)(μ-Br)₂]_n (1), [Pb(μ-bpa)(μ-Br)₂]_n (2) and [Pb(μ-bpe)(μ-Br)₂]_n (3) have been synthesized and characterized by elemental analysis, IR spectroscopy and their structures studied by X-ray crystallography. The thermal stability of compounds 1-3 was studied by thermal gravimetric (TG) and differential thermal analyses (DTA). The single-crystal X-ray data shows that the Pb²⁺-ions have coordination numbers of six and contain the rarely holodirected geometries.