Phenanthrene epoxide

Methods for the synthesis of the biologically active dihydrodiol and diol epoxide metabolites of both carcinogenic and noncarcinogenic polycyclic aromatic hydrocarbons are reviewed. Four general synthetic routes to the trans-dihydrodiol precursors of the bay region anti and syn diol epoxide derivatives have been developed. Syntheses of the oxidized metabolites of the following hydrocarbons via these methods are described benzo(a)pyrene, benz(a)anthracene, benzo-(e)pyrene, dibenz(a,h)anthracene, triphenylene, phen-anthrene, anthracene, chrysene, benzo(c)phenanthrene, dibenzo(a,i)pyrene, dibenzo(a,h)pyrene, 7-methyl-benz(a)anthracene, 7,12-dimethylbenz(a)anthracene, 3-methylcholanthrene, 5-methylchrysene, fluoranthene, benzo(b)fluoranthene, benzo(j)fluoranthene, benzo(k)-fluoranthene, and dibenzo(a,e)fluoranthene. 

This PAH is a common environmental contaminant. However, it is inactive as a carcinogen in animal tests (50. The trans-1,2-di-hydrodiol of triphenylene has been synthesized from phenanthrene by a route analogous to that employed for the preparation of BeP 9,10-dihydrodiol (48). Like the latter compound, epoxidation with per-acid affords a mixture of the anti and syn diol epoxides (Figure 9) (48,50). 

Synthesis of the anti and syn isomers of the 1,2-diol-3,4-epoxide of phenanthrene by epoxidation of the 1,2-dihydrodiol has been reported by Whalen et al. (57). 

Benzo(c)phenanthrene (BcP) is exceptionally weak or inactive as a carcinogen in experimental animals (51). On the other hand, the bay region anti diol epoxide of BcP (14) exhibits high tumor initiating activity on mouse skin (65). 

At first three K-region oxides were studied, those of DMBA (XI), BP (XII) and phenanthrene, the non-carcinogenic parent (XIII) the structures are shown in Figure 8. These epoxides, which were considered very reactive, were found to remain stable both in air and in the X-ray beam when in the crystalline state (82, 83). 

Figure 8. The structures of the K-region oxides of DMBA (XI) (a, b and c), BP (XII) (d) and phenanthrene (XIII) (e). Views (c), (d) and (e) are directly onto the plane of the epoxide group.

The carcinogenicity of PAH with relativelyTigh IP, such as benzo[c]phenanthrene, benz[a]anthracene, chrysene, 5-methyl chrysene and dibenz[a,h]anthracene (Table I), can be related to the formation of bay-region diol epoxides catalyzed by monooxygenase enzymes (j>). However, the most potent carcinogenic PAH have IP < ca. 7.35 eV. 

The arene (5 mmol) in CHCl3 (100 ml) is added to aqueous NaOCl (0.6 M, 250 ml) and the pH is adjusted to 8-9 by the addition of cone. HCl. TBA-HS04 (0.34 g, l mmol) is added and the mixture is stirred until TLC analysis shows complete conversion of the arene. The organic phase is separated, washed well with H20, dried (K2CO ), and evaporated to yield the epoxide (e.g. 90% from phenanthrene, 76% from 1,2-benz-anthracene, 70% from acenaphthene, 19% 2,3 4,5-bis-epoxide from naphthalene). 

Phenanthrene (10.28, Fig. 10.10) is the positional isomer of anthracene, yet the differences in reactivity and metabolism between the two compounds are marked. Whereas epoxidation of anthracene in mammals occurs only at the 1,2-position (Fig. 10.9), phenanthrene is epoxidized at the 9,10- (major), 1,2- (minor), and 3,4-positions (trace). The reason for preferential oxygenation at the 9,10-position is due at least in part to its higher reactivity. This position within a phenanthrene-like topography, known as the K region, is found in a number of PAHs with four or more cycles. Phenanthrene is also representative of higher PAHs since it contains a so-called bay region (Fig. 

As discussed below for higher PAHs, their epoxidation and hydration at the neighboring M region (C(l)-C(2) in phenanthrene) is of major toxicological significance when followed by epoxidation near the bay region (C(3)-C(4) in phenanthrene) [10] [88],... 

Detailed kinetic studies comparing the chemical reactivity ofK-region vs. non-K-region arene oxides have yielded important information. In aqueous solution, the non-K-region epoxides of phenanthrene (the 1,2-oxide and 3,4-oxides) yielded exclusively phenols (the 1-phenol and 4-phenol, respectively, as major products) in an acid-catalyzed reaction, as do epoxides of lower arenes (Fig. 10.1). In contrast, the K-region epoxide (i.e., phenanthrene 9,10-oxide 10.29) gave at pH < 7 the 9-phenol and the 9,10-dihydro-9,10-diol (predominantly trans) in a ratio of ca. 3 1. Under these conditions, the formation of this dihydrodiol was found to result from trapping of the carbonium ion by H20 (Fig. 10.11, Pathway a). At pH > 9, the product formed was nearly ex-... 

In other words, the non-K-region epoxides of phenanthrene react like epoxides of lower arenes (Fig. 10.1). In contrast, the K-region epoxide of phenanthrene, under alkaline conditions, hydrolyzes as does an olefin epoxide (i.e., as in Fig. 10.4), but seemingly faster. Under acidic conditions, however, it exhibits dual behavior, isomerizing mainly like an arene oxide (i.e.,... 

Turning to enzymatic hydration, we see from the data in Table 10.1 that phenanthrene 9,10-oxide Fig. 10.10, 10.29) is an excellent substrate for epoxide hydrolase. Comparison of enzymatic hydration of the three isomeric phenanthrene oxides shows that the Vmax with the 9,10-oxide is greater than with the 1,2- or the 3,4-oxide the affinity was higher as well, as assessed by the tenfold lower Km value [90]. Furthermore, phenanthrene 9,10-oxide has a plane of symmetry and is, thus, an achiral molecule, but hydration gives rise to a chiral metabolite with high product enantioselectivity. Indeed, nucleophilic attack by epoxide hydrolase occurs at C(9) with inversion of configuration i.e., from below the oxirane ring as shown in Fig. 10.10) to yield the C-H9.S, 10.S )-9,10-dihydro-9,10-diol (10.30) [91],... 

The EH-catalyzed hydration of the enantiomers of the K-region epoxides of BaA, CR, and BcPh allows informative comparisons to be made [92 - 94], With four among the six substrates, nucleophilic attack is selective for the oxirane C-atom with (5)-configuration (Fig. 10.12). This is, for example, true for the two enantiomers of chrysene 5,6-oxide. Looking at the data in another way, it is also apparent that, irrespective of the enantiomer, nucleophilic attack occurs preferentially at C(5) for benz[a]anthracene 5,6-oxide, but at C(6) for benzo[c]phenanthrene 5,6-oxide. In other words, the regio- and... 

Fig. 10.12. Upper part The K, M, bay, and fjord regions of three isomeric tetracyclic aromatic hydrocarbons (benz[a]anthracene (BaA, 10.31), chrysene (CR, 10.32), and benzo[c]phenanthrene (BcPh, 10.33)). Lower part. The three pairs of enantiomeric (S,R)- and (R,S)-K-region epoxides and...

A. Harsch, J. M. Sayer, D. M. Jerina, P. Vouros, HPLC-MS/MS Identification of the Positionally Isomeric Benzo[c]phenanthrene Diol Epoxide Adducts in Duplex DNA , Chem. Res. Toxicol. 2000, 13, 1342 - 1348. 

L. Lewis-Bevan, S. B. Little, J. R. Rabinowitz, Quantum Mechanical Studies of the Structure and Reactivities of the Diol Epoxides of Benzo[c]phenanthrene , Chem. Res. Toxicol. 1995, 8, 499 - 505. 

A parallel was drawn between stable ion and AMI studies of methylphenanthrenes and solvolytic studies of K-region and non-K-region phenanthrene oxides. The carbocation formed by opening of the 1,2-epoxide closely resembled the 2-methylphenanthrene cation (and 7H ), and the regiochemistry of phenol formation (1-phenanthrol) could be understood. Similarly, phenanthrenium cations derived from the 3-methyl and dimethylated compounds served as models for carbo-cations formed by solvolysis of phenanthrene-3,4-epoxide (formation of 4-phenanthrol following hydride shift). 

Isocyanates 345 react with phenanthrenequinone 346 and triphenylarsine oxide to give photochromic oxazines 347 (Equation 48) <1993PS(81)37>. The isocyanate can be replaced by a phosphinimine and the phenanthrene structure can also be replaced by the corresponding phenanthroline (Equation 49) <2003WO42195>. The /ra r-fused tetrahydrooxazine 349 was prepared from epoxide 348 and 2-aminoethyl sulfate (ethanolamine 0-sulfonic acid) (Equation 50) <1987AP625>. 

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