Bond length-reactivity correlations for sulfate monoesters. The crystal structure of potassium 4-nitrophenyl sulfate, C6H4KNO6S

Effective synthesis of sulfate metabolites of chlorinated phenols

Chlorophenols are an important class of persistent environmental contaminants and have been implicated in a range of adverse health effects, including cancer. They are readily conjugated and excreted as the corresponding glucuronides and sulfates in the urine of humans and other species. Here we report the synthesis and characterization of a series of ten chlorophenol sulfates by sulfation of the corresponding chlorophenols with 2,2,2-trichloroethyl (TCE) chlorosulfate using N,N-dimethylaminopyridine (DMAP) as base. Deprotection of the chlorophenol diesters with zinc powder/ammonium formate yielded the respective chlorophenol sulfate ammonium salts in good yield. The molecular structure of three TCE-protected chlorophenol sulfate diesters and one chlorophenol sulfate monoester were confirmed by X-ray crystal structure analysis. The chlorophenol sulfates were stable for several months if stored at -20 °C and, thus, are useful for future toxicological, environmental and human biomonitoring studies.

3,4',5-Trichloro-biphenyl-4-yl 2,2,2-trichloro-ethyl sulfate

Crystals of the title compound, C14H8Cl6O4S, are twinned by inversion, with unequal components [0.85 (3):0.15 (3)]. The asymmetric unit contains two independent mol-ecules that are related by a pseudo-inversion center. The Car-O [1.393 (9) and 1.397 (9) Å] and ester S-O bond lengths [1.600 (5) and 1.590 (5) Å] of both mol-ecules are comparable to the structurally related 2,3,5,5-trichloro-biphenyl-4-yl 2,2,2-trichloro-ethyl sulfate. The dihedral angles between the benzene rings in the two mol-ecules are 37.8 (2) and 35.0 (2)°.

An efficient approach to sulfate metabolites of polychlorinated biphenyls

Polychlorinated biphenyls (PCBs), a major class of persistent organic pollutants, are metabolized to hydroxylated PCBs. Several hydroxylated PCBs are substrates of cytosolic phase II enzymes, such as phenol and hydroxysteroid (alcohol) sulfotransferases; however, the corresponding sulfation products have not been isolated and characterized. Here we describe a straightforward synthesis of a series of ten PCB sulfate monoesters from the corresponding hydroxylated PCBs. The hydroxylated PCBs were synthesized by coupling chlorinated benzene boronic acids with appropriate brominated (chloro-)anisoles, followed by demethylation with boron tribromide. The hydroxylated PCBs were sulfated with 2,2,2-trichloroethyl chlorosulfate using DMAP as base. Deprotection with zinc powder/ammonium formate yielded the ammonium salts of the desired PCB sulfate monoesters in good yields when the sulfated phenyl ring contained no or one chlorine substituent. However, no PCB sulfate monoesters were isolated when two chlorines were present ortho to the sulfated hydroxyl group. To aid with future quantitative structure activity relationship studies, the structures of two 2,2,2-trichloroethyl-protected PCB sulfates were verified by X-ray diffraction.

4'-Chloro-biphenyl-3-yl 2,2,2-trichloro-ethyl sulfate

The title compound, C₁₄H₁₀Cl₄O₄S, is a 2,2,2-trichloro­ethyl-protected precursor of 4′-chloro­biphenyl-3-yl sulfate, a sulfuric acid ester of 4′-chloro­biphenyl-3-ol. The C_aromatic—O and O—S bond lengths of the C_aromatic—O—S unit are comparable to those in structurally analogous biphenyl-4-yl 2,2,2-trichloro­ethyl sulfates with no electro­negative chlorine substituent in the benzene ring with the sulfate ester group. The dihedral angle between the aromatic rings is 27.47 (6)°.

3',4'-Dichloro-biphenyl-4-yl 2,2,2-trichloro-ethyl sulfate

The four independent mol­ecules in the asymmetric unit of the title compound, C₁₄H₉Cl₅O₄S, are related by pseudo-inversion centres. The mol­ecules have C_aromatic—O bond lengths ranging from 1.426 (10) to 1.449 (9) Å and biphenyl-4-yl sulfate ester bond lengths ranging from 1.563 (6) to 1.586 (6) Å, which is comparable to structurally related sulfuric acid diesters. The dihedral angles between the benzene rings range from 22.5 (4) to 29.1 (4)° and are significantly smaller than the calculated dihedral angle of 41.2°.

Biphenyl-4-yl 2,2,2-trichloro-ethyl sulfate

The mol-ecular structure of the title compound, C(14)H(11)Cl(3)O(4)S, displays a biphenyl dihedral angle of 4.9 (2)° between the benzene rings, which is significantly smaller than the calculated dihedral angle of 41.2° of biphenyl derivatives without ortho substituents. The C(Ar)-O bond length of 1.432 (4) Å is comparable with other sulfuric acid biphenyl-4-yl ester 2,2,2-trichloro-ether ester derivatives without electronegative substituents in the sulfated phenyl ring.

Electron ionization mass spectral fragmentation study of sulfation derivatives of polychlorinated biphenyls

Background

Polychlorinated biphenyls are persistent organic pollutants that can be metabolized via hydroxylated PCBs to PCB sulfate metabolites. The sensitive and selective analysis of PCB sulfate monoesters by gas chromatography-mass spectrometry (GC-MS) requires their derivatization, for example, as PCB 2,2,2-trichloroethyl (TCE) sulfate monoesters. To aid in the identification of unknown PCB sulfate metabolites isolated from biological samples, the electron impact MS fragmentation pathways of selected PCB TCE sulfate diesters were analyzed and compared to the fragmentation pathways of the corresponding methoxylated PCBs.

Results

The most abundant and characteristic fragment ions of PCB TCE sulfate diesters were formed by releasing CHCCl₃, SO₃, HCl₂ and/or CCl₃ from the TCE sulfate moiety and Cl₂, HCl, ethyne and chloroethyne from an intermediate phenylcyclopentadienyl cation. The fragmentation pattern depended on the degree of chlorination and the position of the TCE sulfate moiety (i.e., ortho vs. meta/para to the second phenyl ring), but were independent of the chlorine substitution pattern. These fragmentation pathways are similar to the fragmentation pathways of structurally related methoxylated PCBs.

Conclusion

Knowledge of the fragmentation patterns of PCB TCE sulfate diesters will greatly aid in determining the position of sulfate moiety (ortho vs. meta/para) of unknown PCB sulfate metabolites isolated from environmental or laboratory samples.

4'-Chloro-biphenyl-4-yl 2,2,2-trichloro-ethyl sulfate

The title compound, C(14)H(10)Cl(4)O(4)S, is an inter-mediate in the synthesis of the PCB sulfate monoester of 4'-chloro-biphenyl-4-ol. Both the sulfate monoester and 4'-chloro-biphenyl-4-ol are metabolites of PCB 3 (4-chloro-biphen-yl). There are two mol-ecules with different conformations in the asymmetric unit. The solid state dihedral angles between the benzene rings are 18.52 (10) and 41.84 (16)° in the two mol-ecules, whereas the dihedral angles between the least-squares plane of the sulfated benzene ring and O-S (Ar-C-O-S) are 66.2 (3) and 89.3 (3)°. The crystal was an inversion twin with a refined component fraction of 0.44 (7).

Ground state structures of sulfate monoesters and sulfamates reveal similar reaction coordinates for sulfuryl and sulfamyl transfer

Structure/reactivity and structure/structure correlations of 5 sulfate monoesters and 11 sulfamate esters determined by low temperature X-ray crystallography reveal similar ground state deformations that suggest similar reaction coordinates for sulfuryl and sulfamyl group transfer.