Stereochemical effects during [M-H]- dissociations of epimeric 11-OH-17beta-estradiols and distant electronic effects of substituents at C(11) position on gas phase acidity

ERE-dependent transcription and cell proliferation: Independency of these two processes mediated by the introduction of a sulfone function into the weak estrogen estrothiazine

The synthetic coumestrol derivative 6,12-dihydro-3-methoxy-1-benzopyrano[3,4-b][1,4]benzothiazin-6-one (estrothiazine, ESTZ) has been identified as a weak estrogen receptor α (ERα) ligand unable to compete with tritiated estradiol. The biological activity of this compound, supported by a methoxy group in position 3, seems mainly to result from its capacity to activate ERα dimerization without any participation of coactivators. In support of this view and referring to conventional estrogens, an ESTZ metabolism study conducted with hepatic human microsomes failed to provide any argument in favour of an estrogenic activity dependent on a metabolic conversion of the compound into hydroxylated metabolites with strong receptor activation ability. Interestingly, we failed to detect any oxidation of the sulfur atom of the compound. In the light of pharmacological literature data concerning sulfonylation, we assessed ERα-mediated activities generated by two sulfonylated ESTZ derivatives in which the methoxy group that plays a key role in its mechanism of action was maintained or removed. Sulfonylated ESTZ, even in its demethoxylated form, induced ERE-mediated transcriptions in MCF-7 breast cancer cells, without affecting the ERα turnover rate. In contrast to ESTZ, this compound failed to enhance the proliferation of ERα-positive breast cancer cells, suggesting that its sulfone function confers upon the receptor a capacity to elicit some of the known characteristics associated with estrogenic responses. Moreover, we demonstrated that this sulfone may contribute to ERα dimerization without any requirement of the methoxy group. Nevertheless, it seems to cooperate with this group, as reflected by a weak ability of the sulfonylated form of ESTZ to compete with tritiated estradiol for ERα-binding. Assessment of the docking of this compound within the ligand-binding domain of the receptor by molecular dynamics provided an explanation for this observation since the sulfone is engulfed in a small hydrophobic pocket involving the residues Leu-346, Leu-349, Ala-350 and Leu-384, also known to recruit coactivators. This work not only reports the sulfone functional group as a pharmacophore for estrogenic activity, but also opens new perspectives for the development of estrogenic molecules with therapeutic purpose and devoid of proliferative side effects.

A photodegradable hexaaza-pentacene molecule for selective dispersion of large-diameter semiconducting carbon nanotubes

4HP exhibits high selectivity for large-diameter s-SWCNTs.

Collision induced dissociations of non-derivatized and trimethylsilyl-derivatized estradiols: similarities in fragmentation patterns

Fragmentation mechanisms of estradiol and trimethylsilyl (TMS)-derivatized estradiol were studied by triple quadrupole tandem mass spectrometry (MSMS) and density functional theory (DFT) at B3LYP/6-311G(d,p) level. Collision induced dissociations (CID) of estradiol give product ions that are associated with the cleavage of B, C and D rings. Characteristic fragments from the cleavage of the aromatic ring A were not identified, and this was confirmed with both labeled estradiol and trimethylsilyl (TMS)-derivatized estradiol. The mechanisms are based on charge-site directed, radical-directed and charge remote fragmentations that are consistent with previous studies of steroids. CID spectra show ion pairs at m/z: 145/146, 157/158, 185/186, 211/213 and 225/226 with significant intensities, suggesting that these pairs are not from isotopic contributions. The mechanisms show similarities with some minor differences in the fragmentation patterns between the non-derivatized and the TMS-derivatized estradiol.

Instrumental dependent dissociations of n-propyl/isopropyl phosphonate isomers: evaluation of resonant and non-resonant vibrational activations

Structural elucidation and distinction of isomeric neurotoxic agents remain a challenge. Tandem mass spectrometry can be used for this purpose in particular if a "diagnostic" product ion is observed. Different vibrational activation methods were investigated to enhance formation of diagnostic ions through consecutive processes from O,O-dialkyl alkylphosphonates. Resonant and non-resonant collisional activation and infrared multiphoton dissociation (IRMPD) were used with different mass spectrometers: a hybrid quadrupole Fourier transform ion cyclotron resonance (Qh-FTICR) and a hybrid linear ion trap-Orbitrap (LTQ/Orbitrap). Double resonance (DR) experiments, in ion cyclotron resonance (ICR) cell, were used for unambiguous determination of direct intermediate yielding diagnostic ions. From protonated n-propyl and isopropyl O-O-dialkyl-phosphonates, a diagnostic m/z 83 ion characterizes the isopropyl isomer. This ion is produced through consecutive dissociation processes. Conditions to favor its formation and observation using different activation methods were investigated. It was shown that with the LTQ, consecutive experimental steps of isolation/activation with modified trapping conditions limiting the low mass cut off (LMCO) effect were required, whereas with FT-ICR by CID and IRMPD the diagnostic ion detection was provided only by one activation step. Among the different investigated activation methods it was shown that by using low-pressure conditions or using non-resonant methods, efficient and fast differentiation of isomeric neurotoxic agents was obtained. This work constitutes a unique comparison of different activation modes for distinction of isomers showing the instrumental dependence characteristic of the consecutive processes. New insights in the dissociation pathways were obtained based on double-resonance IRMPD experiments using a FT-ICR instrument with limitation at low mass values.

Electronic effects of 11β substituted 17β-estradiol derivatives and instrumental effects on the relative gas phase acidity

Numerous studies have highlighted the role of the proton donor characteristics of the phenol group of 17β-estradiol (E(2)) in its association with the estrogen receptor alpha (ERα). Since the substitutions at position C((11)) have been reported to modulate this association, we hypothesized that such substitutions may modify the phenol acidity. Hence, phenol gas-phase acidity of nine C((11))-substituted E(2)-derivatives were evaluated using the extended Cooks' kinetic method, which is a method widely used to determine thermochemical properties by mass spectrometry. To enhance accuracy in data collection we recorded data from several instruments, including quadrupole ion trap, triple quadrupole, and hybrid QqTOF. Indeed, we report for the first time the use of the QqTOF instrument to provide a novel means to improve data accuracy by giving access to an intermediate effective temperature range. All experimental gas-phase acidity values were supported by theoretical calculations. Our results confirmed the ability of distant substituents at C((11)) to modulate the phenol acidity through electrostatic interactions, electron withdrawing inductive effects, and mesomeric effects. However, no relationship was found between the phenol gas-phase acidity of investigated steroids and their binding affinity for ERα assessed in solution. Thus, our results highlight that the intrinsic properties of the hormone do not influence sufficiently the stabilization of the hormone/ERα complex. It is more likely that such stabilization would be more related to factors depending on the environment within the binding pocket such as hydrophobic, steric as well as direct intermolecular electrostatic effects between ERα residues and the substituted steroidal estrogens.

Rapid differentiation of nucleotide phosphoramidate diastereomers by electrospray ionization tandem mass spectrometry

RATIONALE

Nucleotide phosphoramidates are prodrugs which effectively deliver the active nucleotide to target tissues. It was shown that the individual phosphoramidate diastereomers have different antiviral activity, although the active nucleotide is the same. Therefore, a fast and simple analytical method is needed to characterize the individual diastereomeric phosphoramidate prodrugs.

METHODS

Stock solutions of diastereomeric nucleotide phosphoramidate prodrugs, i.e., 5'-phosphate derivatives of the β-D-2'-deoxy-2'-α-fluoro-2'-β-C-methyluridine nucleotide, were made in 25% acetonitrile to achieve a final concentration of 10 µg/mL. The samples were studied using high-performance liquid chromatography (HPLC) coupled with electrospray ionization tandem mass spectrometry (ESI-MS/MS).

RESULTS

The MS/MS spectra of diastereomeric pairs showed substantial differences in the relative abundances of a characteristic ion in negative mode, which is proposed to be a cyclic phosphoramidate ion. Results were confirmed by the MS/MS spectrum of an analog without the NH proton and deuterium exchange experiment. Furthermore, the diastereomer-specific fragmentation behavior in negative ESI-MS was used to characterize a series of nucleotide phosphoramidates with different amino acid and aromatic substituents.

CONCLUSIONS

An HPLC/MS/MS method was developed for the differentiation of the diastereomers of phosphoramidate prodrugs. In negative mode MS/MS spectra, the cyclic phosphoramidate ions yielded unambiguous distinction. This method presented a rapid and simple way for the characterization of nucleotide phosphoramidates.

Hydrogen rearrangement and ring cleavage reactions study of progesterone by triple quadrupole mass spectrometry and density functional theory

The fragmentation mechanisms of progesterone have been studied by triple quadrupole tandem mass spectrometry (MSMS) and density functional theory (DFT). Mechanisms leading to major product ions are proposed. The data suggest that progesterone fragments preferentially via hydrogen and other rearrangements lead to neutral losses. These fragmentations are quite complex and are preceded by σ-bond cleavages in most cases. Four major pathways for progesterone fragmentation are proposed involving: (1) cleavage of ring B at C9-C10, (2) cleavage of C6-C7 bond in ring B through m/z 191, (3) two types of cleavages of ring D, and (4) ketene elimination in ring A. Pathways (1)-(3) proceed via charge-remote fragmentations while pathway (4) proceeds via charge-site initiated mechanism. The geometry of product ions in these pathways were optimized using DFT at the B3LYP/6-311G(d,p) level of theory from which the free energies of the pathways were calculated. The effect that the choice of basis sets and density functionals has on the results was tested by performing additional calculations using B3LYP/6-31G(d) and B3PW91/6-311G(d,p).

Capacity of type I and II ligands to confer to estrogen receptor alpha an appropriate conformation for the recruitment of coactivators containing a LxxLL motif-Relationship with the regulation of receptor level and ERE-dependent transcription in MCF-7 cells

Estrogen receptor alpha (ERalpha) belongs to the superfamily of nuclear receptors and as such acts as a ligand-modulated transcription factor. Ligands elicit in ERalpha conformational changes leading to the recruitment of coactivators required for the transactivation of target genes via cognate response elements. In many cells, activated ERalpha also undergoes downregulation by proteolysis mediated by the ubiquitin/proteasome system. Although these various molecular processes have been well characterized, little is known as to which extent they are interrelated. In the present study, we used a panel of type I (estradiol derivatives and "linear", non-steroidal ligands) and type II ("angular" ligands) estrogens, in order to identify possible relationships between ligand binding affinity, recruitment of LxxLL-containing coactivators, ERalpha downregulation in MCF-7 cells and related transactivation activity of ligand-bound ERalpha. For type I estrogens, there was a clear-cut relationship between ligand binding affinity, hydrophobicity around C-11 of estradiol and ability of ERalpha to associate with LxxLL motifs, both in cell-free condition and in vivo (MCF-7 cells). Moreover, LxxLL motif recruitment by ERalpha seemed to be a prerequisite for the downregulation of the receptor. By contrast, type II ligands, as well as estradiol derivatives bearing a bulky side chain at 11beta, had much less tendency to promote ERalpha-LxxLL interaction or even behaved as antagonists in this respect, in agreement with the well known partial estrogenicity/antiestrogenicity of some of these compounds. Interestingly, some type II ligands which antagonized LxxLL motif recruitment were nonetheless able to enhance ERalpha-mediated gene transactivation.