Validity of Tier 1 Modelling Tools and Impacts on Exposure Assessments within REACH Registrations-ETEAM Project, Validation Studies and Consequences.

In the last years, the evaluation and validation of exposure modelling tools for inhalation exposure assessment at workplaces received new and highly increased attention by different stakeholders. One important study in this regard is the ETEAM (Evaluation of Tier 1 Exposure Assessment Models) project that evaluated exposure assessment tools under the European REACH regulation (Registration, Evaluation, Authorisation and Restriction of Chemicals), (but next to the ETEAM project-as a project publicly funded by the German Federal Institute for Occupational Safety and Health (BAuA)-it is a rather new development that research groups from universities in Europe, but also internationally, investigated this issue. These other studies focused not only on REACH tier 1 tools but also investigated other tools and aspects of tool validity. This paper tries to summarise the major findings of studies that explored the different issues of tool validity by focusing on the scientific outcomes and the exposure on the science community. On the other hand, this publication aims to provide guidance on the choice and use of tools, addressing the needs of tool users. The consequences of different stakeholders under REACH are discussed from the results of the validation studies. The major stakeholders are: (1) REACH registrants or applicants for REACH authorisations, meaning those companies, consortia or associations who are subject to REACH; (2) Evaluating authorities within the scope of REACH, meaning the ECHA (European Chemicals Agency) secretariat and committees, but also the competent authorities of the member states or the European Union; (3) Developers of the different models and tools; (4) Users of the different models and tools.

Synthesis of a malaria candidate glycosylphosphatidylinositol (GPI) structure: a strategy for fully inositol acylated and phosphorylated GPIs.

A congener of the glycosylphosphatidylinositol (GPI) membrane anchor present on the cell surface of the malaria pathogen Plasmodium falciparum has been synthesized. This GPI is an example of a small number of such membrane anchors that carry a fatty acyl group at O-2 of the inositol. Although the acyl group plays crucial roles in GPI biosynthesis, it rarely persits in mature molecules. Other notable examples are the mammalian GPIs CD52 and AchE. The presence of bulky functionalities at three contiguous positions of the inositol moiety creates a very crowded environment that poses difficulties for carrying out selective chemical manipulations. Thus installations of the axial long-chain acyl group and neighboring phosphoglyceryl complex were fraught with obstacles. The key solution to these obstacles in the successful synthesis of the malarial candidate and prototype structures involved stereoelectronically controlled opening of a cyclic ortho ester. The reaction proceeds in very good yields, the desired axial diastereomer being formed predominantly, even more so in the case of long-chain acyl derivatives. The myoinositol precursor was prepared from methyl alpha-d-glucopyranoside by the biomimetic procedure of Bender and Budhu. For the glycan array, advantage was taken of the fact that (a). n-pentenyl ortho ester donors are rapidly and chemospecifically activated upon treatment with ytterbium triflate and N-iodosuccinimide and (b). coupling to an acceptor affords alpha-coupled product exclusively. A strategy for obtaining the GPI's alpha-glucosaminide component from the corresponding alpha-mannoside employed Deshong's novel azide displacement procedure. Thus all units of the glycan array were obtained from a beta-d-manno-n-pentenyl ortho ester, this being readily prepared from d-mannose in three easy, high-yielding steps. The "crowded environment" at positions 1 and 2, noted above, could conceivably be relieved by migration of the acyl group to the neighboring cis-O-3-hydroxyl in the natural product. However, study of our synthetic intermediates and prototypes indicate that the O-2 acyl group is quite stable, and that such migration does not occur readily.

Orthoesters versus 2-O-acyl glycosides as glycosyl donors: theorectical and experimental studies.

n-Pentenyl orthoesters (NPOEs) undergo routine acid catalyzed rearrangement into 2-O-acyl n-pentenyl glycosides (NPGs). The reactant and product can both function as glycosyl donors affording 1,2-trans linked glycosides predominantly. However, both donors differ in their rates of reactions, the yields they produce, and the nature of their byproducts, indicating that the NPOE/NPG pair may not be reacting through the same intermediates. We have therefore applied quantum chemical calculations using DFT methods and MP second order perturbation theory to learn more about orthoesters and their 2-O-acyl glycosidic counterparts. The calculations show that in the case of a manno NPG and NPOE pair, each donor goes initially to a different cationic intermediate. Thus, the former goes to a high-energy oxocarbenium ion before descending to a trioxolenium ion in which the charge is distributed over the pyrano ring oxygen, as well as the carbonyl and ether oxygen atoms of the putative C2 ester. On the other hand, ionization of the NPOE produces a dioxolenium ion lying slightly above the more stable trioxolenium counterpart. For the gluco pair, the NPG also goes to a very high-energy oxocarbenium ion, which also descends to a trioxolenium ion. However, unlike the manno analogue, the gluco NPOE does not give a dioxolenium ion; indeed, the dioxolenium is not energetically distinguishable from the trioxolenium counterpart. The theoretical observations have been tested experimentally. Thus, it was found that with manno derivatives, the orthoester is a more reactive donor than the corresponding NPG donor, whereas, for gluco derivatives, there is no advantage to using one over the other, unless one resorts to carefully selected promoters.

Synthetic approaches to heavily lipidated phosphoglyceroinositides.

[reaction: see text] Naturally occurring phosphoinositide glycoconjugates are equipped with varied acyl residues that are important for their biological activity and biosynthesis. This paper reports that acylation at O2 of the myo-inositol moiety can be achieved by stereocontrolled ortho ester rearrangement. Coupling to homo- or heterodiacylated glycerols was achieved via phosphoramidite methods, and exhaustive debenzylation by transfer hydrogenation afforded the deprotected phosphoglyceroinositides. The latter can be kept in chloroform solution at room temperature for over two months without migration of the inositol acyl group.

Unexpected role of O-2 "protecting" groups of glycosyl donors in mediating regioselective glycosidation.

Glycosidation of several vicinal diols reveals that exquisite regioselectivity can be achieved by using 2-O-benzoyl n-pentenyl glycoside donors and/or their cyclic 1,2-ortho ester counterparts. The regioselective preferences for both are the same, although ratios and yields may differ. In stark contrast, glycosidation of the diols with the corresponding 2-O-benzylated donors gives poor, if any, regioselectivity.