Structures of minor components of the validamycin complex.
complicated oligosaccharides using NMRspectroscopy have developed quite remarkably. The structure of validamycin G (VM-G),43 the most recently discovered congener was established by making use of these techniques. Wehave now used NMRto reinvestigated the position of the glycosidic linkage of the minor components which had remained obscure. The results were first disclosed in a patent application,53 though without experimental data. Here we discussed the structures of the minor components with experimental results. To elucidate the unidentified positions of the glucosidic linkage by *H NMRspectroscopy, VM-B~ F were acetylated with acetic anhydride and pyridine to give the corresponding peracetyl derivatives. The chemical shifts of 1-H and l'-H of the peracetates, recognized in the region of 3.2~3.6 ppm, indicate that the imino group is not acetylated. Therefore, these peracetates must be dodeca-O-acetyl validamycin B (Ac-
Synthesis of N-Linked Carbaoligosaccharides: Total Synthesis of Antibiotic Validamycins and Related Compounds
Abstract This review describes the results of synthetic studies undertaken by the authors of this chapter on carbasugars over the last 30 years or so. These studies took advantage of the long-anticipated discovery of a sole crystalline cycloaddition adduct, which under favorable conditions could play a reliable role in laying down the foundation stone for the synthetic carbasugar chemistry. Although glycosidase inhibitors with chaperone activity have recently been evaluated as if they were a final goal, it seems from another synthetic point of view that the results accumulated have made total synthesis of natural carbaoligosaccharide validamycins and acarbose possible.
Human Rights Obligations and Transnational Corporations: The Limits of Direct Corporate Responsibility
To date, multinational corporations have had no direct human rights obligations under international law. Nonetheless, international lawyers can no longer ignore the increasing role of non-state actors in international society. This article suggests analysing existing mechanisms and new proposals for enhancing the accountability of transnational corporations, grouped into those focusing on the responsibility of the home and host states and those centred on the imposition of direct obligations on corporations. This article will specifically draw attention to the limits of some of the suggested normative changes, from a legal-theoretical perspective and in terms of their capacity to address effectively the challenges of the lack of respect for human rights laws.