From structural motifs

Finally, many disulfides have a quite different structure motif, being composed of infinite three-dimensional networks of M and discrete Sj units. The predominate structural types are pyrites, FeSa (also for M = Mn, Co, Ni, Ru, Os), and marcasite (known only for FeS2 among the disulfides). Pyrites can be described as a distorted NaCl-type structure in which the rodshaped S2 units (S-S 217 pm) are centred on the Cl positions but are oriented so that they are inclined away from the cubic axes. The marcasite structure is a variant of the rutile structure (Ti02,... 

With the adequacy of lipid bilayer membranes as models for the basic structural motif and hence for the ion transport barrier of biological membranes, studies of channel and carrier ion transport mechanisms across such membranes become of central relevance to transport across cell membranes. The fundamental principles derived from these studies, however, have generality beyond the specific model systems. As noted above and as will be treated below, it is found that selective transport... 

Much of our knowledge of the structure and function of endocytic receptors is based on the analysis of the LDL receptor gene family. Member s of this extended gene family can be found in a variety of species ranging from roundworms to insects, to vertebrates. Ten receptors exist in mammalian organisms, all of which share common structural motifs required for receptor-mediated... 

Upon mutagenesis of the monoamine oxidase from Aspergillus niger (MAO-N) within several rounds of directed evolution [65], variant biocatalysts were identified with largely expanded substrate acceptance, enabling also the deracemization of tertiary amines incorporating straight-chain and cyclic structural motifs [66]. 

This reviews contends that, throughout the known examples of facial selections, from classical to recently discovered ones, a key role is played by the unsymmetri-zation of the orbital phase environments of n reaction centers arising from first-order perturbation, that is, the unsymmetrization of the orbital phase environment of the relevant n orbitals. This asymmetry of the n orbitals, if it occurs along the trajectory of addition, is proposed to be generally involved in facial selection in sterically unbiased systems. Experimentally, carbonyl and related olefin compounds, which bear a similar structural motif, exhibit the same facial preference in most cases, particularly in the cases of adamantanes. This feature seems to be compatible with the Cieplak model. However, this is not always the case for other types of molecules, or in reactions such as Diels-Alder cycloaddition. In contrast, unsymmetrization of orbital phase environment, including SOI in Diels-Alder reactions, is a general concept as a contributor to facial selectivity. Other interpretations of facial selectivities have also been reviewed [174-180]. 

The cis-2,3-diaryl-2,3-dihydro-l,4-benzoxathiin is a very unique structural motif. Other than scattered reports in the literature on the formation of this scaffold, there was no effective asymmetric synthesis for it [6]. We explored two major synthetic approaches to realize the key chiral as-diaryl dihydrobenzoxathiin scaffold, as shown in Scheme 5.3. One was the quinone ketal route in which the quinone ketal 13 and the chiral mercaptol alcohol 14 were the key intermediates. The other approach was the stereo- and enantioselective reduction of the diaryl benzoxathiin 16. The key mercaptol alcohol 14 and the diaryl benzoxathiin 16 were both envisioned to be prepared from the key, common iodoketone intermediate 15. 

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