Fortschritte der Chemie der Vitamine D und ihrer Abkömmlinge

Inhoffen, Hans Herloff; Irmscher, Klaus

doi:10.1007/978-3-7091-8052-5_2

Cited by 4 publications

(3 citation statements)

References 54 publications

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“…(1 -So)(14423 | -¡4423|) (49) where Sa is the overlap integral between the orbitals on centers A and D, the bar represents ß spin, and normalization constants have been suppressed. Thus, the two valencebond structures in eq 45 and 46 are composed of the same two determinantal configurations, 1123 and 4423, but differ in the coupling of the electron spins.…”

Section: Interaction Energy Along Reaction Pathsmentioning

confidence: 99%

Valence-bond approach to conservation of symmetry in concerted reactions

Silver¹,

Karplus²

1975

J. Am. Chem. Soc.

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Generalized electron-pair wave functions are used to describe the electronic states involved in a concerted reaction process. For symmetry preserving reaction paths, it is shown that primitive symmetry labels for the electron pairs can be used to determine the nature of the interaction energy between reactant and product functions and to make an assessment of the relative heights of the potential energy barriers that would be encountered along various stereospecific reaction paths. A conservation of symmetry principle is introduced for the simplest form of electron-pair function, that based on the canonical valence-bond description. This provides a generalization of the Woodward-Hoffmann rules for the conservation of molecular orbital symmetry. Illustrative examples are considered and the limitations of the symmetry conservation principle are discussed.

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Section: Interaction Energy Along Reaction Pathsmentioning

confidence: 99%

Valence-bond approach to conservation of symmetry in concerted reactions

Silver¹,

Karplus²

1975

J. Am. Chem. Soc.

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“…Vitamin D, is derived from ergosterol and vitamin D, from 7-dehydrocholesterol by a complex series of photochemical reactions when the provitamin is irradiated with ultraviolet light. A number of excellent review articles on the detailed chemistry and structure of vitamin D are available (Bills, 1954;Inhoffen & Irmscher, The structure of vitamin D and a number of related compounds without their side-chains is shown in Fig. I.…”

Section: Structural Requirements Of Vitamin D For Biological Actimentioning

confidence: 99%

The Mode of Action of Vitamin D

Norman

1968

Biological Reviews

108

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Summary 1. The purpose of this review article is to re‐evaluate and integrate many of the observations related to the physiological effects of vitamin D, using as a working hypothesis the concept that the vitamin may be acting analogously to a steroid hormone in terms of its ability to interact with genetic information and ultimately elicit a physiological response. Prior to this time the problem of the mechanism of action of vitamin D has primarily been approached from the point of view that the vitamin was acting as a cofactor for some specific enzymic reaction. 2. The physiological activities of vitamin D are integrated with those of parathyroid hormone to provide a homeostatic control for the regulation of primarily calcium and secondarily phosphate metabolism. It is proposed that the role of vitamin D in this homeostatic control mechanism is older and more fundamental than that of parathyroid hormone. The interaction of vitamin D on skeletal calcium metabolism may have evolved before the effects of the vitamin on intestinal calcium absorption. 3. There are several physiological defects of calcium metabolism—rickets, osteo‐malacia, vitamin D‐resistant rickets and idiopathic hypercalcaemia—all of which may be a consequence of an aberration in one or another of the interlocking steps of the vitamin D‐dependent and calcium‐dependent homeostatic control mechanism. 4. The most thoroughly established action of vitamin D in vivo is to promote or facilitate the intestinal absorption of calcium. Although the exact biochemical details of this process are not available, this may involve vitamin D‐mediated synthesis of the appropriate enzyme systems or the alteration of membrane structure necessary for calcium absorption. It is not yet unequivocally established whether calcium absorption is an energy‐dependent active transport process or is a passive carrier‐mediated or simple diffusion process. 5. The exact action of vitamin D on bone metabolism is not as well established, but the primary effect of the vitamin is likely to mediate bone resorption. The vitamin D‐dependent activities of the cell in both the intestine and bone are to absorb calcium and transfer it to the blood. 6. No direct effects of vitamin D on intestinal absorption of phosphate have been found. Furthermore the validity of a vitamin D‐mediated renal reabsorption of phosphate is questioned, for the major effects of vitamin D are cation oriented. If the renal effects of vitamin D are true, it is postulated that the mechanism of action of the vitamin here on the anion, phosphate, is fundamentally different from its cation oriented mechanism. 7. There is a lag in the action of vitamin D on the vitamin mediated: (a) transport of calcium both in vivo in rats and chicks, and in vitro with everted intestinal slices; (b) the apparent increased permeability of intestinal mucosa; (c) increased levels of citric acid in serum or bone; (d) the increased incorporation of radioactive inorganic phosphorus into intestinal mucosa phospholipids. As shown by the use of radi...

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“…One of these compounds, cis-isotachysterol, was originally described by Ver loop et al 3 who noted that prolonged heating (60 °C) of a methanol solution of this compound produced a shift of the UV absorption maximum from 253 to 265 nm and an increase in absorption intensity. A spectral change of this kind is reminiscent of that occurring in the thermal isomerization of previtamin D (1) to vitamin D (2) via a [l,7]sigmatropic shift. In the case of cisisotachysterolg (3), an exactly analogous rearrangement (C-19 -* C-14 H migration) would yield the new and unusual vitamin D isomer(s) 4 (C-14 stereochemistry R or S, or both) featuring (5Z,7Z) double-bond geometry, A reinvestigation of this reaction has now shown that cis-isotachysterols (3) undergoes an alternative sigmatropic rearrangement involving intramolecular hydrogen transfer from C-15 to C-10 and resulting exclusively in (3S,10S)-(Z,Z)-9,10-secocholesta-5,7,14-trien-3-ol (5a) and its (10/?…”

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confidence: 99%