Heterotopicity

The two protons at C-1 are topologically nonequivalent, since substitution of one produces a product tiiat is stereochemically distinct fiom that produced by substitution of the other. Ligands of this type are termed heterotopic, and, because the products of substitution are enantiomers, the more precise term enantiotopic also applies. If a chiral assembly is generated when a particular ligand is replaced by a new ligand, the original assembly is prochiral. Both C-1 and C-3 of 1,3-propanediol are prochiral centers. 

The concept of heterotopic atoms, groups, and faces can be extended from enantiotopic to diastereotopic types. If each of two nominally equivalent ligands in a molecule is replaced by a test group and the molecules that are generated are diaster-eomeric, then the ligands are diastereotopic. Similarly, if reaction at one face of a trigonal atom generates a molecule diastereomeric with that produced at the alternate face, the faces are diastereotopic. 

In this way hosts 141-145 with both a cr-bonded Lewis acidic boron atom for complexation of anions and a conventional multidentate ligand for cations are generated. Complexation experiments of the 21-membered crown [6] boronate 142 with different potassium salts KX (X = F, Cl, Br, I, SCN, CN, OMe) indicate that there is a high specificity for the incorporation of KF, whereby F is bound covalently to the boron atom and is complexed by the crown ether (146, Fig. 39). An X-ray study has shown that the complexation of KF is heterotopic, i.e., both ions are complexed inside the same host. Some of the salts can only be bound in a monotopic way (KI and KSCN) [237]. 

Most kidney transplant procedures are heterotopic, where the kidney is implanted above the pelvic bone and attached to the patient s iliac artery and vein. The ureter of the transplant kidney is attached directly to the recipient s bladder or native ureter. The native kidneys usually are not removed, and data have shown that under most circumstances, removal of the native kidneys does not influence patient survival and allograft survival. Special circumstances, however, such as renal cell carcinoma and PCKD, may necessitate native kidney removal.1,3 There were 16,477 (9914 deceased donors, 6563 living donors) kidney transplants and 903 simultaneous kidney-pancreas procedures done in 2005.3... 

Re and Si Labels used in stereochemical descriptions of heterotopic faces. If the CIP priority of the three ligands a, b, and c is assigned as a > b > c, the face that is oriented clockwise toward the viewer is called Re, while the face with a counterclockwise orientation of a — b — c is called Si, as shown in Figure 1-34 ... 

An element of prostereoisomerism is a partial structure that can be converted into an element of stereoisomerism not otherwise present, by considering one of a pair of homomorphic groups to be different from the other. The groups involved in this operation are necessarily heterotopic. Depending on the character of the element of stereoisomerism thus produced, one can divide the elements of prostereoisomerism into centers, lines, and planes and subdivide them, as appropriate, into those that are (fully) prochiral, only prographochiral, only... 

The stability of the polypyridyl rhenium(I) compounds mentioned above stimulated applications of this coordination chemistry. Thus, new heterotopic bis(calix[4]arene)rhenium(I) bipyridyl receptor molecules have been prepared and shown to bind a variety of anions at the upper rim and alkali metal cations at the lower rim. A cyclodextrin dimer, which was obtained by connecting two permethylated /3-cyclodextrins with a bipy ligand, was used for the preparation of a luminescent rhenium(I) complex. The system is discussed as a model conipound to study the energy transfer between active metal centers and a bound ditopic substrate. The fluorescence behavior of rhenium(I) complexes containing functionalized bipy ligands has been applied for the recognition of glucose. ... 

Figure 13. Two synthetic strategies leading to chiral crown compounds with heterotopic faces starting from asymmetric precursors. Note that, although the product obtained in (b) has Cj symmetry, the symmetry element does not exchange the environment of the two faces.

For modulation of the size and shape of these metallacalixarene cavities, combinations of various pyrimidine and phen ligands have been used to form heterotopic metallacalixarenes. The multicomponent reactions of 3 1 2 mixture of [(en)Pd l, pyrimidine, and phen preferably formed heterotopic trimeric species [(en)3Pd3(L-Nl N3)(phen-N4 N7)2] (127) (L, a = 2-pymo, b = 2-mpymo,... 

Heterotopic ossification (etidronate) Prevention and treatment of heterotopic ossification following total hip replacement or caused by spinal injury. 

Lactation It is not known whether these drugs are excreted in breast milk. Because zoledronic acid binds to bone long-term, do not administer to a nursing woman. Children Safety and efficacy for use in children have not been established. Children have been treated with etidronate at doses recommended for adults, to prevent heterotopic ossifications or soft tissue calcifications. 

Weijerman PC, Schurmans JR, Hop WC. Morbidity and quality of life in patients with orthotopic and heterotopic continent urinary diversion. Urology 1996 51 51-56. 

The simultaneous photolyses of two different species of dithiocarbamates (R - DC and R2 - DC) in the absence of monomers and at high concentrations result in enforced recombination between alkyl radicals produced by photolysis to produce three types of alkyl-alkyl recombination product namely Ri - Ri, R2 - Ri and Ri- R2, as shown in Scheme 5. If the concentration of one species (Ri - DC) is much higher than the other R2 - DC), a relative fraction of heterotopically recombined product, Ri - R2, must increase. If such a heterotopic cross-recombination reaction predominantly occurs at a solution/solid interface, an it2-alkylated dithiocarbamated surface is converted into an it 1-alkylated surface, as schematically shown in Scheme 6. 

Heterotopic ossification caused kg spinal cord infurg PO 20mg/kg/dayfor2 wk then 10 mg/kg/day for 10 wk. 

Heterotopic ossification complicating total hip replacement PO 20 mg/kg/day for 1 mo before surgery then 20 mg g/day for 3 mo after surgery. 

Furthermore, in flexible linear peptides the chemical shifts are typical of random structures similar to nonfolded proteins. Deviation from these random shifts sometimes identifies specific conformational preferences. NH-proton chemical shifts depend strongly on external influences (solvent, temperature, concentration, specific sequence). Random coil shifts for these protons correlate less well than chemical shifts of the a-protons or a-carbonsJ19-261 Not only are the shift differences of different heterotopic protons similar, but also those of diastereotopic P-protons. A preferred side-chain conformation is normally only found when there is also a preferred backbone conformation. 

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