Linkers cyclic

Finally, the chiral auxiliary was removed by a Birch reduction or a catalytic hydrogenation. After ring opening several optically active 6-aminohexanoic acids served as linkers in cyclic peptides as /1-turn mimetics (Table 12, Scheme 49) [51c],... 

Hyun et al. [345] prepared PbS Q-dots in a suspension and tethered them to Ti02 nanoparticles with a bifunctional thiol-carboxyl linker molecule. Strong size dependence due to quantum confinement was inferred from cyclic voltammetry measurements, for the electron affinity and ionization potential of the attached Q-dots. On the basis of the measured energy levels, the authors claimed that pho-toexcited electrons should transfer efficiently from PbS into T1O2 only for dot diameters below 4.3 nm. Continuous-wave fluorescence spectra and fluorescence transients of the PbS/Ti02 assembly were consistent with electron transfer from small Q-dots. The measured charge transfer time was surprisingly slow ( 100 ns). Implications of this fact for future photovoltaics were discussed, while initial results from as-fabricated sensitized solar cells were presented. 

Jensen KJ, Alsina J, Songster MF, Vagner J, Albericio F, Barany G. Backbone amide linker (BAL) strategy for solid-phase synthesis of C-terminal-modified and cyclic peptides. J Am Chem Soc 1998 120 5441— 5452. 

Ozonolysis of Cyclic Nitronates This very interesting approach to cleavage of the nitronate fragment has been recently demonstrated by Linker and coworkers using two optically pure five-membered cyclic nitronates as an example (263a) (Scheme 3.118). 

Scheme 1.5 Disaccharide synthesis on a solid support using a cyclic horonic acid ester linker.

FIGURE 5.23 Synthesis of cyclic peptides by head-to-tail cyclization of resin-bound peptides using Boc/Bzl chemistry59 and Fmoc/tBu chemistry.60 The carboxy-terminal protectors are orthogonal to the other protectors. The nature of the linker determines the nature of the product. Both chemistries are compatible with the two types of linkers. All = allyl. 

Figure 9. Dependence of Dapp of compound 6 (O, right axis) and compound 7 (, left axis) on the weight fraction of the cross-linker. Obtained by cyclic voltammetry and potential-step chronoamperometry on a 3-mm-diameter glassy carbon electrode under argon 0.1 M NaCl, 20 mM phosphate buffer, pH 7, 37 °C, 20 mV/s. Reprinted with permission from ref 126. Copyright 2003 American Chemical Society.

Syntheses of this class of compounds usually involve 1,2,5-thiadiazepine ring 333 (Figure 6) which is stable in the S-oxidized form and structurally represents cyclic pyrrole N-sulfonyl derivatives. Most of the synthetic strategies include formation of an S-Npyrroie bond in the early stages. A final cyclization step typically includes (i) intramolecular cyclization by creation of an N-X bond from a suitable pyrrole precursor or (ii) a 6 + 1 type cyclization that involves dielectrophilic species to form linker X and utilizes the nucleophilicity of the phenyl amino group and of the pyrrole ring at C2. Intramolecular processes with the formation... 

Chambers TC, Pohl J, Glass DB, Kuo JF (1994) Phosphorylation by protein kinase C and cyclic AMP-dependent protein kinase of synthetic peptides derived firom the linker region of human P-glycoprotein. Biochem J 299 309-315... 

While the thiol groups were found to be suitable for gold surfaces, cyclic disulfide systems were preferred. The spacer length was also found to be a critical parameter, as very short linkers produce ill defined layers that improve considerably with increased length. On the other hand, highly organized layers tend to limit the number of bacteria bound to them, whereby extended spacers form a brush -like surface coat and increase bacterial trapping ... 

Dihydroxyethyleneurea (DHEU) (6) is also a cross-linker, but is extremely vulnerable to hydrolysis in an alkaline home laundering. Another approach toward formaldehyde-free agents has been the use of glyoxal in the bridging group between cyclic DHEU and related ring systems (108). 

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