Thioether bridge

Fig. 5.18. 360 MHz H NMR spectra of oxidized horse heart cytochrome c. The labeled signals are assigned to a = 8-CH3, b = 3-CH3, c = 5-CH3, d = thioether bridge 2-CH3, e = axial methionine S-CH3 the resonances at 7.4 ppm (1-CH3) and 3.1 ppm (thioether bridge 4-CH3) are not shown. Chemical shifts are in ppm from DSS (adapted from [42]) (labeling as in Fig. 5.7B).

A new oxyhemocyanin molluskan (octopus) protein x-ray structure has been reported [188a]. The active-site is very similar to that observed for the horseshoe crab structure one of the six histidine ligands is involved in a thioether bridge, i.e., to a nearby cysteine. 

The amatoxins are cyclic octapeptides composed only of L-amino acids and containing a sulfoxide group instead of the thioether bridge in phallotoxin. Over 90% of the fatal cases of mushroom poisoning can be traced back to the amatoxins. Wieland et al. 234) have shown that, in addition to the toxins, the death cup contains a low concentration of an antitoxic cyclic decapeptide antamanide 108. 

J. Liu, J. Yang, Q. Yang, G. Wang, and Y. Li, Hydrothermally stable thioether-bridged mesoporous materials with void defects in the pore walls, Adv. Fund. Mater. 15(8), 1297-1302 (2005). 

The structure of cytochrome c determined by Dickerson and his colleagues (23, 24, 25, 26) is depicted in Figure 1. The heme group, which lies in a crevice of the essentially globular protein, is covalently bonded to the protein by thioether bridges between the porphyrin ring and two cysteine residues in the peptide chain. The iron atom is situated... 

Scheme 2 The synthesis of a carcerand, 3, from the joining of two differently substituted, deep cavity species via thioether bridges [7], reproduced by permission of The Royal Society of Chemistry...

Carcerands have also been prepared with OCH20 bridging units instead of the CH2SCH2 thioether bridges. The oxygen bridged carcerands have a slightly... 

Siegel s group is the synthesis of the first coran-nulene cyclophane 80 [56]. A striking feature of its H NMR spectrum is that the endo aromatic protons (Hj.) of the benzene ring, which are positioned almost directly over the center of the corannulene system, appear at remarkably high field ( =1,89). Furthermore, with no peak broadening up to 148 °C, it was established that dynamic conformational processes in the thioether bridges and bowl-to-bowl inversion of the corannulene moiety both have lower limits of 18 1 kcal mol . ... 

The cyclic polythioether complex [W(CO)4L] (L = 2,5,8,ll-tetrathia[12](2,5)thiophenophane was prepared by UV irradiation of [W(CO)6] in the presence of the ligand in thf. Variable-temperature H NMR studies showed that this species was fluxional, and the derived molecular structure indicated k -L-S S coordination (17). The thioether-bridged complexes [ W(CO)4)2T] (18), where L is the hexakis(alkylsulfanylmethyl)benzene, C6(CH2SR)6 (R = C5H11, Pr ) were obtained by reaction of [W(CO)4(NCMe)2] with the appropriate thioether. Reaction of [W(CO)4(tmpa)] (tmpa = V,iV,iV, iV -tetramethyl-l,3-propanediamine) with 1,5-diselenacyclooctane ([8]aneSe2) gave the cis-disubstituted produce [W(CO)4 [8]aneSe2 ]. 

Mitochondrial cytochrome c is perhaps the most widely studied of all metalloproteins with respect to its electrochemical properties. It is located in the inner-membrane space of mitochondria and transfers electrons between membrane-bound complex III and complex IV. The active site is an iron porphyrin with a redox potential (7) of -1-260 mV vs. NHE. The crystal structures of cytochrome c from tuna have been determined (8, 9) in both oxidation states at atomic resolution. It is found that the heme group is covalently linked to the protein via two thioether bridges, and part of its edge is exposed at the protein surface. Cytochrome c is a very basic protein, with an overall charge of -1-7/-l-8 at neutral pH. Furthermore, many of the excess basic lysine residues are clustered around the mouth of the heme crevice, giving rise to a pronounced charge asymmetry. 

Figure 35 Conversion of LctA to the mature form of lacticidin 481 catalyzed by LtcM. (a) Thioether bridge formation in lantibiotic biosynthesis leading to dehydration (-18 Da), (b) MS time course of isotopically depleted LctA conversion to lacticidin 481 by LtcM shows that little dehydration intermediates are observed.

In Rp. viridis the four hemes in the cytochrome suhunit are connected to the cysteine residues in the protein via thioether bridges. The heme planes are parallel to the helical axes, but only the special bacterio-chlorophyll pair and the heme of the nearest cytochrome share the same axis. The distance between this cytochrome iron atom and either Mg atom of [BChl b]2 is 21 A. The iron-iron distance within each cytochrome pair is 14 A while that between two cytochrome pairs is 16 A. As expected, [BChl 6)2 extracts electrons from the nearest cytochrome. 

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