Thioether moiety

The 1,4-addition of ZnEt2 to 2-cyclohexenone was also performed by these workers in the presence of thioether-phosphite D-xylose-derived ligands, depicted in Scheme 2.11. In all cases, the chemoselectivities in the 1,4-product were higher than 97% but the enantioselectivities were modest (<41% ee). It was noted that changing the substituent in the thioether moiety produced an elfect on both the reactivity and the enantioselectivity, as shown in Scheme 2.11. 

The deprotection of the polyamine-thioethers 40a,b can also be accomplished in similar good yields with Li/naphthalene in THF (214). Cleavage of the thioether functions also commenced with [PdCl2(NCMe)2] in the case of 40b (216), and it is likely that the other macrobicycles will also undergo this metal-ion mediated cleavage reaction as well (Scheme 2). Note that this reaction cleaves only one of the two thioether bonds forming a macrocyclic ligand with one thiophenolate and one vinyl-thioether moiety, as... 

The protonation of 3-thio methyl-l-methoxy-l,2-allenes 90 affords 3-methylthio-enals 91 [43]. Hydrolysis can, on the other hand, be directed to the thioether moiety with HgCl2-MeOH leading to l,l-dimethoxy-3-ketones 92 [43],... 

The reaction of 389 with hydrazine hydrate resulted in replacement of the thioether moiety by hydrazine and formation of 390 (Equation 58) <2002PS2745>. 

Pd),99 and quasi-symmetrical MCipSo and MCortho contacts (2.019(3)/2.081 (3) A for Ni, and 2.198(4)/2.325(4) A for Pd). The preference for ip -BCC vs. ri1-B bonding of the PSB ligand in these complexes was attributed to the coordinatively unsaturated nature of the metal fragments (formal 14e counts when only the coordination of the phosphine and thioether moieties are taken into account). 

In another route (Scheme 2), mixing benzhydrol 12 with thioglycolic acid 13 in trifluoroacetic acid afforded benzhydrylsulfanylacetic acid 14 in 99% yield. The treatment of acid 14 with thionyl chloride, followed by concentrated ammonium hydroxide gave acetamide 11 in 87% yield. The oxidation of the thioether moiety with 30% H202 in acetic acid produced racemic modafmil 1 in 67% yield.27 The overall yield of the three-step route is approximately 57%. 

Finally, a thia Diels-Alder reaction representing a less common cycloaddition type in natural product synthesis shall be discussed. Thus, Vedejs et al. have included such a cycloaddition into an elegant strategy aimed at the synthesis of macrocyclic [ll]-cytochalasans such as zygosporin E 7-76 [536-538]. Thus, release of the thioaldehyde 7-73 from its phenacyl sulfide precursor in the presence of the silyloxydiene 7-74 yielded 7-75 as 2 1 mixture with its C20 epimer. Fortunately, equilibration of this mixture raised the ratio up to 10 1. Several subsequent steps yielded the tetracyclic intermediate 7-77 cleavage of its thioether moiety then liberated the 11-membered macrocycle present e.g. in zygosporin E 7-76 (Fig. 7-16). 

Hypochlorous acid, whose pKa value is close to 7, reacts with various compounds as a one- or two-electron oxidant, or as the chlorinating agent. Due to the presence of multiple potential reductants, HOC1/OC1- lifetime in biological systems is very short. Thiol and thioether moieties of cysteine and methionine (FI 1),... 

The application as optical sensor is possible based on sensitive films containing thioether moieties which exhibit changes in optical absorption when probed by guided light. Moreover, by combination with the fiber coating material described above (Fig. 2) the potential for fabrication of fiber optical sensors is evident. 

Finally, a recent report described the synthesis of 2D sql frameworks from the reactions of BiBr3 and Zn(T3MTPP), or Cu(T3MTPP) (T3MTPP = 5,10,15,20-tetrakis[3,4,5-tris(methylthio)phenyl]porphyrin) in a nitrobenzene-benzene solvent mixture (124). As shown in Fig. 28, the frameworks contain four-connected porphyrins that bridged two-connected Bi2 units. Thioether moieties of tris-(methylthio)phenyl groups coordinated to the Bia... 

Icmt catalyzes the methyl esterification of the prenylated cysteine residue after Reel has proteolyzed the -CaaX-containing proteins. The first step in identification of the minimal substrate for Icmt was through identification of AFC (Figure 9.2) as described above. Interestingly, farnesylcys-teine (FC), which is devoid of the acetyl substitution, was not a substrate but did possess some activity as an inhibitor [51], suggesting that the free amine of FC requires modification for catalytic turnover. Alterations in the stereochemistry about the FC backbone also appeared to be detrimental to substrate activity. The stereoisomer, d-AFC, was not a substrate for Icmt but was a modest mixed-type inhibitor of the enzyme. AFC-methyl ester (AFC-Me) was also reported to be a mixed-type inhibitor with respect to both l-AFC and -adenosylmethionine (SAM), the methyl donor, with Ki values of 41 and 73 pM, respectively [52,53] The farnesyl homocysteine homolog of AFC is not a substrate for the enzyme however, the racemic DL-homocysteine farnesyl derivative is in fact a weak inhibitor [40]. Similar to the results with racemic prenylcysteine, these data demonstrate that the linker between the carboxylate and thioether moieties is critical for substrate activity. 

As mentioned in Sect. 1, bis(naphthalic anhydrides) are characterized by lower electrophilic reactivity compared to that of bis(phthalic anhydrides) introduction of ether and thioether moieties, i.e. electron-donating substituents, leads to a further decrease in electrophilic reactivity. These circumstances have predetermined an expedient transition from electron-donating hinge moieties to electron-accepting ones, in particular from dianhydrides with thioether groups to dianhydrides with sulfone fragments. This is carried out according to... 

The interaclion between g and g was investigated through laser pumped dye laser spectroscopy at X=430 nm and steady state fluorescence measurements. Rgure 2 clearly shows that the thioether moiety is mostly responsible for the deactivation process occuring in the S. state and which is admittedly related to a back electron transfer. 

The thioether moieties are supposedly generated by addition of the thiol groups of cysteines to one of the unsaturated side chains formed by H2O-elimination in the peptides after their biosynthesis (Fig. 27). 

By treatment with gaseous CO2, a layer containing the amino derivative (X = NH) exhibited new signals at 1560 and 1540 cm in the infrared spectra due to formation of carbamic acid derivatives [7] (Scheme 4). By treating a cured layer containing the thioether moiety (X = S) with gaseous SO2 a new signal at 320 nm was observed by UV-Vis spectroscopy this is attributed to the formation of a thioether/S02 adduct [8] (Scheme 4). 

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