Phenyl thioesters

Simple alkyl or aryl thioesters are commonly assayed as substrates of hydrolases, witness the hydrolysis of phenyl thioesters by horse serum carbox-ylesterase [150], For most substrates investigated, e.g., phenyl thioacetate, phenyl thiopropionate, and phenyl thiobutyrate (7.66, R = Me, Et, and Bu, respectively), kcat values were found, which were a few times larger than those of corresponding nitrophenyl esters, whereas the affinities were lower by approximately one order of magnitude. Methyl and phenyl esters of various linear thioacids were also found to be good substrates of mammalian liver carboxylesterases and serum cholinesterases [151]. 

A full-length human csk DNA that codes for Csk, a 50-kDa protein that catalyzes the phosphorylation of a tyrosine within the C-terminal tail of Srk, was inserted in a plasmid and in-frame with a modified intein-chitin binding domain (CBD) encoding sequence, where intein is a protein-splicing element. 130 The expressed protein underwent a conversion into a thioester of the N-terminal cysteine of the intein, but the normal second step of an intein splicing did not occur. The protein was then bound to a chitin resin and washed. The resin containing the bound protein was treated with 2% benzenethiol to cleave the thioester and give the free phenyl thioester, which was immediately treated with one of the synthetic... 

In order to better understand the early photophysics of PYP, we have carried out a comparative study of three model chromophores, the deprotonated frans-p-coumaric acid (pCA2 ) and its amide (pCM ) and phenyl thioester (pCT) analogues, in aqueous solution (see structures in Fig. 1). The excited-state relaxation dynamics was followed by subpicosecond transient absorption and gain spectroscopy. 

Similarly, enantiopure 3-substitutcd-/V-rnc thy I benzyl /3-sultams have been converted into A -methylbenzyl-a-amino acid thioesters via sulfenylation and Pummerer rearrangement with high or complete retention of configuration. Chiral sulfoxides were prepared by sulfenylation followed by oxidation of trans-isomers as two separable A and B stereoisomers. Treatment with TFAA gave chiral cr-amino acid thioesters in high yields with a de > 90%. Slight epimerization of the cr-chiral center of the cr-phenyl thioesters has been observed under the reaction conditions whereas no epimerization was observed in the case of -/-butyl thioesters (Scheme 28) <1998JOC8355>. 

Recognition of the value of active esters for peptide bond formation emerged from work with vinyl esters ly cyanomethyl esters 5-phenyl thioesters 9,P1 piperidino esters 10, 3-pyridyl esters 4-nitrophenyl esters 12 2,4,6-trichlorophenyl esters,and phthalimido esters 17.t l Many activating moieties have surfaced over the years but only a limited number have survived the test of time and are in use today. These include 4-nitrophenyl 12,M 2,4,5-trichlorophenyl pentachlorophenyl pentafluorophenyl succininoido... 

In studies directed toward intermediates for the synthesis of quadrone, Livinghouse demonstrated the utility of lithiated methoxy(phenylthio)(trimethylsilyl)methane (327) for the conversion of aldehydes and ketones to ketene 0,5-acetals (328) in good to excellent yields (Scheme 46). These Peterson alkena-tions gave predominantly the ( )-double bond isomer. As the example depicted in the scheme demonstrates, this procedure may be used to homologate a carbonyl to the phenyl thioester (329) in excellent yields. 

The excited-state deactivation pathway of PYP model chromophores is foimd to depend strongly on the substituent adjacent to the carbonyl group. The photoisomerization reaction of the deprotonated p-coumaric acid (pCA ) and of its amide analogue (pCNT) in solution does not show any spectroscopically detectable intermediate, which is quite different from PYP. On the contrary, the phenyl thioester derivative pCT exhibits a photophysical behavior in solution surprisingly close to that of the protein during its initial deactivation step. This study highlights the determining role of the thioester bond in the primary molecular events in PYP. 

The acylpalladiums such as 138 are generated by oxidative addition of thioesters and used for ketone synthesis as reported by Fukuyama. Coupling of ethyl thioester of phenylalanine 137 with alkylzinc reagent 139 using P(o-Tol)3 as a ligand gave 140 in high yield [59], Phenyl thioesters are also used [60],... 

Cleavage of the ketene 0,5-acetals under neutral or mildly basic conditions can be executed by using iodotrimethylsilane to give the phenyl thioester or the ketene 0-silyl,5-acetal (eqs 3 and 4). In addition, amides can be prepared by sequential treatment of ketene 0,5-acetals with lithium thiomethoxide in HMPA followed by addition of an amine (eq 5). ... 

T. Cohen and R. E. Gapinski. The conversion of esters to phenyl thioesters by boron thiophcn-oxide and aluminium thiophenoxide. Tetrahedron Letters, 1978, 4319. 

The adduct (31) formed from dialkyl sulphates and DMF is a potent esteri-fying agent for a range of carboxylic acids. Carbon dioxide-catalysed ester exchange has been described. Carboxylic acids react readily with diphenyl disulphide in the presence of triphenylphosphine to afford the corresponding phenyl thioesters. ... 

Tanabe and coworkers reported the first instances of additions of titanium enolates to ketones [8]. They reported moderate to excellent yields for several reactions. When the two substituents on the ketone were sufficiently sterically differentiated, good to excellent syn diastereoselectivity was observed. Representative examples of these crossed-aldol reactions are shown in Table 2.1. The initial method involved a catalytic (5 mol%) amount of trimethylsilyl trifiate in the reaction mixture it was suggested this generates a trichlorotitanium trifiate species in situ which is more effective at enoli-zation. This theory was, however, called into question by reports of additions of enolates to ketones with trimethylsilyl chloride as catalyst, which also provides moderate to good yields [9]. Additions of enolates of phenyl esters or phenyl thioesters to ketones were also shown to proceed in good yield and with syn diastereoselectivity in the absence of silyl additive [10]. 

Potassium acetate is used as a nucleophilic catalyst in the regioselective reaction of epoxides with 5-phenyl thioesters (eq 15).Similarly, the anionic polymerization of /3-butyrolactone is catalyzed with KOAc in combination with 18-crown-6 (eq 16). The title compound has been used as a fluoride ion-free method for the deprotection of TIPS-protected phenols (eq 17), and the mechanism of the carboxylate anions with TBS-protected phenols has been studied. 

Phenyl orthothioesters can be easily degraded to the corresponding phenyl thioesters by reaction with silver tetrafluoroborate. ... 

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