Sulphenyl derivatives

Bridged cations have been indicated as intermediates of the addition of bromine to dialkylacetylenes on the basis of the exclusive trans mode of the reactions. Bridged cations are in each case likely to be formed in the addition of sulphenyl derivatives to alkyl- as well as to arylacetylenes. The retention of trans configuration and the anchimeric assistance effects observed in SNl-type reactions of j8-arylthiovinyl sulphonates indicate that the bridged geometry is always favoured over a linear one. 

There have been frequent difficulties relating physiological effects to cyclic AMP levels. For example, adenosine inhibits the effect of noradrenaline on cyclic AMP accumulation in rat fat cells but does not interfere with the lipolytic effect of the catecholamine [58]. Both ACTH and its o-nitrophenyl sulphenyl derivative stimulate corticosterone synthesis in isolated rat adrenal cells to the same maximal rate, but the analogue has a 30- to 100-fold smaller effect than ACTH on cyclic AMP accumulation [60]. 

The preparation of some N-sulphenyl derivatives of S(NSO)2 has been described98 using the reaction ... 

The Chemistry of Thiiranium Ions. - The chemistry of episulphonium ions and the reactions of alkenes with sulphenyl derivatives have been reviewed Stable thiiranium and thiirenium chlorides have been generated in S02. Kinetic studies for the quantitative generation of (329 R =R = Bu, X = Cl) from the ionization of (328) and the equilibrium between (330) and (331) in SO2 were followed, using n.m.r. spectrometry. Compounds (329 R = Bu, X = SbCls or BF4) have been isolated as stable salts at room temperature... 

Sulphenyl derivatives, particularly the chlorides, add to olefinic double bonds, often with great facility (Scheme 4). This reaction has been exploited recently to... 

The conversion of thiols to various sulphenyl derivatives has been utilized as a means of thiol protection as well as, in many cases, a route to disulphides. Sulphenyl derivatives considered in this section include S-sulphonates, sulphenyl iodides, symmetrical and unsymmetrical disulphides (as used for protection) and certain heavy-metal derivatives. A summary of the chemistry of certain sulphenyl derivatives appeared earlier [159]. 

The reversible protection of the thiol group by conversion to an unsymmetrical disulphide has been accomplished by the action of various sulphenyl derivatives on peptide- or protein-bound cysteine residues. Althou these derivatives are likely to be most useful when only one disu hide bond (or one or more thiol groups) are desired, recent experiments by several laboratories indicates the promise of these S-protective groups which include S-aryl [167], S-ethyl [13], and S-t-butyl mercapto groups [168]. 

The formation of unsymmetrical disulphides by the reaction of S-sulphonates with thiols is analogous to a number of other sulphenyl derivatives. In general terms the reaction may be represented as shown in eq. 7.14. A number of intermediates in addition to the sulphenyl iodides [92], sulphenyl thiocyanates [108] and sulphenyl sulfonates [175] have been utilized to advantage in the synthesis of unsymmetrical disulphides. These include the monodisulphide dioxides (RSO2—), studied in detail by Field and his colleagues [178], the disulphide monoxides (RSO—) [178, 179] and more recently the S-monothiocar-bonates (ROCS--) [180] and sulphenamides [186]. 

A similar penicillin sulphoxide-cephalosporin transformation, initiated with acetyl chloride-pyridine, has also been described. The disulphide (93 b) and sulphenanilide (94 b) have been prepared from the sulphenic acid (80). These sulphenyl derivatives readily cyclize to penicillins (95 b) and cephems (96 b). 

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