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Cleavage by iodine

FIGURE 6.21 (A) Removal of trityl and acetamidomethyl from sulfhydryl by oxidative cleavage by iodine. (B) Cleavage of terf-butylsulfanyl by mercury(II) acetate,88 followed by displacement of the metal ion by hydrogen sulfide. [Pg.183]

Similarly in 5-4, the cleavage by iodine of the methyl-tin bond rather than the benzyl-tin bond is suggested to be due to stabilisation of the Se2 transition state by ligation by the nitrogen.39... [Pg.74]

Random incorporation of modified residues in in vitro transcribed RNA is of particular interest in analogue interference experiments (Section 4.6.3) where randomly modified RNA molecules with altered properties are selected and compared to the original pool of RNA molecules. A crucial prerequisite for the interference analysis is the ability to identify the modified residues. A convenient and efficient method is the use of nucleotides which contain both the modification of interest (e.g. 2 -0-methyl NTP, dNTP, inosinetri-phosphates) and an a-phosphorothioate group (one of the nonbridging oxygens is replaced with a sulphur).14-16 The concurrent incorporation of the phosphorothioate renders the modified nucleotides sensitive to a selective cleavage by iodine. [Pg.41]

As inert as the C-25 lactone carbonyl has been during the course of this synthesis, it can serve the role of electrophile in a reaction with a nucleophile. For example, addition of benzyloxymethyl-lithium29 to a cold (-78 °C) solution of 41 in THF, followed by treatment of the intermediate hemiketal with methyl orthoformate under acidic conditions, provides intermediate 42 in 80% overall yield. Reduction of the carbon-bromine bond in 42 with concomitant -elimination of the C-9 ether oxygen is achieved with Zn-Cu couple and sodium iodide at 60 °C in DMF. Under these reaction conditions, it is conceivable that the bromine substituent in 42 is replaced by iodine, after which event reductive elimination occurs. Silylation of the newly formed tertiary hydroxyl group at C-12 with triethylsilyl perchlorate, followed by oxidative cleavage of the olefin with ozone, results in the formation of key intermediate 3 in 85 % yield from 42. [Pg.245]

The cleavage of phenylmercuric iodide by iodine in the presence of excess iodide ion (to suppress free-radical reactions) at 25 °C in aqueous dioxan was reported to be first-order in both aromatic and tri-iodide ion, and faster than the reaction of alkylmercuric iodides724. A further study, together with bromodemercuration, both reactions being generally represented by... [Pg.361]

Using day supported ammonium nitrate (dayan), selective deprotection of methoxyphenyl methyl (MPM) ether has been achieved recently using microwave irradiation in solvent-free conditions (Scheme 6.15) [56]. The same reagent has been used for the cleavage of tetrahydropyranyl (THP) ethers. A similar selective preparation and deavage of THP ethers has been achieved under microwave irradiation catalyzed by iodine [57] or neat reaction in an ionic liquid [28],... [Pg.190]

A reasonable mechanism for the iodine oxidation of 5-Trt cysteine peptides is given in Scheme 6. 45 Reaction of iodine with the divalent sulfur atom leads to the iodosulfonium ion 5 which is then transformed to the sulfenyl iodide 6 and the trityl cation. Sulfenyl iodides are also postulated as intermediates in the iodine oxidation of thiols to disulfides. The disulfide bond is then formed by disproportionation of two sulfenyl iodides or by reaction between the electrophilic sulfur atom of R -S-I and the nucleophilic S-atom of a second R -S-Trt molecule. The proposed mechanism suggests that any sulfur substitution (i.e., thiol protecting group) capable of forming a stabilized species on cleavage, such as the trityl cation, can be oxidatively cleaved by iodine. [Pg.107]

A general procedure for the iodine reaction in the solid phase is shown in Scheme 9. Both Boc and Fmoc chemistry can be used to assemble the linear S-protected bis-cysteine peptides and for thiol protection the well-established Acm and Trt groups are usually used. Suitable solvents for the thiol-deprotection/oxidation step by iodine to form the disulfide are CH2C12, DMF, or aqueous AcOH. The final deblocking and cleavage from the resin is carried out under standard conditions. Modification at sensitive amino acid residues caused... [Pg.112]

STATISTICALLY CORRECTED SECOND-ORDER RATE COEFFICIENTS (l.mole-. SeC" ) FOR THE CLEAVAGE OF ALKYL-TIN BONDS BY IODINE IN SOLVENT METHANOL AT 20 °C AND IONIC STRENGTH 0.025 M3S... [Pg.164]

As a further illustration of this chemistry, the complexes Cp CO MSnPl and Cp(CO)3MSnPh2X (M = Mo, W X = Cl, Br) react with HC1 or HBr to yield trihalogenotin derivatives. There are even examples of the cleavage of Sn—C bonds preferentially to the M—Sn bond by iodine (equation 155)353. [Pg.1298]


See other pages where Cleavage by iodine is mentioned: [Pg.57]    [Pg.298]    [Pg.44]    [Pg.1296]    [Pg.44]    [Pg.1296]    [Pg.168]    [Pg.108]    [Pg.57]    [Pg.46]    [Pg.91]    [Pg.438]    [Pg.57]    [Pg.298]    [Pg.44]    [Pg.1296]    [Pg.44]    [Pg.1296]    [Pg.168]    [Pg.108]    [Pg.57]    [Pg.46]    [Pg.91]    [Pg.438]    [Pg.172]    [Pg.434]    [Pg.105]    [Pg.23]    [Pg.131]    [Pg.177]    [Pg.113]    [Pg.78]    [Pg.55]    [Pg.56]    [Pg.87]    [Pg.185]    [Pg.49]    [Pg.14]    [Pg.44]    [Pg.44]    [Pg.45]    [Pg.45]    [Pg.93]    [Pg.1592]    [Pg.696]   
See also in sourсe #XX -- [ Pg.375 , Pg.376 ]

See also in sourсe #XX -- [ Pg.375 , Pg.376 ]

See also in sourсe #XX -- [ Pg.375 , Pg.376 ]




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