Phenylisothiocyanate substituted

FIGURE 5.19 N-Tertninal analysis using Edman s reagent, phenylisothiocyanate. Phenylisothiocyanate combines with the N-terminus of a peptide under mildly alkaline conditions to form a phenylthiocarbamoyl substitution. Upon treatment with TFA (trifluo-roacetic acid), this cyclizes to release the N-terminal amino acid residue as a thiazolinone derivative, but the other peptide bonds are not hydrolyzed. Organic extraction and treatment with aqueous acid yield the N-terminal amino acid as a phenylthiohydantoin (PTH) derivative. 

The mechanism involves the initial formation of a substituted urea followed by ring closure to form the thiohydantoin. The amino acid is dissolved in 60% aqueous pyridine containing the phenylisothiocyanate... 

Reaction 83 of with 4-substituted 1,3-oxazol-5(4//)-one 87 led to diacylhydra-zines 88 or to imidazole derivatives 89 depending on the reaction temperature (Scheme 14). l,2,4-Triazole-3-thione 91 was obtained by a two-step sequence from 83 with phenylisothiocyanate and subsequent base-catalyzed cyclization of thiosemicarbazide 90 [25],... 

The second special case is formed by the photoreactions of 2,4-dinitro-6-(phenyliodonio)phenolate (266) with several nucleophiles759. Upon irradiation of this fairly stable zwitterion in methanol, 6-methoxy-2,4-dinitrophenol is formed in 65% yield. Photoreaction with pyridine affords 2,4-dinitro-6-pyridiniophenolate (85%) and irradiation in the presence of phenyl isothiocyanate in acetonitrile affords a mixture of two stereoisomeric 2-phenylimino-5,7-dinitro-1,3-benzoxathioles (269) (71%) which could not be separated. The reaction starts with attack of the nucleophile on the positively charged iodine atom, leading to an iodinane (267) and proceeds by expulsion of iodobenzene. The mechanism is illustrated for phenylisothiocyanate, a case in which the substitution product (268) can undergo further photocyclization to a benzoxathiole derivative (269) (equation 196). 

Reaction of tertiary enaminones with benzoyl isothiocyanate gives substituted 2-pyridinethiones in moderate yields, indicating the reactivity of enaminones at a-methyl group6 (equation 2). Phenylisothiocyanate reacts simply at the -position7 (equation 3). 

Sequence Determination with the Help of Mass Spectra 25 ment with substituted phenylisothiocyanate can be applied... 

Early examples were restricted to the insertion into sulfur-hydrogen bonds (214-216). For example, addition of phenylisothiocyanate to [Au(SH)2] affords the bis(dithiocarbamate) complex [Au(S2CNHPh)2] (216). More recently, Shaver and co-workers (217) demonstrated a similar insertion into the sulfur-silicon bond of [CpRu(PPh3)2(SSi-i-Pr3)], yielding unusual silicon-substituted dithiocarbamate ligands (Eq. 35). 

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