Formamidinesulfonic acid

The ornithine related phosphonate (n = 3) can be guanidylated at the 4-amino group by treatment with formamidinesulfonic acid to provide Argp(OPh)2. This method can be used for the synthesis of substrate-related thrombin inhibitors such as Ac-Phe-Pro-Argp(OPh)2. 41 Proline analogues required a special approach and a few synthetic methods are reported since dipeptides of Prop(OPh)2 are excellent inhibitors of dipeptidyl peptidase IV (DPP IV or CD 26), the serine protease involved in immune response. 4 Diphenyl phosphite and dialkyl phosphites react smoothly with 1-pyrrolidine (3,4-dihydro-2//-pyrrole) trimer 20 to give the corresponding pyrrolidine-2-phosphonate 21 (Scheme 14). 42 ... 

Equimolar amounts of cyclooctylamine and a suspension of aminoiminomethanesul-fonic acid (formamidinesulfonic acid) in methanol stirred at room temp, for 2 h product. Y 78%. F.e. incl. reaction with fcrf-butylamine s. K. Kim et al.. Tetrahedron Letters 29, 3183-6 (1988). 

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