SYNTHESIS OF 2-(PARA-BIPHENYLYL)ISOPROPYLOXYCARBONYLAMINO ACIDS AND DECOMPOSITION OF ARALKYL PHENYL CARBONATES

The syntheses of a number of new Bpoc‐amino acids and the preparation of some activated esters of Bpoc‐amino acids are described. In recent work on the total synthesis of calcitonin hormones the Bpoc residue has been found to be very useful for the selective protection of α‐amino groups of complicated intermediate peptide fragments. The reagent preferentially used for the introduction of the Bpoc group into amino acids, [2‐(p‐biphenylyl)‐isopropyl]‐phenyl‐carbonate (I), is stable at 0°, but undergoes at higher temperatures a decomposition which is a accelerated by phenol. Based on the reaction products formed — [2‐(p‐biphenylyl)‐isopropyl]‐phenyl‐ether (II), 2‐(p‐biphenylyl)‐propene (III), and phenol — a scheme is proposed for this thermal decomposition, and the possibility of a correlation between the stability of carbonates R3C—O—CO—OC6H5 and the rate of the acidolytic cleavage of urethanes R3C—O—CO—NHR′ depending on the substituents R is discussed. Copyright © 1969 Verlag GmbH & Co. KGaA, Weinheim