| Abstract | Piperazinc-2, 5 diones have been prepared frequently by the cyclisation of dipeptide methyl esters under the action of methanol-ammonia. Prolonged exposure (up to 5 days) of dipeptide methyl esters to there conditions led to extensive racemization and an alternative synthesis was described by Nitecki et al. in which racemization did not occur. In this method, a tert-butyloxycarbonylpeptide methyl ester was treated with formic acid and he peptide methyl ester formate cyclized by boiling in mixture of toluene and sec-butanol. The preparation of sterically pure piperazine-2,5-diones by heating an unprotected dipeptide in phenol has also been described by Kopple and Ghazarian.
In this laboratory, the four stereo-isomeric cycloalanyl-tryptophans were obtained by the Fischer method without recemisation, and it was intended to use this method for the synthesis of other piperazine-2, 5-diones for optical rotatory dispersion studies. |
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