Synthesis of Carboranyl Amino Acids, Hydantoins, and Barbiturates

The syntheses of three novel boronated hydantoins, 5-( o -carboran-1-ylmethyl)hydantoin, 14, the tetraphenylphosphonium salt of 7-(hydantoin-5-ylmethyl)dodecahydro-7,8-dicarba- nido -undecaborate, 15, 5-( o -carboran-1-ylmethyl)-2-thiohydantoin, 16, and two new barbiturates, 5,5-bis(but-2-ynyl)barbiturate, 18, and 5,5-bis[(2-methyl- o -carboran-1-yl)methyl]barbiturate, 20, are described. Hydantoins 14−16 were synthesized from o -carboranylalanine (Car, 13 ). The detailed syntheses of Car and two other carborane-containing amino acids, O -( o -carboran-1-ylmethyl)tyrosine (CBT, 5a ) and p -( o -carboran-1-yl)phenylalanine (CBPA, 5b ), presented earlier as a communication, 16 are also described. Hydantoin 14 and barbiturates 18 and 20 were tested for their potential anticonvulsant activity. Initial qualitative screening showed moderate activities for hydantoin 14 and barbiturate 18 . Barbiturate 20 had no activity. Compound 14 appeared to be nontoxic at doses of 300 mg/kg (mice, ip) and 50 mg/kg (rats, oral). However, 18 was very toxic under similar conditions.