Synthesis of boron-cluster containing amino acids and preparation of their polymers

Abstract

The first aim of this work was to prepare water soluble [B12H12]2- containing amino acids. This task was reached by using the ability of dodecaborate derivatives such as ammonio-undecahydro-closo-dodecaborate BNH3, hydroxo-undecahydro-closo-dodecaborate BOH and S-(2-cyanoethyl)-thio-undecahydro-closo-dodecaborate(2-)CE-BSH to undergo alkylation reactions. With this idea we used halogen substituted monoalkylated educts such as:- 4-Bromobutylacetamidodiethylmalonate. Alkylation reactions with BOH 4 and CE-BSH were made with high yield (93%) for CE-BSH and with moderate yield (53%) for BOH. Alkylation of BNH3 gave a mixture of mono- and dialkyl-substituted products. Separation of this mixture could not be achieved.- Chloroacetone. Alkylation of CE-BSH and BOH with chloroacetone was carried out with quantitative yields. We showed the ability of these ketones formed to give appropriate hydantoins.- (2S)-2-[(Tert-butoxycarbonyl)amino]-3-(p-tolylsulfonyl-oxy)propionate. It was shown that alkylation of CE-BSH with tosylated serine is possible.All alkylated derivatives were hydrolyzed in 6M NaOH to yield free amino acids. The solubility of synthesized amino acids depends of the cation. Cs increases solubility in water.In vitro toxicity tests were carried out with two amino acids having different number of carbons and two different heteroatoms between cluster and side chain. Toxicity test was done with V 79 Chinese hamster cells. For amino acid 13a LD50 was 5.7 mM and for 16a LD50 was 5.0 mM. According to these results, we can say that addition of an amino acid group to, e.g. the BSH cage, does not change the toxicity.For the second task of this work - synthesis of D,L-polypeptides - the ring-opening polymerization method was chosen. We showed the ability of the synthesized dodecaborate-containing amino acids to form N-carboxy anhydride by phosgenation. Polymerization was carried out with two initiators: n-butylamine and dansyl amine. It was shown that the initiator did not interact to the polymer structure, but act as a catalyst in the AM mechanism. The determination of the molecular weight of the synthesized polymers (number of monomers) failed, however.All synthesized compounds were identified by 1H-, 13C-, 11B-NMR, mass spectrometry, IR spectra. In the course of the characterization of [B12H12]2- containing compounds we found that the [B12H11]- ion is easily formed in ESI-MS. The origin of the peak at m/z 141 was found and proven in a MS/MS experiment. The MS/MS experiment of peak at m/z 141 showed of the following processes proceeding:- Hydroxylation - Addition of H2 - Exchange of D to H