PubMed · 3701474
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W Diller. 1986. Isocyanate effects.. https://pubmed.ncbi.nlm.nih.gov/3701474/
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alpha-Methyllysine and 2-amino-2-methylundecanoic acid, two alpha,alpha-disubstituted unnatural glycines, were synthesized using highly diastereoselective allylation or propargylation of chiral (1S,2R,4R)-10-dicyclohexylsulfamoylisobornyl 2-cyanopropanoate as the key step to introduce the long side chain. Chirality 16:106-111, 2004.
The current study has investigated the influence of esterase activity (80-400units/ml) on the biodegradation of polycarbonate-urethanes (PCNUs) by cholesterol esterase (CE), with a particular interest in studying the influence of different hard segment structures and their contribution to sensitizing the polymer towards enzyme catalyzed hydrolysis. Polycarbonate based polyurethanes were synthesized with varying hard segment content as well as hard segment chemistry based on three different diisocyanates, 1,6-hexane diisocyanate (HDI), 4,4'-methylene bisphenyl diisocyanate (MDI) and 4,4-methylene biscyclohexyl diisocyanate (HMDI). The effect of different chemistry on surface contact angle was measured in order to define the relative chemical nature of the surfaces. The enzyme dose response was found to be lower when hard segment content in the polymer was high. There was a very strong dependence on enzyme concentration for polyurethanes with different hard segment chemistry, despite the fact that the nature of the hydrolysable polycarbonate segment remained the same. The PCNU which showed the most dramatic dependence on enzyme concentration was synthesized with HMDI. At low enzyme concentration (80units/ml) this material was the most stable of the polymers while at elevated CE concentration (400units/ml) the polymer underwent a catastrophic breakdown. The findings suggested that protein binding on the surfaces was saturated even though enzyme degradation did not achieve saturation on any of the surfaces. The role of protein binding in modulating the hydrolytic action of the enzymes at different activity levels highlights a need for further study in this area.
Various aliphatic and aromatic [(75)Se]selenoethers were prepared at the no-carrier-added (n.c.a.) level using a new radiosynthetic pathway, based on the formation of alkyl[(75)Se]selenocyanates as intermediates. Using one-pot model reactions of elemental (75)Se, sodium cyanide and various alkylbromides in ethanol, the preparation of alkyl[(75)Se]selenocyanates was examined and optimized. Purification of these (75)Se-labeled intermediates and subsequent conversion with alkyl and aryl lithium or Grignard compounds in anhydrous diethyl ether yielded radioselenoethers with radiochemical yields of up to 55% (related to (75)Se(0)) within an overall reaction time of 20 min. This is the first method described to obtain n.c.a. arylselenoethers.