Estimation in a Cox regression model with a change-point according to a threshold in a covariate

The building block approach was identified as a useful alternative to the commonly used Bucherer-Berg method for the preparation of cyclic unusual (alpha)-amino acid derivatives. The symmetrical building blocks were prepared by dialkylation of ethyl isocyanoacetate under solid—liquid phase transfer catalysis conditions while the unsymmetrical building blocks were prepared by a stepwise alkylation of the OʹDonnell Schiff base. Metathesis reactions, Suzuki couplings, and cycloaddition reactions were utilized to assemble the building blocks.