Piperidine heterocycles are present in the structure of many alkaloids, for example coniine in the structures of lobelia, cocaine alkaloids and sedum alkaloids, Sedum alkaloids are 2,6-disubstituted derivatives of piperidine or N-methylpiperidine. Extracts obtained from Sedum acre L. were investigated for the presence of alkaloids by gas chromatography/mass spectrometry. Identification has been carried out on the basis of retention time, molecular ion mass and characteristic fragmentation. Investigated extracts contained unknown alkaloids which belong to the piperidine group of sedum alkaloids. Mass spectral fragmentation patterns and a proposed structure for the unknown alkaloids are discussed.

The optimal solution of the weakly coupled algebraic discrete Riccati equation is obtained in terms of a reduced-order continuous-type algebraic Riccati equation via the use of a bilinear transformation. The proposed method has a rate of convergence of O( epsilon /sup 2/) where epsilon represents a small coupling parameter. A real-world physical example (a chemical plant model) demonstrates the efficiency of the proposed method. Simulation results obtained using a package for a computer-aided control system are presented. For this specific real-world example, the algorithm perfectly matches the presented theory, since convergence, with an accuracy of 10/sup -4/, is achieved after nine iterations (i.e., 0.68/sup 18/=10/sup -4/). >