A high voltage programmable ramp generator.

In this paper, a ramp generator with programmable slope is presented. It consists of a high voltage step generator, followed by integrator. The capacitor and inductor in the integrator are designed such that they can be varied by a microcontroller. This circuit generates two bipolar ramps with fastest speed <1 ns and provides continuous speed variation from 6 to 30 ns for a ramp of 500 V. This is being developed as a part of automated streak camera for deflection of electron beam.

Synthesis of C-glycosylarenes by way of internal reactions of benzylated and benzoylated carbohydrate derivatives.

"Internal" C-glycosylarenes [e.g., (2R,3S,3aS,9bR)-3,3a,5,9b-tetrahydro-3-methoxy- and -3,7-dimethoxy-2-methoxymethyl-2H-furo[3,2-c][2]benzopyran] were prepared by intramolecular reactions of 2-O-benzyl derivatives of methyl 3,5-di-O-methyl-D-xylofuranoside (2) and their conversion into authentic C-glycosylated aromatic systems was investigated. The auxiliary benzylic linkage could not be cleaved by hydrogenolysis; isochroman derivatives (e.g., (3S)-3,4-dihydro-3-[(1R,2R)-2-hydroxy-1,3-dimethoxypropyl]-5-metho xy-1H- 2-benzopyran) were obtained under these conditions. However, oxidation of the primary benzylic position with ruthenium tetraoxide gave the corresponding lactone (a dihydroisocoumarin derivative, e.g., (2R,3S,3aS,9bR)-2,3,3a,9b-tetrahydro-3,7-dimethoxy-2-methoxy - methyl-5H-furo[3,2-c][2]benzopyran-5-one) which could be opened by saponification, thereby leading to a stereochemically unique C-glycosylbenzoic acid derivative. The same type of lactone was obtained directly from a derivative of 2 bearing a sufficiently reactive benzoyl group at O-2 (3,5-dimethoxybenzoyl); this process provides a useful approach to a heterocyclic system present in a variety of natural products. In related studies, the 2-O-phenyl substituent was found to be much less reactive than the 2-O-benzyl group in intramolecular Friedel-Crafts reactions of 2-O-substituted glycofuranosides. The first examples of successful internal C-arylation in the pyranoid series were achieved from 2-O-(3-methoxybenzyl)-D- mannopyranosides; the resulting "internal C-glycosides" [( 2R,3S,4S,4aS,10bS)-2,3,4,4a,6,10b- hexahydro-3,4,8-trimethoxy-2-methoxymethylpyrano[3,2-c][2]benzopyr an and 3,4-bis(benzyloxy)-2-benzyloxymethyl-8-methoxy analog] contain a heterocyclic skeleton closely related to that of the natural product bergenin.

Design of microcontroller based system for automation of streak camera.

A microcontroller based system has been developed for automation of the S-20 optical streak camera, which is used as a diagnostic tool to measure ultrafast light phenomenon. An 8 bit MCS family microcontroller is employed to generate all control signals for the streak camera. All biasing voltages required for various electrodes of the tubes are generated using dc-to-dc converters. A high voltage ramp signal is generated through a step generator unit followed by an integrator circuit and is applied to the camera's deflecting plates. The slope of the ramp can be changed by varying values of the capacitor and inductor. A programmable digital delay generator has been developed for synchronization of ramp signal with the optical signal. An independent hardwired interlock circuit has been developed for machine safety. A LABVIEW based graphical user interface has been developed which enables the user to program the settings of the camera and capture the image. The image is displayed with intensity profiles along horizontal and vertical axes. The streak camera was calibrated using nanosecond and femtosecond lasers.

Total synthesis of the potential anticancer vaccine KH-1 adenocarcinoma antigen.

Human tumours are often marked by the expression of unusual carbohydrate structural motifs. These carbohydrate domains are manifested as cell-surface bound glycolipids or glycoproteins. This raises the possibility of using cell-free equivalents of these domain compounds, obtained by total synthesis with a view towards triggering some level of immune response. In fact, the serum of mice immunized with fully synthetic compounds that mimic cell-surface tumour antigens has already been shown to recognize pertinent human cancer cell lines. Further advances in this field depend critically on the availability of these tumour-associated carbohydrate antigens which cannot be readily isolated from natural sources in sufficient quantities. Here we present the successful total synthesis of an adenocarcinoma antigen, KH-1, and of a bioconjugatable analogue which can bind to a carrier protein. These results illustrate the capabilities of oligosaccharide synthesis for reconstructing the challenging structural motifs characteristic of carbohydrate antigens, and thereby open up new possibilities for the development of anticancer vaccines.