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R K Sehgal

Publications and source records attributed to R K Sehgal.

14 recordsLinked to original sources
PubMed1992

Isolation of experimental anti-AIDS glycerophospholipids by micro-preparative reversed-phase high-performance liquid chromatography.

The experimental anti-AIDS glycerophosphatidic acid: nucleoside (sn-1/sn-2 diacylglycerol:dideoxynucleotide) drugs 3'-azido-3'-deoxythymidine monophosphate diglyceride (AZT-MP-DG) and 2',3'-dideoxycytidine monophosphate diglyceride (ddC-MP-DG) were isolated and purified by reversed-phase high-performance liquid chromatography (HPLC). The chromatographic separation was based on the glycerophospholipid moiety of the drugs and detection of the nucleoside component. The separations were optimized on method development columns packed with the stationary phase to be used in the micro-preparative column and monitored by a UV detector. Fractions were collected and analyzed for purity by analytical-scale HPLC and by thin-layer chromatography (TLC). The purity of the recovered drugs based on UV and light-scattering detection and on TLC was greater than 99%. The purified compounds were isolated for studies on structure confirmation, physical, biophysical and formulation properties and anti-HIV efficacy in culture.

Acquired Immunodeficiency Syndrome↗
PubMed1991

High-performance liquid chromatographic analysis of 3'-azido-3'-deoxythymidine monophosphate diglyceride, an anti-HIV glycerophospholipid.

A reversed-phase chromatographic method is described for the analysis of an experimental anti-AIDS drug 3'-azido-3'-deoxythymidine monophosphate diglyceride (AZT-MP-DG) [J.M. Steim et al., Biochem. Biophys. Res. Commun. 171, 458-464 (1990)] [1], a phosphatidic acid derivative of AZT. Analytical conditions were based upon conventional separations of glycerophospholipid species. Where AZT-MP-DG was monitored by UV absorption, there were two wavelength maxima. The response was linear in the concentration range used in this study. The peak was characterized by absorbance ratios with a rapid scanning UV detector.

Acquired Immunodeficiency Syndrome↗
PubMed1990

Lipid conjugates of antiretroviral agents. I. Azidothymidine-monophosphate-diglyceride: anti-HIV activity, physical properties, and interaction with plasma proteins.

3'-Azido-3'-deoxythymidine-5'-phosphate diglyceride (16:0/18:1 omega 9), a phosphatic acid conjugate of AZT, is active against HIV replication in H9 cells and syncytia formation in MOLT-3 cells. The activities rank as AZT greater than pure conjugate greater than conjugate in mixed liposomes, with the pure conjugate having about one-third the activity of free AZT. The compound binds very rapidly to serum lipoproteins, but not to serum albumin, alpha and beta globulins, or red cells. Pancreatic phospholipase A2 hydrolyzes it to the lysophosphatidic acid conjugate.

Antiviral Agents↗
PubMed1990

Preparative-scale high-performance liquid chromatographic separation and purification of 3'-azido-3'-deoxythymidine-5'-phosphate.

Crude 3'-azido-3'-deoxythymidine-5'-phosphate (AZT-P), obtained from direct phosphorylation of 3'-azido-3'-deoxythymidine (azidothymidine, AZT), was separated and purified by isocratic preparative high-performance liquid chromatography. The components in a 2.5-g load of crude AZT-P, obtained from work-up of the phosphorylation reaction, were separated in 50 min to give 1.8 g of 99.5% pure AZT-P. AZT-P was analyzed by high-performance liquid chromatography and by high-resolution nuclear magnetic resonance (1H, 13C, 31P) spectroscopy. The practical and rapid preparative chromatographic method is being applied to the purification of AZT-P and other antiretroviral dideoxynucleotides, used as intermediates in the synthesis of target-directed experimental drugs for the treatment of AIDS.

Chromatography, High Pressure Liquid↗
PubMed1988

Synthesis and biological properties of actinomycin D chromophoric analogues substituted at carbon 7 with aziridine and cyclopropyl functions.

The growing importance of functionalized tricyclic rings, e.g., cyclopropyl and aziridine, in numerous organic biomolecules led us to develop syntheses of novel actinomycin D (AMD) analogues substituted with aziridine and cyclopropyl functions. Reaction of 7-hydroxyactinomycin D with 1-aziridineethyl iodide and bromomethylcycloporopane afforded the desired 7-[2-(1-aziridinyl)ethoxy] and cyclopropylmethoxy analogues, respectively. Calf thymus DNA binding of these analogues was comparable to that of AMD as examined by UV-vis difference spectral measurements, CD techniques, and relaxation of supercoiled closed circular SV40 DNA, indicating an intercalative mode of binding to the DNA duplex. Thermal denaturation of DNA experiments employing higher temperatures than room temperature exhibit a thermal lability of the DNA analogue complexes, suggestive of a probable covalent bond formation with DNA bases. The analogues were found to be 1/4-1/40 as cytotoxic to human lymphoblastic CCRF-CEM leukemia and B16 melanoma cells in vitro as AMD, with ID50 values in the nanomolar concentration range.

Aziridines↗
PubMed1988

Enantiomers of 7-(2,3-epoxypropoxy)actinomycin D as dual-action DNA-acting antitumor agents.

Enantiomeric forms of (+/-)-EPA [racemic 7-(2,3-epoxypropoxy)actinomycin D] have been synthesized; these are (R)-(+)- and (S)-(-)-EPA, which are active against a range of actinomycin resistant and marginally responsive tumors. The R-(+) enantiomer is uniformly superior to the other forms in all the tumor lines tested. These enantiomers act by binding to DNA, both by intercalation and alkylation at the guanine base of DNA. They are superior to actinomycin D in their in vitro activity against mouse leukemias (L1210 and P388/ADR) and mouse melanoma B16. This superior activity is also evident against all the preceding mouse leukemias and against solid tumors B16 and C26 in vivo. In biochemical action, the enantiomers behave similarly and act primarily by inhibiting DNA synthesis in tumor cells; the only difference found was in their preference for sites in DNA bases during alkylation. The R-(+) enantiomer generates an adduct that is believed to be bonded to the N7-site of guanosine; conversely, the S-(-) isomer forms two adducts with DNA that are different from the preceding one by HPLC and are tentatively assigned O6-guanosine-substituted structures on the basis of their UV, CD, and other chemical behaviors.

Animals↗
PubMed1987

Synthesis and biological properties of actinomycin D chromophoric analogues substituted at the 7-carbon with aziridine and aminopropoxy functions.

The growing importance of functionalized aziridines in numerous organic biomolecules led us to develop syntheses of novel actinomycin D (AMD) analogues substituted with an aziridine. Reaction of 7-hydroxyactinomycin D with 2-(iodomethyl)aziridine produced the desired 7-(2-aziridinylmethoxy)actinomycin analogue. In an attempt to develop an alternate route to this analogue, 7-(2-azido-3-iodopropoxy)actinomycin was subjected to reduction with dimethylamine-borane complex; the reaction did not produce the three-membered aziridine; instead the reaction product was found to be linear 7-(2-aminopropoxy)actinomycin D. Calf-thymus-DNA binding of these analogues was comparable to that of AMD as examined by UV-visible difference spectral measurements, thermal denaturation of DNA, and CD techniques. The analogues were found to be about 1/4 to 1/30 as cytotoxic to human lymphoblastic CCRF-CEM leukemia and B16 melanoma cells in vitro as AMD.

Cell Line↗
PubMed1985

"Reverse" and "symmetrical" analogues of actinomycin D: metabolic activation and in vitro and in vivo tumor growth inhibitory activities.

Two new classes of actinomycin D analogues, tetracyclic "reverse" analogues and a tricyclic "symmetrical" analogue of actinomycin D, are reported. These analogues bind to DNA and the binding does not occur by an intercalation mechanism. The analogues inhibit the synthesis of DNA and RNA in P388 tumor cells and the growth of CCRF-CEM cells in vitro at nanomolar concentrations. The tetracyclic "reverse" analogues, which are structurally related to the previously reported actinomycin D oxazolyl analogues, are metabolized in the presence of rat hepatic microsomes and tumor cell homogenates. The metabolism takes place with the loss of the oxazole ring; thus the "reverse" analogues produce a major metabolite which is the "symmetrical" analogue; the actinomycin oxazolyl analogues generate 7-hydroxyactinomycin D. Further, the microsomes activate the analogues to free-radical states which catalyze the production of superoxide as shown by stimulation of epinephrine oxidation and also indicated by electron paramagnetic resonance studies. The "symmetrical" and "reverse" analogues also demonstrate very high activities in these systems. In in vivo studies using P388/S, P388/ADR leukemia, and B16 melanoma in mice, the analogues showed increased activity and superior therapeutic index values, in comparison to actinomycin D.

Animals↗
PubMed1985

Enzymic and chemical reduction of 2-deaminoactinomycins to free radicals.

The antitumour activity of actinomycin D (AMD) has been proposed to result, in part, from its intercalation into DNA dG-dC base-pairs leading to an inhibition of RNA synthesis. We have recently prepared 2-deamino-2-nitroactinomycin D and 2-deamino-actinomycin D and determined that, unlike AMD, these analogues do not intercalate into calf-thymus DNA. In the present study we show that these analogues and their corresponding peptide-free diethylamino derivatives are more effective than the parent AMD in forming ion radicals, in stimulating oxygen uptake and in forming superoxide anion when incubated in the presence of NADPH and NADPH cytochrome P-450 reductase. NaBH4-mediated reduction of these compounds yielded free radicals as shown by electron paramagnetic resonance (e.p.r.) spectroscopy. Free radicals could also be generated by incubation of these actinomycins with NADPH and either liver microsomes or purified NADPH cytochrome P-450 reductase. In the presence of molecular oxygen these free radicals spontaneously reoxidized by transfer of a single electron to molecular oxygen to form superoxide. Relative rates of superoxide formation were established for these substrates with the 2-deamino-2-nitroactinomycin D exhibiting the highest activity. It is proposed that the antitumour activity of these AMD analogues results, in part, from their ability to form reactive reduced oxygen species and, as such, these actinomycin derivatives may serve as useful probes for the tumouricidal mechanism of this family of agents.

Dactinomycin↗
PubMed1979

Potential radiosensitizing agents. Dinitroimidazoles.

New compounds of the nitroimidazole series have been synthesized as radiosensitizers which selectively sensitize hypoxic cells to the lethal effect of radiation. The reaction of 2,4(5)-dinitroimidazole (2) with chloroethanol or hydrochloric acid yielded 4(5)-nitro-5(4)-chloroimidazole (3), which upon reaction with ethylene oxide yielded the 4-nitro-5-chloroimidazole-1-ethanol (6). Reaction of 2 with ethylene oxide resulted in a mixture of two compounds, the 2,4-dinitroimidazole-1-ethanol (4) and 2,3-dihydro-5-nitroimidazo[2,1-b]oxazole (5). The structure of the new heterocyclic compound 5 was confirmed by 1H NMR, mass spectrum, and X-ray crystallography. These agents were tested for their ability to sensitize hypoxic Escherichia coli cells to killing by ionizing radiation. Compound 4 was found to be the most active agent of this series of compounds.

Chemical Phenomena↗