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K A Sastry

Publications and source records attributed to K A Sastry.

At least 19 recordsLinked to original sources
PubMed1985

Reversible inhibitors of beta-glucosidase.

A variety of reversible inhibitors of sweet almond beta-glucosidase were examined. These included simple sugars and sugar derivatives, amines and phenols. With respect to the sugar inhibitors and, indeed, the various glycoside substrates, the enzyme has what can be considered a "relaxed specificity". No single substituent on glucose, for example, is essential for binding. Replacement of a hydroxyl group with an anionic substituent reduces the affinity while substitution with a cationic (amine) substituent enhances the affinity. Amines, in general, are good inhibitors, binding more tightly than the corresponding alcohols: pKiRNH3+ = 0.645pKiROH + 1.77 (n = 9, r = 0.97). The affinity of a series of 10 primary amines was found to be strongly influenced by substituent hydrophobicity: pKi = 0.52 pi + 1.32 (r = 0.95). The major binding determinant of the glycoside substrates is the aglycon moiety. Thus, the Ki values of phenols are similar in magnitude to the Ks values of the corresponding aryl beta-glucoside. The pH dependence for the inhibition by various phenols indicates that it is the un-ionized phenol which binds to the enzyme when an enzymic group of pKa = 6.8 (+/- 0.1) is protonated. The affinity of the phenol inhibitor is dependent on its basicity with a Brønsted coefficient for binding of beta = -0.26 (n = 14, r = 0.98). The pH dependence of the binding of two particularly potent beta-glucosidase inhibitors was also examined. 1-Deoxynojirimycin (1,5-dideoxy-1,5-imino-D-glucitol) has a pH-corrected Ki = 6.5 microM, and D-glucono-1,5-lactam has a pH-corrected Ki = 29 microM.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucosidases↗
PubMed1985

Myocardial imaging agents: synthesis, characterization, and evaluation of (Z)- and (Z,E)-18-[82Br]bromo-5-tellura-17-octadecenoic acids.

The effects of replacement of radioiodide with radiobromide on the biological properties of a model vinyl halide substituted tellurium fatty acid have been evaluated. The use of a facile radiobromination method involving the reaction of [82Br]Br2 with vinylmercuric bromide substrates has been investigated. Unexpectedly, both the cis- and trans-vinyl bromide products are formed as confirmed by chromatographic and spectral studies. With use of this technique, (E,Z)-1-[82Br]bromo-13-iodo-1-tridecene was prepared and used as the substrate to prepare (E,Z)-18-[82Br]bromo-5-tellura-17-octadecenoic acid (13-E,Z), which was evaluated in rats. Both [82Br]-13-E,Z and [82Br]-13-Z, prepared by an established procedure using N-chorosuccinimide-Br- reaction with the trans-boronovinyl substrates, showed tissue distribution properties similar to those of (E)-18-[125I]iodo-5-tellura-17-octadecenoic acid. These results demonstrate that replacement of I with Br and also the stereochemistry about the olefinic bond do not drastically affect heart uptake and retention.

Animals↗
PubMed1984

Effect of tellurium position on the myocardial uptake of radioiodinated 18-iodotellura-17-octadecenoic acid analogues.

The effect of tellurium (Te) position on myocardial specificity and retention of fatty acids in which radioiodide is stabilized as a trans-(E)-vinyl iodide has been evaluated in rats. Five analogues of 18-iodo-17-octadecenoic acid (ICH = CH-R-Te-R'-COOH) with Te at positions 5, 7, 9, 11, and 13 were prepared by coupling of a trans-diiodoalkene (ICH = CH-R-I) with the requisite sodium [(alkoxycarbonyl)alkyl]telluride substrate (NaTe-R'-COOR"; R" = Me or Et), followed by basic hydrolysis. By varying R and R', a series of analogues with a chain length of 18 carbon atoms was prepared. The telluride substrates were generated in situ by NaBH4 reduction of the corresponding ditellurides, and the diiodoalkenes were prepared by sodium iodide-chloramine-T treatment of the corresponding vinylboronic acids [(HO)2BCH = CH-R-I)]. The vinylboronic acids were prepared by treatment of the terminal acetylenes (HC identical to C-R-I), synthesized from commercially available materials, with catecholborane. All new compounds were analyzed by TLC, NMR, MS, and elemental analyses. The 125I analogues [(E)-125ICH = CH-R-Te-R'-COOH] were prepared in the same manner and evaluated in rats (four per group). Heart uptake and retention were dependent upon the Te position. The analogue with Te at position 5 showed the most pronounced (5-min values) heart uptake (3.7-4.1 dose/g), myocardial retention, and heart/blood ratios (37:1) and is a candidate for radiolabeling with 123I and further evaluation as a myocardial imaging agent.

Animals↗
PubMed1984

Synthesis and evaluation of radioiodinated (E)-18-iodo-17-octadecenoic acid as a model iodoalkenyl fatty acid for myocardial imaging.

125I-labeled (E)-18-iodo-17-octadecenoic acid (13) has been prepared and evaluated in rats to determine the myocardial uptake and retention and degree of in vivo deiodination of this model iodovinyl-substituted fatty acid, which contains no structural perturbation to inhibit metabolism. This new agent was prepared by NaI-chloramine-T treatment of (17-carbomethoxyheptadec-1-en-1-yl)boronic acid (11) prepared by catecholborane treatment of methyl 17-octadecynoate (10), followed by basic hydrolysis to the free acid (13). The pivotal substrate, 17-octadecynoic acid (9), was prepared by two new routes. The 125I-labeled acid 13 showed high myocardial uptake (1 h, 1.90-2.28% dose/g) with 45% washout after 2 h but lower heart/blood ratios in comparison to analogues containing the tellurium heteroatom. Deiodination was low for the first 2 h after injection (2 h, 61% dose/g). Excellent myocardial images were obtained in a dog with the 123I-labeled agent.

Animals↗
PubMed1983

New myocardial imaging agents: stabilization of radioiodine as a terminal vinyl iodide moiety on tellurium fatty acids.

To determine the myocardial uptake and retention properties of radioiodinated tellurium fatty acids, we prepared two new tellurium fatty acids in which iodine-125 has been chemically stabilized by attachment as a trans-vinyl iodide (I-CH = CH-R-Te-R'-COOH) and evaluated them in rats. Fabrication of 18-iodo-13-tellura-17-octadecenoic acid was accomplished by coupling 1,5-diiodo-1-pentene with sodium 12-(methoxycarbonyl)-n-dodecan-1-yl telluride. The [5-125I]-1,5-diiodo-1-pentene was prepared by an organoborane technique involving 125I+ treatment of 5-iodo-1-penten-1-ylboronic acid [I(CH2)3CH = CHB(OH)2]. The absolute heart uptake of this agent was moderate (1.47-2.52% dose/g after 60 min), but the heart/blood ratios were low (approximately 2.6:1). Only marginal in vivo deiodination occurred, since the thyroid uptake was low (15-18% dose/g after 60 min). The effect of tellurium in position 13 was unexpected. To determine if the low heart specificity and low heart/blood ratios were dependent upon the position of the tellurium, we prepared an analogue with the same chain length, 18-[125I]iodo-7-tellura-17-octadecenoic acid, in the same manner by reaction of [11-125I]-1,11-diiodo-1-undecene with sodium 6-(methoxycarbonyl)-n-hexan-1-yl telluride. This agent showed pronounced heart uptake (2.47-3.94% dose/g after 60 min) and prolonged retention (1.76-3.14% dose/g after 4 h) in rats. Furthermore, the heart/blood ratios remained high for several hours (13:1 after 60 min; 9:1 after 4 h). Iodine-123 labeled 18-iodo-7-tellura-17-octadecenoic acid is an attractive new compound for evaluation as a myocardial imaging agent.

Animals↗
PubMed1981

Rapid and mild syntheses of radioiodine-labeled radiopharmaceuticals.

Radioiodine-labeled pharmaceuticals have been used extensively in diagnostic nuclear medicine. We have developed a rapid and mild method for incorporating radioiodine into functionally substituted molecules. The new process involves the reaction of the radioiodide ion with organoboranes in the presence of gentle oxidizing reagents. The radioiodide is utilized nearly quantitatively in a matter of seconds. The radiochemical yields are excellent, and parallel those obtained when iodine monochloride is reacted with organoboranes.

Animals↗