Moheswar Sharma

ROSFIT: An enzyme kinetics nonlinear regression curve fitting package for a microcomputer

Abstract A nonlinear regression curve fitting package has been specifically developed for enzyme kinetic analyses for use on the Hewlett-Packard HP-85 microcomputer. Data are entered in a conversational manner. Data can be changed, deleted or added, and data sets can be stored and retrieved from a magnetic tape cassette. Data can be fit to any of nine models: the Michaelis-Menten equation, substrate inhibition, random bi bi, ordered bi bi, ping pong bi bi, competitive inhibition, classical noncompetitive inhibition, modern noncompetitive inhibition, or uncompetitive inhibition. The printout for each model consists of several goodness-of-fit statistics, the parameter estimates with 95% confidence intervals, the variance-covariance, and correlation matrices, a residual analysis, and graphs. For example, for competitive inhibition the graphs provided are v vs [S], v vs [I], 1 v vs 1 [S] , and 1 v vs [I] with up to four concentrations of the second compound plotted on each graph. The nonlinear regression algorithm in the package is that of Marquardt. The values determined by ROSFIT are essentially the same as those found using the BMDPAR, BMDP3R, and NONLIN programs on a Univac 90 60 mainframe computer. A typical run for competitive inhibition with 46 data points took a total time of about 18.5 min, not including dat entry time, 14 min for the graph generation, 2 min for the three required iterations, and 2.5 min for miscellaneous operations.

Analogs of cell surface carbohydrates. Synthesis of d-galactose derivatives having an ethynyl, vinyl or epoxy residue at C-5☆

Compounds derived from D-galactose having an ethynyl, vinyl, or epoxide residue at C-5, as well as 7,7-dibromo olefinic, isomeric 7,7-gem-bromofluoro olefinic, and 6,6-gem-difluoro derivatives were obtained from 1,2:3,4-di-O-iso-propylidene-alpha-D-galacto-hexodialdo-1,5- pyranose.

Fluorinated carbohydrates as potential plasma membrane modifiers. Synthesis of 3-deoxy-3-fluoro derivatives of 2-acetamido-2-deoxy-d-hexopyranoses☆

Treatment of benzyl 2-acetamido-4,6-O-benzylidene-2-deoxy-alpha-D-allopyranoside with diethylaminosulfur trifluoride or of the 3-O-mesyl derivative with tetrabutylammonium fluoride gave the 2,3-unsaturated compound instead of the expected 3-deoxy-3-fluoro derivative. The latter was obtained when benzyl 2-acetamido-4,6-di-O-benzyl-2-deoxy-3-O-mesyl-alpha-D-allopyran oside was treated with potassium fluoride. Methyl 2-azido-4,6-O-benzylidene-2-deoxy-alpha-D-altropyranoside was converted into the 2-acetamido- and 2-phthalimido-3-O-mesyl derivatives; when treated with fluoride nucleophile, these gave only the 2,3-aziridine derivative. However, treatment of the 2-azido-2-deoxy derivative with diethylaminosulfur trifluoride gave methyl 2-azido-2,3-dideoxy-3-fluoro-alpha-D-mannopyranoside which, after reduction, deprotection, and acetylation, gave the acetylated derivative of methyl 2-acetamido-2,3-dideoxy-3-fluoro-alpha-D-mannopyranoside in excellent yield. These acetylated 3-fluoro derivatives exhibited inhibition of cell growth of murine L1210 leukemia cells in culture at micromolar concentrations.

General methods for modification of sialic acid at C-9. Synthesis of N-acetyl-9-deoxy-9-fluoroneuraminic acid

Methyl 5-acetamido-3,5-dideoxy-2-O-methyl-D-glycero-D-galacto-2-nonulopyrano sate was converted into the 9-O-trityl derivative and the remaining hydroxyl groups were protected as benzyl ethers. Removal of the trityl group, followed by treatment with diethylaminosulfur trifluoride gave the 9-deoxy-9-fluoro derivative, and deprotection N-acetyl-9-deoxy-9-fluoroneuraminic acid (8). In another procedure, coupling of 2-acetamido-2,6-dideoxy-6-fluoro-D-glucopyranose with potassium di(tert-butyl) oxaloacetate, followed by hydrolysis and decarboxylation gave 8. Some of the derivatives were active as inhibitors of growth of mouse mammary adenocarcinoma (TA3) and L1210 cells in culture.

Versatile intermediates in the selective modification of the amino function of 2-amino-2-deoxy-d-mannopyranose and the 3-position of 2-acetamido-2-deoxy-d-mannose: Potential membrane modifiers in neoplastic control

A general method has been developed to selectively modify the amino group of 2-amino-2-deoxy-D-mannopyranose (D-mannosamine), a precursor of the terminal membrane sugar, sialic acid. 1,3,4,6-Tetra-O-acetyl-2-amino-2-deoxy-alpha-D-mannopyranose oxalate was prepared via two routes that allowed introduction of various acyl groups onto the amino function. These compounds were evaluated for their antineoplastic properties. The most significant preclinical therapeutic finding was the antileukemic activity found in mice for tetra-O-acetyl-2-epi-streptozotocin (the acetylated alpha-mannosamine epimer of streptozotocin). Administration of 50 mg/kg/day x 5 to leukemia L1210-bearing DBA/2Ha mice resulted in 5/5 35-day survivors. Neutralization of 1,3,4,6-tetra-O-acetyl-2-amino-2-deoxy-alpha-D-mannopyranose oxalate under aqueous conditions led to 2-acetamido-1,4,6-tri-O-acetyl-2-deoxy-alpha-D-mannopyranose, the oxidation of which gave 2-acetamido-4,6-di-O-acetyl-1,5-anhydro-2-deoxy-D-erythro-hex-1-en-3- ulose. This agent demonstrated an IC50(2) of 25 microM with a murine L1210 cell culture. Administration of 100 mg/kg/day x 5 resulted in 42% ILS3 in DBA/2 mice with ip L1210 leukemia. Several other nonacetylated derivatives were also prepared by direct N-acylation, producing, for example, fluorescently tagged N-dansylmannosamine.

Antioxidant inhibits tamoxifen-DNA adducts in endometrial explant culture

Fresh human endometrial explants were incubated for 24h at 37 degrees C with either tamoxifen (10-100 micro M) or the vehicle (0.1% ethanol). Three metabolites namely, alpha-hydroxytamoxifen, 4-hydroxytamoxifen, and N-desmethyltamoxifen were identified in the culture media. Tissue size was limited but DNA adducts formed by the alpha-hydroxytamoxifen pathway were detected using authentic alpha-(deoxyguanosyl-N(2)) tamoxifen standards. Relative DNA-adduct levels of 2.45, 1.12, and 0.44 per 10(6) nucleotides were detected following incubations with 100, 25, and 10 micro M tamoxifen, respectively. The concurrent exposure of the explants to 100 micro M tamoxifen with 1mM ascorbic acid reduced the level of alpha-hydroxytamoxifen substantially (68.9%). The formation of tamoxifen-DNA adducts detectable in the explants from the same specimens exposed to 100 micro M tamoxifen with 1mM ascorbic acid were also inhibited. These results support the role of oxidative biotransformation of tamoxifen in the subsequent formation of DNA adducts in this tissue.

A General Method for the Modification of the 9-Position of N-Acetyl-neuraminic Acid (NANA) and the Synthesis of Its 9-Fluoroanalogue

Abstract Analogs of N-acetylneuraminic acid (1, NANA) are of considerable interest as potential modifiers of cell surface sialic acid. NANA is greatly responsible for the negative charge on cell surface, and plays an important role in cell-to-cell Interactions, immunogenic properties, and metastasis.1 Considerable difficulty has been encountered in the development of approaches for the modification of this molecule.2 The only fluorinated sialic acid which has been reported 1s N-acetyl-3-fluoro-neuraminic acid, a compound which was obtained in only 1% yield.3 A systematic approach to the introduction of protecting groups into NANA, a process which would make specific groups amenable for modification, has not been explored. In this communication we report a successful application of a protection-deprotection approach (Scheme 1) to the synthesis of N-acetyl-9-deoxy-9-fluoroneuraminic acid (7).

Fluorinated carbohydrates as potential plasma membrane modifiers and inhibitors. Synthesis of 2-acetamido-2,6-dideoxy-6-fluoro-D-galactose.

Reaction of benzyl 2-acetamido-3,4-di-O-benzyl-2-deoxy-6-O-mesyl-alpha-D-galactopyran oside with cesium floride gave benzyl 2-acetamido-3,6-anhydro-4-O-benzyl-2-deoxy-alpha-D-galactopyranoside instead of the desired 6-fluoro derivative. Acetonation of benzyl 2-acetamido-2-deoxy-6-O-mesyl-alpha-D-galactopyranoside gave the corresponding 3,4-O-isopropylidene derivative. The 6-O-mesyl group was displaced by fluorine with cesium fluoride in boiling 1,2-ethanediol, and hydrolysis and subsequent N-acetylation gave the target compound. In another procedure, treatment of 2-acetamido-1,3,4-tri-O-acetyl-2-deoxy-alpha-D-galactose with N-(diethylamino)sulfur trifluoride gave 2-acetamido-1,3,4-tri-O-acetyl-2,6-dideoxy-6-fluoro-D-galactose which, on acid hydrolysis followed by N-acetylation, gave 2-acetamido-2,6-dideoxy-6-fluoro-D-galactose.

Modifications at C-3 and C-4 of 2-amino-2-deoxy-d-glucose☆

Modifications at C-3 and C-4 of 2-amino-2-deoxy-D-glucose have been developed. A 3,4-double bond was introduced into benzyl 2-acetamido-2-deoxy-3,4-di-O-methylsulfonyl-alpha-D-glucopyranoside by treatment with NaI and Zn. Epoxidation of the double bond with m-chloroperoxybenzoic acid gave an exo-epoxide exclusively. The stereochemistry of the epoxidation product has been confirmed by an alternative synthesis. An analysis of the 1H-n.m.r. spectra indicates that both the 3,4-unsaturated derivatives and the epoxide exist in the OH1 (D) conformation. Nucleophilic reagents (F-, I-) opened the 3,4-epoxide to give 4-substituted derivatives having the D-gulo configuration. Thus, 2-acetamido-1,3,6-tri-O-acetyl-2,4-dideoxy-4-iodo-alpha-D-gulopyranose and 2-acetamido-1,3,6-tri-O-acetyl-3,4-dideoxy-4-fluoro-alpha-D-gulopyranose have been synthesized. Reduction of the double bond in the key intermediate and deprotection gave 2-acetamido-2,3,4-trideoxy-D-glucopyranose. Some of the derivatives were active as inhibitors of growth of mouse, mammary adenocarcinoma cells in culture.

Nuclease P1-mediated fluorescence postlabeling assay of AAF modified DNA model d(TACGTA) and calf-thymus DNA

Fluorescence postlabeling assay for DNA damage combines enzymatic digestion of modified DNA to nucleoside monophosphates and fluorescence postlabeling. However, to facilitate the quantitative release of bulky adducts that are not readily obtained as mononucleotides, a different mechanism is essential. In order to test the application potential of nuclease P1-mediated fluorescence postlabeling to assay bulky adduct, d(TACGTA) was reacted with N-acetoxy-2-acetylamino-fluorene. The major product, characterized by nmr as AAF adduct of the guanine moiety at the C-8 position, was used as a DNA model. Nuclease P1 digestion of the modified oligomer excised the adduct in two forms (3:1) which were identified as AAF modified d(pGpT) and dpG respectively by cochromotography with authentic markers. Fluorescence postlabeling assay of AAF modified d(TACGTA) detected both forms of the excised adduct. The application of the overall procedure to assay AAF modified calf-thymus DNA demonstrated that the extension of fluorescence postlabeling technique from the mononucleotide to the dinucleotide version expands the scope of the assay.