Satinder K. Sethi

Determination of active hydrogen content by fast atom bombardment mass spectrometry following hydrogen-deuterium exchange

Fast atom bombardment mass spectrometry following hydrogen--deuterium exchange in [hydroxy-2H3]glycerol and 2H20 has been studied as a means of establishing active hydrogen content in molecules of unknown structure. Nucleotides, carbohydrates, one peptide and complex antibiotics, in the mass region to 1500 daltons and 29 exchangeable hydrogens were examined, with a correct hydrogen count unambiguously measured in every case. The method is experimentally simple and applicable on a microgram scale, to salts and a variety of polar compounds of biological origin.

Isolation and Characterization of a Novel Nucleoside from the Urines of Chronic Myelogenous Leukemia Patients

Abstract From 24 hour collections of urines of chronic myelogenous leukemia (CML) patients, a novel nucleoside was isolated. It was assigned the structure, 5′-deoxyinosine (I) on the basis of UV, NMR and mass spectrometry and by comparison of the spectral data and HPLC and TLC mobilities with those of the authentic sample. Another nucleoside, 5′-deoxy-5′-methylthioadenosine sulfoxide previously isolated from the urines of immunodeficient children was also found in the urine of a CML patient. Possible origin and significance of both of these nucleosides are discussed.

The structure of lipopeptin a

Abstract The structure of lipopeptin A, an antifungal peptolide antibiotic was determined as 1 on the basis of chemical and spectroscopic evidence.

Conversion of formycin into the fluorescent isoguanosine analogue 7-amino-3-(β-D-ribofuranosyl)-1H-pyrazolo[4,3-d]pyrimidin-5(4H)-one

On u.v. irradiation, in aqueous solution, formycin N(6)-oxide (3) undergoes photorearrangement to give 5-cyano-3-(β-D-ribofuranosyl)-4-ureido-1H-pyrazole (5) as the major product; small amounts of 7-amino-3-(β-D-ribofuranosyl)-1H-pyrazolo[4,3-d]pyrimidin-5(4H)-one (4) and formycin (1) are also formed. When treated with aqueous ammonia, compound (5) cyclizes to the isoguanosine analogue (4). The latter compound is strongly fluorescent and its c.d. spectrum resembles that of formycin. Its u.v. absorption and fluorescence characteristics are compared with those of the corresponding guanosine analogue 5-amino-3-(β-D-ribofuranosyl)-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one (2).

Reaction of 5-Halocytosine Derivatives with Cysteine

Abstract 5-Bromo-(1) and 5-iodo-2′-deoxycytidine (2) undergo 100 percent dehalogenation to 2′-deoxycytidine on heating with cysteine in IN aq K2CO3 in a nitrogen atmosphere at 50° for 72 h and 21 h, respectively. 5-Chloro-2′-deoxycytidine (3) and 1-methyl-5-chlorocytosine (3m) on the other hand undergo very little dehalogenation, forming instead two products, 4, 5 and 4m, 5m respectively, whose structures have been determined by mass spectrometry and proton magnetic resonance spectroscopy of the 3m products: 1-methyl-5-(cystein-S-yl)cytosine (4m) and 3-methyl-2,6,7,8 -tatrahydro-2-oxo-3H-pyrimido [5,4-b][1,4]-thiazine-7-carboxylic acid (5m), mp. 236°C, 78 percent yield. Initially produced 4m undergoes a novel and facile cyclization to form 5m with loss of NH3 in the presence of cysteine. The compound 3m, mp. 258°C, has been synthesized by treating 1-methylcytosine with N-chlorosuccinimide in acetic acid at 105° for 3 h in 56 percent yield. Ultraviolet absorption spectral properties of 1, 2, 3, 3m, 4, 4m, ...

Formation of a new derivative of secondary amines during trimethylsilylation with n,o-bis(trimethylsilyl)-fluoroacetamide : N-(aminomethylene)-2,2,2-trifluoroacetamides

Abstract Trimethylsilylation of secondary amines by the common reagent N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) in the presence of dimethylformamide (DMF) produces the previously unknown N-(aminomethylene)-2,2,2-triftuoroacetamide (AMT) derivative, in addition to the trimethylsilyl derivative. This derivative is formed in varying yield by incorporation of CH atoms from DMF, and a CF 3 CO group from BSTFA. The structure of the AMT moiety was characterized in the nucleic acid base queuine using stable isotopic labeling, high-resolution mass spectrometry, and 13 C and 19 F nuclear magnetic resonance spectroscopy. The AMT derivative has unexplored potential for use in gas chromatography and mass spectrometry but its formation may otherwise be undesirable, suggesting that the combined use of BSTFA and DMF be used with caution for silylation of compounds containing secondary amino groups.

Mass spectrometry of the nucleic acid base queuine

Abstract Mass spectrometry has played a major role in the structure elucidation of members of the Q family of bases and nucleosides, which are widely distributed in nature. The volatile N -(aminomethylene)-2,2,2-trifluoroacetamide (AMT) - trimethylsilyl (TMS) derivative of the nucleic acid base queuine has been prepared and its electron ionization mass spectrum studied. A deuterated analog of queuine has been prepared and tested for use as an internal standard for quantitative measurements of queuine in plant and animal materials by selected ion monitoring.