Microbiological and Chemical Transformations of Argentatin B

Argentatin B is a naturally occurring tetracyclic triterpene isolated from Parthenium argentatum x P. tomentosa. It was microbiologically transformed to 16, 24-epoxycycloartan-3α, 25- diol, (isoargentatin D), by Nocardia corallina var. taoka ATCC 31338, Mycobacterium species NRRL B3683 and Septomyxa affinis ATCC 6737. The later microbe also produced 16, 24- epoxycycloartan-3β, 25-diol (argentatin D) and 1, 2-didehydroargentatin B, (isoargentatin D). Sodium hydroxide converted argentatin B to argentatin D and isoargentatin D. Hydrochloric acid treatment gave cycloartan-25-ol-3, 24-dione. Cerium sulfate/sulfuric acid/aqueous methanol induced scission of the isopropanol moiety and provided an isomeric mixture of 24-methoxy-25-27-trinorargentatin B. Oxidation of this isomeric mixture with pyridinium chlorochromate, selectively, attacked the isomer with the equatorial proton at position-24 to give the corresponding lactone, 24-oxo-25-27-trinorargentatin B. The produced compounds were characterized by spectroscopic methods.

Group Travel Time of EM Waves with Frequencies near the Ion Cyclotron Frequency in the Two-ion Magnetosphere

The oblique propagation of electromagnetic (EM) waves with frequencies below the equatorial proton cyclotron frequency is investigated for a two-ion magnetospheric plasma. Attention is focused on the wave group travel time along a geomagnetic field line rom the equatorial wave source region to the ionosphere or the location where the wave is reflected. It is found that the coupling between eft- and right-hand polarised waves occurring at a crossover frequency significantly modifies features of the frequency-time spectrum. ecause of this modification, the spectral tone change of Pc 1 waves observed on the ground (e.g. Dowden 1966; Gendrin and Laurent 1979) is not caused solely by dispersion effects in a multi-component plasma.

Conformations of Sugars: Proton Dihedral Angles from Gauche Coupling Constants

Proton coupling constants have been used in calculating dihedral angles of vicinal gauche protons in variety of pyranose derivatives of glucose, mannose, arabinose, xylose, altrose, and galactose. The calculations involve the use of a formula which was derived from a correlation of the coupling constants of ethane derivatives with the electronegativities of substituents and their orientation relative to the coupled protons.The results indicate that the formula has general applicability and gives more reasonable values than a Karplus equation in which the constants have been adjusted to fit some compounds of the series. The calculated dihedral angles indicate that an equatorial substituent generally causes little distortion of dihedral angles, whereas an axial substituent generally causes the equatorial proton on the same carbon to have a smaller than normal dihedral angle with the adjacent axial proton and a larger than normal dihedral angle with the adjacent equatorial proton.

Nuclear magnetic resonance studies on the configurations and conformations of heterocyclic nitrosamines

The nuclear magnetic resonance spectra of various heterocyclic nitrosamines were studied in solution. A qualitative view of the long-range diamagnetic effects of a nitrosamino group is advanced and correlated with the chemical shifts of α-equatorial protons and the methyl group in those nitrosamines possessing a preferred conformation or a rigid system. The use of this correlation to decide the configuration and conformation of heterocyclic nitrosamines is discussed. A large chemical shift difference (ca. 3 p.p.m.) between a cis α-axial and a cis α-equatorial proton was noted.

Conformational analysis of trans-1,4-dihalocyclohexanes

The conformational equilibria of trans-1,4-dibromo- (I), trans-1,4-dichloro- (II), and trans-1,4-bromochloro-cyclohexane (III) were determined by integration of the separate axial and equatorial proton signals at low temperature. The [Formula: see text] values for compounds I, II, and III were found to be approximately 200 cal/mole.