Acta chemica Scandinavica. Series B: Organic chemistry and biochemistry最新文献

Two new diterpenoids have been isolated from tobacco. They have been identified as the (1S,2E,4S,6R,7R,8R,11E)- and (1S,2E,4S,6R,7S,8S,11E)-7,8-epoxy-2,11-cembradiene-4,6-diols 1 and 2 by synthesis and X-ray analysis. The conformation about the 5,6 bond in some 7,8-epoxycembranoids is discussed, as is the biogenesis of the two new compounds.

A series of alkyl 2-hydroxy-2-cyclopentenones, which comprise biologically and organoleptically active compounds, have been synthesized and subjected to high resolution mass spectrometric studies to clarify structurally significant fragmentation pathways. On the basis of these results, 26 alkyl 2-hydroxy-2-cyclopentenones were identified in the weakly acidic fraction of smoke condensate from American blend type cigarettes, eighteen of which had not been detected in tobacco smoke previously. The utility for identification purposes of the corresponding quinoxaline derivatives, obtained through condensation with o-phenylenediamine, is discussed.

Kinetics for the reactions of various cytosine and uracil nucleosides and their alkyl derivatives with aqueous sodium hydroxide have been studied by liquid chromatography. Blocking of the glycosyl hydroxyl groups with alkyl groups and changes in the glycon moiety configuration have been observed to exert only moderate effects on the rate of deamination of cytosine nucleosides. Methylation of the 4-amino group retards deamination considerably, while a methyl substituent at C5 is rate accelerating and at C6 only moderately rate retarding. These findings have been accounted for by a mechanism involving a rate limiting bimolecular displacement of the 4-amino group by a hydroxide ion. Analogous comparisons with uracil nucleosides suggest that the decomposition of uridine is initiated by an intermolecular attack of hydroxide ion on the C5 atom of the base moiety. In contrast, beta-D-arabino- and beta-D-lyxo-furanosyl derivatives appear to be cleaved via an intramolecular nucleophilic attack of the ionized 2'-hydroxyl group.

For the protection of the O-4 function of uridine and the O-6 of guanosine, 2-, 3- and 4-hydroxypyridines, 2-pyridinethiol, 6-methyl-2-hydroxy- and 6-methyl-3-hydroxypyridines have been employed. These substituted pyridines gave pyridyl-N-and/or pyridyl-O-substituted derivatives, depending both upon the position of the hydroxyl and methyl groups in the pyridine ring, at the C-4 and the C-6 of the uracil and guanine residues, respectively. These groups were found to be good leaving groups for nucleophilic substitution reactions by amines, thiolates and oximate. If needed, the rate of these substitution reactions could be conveniently increased by almost 1000-fold by conversion of the pyridyl moiety to its methiodide.

When reacted with mixtures of phosphorus pentoxide, aniline, and triethylamine hydrochloride, 5-acetamidoisoxazoles (2 and 3) gave isoxazolo[5,4-d]pyrimidines (4 and 7, respectively). The same reagent and cyclohexanone were used to prepare the isoxazoloquinoline 8.

Kinetics for the parallel and consecutive steps of the reactions of 5-bromocytidine, 5-bromouridine and its 5'-O-methyl and 2',3'-O-isopropylidene derivatives with aqueous alkalies were studied by LC. The mechanisms of the partial reactions involved are discussed.

A new synthesis of the cordycepin analogue of 2,5A and its threo isomer is reported along with an assessment of their conformations by circular dichroism spectroscopy. Evidence is also presented showing that these compounds are stable against 2,5A-specific phosphodiesterase and are not able to activate the 2,5A-dependent endoribonuclease, possibly due to a reduced binding to the latter enzyme as compared to that of 2,5A.

Cation binding to three apoparvalbumins was studied by means of 113Cd NMR. The 3 parvalbumins that were investigated were carp pI 4.25, rabbit pI 5.5 and pike pI 5.0. The results showed that Cd2+ ions bind to the EF and CD sites of carp apoparvalbumin pI 4.25 with about the same affinity. For rabbit (pI 5.5) apoparvalbumin, Cd2+ binds preferentially to the EF site, while for pike (pI 5.0) apoparvalbumin, it was the CD site that exhibited somewhat higher affinity for Cd2+. The effect of Mn2+ on the 113Cd signals of rabbit parvalbumin was used to assign the 113Cd NMR signals to the EF and CD sites. The Mn2+ paramagnetic effect on rabbit and pike parvalbumins differed from that obtained for carp parvalbumin. This is in agreement with the assumption that the beta-lineage parvalbumins possess a third external site of higher affinity than the alpha-lineage parvalbumins. Furthermore, 23Na NMR was used to study Na+-Mg2+ competition in the native carp (pI 4.25) parvalbumin. The results showed that Na+ and Mg2+ compete for the same site, the third external site.

The synthetic androgen methyltrienolone (R 1881) was shown to increase steroid delta 1 dehydrogenase activity when added to cultures of Pseudomonas testosteroni at concentrations of 10(-10)-10(-8)M. Incubation with a soluble extract of P. testosteroni showed that (3H)-R 1881 was bound to a macromolecule with high affinity (Kd 0.6 X 10(-9)M) and low capacity (number of binding sites 120 X 10(-15) mol/mg of protein). The (3H)-R 1881-macromolecule complex was partially destroyed following treatment with protease, was precipitated by addition of ammonium sulfate at 20% of saturation, sedimented at 6.3 S both in 0.01 and 0.4 M KCl solutions, and had an isoelectric point of pH 6.3. The complex was partially bound to DNA-cellulose. Analysis by sucrose gradient centrifugation indicated that neither (3H)-testosterone and (3H)-estradiol-17 beta nor (3H)-corticosterone were bound with high affinity to the (3H)-R 1881-binding macromolecule. It is suggested that the partially characterized R 1881-binding macromolecule, which at least in certain respects resembles androgen receptors described in mammalian cells, is involved in the inductive effect of R 1881 on the delta 1 dehydrogenase activity in P. testosteroni.