One-pot-synthesis of α-linked deoxy sugar trisaccharides

Various α-linked 2,6-dideoxy-ribo-trisaccharides, models for part of the antibiotic kijanimicin, were synthesised by the N-iodosuccinimide method employing different pathways. The efficiency of a sequential synthesis suffered from side reactions of the axial HO-3, which are typical of digitoxosides. These problems did not arise in a straightforward polymerisation, performed as a one-pot-procedure. It afforded the trisaccharide directly from the monosaccharide precursor in 30% yield. A combination of the oligomerisation pathway and the sequential synthesis led to trisaccharides with different protecting group patterns. In these reactions different glycal and alcohol components were used and allowed to define the optimal partners in a sequential synthesis: the two components should ideally be of comparable reactivity.     

Comparative analysis of phenolic acids and flavonoids in shoot cultures of Eryngium alpinum L.: an endangered and protected species with medicinal value

Plant Cell, Tissue and Organ Culture (PCTOC) - Phenolic acids and flavonoids, important bioactive compounds of polyphenols, play a significant role in plants; their impact, mainly as antioxidants,...     

Chemical and immunochemical studies on the structure of four snail galactans

The four snail galactans studied are polysaccharides of high molecular weight that are composed entirely of d- and l-galactosyl residues. AaG and CnG, which had not previously been studied, are highly branched galactans composed mainly of (1→3)- and (1→6)-linked galactosyl residues, as shown by the results of periodate oxidation and permethylation studies. On methylation, HpG, CnG, and AaG yielded ～40% of 2,3,4,6-tetra-, 40% of 2,4-di-, 7–14% of 3,4,6-tri-, and 8–12% of 2,4,6-tri-O-methylGal derivatives. BgG gave equal amounts of tetra- and di-O-methyl derivatives, and 8.5% of 2,4,6-tri-O-methylGal, and 10% was unmethylated Gal, indicating 1, 2, 3, 4, and 6 substitution not previously reported in nature. Antisera to the four galactans showed various degrees of cross-reactivity, indicating structural differences ascribable partially to determinants involving a galactose phosphate and, probably, to the linkage and the position of l-Gal in the molecule. The galactans differed in susceptibility to d-galactose oxidase, and some of the immunochemical observations are most probably attributable to species-specific differences in distribution of linear stretches and branches. The first stages of Smith degradation of HpG and AaG showed a substantial increase in unsubstituted (1→3)- and (1→6)-linked residues. These results, and the appearance of linear stretches within the native galactans preclude the strictly dichotomously-branched structure proposed earlier.     

Response of two-spined blackfish <Emphasis Type="Italic">Gadopsis bispinosus</Emphasis> to short-term flow fluctuations in an upland Australian stream

Environmental flows are applied to regulated rivers, predominantly with the aim of benefiting native fauna. However, the outcomes for biodiversity and the mechanisms that underpin changes due to these manipulations are poorly understood. We examined the effects of elevated water release, of the magnitude used for riffle maintenance, on the movement and habitat use of the locally-threatened two-spined blackfish, Gadopsis bispinosus, in the Cotter River, a regulated upland stream in south-eastern Australia. We compared the behaviour of radio-tagged individuals during baseline flow conditions (0.12 m³ s⁻¹) and during elevated flow releases (1.74 m³ s⁻¹). Eight individuals (196 ± 8 mm TL) were radio-tracked at one site over 22 days, and six individuals (180 ± 5 mm TL) were monitored by fixed telemetry stations at a second site for 1 month. At both the sites, two-spined blackfish were nocturnal and occupied small linear ranges (23 ± 6 m). They preferentially used pools, but also used runs and riffles. Elevated discharge did not significantly affect movement, activity or dispersal of two-spined blackfish. Two individuals utilised inundated vegetation during high flow. Despite a small number of behavioural changes, there was no response to elevated flow at the population level. It is likely that the benthic nature of this species precludes its behaviour being affected by a 15-fold increase in-stream discharge. However, the indirect effects of flows of this magnitude on two-spined blackfish, and their responses to discharges of greater magnitude, remain to be investigated.     

Studies on the reaction with N-bromosuccinimide of fixed 2-phenyl-1,3-dioxolane systems in methyl di-O-benzylidene-α-D-hexopyranosides

The reaction of methyl 2,3:4,6-di-O-benzylidene-α-D-mannopyranoside (5) with N-bromosuccinimide gave mainly three, isomeric dibromo dibenzoates, identified as the 3,6-dibromo-altro (1), 3,6-dibromo-manno (2), and 4,6-dibromo-ido (3) derivatives by subsequent chemical transformation and by extended n.m.r.-spectral studies. The reaction of methyl 2,3:4,6-O-benzylidene-α-D-allopyranoside (22) with N-bromosuccinimide gave two isomeric dibromo dibenzoates, the 2,6-dibromo-altro (23) and 3,6-dibromo-gluco (24) products, and their structures were similarly assigned. A similar reaction-sequence with methyl 2,3:4,6-di-O-benzylidene-α-D-glucopyranoside (32), however, yielded two isomeric monobenzoates 33 and 34, which could be identified straightforwardly. The results are consistent with the intermediate formation of benzoxonium ions that undergo favored axial attack. Thus the observed products and their ratios in reactions of 5 and of 22 with N-bromo-succinimide are explicable. Compound 32, however, does not appear to react by way of an intermediate, five-membered 2,3-trans benzoxonium ion.