X-ray fluorescence in some rare earth and high Z elements excited by 661.6 keV γ-rays

The K-shell X-ray fluorescence cross sections are determined experimentally for 10 elements such as Pb, Hg, Ir, W, Lu, Tm, Dy, Tb, Gd and Nd at excitation energy of 661.6 keV associated with γ-rays of ¹³⁷Cs radioisotope. The technique employed involves the measurement of total intensity of fluorescent K X-rays that follow the photoeffect absorption of a known flux of γ-rays using a well type Nal(Tl) detector. The obtained results are compared with the available theoretical values and other measured values.     

Biosynthesis of cylindrospermopsin

Studies on the biosynthesis of cylindrospermopsin (1), a potent hepatotoxin associated with the cyanobacterium Cylindrospermopsis raciborskii, indicate that 1 is an acetogenin with guanidinoacetic acid serving as the starter unit of the polyketide chain. Feeding experiments show that C14 and C15 of 1 are derived from C1 and C2 of glycine, respectively, and C4 through C13 arise from five contiguous acetate units attached head to tail. The methyl carbon on C13 originates from the C(1) pool. The starter unit, established by the incorporation of [guanidino-(13)C,alpha-(15)N]-guanidinoacetic acid into N16 and C17 of 1, does not appear to be formed from glycine by known amidination pathways. The origin of the NH-CO-NH segment in the uracil ring is also unknown.     

Nomofungin: a new microfilament disrupting agent.

A new alkaloid, nomofungin, has been isolated from the fermentation broth of an unidentified endophytic fungus obtained from the bark of Ficus microcarpa L. The structure of nomofungin was determined by application of spectroscopic methods. The absolute stereochemistry of nomofungin was assigned by using the exciton chirality method. Nomofungin disrupts microfilaments in cultured mammalian cells and is moderately cytotoxic with minimum inhibitory concentrations (MICs) of 2 and 4.5 microg/mL against LoVo and KB cells, respectively. The ring system of nomofungin is unprecedented.     

Biosynthesis and structure of aeruginoside 126A and 126B, cyanobacterial peptide glycosides bearing a 2-carboxy-6-hydroxyoctahydroindole moiety

Aeruginosins represent a group of peptide metabolites isolated from various cyanobacterial genera and from marine sponges that potently inhibit different types of serine proteases. Members of this family are characterized by the presence of a 2-carboxy-6-hydroxyoctahydroindole (Choi) moiety. We have identified and fully sequenced a NRPS gene cluster in the genome of the cyanobacterium Planktothrix agardhii CYA126/8. Insertional mutagenesis of a NRPS component led to the discovery and structural elucidation of two glycopeptides that were designated aeruginoside 126A and aeruginoside 126B. One variant of the aglycone contains a 1-amino-2-(N-amidino-Delta(3)-pyrrolinyl)ethyl moiety at the C terminus, the other bears an agmatine residue. In silico analyses of the aeruginoside biosynthetic genes aerA-aerI as well as additional mutagenesis and feeding studies allowed the prediction of enzymatic steps leading to the formation of aeruginosides and the unusual Choi moiety.     

Biosynthesis of vitamin B(6) in yeast: incorporation pattern of glucose.

Two yeasts, Saccharomyces cerevisiae ATCC 7752 and Candida utilis ATCC 9256, were incubated in the presence of variously multiply (13)C-labeled samples of D-glucose. The (13)C incorporation pattern within pyridoxamine dihydrochloride, established by (13)C NMR spectroscopy, differed from that which had previously been found within pyridoxine, isolated from Escherichia coli. Thus, the origin of the carbon skeleton of vitamin B(6) in yeast differs substantially from its origin in E. coli. In particular, in yeast the distribution of (13)C within the C(5) chain C-2',2,3,4,4' of pyridoxamine corresponds to the distribution of (13)C within the C(5) chain C-1,2,3,4,5 of the ribose component of cytidine. It follows that the C(5) chains of pyridoxamine and of ribose originate from a common glucose-derived pentulose or pentose intermediate. By contrast, in E. coli the C(5) chain of pyridoxine is derived from 1-deoxy-D-xylulose 5-phosphate which, in turn, originates by condensation of pyruvic acid with glyceraldehyde 3-phosphate.     

Pellet freezing of in vitro produced bovine embryos using dry ice

In vitro produced bovine embryos were frozen by pellet freezing or vitrification method. In the pellet freezing method, the embryos were cooled on the dry ice and then frozen as pellets. At warming, the pellets were immersed directly into 0.5 M sucrose. The survival rates of blastocysts frozen by the pellet freezing method were higher (P<0.01) in 40% ethylene glycol (EG) than those in the lower concentrations (20 and 30% EG). Higher survival rates of blastocysts frozen by the pellet freezing method were obtained but the development rates did not differ, as compared with those by the vitrification method. There were no significant differences between the pellet freezing and vitrification method in the frequencies of post-thaw survival of hatched blastocysts. These results demonstrate that the pellet freezing method using dry ice can be used successfully for the cryopreservation of blastocysts.     

Olefin cross-metathesis as a tool in natural product degradation. The stereochemistry of (+)-falcarindiol

[reaction: see text] There are conflicting reports in the literature concerning the absolute sterochemistry at C-3 of the common plant polyacetylene oxylipin (+)-falcarindiol. We have employed olefin cross-metathesis using Grubbs' second generation catalyst and ethylene gas to degrade falcarindiol to the symmetrical 1,9-decadiene-4,6-diyne-3,8-diol. The reaction is completely selective for net removal of the aliphatic side chain. Degradation of (+)-falcarindiol from Tetraplasandra hawaiiensis yields a meso product as shown by chiral HPLC. Hence, (+)-falcarindiol from this source has a (3R,8S)-configuration.