Catalytic asymmetric vinylation of ketone enolates

[see reaction]. A protocol for the catalytic asymmetric vinylation of ketone enolates has been developed. Key to the success of this process was the development of new electron-rich chiral monodentate ligands.

Transformation of the nematode-trapping fungus Arthrobotrys oligospora

The nematode-trapping fungus Arthrobotrys oligospora was transformed to hygromycin resistance using the hygromycin-B phosphotransferase gene from Escherichia coli under the control of various heterologous fungal promoters. Plasmid DNA was introduced into fungal protoplasts by polyethylene glycol/CaCl2 treatment. Transformation frequencies varied between 1-6 transformants per microgram DNA. Seven out of 13 integration events analyzed from transformants were single copy integrations, whereas the remaining were multiple and more complex integrations. The addition of restriction enzymes during transformations increased the frequency of single copy integrations. Co-transformation, using the E. coli uidA gene encoding the beta-glucuronidase reporter gene under the control of an Aspergillus nidulans promoter, occurred at frequencies of up to 63%.

Sequence analysis and regulation of a gene encoding a cuticle-degrading serine protease from the nematophagous fungus Arthrobotrys oligospora

The nematode trapping fungus Arthrobotrys oligospora produces an extracellular serine protease (designated PII) that immobilizes free-living nematodes in bioassays and hydrolyses proteins of the nematode cuticle. Peptides were isolated from PII and partly sequenced. Three internal peptide sequences were used to design synthetic oligonucleotides, which allowed the subsequent isolation of the gene encoding PII from a genomic library. The deduced amino acid sequence indicated that PII is synthesized as a preproenzyme containing the mature enzyme, a signal sequence and a propeptide that are removed before the enzyme is secreted into the medium. The primary sequence of PII displayed a high degree of similarity with several other serine proteases of ascomycetes belonging to the subtilisin family. Northern analysis demonstrated that PII was expressed when the fungus was starved of nitrogen and carbon and that the expression was significantly stimulated by the addition to the medium of various soluble and insoluble proteins, including fragments of nematode cuticle. The levels of the mRNA as well as the proteolytic activity of PII were repressed in the presence of more easily metabolized forms of nitrogen (including ammonia, nitrate and amino acids) or glucose. The activity of the enzyme was almost completely inhibited by the peptide Phe-Val, as well as by the amino acid Phe, without a corresponding decrease in mRNA level. Notably, peptides with similar structures are known to be secreted by the host (nematode) and to stimulate the production of infection structures (traps) of the fungus.

Glycosylated peptide hormones: pharmacological properties and conformational studies of analogues of [1-desamino,8-D-arginine]vasopressin

Two analogues of the antidiuretic drug [1-desamino,8-D-arginine]vasopressin (DDAVP), which have a glycosylated serine at position 4, have been prepared by Fmoc solid phase peptide synthesis. The glycosylated analogues had significantly higher bioavailabilities than the nonglycosylated [D-Tyr2,Ser4]DDAVP and DDAVP on intraintestinal administration in rat. The improved bioavailability resulted from an increased absorption from the small intestine and most likely from an increased stability toward enzymatic degradation, whereas plasma clearance was either unaffected or slightly increased by the glycosylation. The glycosylated analogues displayed only very low agonistic and antagonistic activities at the vasopressin V2-receptor. Conformational studies performed by 1H NMR spectroscopy did not reveal any major influence from glycosylation on the conformation of the peptide backbone. The lack of receptor binding displayed by the analogues is therefore most likely explained by steric repulsion between the carbohydrate moiety and the vasopressin receptor which prevents receptor binding.