Studies on the Thorpe-Ziegler-reaction. A new synthesis of the pyridine part of thiamine]

Thorpe-Ziegler cyclization of N′-cyano-N-(2-cyanoethyl)-acetamidine ( 5a ) yields 4-amino-2-methyl-1,6-dihydro-5-pyrimidinecarbonitrile ( 8a ). The acetamidine 5a is accessible either from the N-cyanoimidate 1 and β-aminopropionitrile ( 3a ) or the N-cyanoamidine 2 and acrylonitrile ( 4 ). The dihydropyrimidine 8a is easily converted to 4-amino-2-methyl-5-pyrimidine-carbonitrile ( 13 ) by dehydrogenation or to 4-amino-5-aminomethyl-2-methylpyrimidine ( 15 ) by hydrogenation-dehydrogenation. Both products are important intermediates in the synthesis of thiamine.     

Incorporation of carbon originating from CO2 into different compounds of soil microbial biomass and soil organic matter

In general, soils without the vegetation growing on them are regarded as sources of CO2. However, there are indications that CO2 is also fixed by soil microorganisms. Although this process is not significant from a quantitative point of view, it may change the isotopic composition of soil organic matter. Therefore, we conducted an incubation study with soil and 13C-labeled CO2 to investigate this process. We found that the label was transferred from CO2 into organic compounds in soil. At the end of a 61-day incubation period, 1.3 micromol C g(-1) soil, corresponding to approximately 0.08% of the soil organic carbon, had been fixed. CO2 may, therefore, be an additional source of soil organic carbon. Compound-specific analysis of amino sugars, amino acids, and fatty acids indicated that the label is incorporated into microbial, mainly bacterial, biomass. All groups of microorganisms were involved in the assimilation of CO2, but the relatively high enrichment of mono-unsaturated and mid-chain branched fatty acids indicates that gram negative bacteria and actinomycetes may be slightly more important in this process than other groups of microorganisms.     

Highly regioselective Diels-Alder reactions toward oroidin alkaloids: use of a tosylvinyl moiety as a nitrogen masking group with adjustable electronics

[reaction: see text] The use of the p-toluenesulfonyl (Ts) and tosylvinyl (Tsv) groups as nitrogen masking groups imparted high regioselectivity in Diels-Alder reactions directed toward members of the oroidin-derived marine alkaloid family. The electron-withdrawing Tsv group was utilized as an electronically adjustable nitrogen-protecting group as subsequent hydrogenation provided the more electron-rich tosylethyl (Tse) group. This electronic adjustment strategy avoided a protecting group exchange and provided the required electronics for the key chlorination/ring-contraction sequence.     

Detection of ppm quantities of gaseous SO2 by o9rganoplatinum dendritic sites immobilised on a quartz microbalance

Sensor devices for the detection of low quantities of SO2 gas have been constructed which comprise organoplatinum receptor sites for the selective recognition of SO2 and a quartz crystal microbalance for the detection of small mass changes at the receptor sites.     

The influence of ethylene glycol chains on the thermodynamics of hydrogen-bonded supramolecular assemblies in apolar solvents

Substitution of hydrogen bond directed supramolecular assemblies with ethylene glycol chains leads to a reduction in the association constant in apolar solvents, where the reduction of the association constant is dependent on the length of the aliphatic spacer connecting the hydrogen bonds and the ethylene glycol chain.     

Isolation and structure revision of the actin-binding macrolide rhizopodin from Myxococcus stipitatus (Myxobacteria)

Rhizopodin was isolated as cytostatic and weakly antifungal macrolide (1) and later characterized as potent actin-depolymerizing agent. It is produced by the myxobacterium Myxococcus stipitatus, which enables a fermentative supply of the drug for biological studies. We here report a revised structure that characterizes rhizopodin (2) as the first known dimeric bis-lactone exhibiting side chains that terminate in N-methyl-vinylformamide groups, which are otherwise found in smaller marine toxins also targeting the actin cytoskeleton. Compound 2 might function as bivalent inhibitor forming ternary complexes with actin which would explain its high efficacy.