Total synthesis of snake toxin α-bungarotoxin and its analogues by hydrazide-based native chemical ligation

Nicotinic acetylcholine receptors(nAChRs) play important roles in intercellular communications of nerve cells. α-Bungarotoxins(αBtx) is a moderator for the nAChRs. Chemical synthesis provides a promising way to access aBtx and their analogues. Here, we reported a new method for a-bungarotoxin by combining Fmoc-SPPS and peptide hydrazide based ligation strategy. The two-segment ligation method may enable efficient synthesis of aBtx analogues. These synthetic toxin peptides are useful tools for development of imaging or therapeutic reagents.

The primary dolostone in the Meso-Neoproterozoic:Cases study on platforms in China

Meso-Neoproterozoic dolostone is abnormally well-developed in the platform areas in China,detailly,in the Mesoproterozoic Calymmian Wumishan Formation of North China Basin,Neoproterozoic Ediacaran Qigbulak Formation of Tarim Basin,and the Neoproterozoic Ediacaran Dengying Formation of Sichuan Basin.The outcrops and drilling cores from these basins show that these dolostones are mostly thick-bedded to massive,with mud-sized to silt-sized crystalline dolostone reaching 86%-97%of the total dolostone thickness.These dolostones basically suffered no secondary metasomatism,regardless of containing microorganisms(such as algae and bacteria)or not.The analyses of sedimentary palaeogeographic features indicate that:(1)the Meso-Neoproterozoic dolostone nearly covered the entire area basins,and was widely deposited in supratidal to intertidal zones,as well as in open platform environments;(2)the dolostone was subdivided according to the crystalline size,with the distribution controlled by geomorphology,i.e.,the pure mud-sized crystalline dolostone developing in depression areas,whereas the grainy mud-sized crystalline dolostone or the mound stromatolitic mud-sized crystalline dolostone developing in uplift areas;(3)deep-water basins developed between the carbonate platforms,and the seismic profiles show that these basins were formed by syngenetic deep faults in the Meso-Neoproterozoic strata.These syngenetic faults increased Mg^(2+)concentration in the seawater by injecting rich-Mg2+-bearing hydrothermal fluids into the carbonate platforms.The analyses of geochemical and paleoclimatic indexes reveal that there is no obvious difference in carbon and oxygen isotope ratios between dolostones having different textures,with the ratios similar to those of the global seawater of the Meso-Neoproterozoic,indicating that the silt-sized crystalline dolostone has the same sedimentary origin as the mud-sized crystalline dolostone,i.e.,the former is from authigenic recrystallization of the latter rather than secondary metasomatism.Therefore,whatever the crystalline sizes are,the dolostones are all originated from sedimentation.All the petrological,sedimentary and geochemical data suggest that the dolostones covering almost the whole Meso-Neoproterozoic typical platform areas of China are of relatively primary sedimentary origin.