Copper®, in the absence of other transition metals, catalyzes the cross-coupling of (a-(acyloxy)benzyl)tributylstannanes with allylic bromides in THF in fair to good yields and with aryl/vinyl halides less efficiently or not at all. Simple (a-(acyloxy)alkyl)tributylstannanes react sluggishly even with allyl bromide. However, proximal thiosubstituents on either reaction partner dramatically enhance yields, reaction rates, and the variety of suitable educts. (a-Phthalimidoylalkyl)tributylstannanes afford protected -amino thio esters. In contrast with the Stille reaction, copper-mediated cross-couplings of -heteroatom-substituted alkyltributylstannanes proceed with complete retention of configuration via a coordinatively stabilized organocopper intermediate that can be intercepted in good yield by 1,4-conjugate addition to 2-cyclohexen-1 -one.
These issues were addressed by the use of a synthetic dioctanoyl GlcN␣-PI analogue (GlcN␣-PI(C8)) as an in vitro substrate for GPI-synthesizing enzymes in Chinese hamster ovary cell membranes. GlcN␣-PI(C8) was acylated in an manner requiring acyl-CoA. Thus, the process involving acyl-CoA reported for yeast has been conserved in mammals. Furthermore, both GlcN␣-PI(C8) and GlcN␣-acyl-PI(C8) could be mannosylated in vitro, but mannosylation of the latter was significantly more efficient. This provides direct support for the earlier suggestion that acylation precedes mannosylation in rodents cells. A similar result was also observed with the Saccharomyces cerevisiae mannosyltransferase.In contrast, it has been reported that mannosylation of endogenous GlcN␣-PI by Trypansoma brucei membranes occurs without prior acylation. The same result was obtained with GlcN␣-PI(C8), confirming that the mannosyltransferase of trypanosomes is divergent from those in yeasts and rodents.
Magnesium hydride and its compounds have a high hydrogen storage capacity and are inexpensive, and thus have been considered as one of the most promising hydrogen storage materials for on-board applications.
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