RESUMO
The short syntheses of each of the mono-acetates of N-acetyl-D-neuraminic acid are reported. These are important molecules for studying the mechanism and function of enzymes which utilise Neu5Ac as a substrate. However, until now these molecules were not available as pure compounds and instead had to be studied as mixtures. Neu4,5Ac(2) and Neu5,8Ac(2) were synthesised from a common precursor in 2 and 4 steps respectively, while Neu2,4Ac(2) and Neu5,7Ac(2) were synthesised in 3 and 4 steps respectively from another common precursor. Both precursors could be easily prepared in 3 steps from Neu5Ac itself. Importantly, no scrambling of the anomeric stereochemistry was detected throughout the course of these syntheses.
Assuntos
Acetatos/química , Técnicas de Química Sintética/métodos , Ácido N-Acetilneuramínico/química , Ácido N-Acetilneuramínico/síntese química , AcilaçãoRESUMO
The coordination modes of the [Au(PPh3)](+) cation to metal alkynyl complexes have been investigated. On addition to ruthenium, a vinylidene complex, [Ru(η(5)-C5H5)(PPh3)2([double bond, length as m-dash]C[double bond, length as m-dash]CPh{AuPPh3})](+), is obtained while addition to a gold(iii) compound gives di- and trinuclear gold complexes depending on the conditions employed. In the trinuclear species, a gold(i) cation is sandwiched between two gold(iii) alkynyl complexes, suggesting that coordination of multiple C-C triple bonds to gold is facile.
RESUMO
The synthesis of the C1-C19 bis-pyran unit of phorboxazole B has been achieved. The key pyran rings were constructed by means of an asymmetric Maitland-Japp reaction and a second Maitland-Japp resolution/cyclization reaction. The longest linear sequence was 14 steps, and the C1-C19 bis-pyran unit was formed in an impressive 10.4% yield.