RESUMO
Kinetic measurements suggest that neighbouring acetamido-group participation occurs in the spontaneous hydrolysis and methanolysis of o-carboxyphenyl 2-acetamido-2-deoxy-beta-D-glucopyranoside and in the spontaneous hydrolysis of 2,4-dinitrophenyl 2-acetamido-2-deoxy-beta-D-glucopyranoside and 2-acetamido-2-deoxy-beta-D-glycopyranosyl fluoride. The methanolyses of these compounds proceed with predominant retention of configuration which is also consistent with neighbouring acetamido-group participation. The oxazoline intermediate which would arise from such a process was detected during methanolysis of 2-acetamido-2-deoxy-beta-D-glucopyranosyl fluoride in the presence of bases by n.m.r., i.r., and u.v. spectroscopy. Attempts to isolate the oxazoline were unsuccessful.
Assuntos
Acetilglucosamina , Glucosamina , Acetilglucosamina/análogos & derivados , Fenômenos Químicos , Química , Glucosamina/análogos & derivados , Espectroscopia de Ressonância Magnética , Conformação Molecular , Espectrofotometria Infravermelho , Espectrofotometria UltravioletaRESUMO
The plurilocular zoosporangium of Ectocarpus parvus Saunders in initiated as a uniseriate branch from a vegetative cell. Subsequent anticlinal and periclinal divisions of the cells leads to enlargement of the sporangium and the formation of multiple locules. Each locule containes a single biflagellate zoospore. Ultrastructural changes accompanying these events include a reduction in the size of chromatophores, a reduction in the number of dictyosomes and the appearance of plasmalemmasomes in later stages. Enlargement of the mitochondria and a decrease in size of the nucleus occur in the final stages of zoospore formation. Comparison with the vegetative and sporogenous cells of other brown algae are made.