Synthesis of regioselectively 18O-labelled chlorophyll derivatives at the 31- and/or 131-positions through one-pot exchange of carbonyl oxygen atoms
2005; Elsevier BV; Volume: 61; Issue: 25 Linguagem: Inglês
10.1016/j.tet.2005.04.012
ISSN1464-5416
AutoresHidetada Morishita, Hitoshi Tamiaki,
Tópico(s)Plant Stress Responses and Tolerance
ResumoAbstract 3 1 - and/or 13 1 - 18 O-oxo-labelled methyl pyropheophorbides (84–90% 18 O atoms at each position) were prepared by exchanging carbonyl oxygen atoms under biphasic conditions of acidic H 2 18 O (ca. 95% 18 O) and dichloromethane. The (un)labelling occurred more rapidly at less sterically hindered (13-C O possessing 13 2 -COOCH 3 >13-C O lacking it) or more reactive carbonyl groups (formyl>keto group), and not at any hydroxy groups. Reduction of a carbonyl to carbinol group was useful for preparation of regioselectively 18 O-labelled chlorophyll derivatives. Following the labelling procedure, 13 1 - 18 O-pheophytin- a and 3 1 - 18 O-pheophytin- d were obtained. All the synthetic 18 O-labelled compounds were characterized by their FAB-mass, 13 C NMR and IR spectra. Especially, 18 O-labelling induced 0.02 ( 13 C–O) and 0.04–0.05 ppm high field shifts ( 13 C O) in 18 O-attached carbon resonances and about 30 cm −1 down-shifts in 18 O-labelled carbonyl stretching vibrational bands.
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