posted on 2016-02-20, 16:54authored byWenhui Zhang, Anthony S. Serianni
Pathways in the degradation of the C6 1,2-dicarbonyl
sugar (osone) d-glucosone 2 (d-arabino-hexos-2-ulose) in aqueous phosphate buffer at pH
7.5 and 37 °C have been investigated by 13C and 1H NMR spectroscopy with the use of singly and doubly 13C-labeled isotopomers of 2. Unlike its 3-deoxy
analogue, 3-deoxy-d-glucosone (3-deoxy-d-erythro-hexos-2-ulose) (1), 2 does
not degrade via a 1,2-hydrogen shift mechanism but instead initially
undergoes C1–C2 bond cleavage to yield d-ribulose 3 and formate. The latter bond cleavage occurs via a 1,3-dicarbonyl
intermediate initially produced by enolization at C3 of 2. However, a careful monitoring of the fates of the sketetal carbons
of 2 during its conversion to 3 revealed
unexpectedly that C1–C2 bond cleavage is accompanied by C1–C2
transposition in about 1 out of every 10 transformations. Furthermore,
the degradation of 2 is catalyzed by inorganic phosphate
(Pi), and by the Pi-surrogate, arsenate. C1–C2
transposition was also observed during the degradation of the C5 osone, d-xylosone (d-threo-pentose-2-ulose), showing that this transposition may be a common
feature in the breakdown of 1,2-dicarbonyl sugars bearing an hydroxyl
group at C3. Mechanisms involving the reversible formation of phosphate
adducts to 2 are proposed to explain the mode of Pi catalysis and the C1–C2 transposition. These findings
suggest that the breakdown of 2 in vivo is probably catalyzed
by Pi and likely involves C1–C2 transposition.