Aldehydes derived from lipid peroxidation, such as 4-hydroxynon-2-enal, are
implicated in various diseases, and, therefore, reduction of these aldehydes to the
corresponding alcohol may lead to detoxification. The same pyridinecarboxamidate
iridium complex reduced 4-hydroxynon-2-enal with NADH acting as a hydrogen
source. Under the conditions shown in Scheme 25, 88% of 4-hydroxynon-2-en-1-ol
and 6% of 4-hydroxynonan-1-ol were obtained. Increasing the reaction time led to
higher ratios of the saturated dialcohol suggesting that the C¼O group is first
hydrogenated. The putative hydride intermediate [Cp*IrH(pyridinecarboxamidate)]
was detected and characterised by NMR spectroscopy [139].
Do’s group showed that the reduction of aldehydes catalysed by the
pyridinecarboxamidate iridium complex above-mentioned can take place inside
living cells [140]. This complex catalyses the reduction of BODIPY-CHO to
BODIPY-OH (Scheme 26) inside of NIH-3T3 mouse embryo fibroblast cells,
using NADH as the hydrogen donor. The fluorescence that the BODIPY-OH
compound develops within the cytoplasm of the cell was employed to monitor the
TH reaction. When the generation of NADH was artificially reduced, the cells did
N
Ir
Cl
N
Cp*
O
Ph
HO
O
H
HO
HO
HO
HO
+
NADH 2.0 equiv.
Cat
t-ButOH/M199 5:95
air, 37 ºC, 15h
Cat:
Scheme 25 TH of 4-hydroxynon-2-enal pyridine catalysed by the carboxamidate iridium complex
shown. NADH was the H-donor
NADH
Cat
O
H
B
F
F
N
N
OH
B
F
F
N
N
Bodipy-CHO
Bodipy-OH
Cat:
N
Ir
Cp*
N
Cl
O
Ph
Scheme 26 Reduction of BODIPY-CHO
100
M. Pilar Lamata et al.