E. C. Naumann et al. / Bioorg. Med. Chem. Lett. 23 (2013) 3852–3856
3853
O
halogenides 6 and 7 were generated from the commercially avail-
able phytol (mix of cis/trans-isomers) 8 and trans,trans-farnesol 9
(see Supplementary data).
Indeed the carprofen derivatives 5a–b showed GSM activity in
the low micromolar range (Table 1). The carprofen derivative 5a
OH
Cl
N
H
N
H
1 Carprofen
2 Carbazole
(IC50 (Ab42) = 4
lM) was the most active GSM and derivative 5b
(IC50 (Ab42) = 23
l
M) also lowered Ab42 levels significantly. These
O
O
OH
Cl
oligo-isoprenylated GSMs are characterized by a high clogP (Ta-
ble 4) and amphiphilic behavior, but they do resemble terpenes
with essential biological activity in humans. Based on the GSM
activity of the terpene-derived compounds 5a–b, we aimed at
OH
Cl
N
S
N
O
O
C10H21
tocopherol-derived GSMs with the R,R,R-
a-tocopherol 10a and
β
μ
M
3 IC50(A 42) = 3
β
μ
M
EC50(A 38) = 6
the all-rac- -tocopherol 10b and the structurally related 6-hydro-
a
xy-2,5,7,8-tetramethylchroman-2-carboxylic acid 11 as starting
materials (Fig. 2).
β
μ
M
4 IC50(A 42) = 12
β
μ
M
EC50(A 38) = 12
Referring to our previous studies we added a carboxylic acid to
the tocopherol scaffolds 10a–b and lipophilic chains to the chro-
man derivative 11. The syntheses are outlined in Schemes 2–434
We synthesized two tocopherol derivatives 13a–b in order to com-
pare the influence of the different centers of chirality of the lipo-
Figure 1. Carprofen (1), carbazole (2) and two selected
4).25
c-secretase modulators (3,
suggested the introduction of natural lipophilic chains with ter-
pene-related structures like the farnesyl- and the phytyl moiety
on the carprofen core. Phytol- and farnesol-derived compounds
are natural components of essential oils or of chlorophyll. Tocoph-
erol, a terpene-derived natural compound, located in cell mem-
branes, is an effective antioxidant and anti-inflammatory agent
and protects cell membranes from oxidative damage.26 It was pro-
posed as a therapeutic agent for AD and other neurodegenerative
disorders, and clinical trials have already been performed based
on the hypothesis that AD might be caused by oxidative stress.26,27
philic side chain on
c-secretase activity. Additionally we
generated two classes of chroman derivatives 16a–e and 18a–e
to explore the impact of the acidic moiety‘s location on the puta-
tive GSM activity. We further compared the influence of several
lipophilic chains of various lengths like octyl-, undecyl, tetradecyl
and the terpene-related farnesyl- and phytyl moieties.
The experimental data confirmed our initial hypothesis: all syn-
thesized tocopherol derivatives with an acidic moiety (see Table 3,
entries 3–14) exhibit GSM activity and increased the generation of
Ab38 and reduced the generation of Ab42; no other modes of action
Studies indicated that a-tocopherol levels are significantly altered
like inverse modulation or inhibition of
observed. The tocopherol 10b itself displayed no GSM activity
(IC50 (Ab42) > 100 M). The tocopherol ester 12b (IC50
(Ab42) > 100 M) was also inactive while the corresponding
tocopherol acid 13a (IC50 (Ab42) = 11 M) had strong GSM activity.
This confirms the crucial role of the acidic functionality in these
GSMs. The stereoisomers 13a (IC50 (Ab42) = 11 M) and 13b (IC50
(Ab42) = 12 M) displayed equipotent activities; thus the configu-
c-secretase activity were
in the brain of AD patients.28,29 Changes of the tocopherol levels in
the brain might be affected by the APOE status.30 The major risk
factor for late-onset AD is a polymorphism of the APOE gene on
chromosom 19.31 Smoking or non-smoking carriers of the APOE4
isoform displayed remarkable differences in the pharmacokinetics
l
l
l
of enantiopure and all-rac-
a
-tocopherol with its eight stereoiso-
l
mers.32 The animal food additive all-rac-
a
-tocopherol, with its var-
l
ious stereoisomers, is ingested by humans via comsumption of
ration of the chiral carbon atoms did not seem to influence GSM
activity. All chroman derivatives (Table 3, entries 5–14) show
animal fats.33 These observations encouraged us to investigate
the impact of enantiopure and all-rac-a-tocopherol analogues on
GSM activity. The new carprofen derivatives 5a–b were prepared
by a one step synthesis (Scheme 1). The reaction of the carprofen
1 and the corresponding phytyl- and farnesyl halogenides 6 and
7 yielded the carprofen derivatives 5a–b. The phytyl- and farnesyl
HO
HO
HO
O
O
O
OH
O
11 6-hydroxy-2,5,7,8-tetramethyl
chroman-2-carboxylic acid
Scheme 1. Synthesis of carprofen derivatives. Reagents and conditions: (a) NaH,
R1-X, THF, 0 °C to rt. A cell-based assay was used to quantify the GSM activity of
novel derivatives and to determine the altered generation of Ab38, Ab40 and Ab42
peptides (see Supplementary data).
10a R,R,R-tocopherol
α
10b all-rac- -tocopherol
Figure 2. Starting materials of the tocopherol-derived compounds as GSMs.
Table 1
Activity of trans,trans-farnesyl-(5a) and phytyl (5b) derivatized carprofens
R1
EC50 Ab38
1.1
>50
(
lM)
IC50 Ab40
(lM)
IC50 Ab42
0.4
23 0.1
(lM)
a
a
a
Compd
5a
5b
2
26 0.2
>50
4
a
Enzyme-linked immunosorbent assay, CHO cells, for the increase of Ab38 see Supplementary data .