with only a 3.6% reduction compared to a 18.3% and 19.4%
reduction in AG-treated and untreated controls respectively.
Outside of its inhibitory activity, bis 2-AI 3 also demonstrated
the ability to break preformed AGEs. The ability to reverse AGE
formation is potentially more useful from a clinical standpoint as
the ability to reverse mis-glycation may have the potential to
delay or prevent disease progression. To this end, we established
that compound 3 restored the primary amine content of glycated-
BSA to 78.9% of the baseline value after 48 hours, exceeding the
71.9% restoration afforded by ALT-711 as quantified with the
TNBSA assay, while AG 1 (as previously established) showed no
significant breaking activity.
To further develop this new class of anti-AGE compounds, we
set out to investigate the structure activity relationship of
compound 3 in the context of its anti-glycating activity. We first
explored the effect of the alkyl linker length between the two 2-
AI heterocycles in compound 3. Compound 3, along with
compound 4, which possesses an increased linker length of five
methylene units as compared to four methylene units in
compound 3, were readily synthesized from the corresponding
di-acid chlorides via the Nierenstein reaction to the di-α-
chloroketones 5 and 6, followed by cyclization with Boc-
guanidine and subsequent Boc deprotection (Scheme 1).
Compound 4 was then assayed for its ability to inhibit AGE
formation on bovine serum albumin by glycolaldehyde (GO)
using a standard fluorescence assay, and its activity compared to
compound 3. Interestingly, we noted no significant decrease in
Scheme 2. Attempted synthesis of bis 2-AIs with shortened linkers.
o
Reagents and Conditions: i) CH
imidazole, DCM, 0 °C; iv) (COCl)
CH , Et O, 0 °C; vi) HBr; vii) Boc-guanidine, DMF, rt; viii)1M TBAF
in THF, rt; ix) 5% Na/Hg, H O, pH 1.5, 0 – 5 °C; x) NH CN, H O, pH
.3, 95 °C; xi) Br , MeSO H then 2-aminoimidazole sulfate.
2
N
2
, Et
2
O, 0 C; ii) HCl; iii) TBDPSCl,
2
, cat. DMF, DCM, 0 °C – rt; v)
2
N
2
2
2
2
2
4
2
4
with TBDPS-Cl and converted the resulting carboxylic acid into
the corresponding α-bromoketone 20 using a standard three-step
sequence (oxalyl chloride, diazomethane, and then HBr quench).
Cyclization with Boc-guanidine followed by TBAF mediated
cleavage of the TBDPS silyl ether then delivered the
corresponding Boc-protected 2-AI alcohol 21. Repetition of this
reaction sequence to carboxylic acid 22 first generated the α-
bromoketone 23 that, following cyclization and silyl ether
cleavage, produced the corresponding Boc-protected 2-AI
alcohol 24. With both compounds in hand, we simply needed to
oxidize the primary alcohol to the corresponding carboxylic acid
and then install the last 2-AI ring. Unfortunately, all attempts at
oxidizing the primary alcohol of 20 or 22 to the carboxylic acid
(directly via Jones or stepwise via Swern-Pinnick) also led to
decomposition.
Scheme 1. Synthetic route to 4 and 5 methylene linked bis-2-AIs.
o
O, 0 C; ii) HCl; iii) Boc-
Reagents and conditions: i) CH
2
N
2
, Et
guanidine, NaI, DMF, rt; iv) TFA:DCM (1:2) then MeOH:HCl.
2
Finally, we tried to access compounds 13 and 14 through
1
4
activity between the two compounds (data not shown).
bromine-mediated oxidative heterodimerization. 2-AIs 25 and
6 (Scheme 2) were accessed through standard Akabori reduction
of the corresponding amino acid methyl esters followed by pH
controlled cyanamide condensation. Treatment of each
compound with 1 eq. of Br followed by attempted dimerization
2
With no real activity differential between 3 and 4, we
attempted to delineate the effect that shortening the tether had
upon activity. To this end, we attempted to access compounds 7,
2
8
, and 9 via Boc-guanidine cyclization of the corresponding bis-
with 2-aminoimidazole under acidic conditions also failed to
deliver compounds 13 and 14.
α-chloroketones 10, 11, and 12 (Scheme 1, n = 1, 2, and 3
respectively). Starting from the commercially available acid
chlorides, we observed decomposition of compound 7 and 8 upon
treatment with diazomethane, while we were able to access bis-
α-chloroketone 12. Unfortunately, treatment of 12 with Boc-
guanidine also led to decomposition.
With this failure, we re-designed our target molecules to bis-
-AIs 13 and 14 (Scheme 2). Our reasoning was that if
2
Figure 2. AGE inhibitor redesign
proximity between the two 2-AI groups correlated with activity,
then altering their bite angle through the Thorpe-Engold effect
would deliver significantly more active compounds than 3, 4, or
the activity that compounds 7-9 could have potentially possessed.
However, similar to 10 and 11, treatment of acid chlorides 15 and
With repeated failures to access our targeted bis-2-AI
derivatives, we elected to reconsider our AGE-inhibitor design.
Although we are confident that synthetic procedures could be
developed to access bis-2-AIs with compressed tether lengths
1
6 with diazomethane followed by an HCl quench in an effort to
(
and these efforts are ongoing), our overarching goal is to
access bis- α-chloroketones 17 and 18 also led to decomposition.
develop potent anti-AGE compounds that can be evaluated for
efficacy in vivo. In this regard, we considered the possibility that
bis 2-AIs 3 and 4 could be simply viewed as a 2-AI group
tethered to another reactive group (Figure 2) in which both
entities were capable of sequestering reactive aldehyde species.
With repeated failures to access the shorter tethered 2-AIs
through one-pot cyclizations, we next attempted to synthesize 13
and 14 through sequential installation of each 2-AI heterocycle.
To this end (Scheme 2), we protected the hydroxyl group of 19
Furlani, Robert E.
