A. J. Salmon et al. / Bioorg. Med. Chem. Lett. 21 (2011) 6058–6061
6061
and glucosyl (17: Ki 1360 nM) derivatives. At CA II, most triazoles
were potent inhibitors, many with Kis below 10 nM, and selectivity
for CA II over CA I, similarly to the parent alkyne 1 (Ki 5.1 nM, 211-
fold selective for CA II over CA I). The most noteworthy selectivity
compared to CA I was with the 1,5-disubstituted per-O-acetyl arabi-
nosyl triazole derivative 20 (CA II Ki = 2.9 nM) which was 1514-fold
selective for CA II compared to CA I. This differs to the corresponding
1,4-disubstituted per-O-acetyl arabinosyl triazole derivative 10
which had no selectivity (CA I Ki = 10.5 nM and CA II Ki = 8.2 nM).
At CA IX triazoles displayed a range of inhibition constants (Kis
7.0–134 nM) compared to the parent alkyne 1 (Ki 8.1 nM) and with
activity similar to CA II. The 1,5-disubstituted triazoles had good
CA IX inhibition(Kis 7.0–68.3 nM), nearly all were better CA IX inhib-
itors than their 1,4-disubstituted counterparts, for example the 1,4-
per-O-acetyl galactosyl derivative 8 (Ki 110 nM) is 15-fold less active
than the corresponding 1,5- galactose derivative 18 (Ki 7.3 nM). The
per-O-acetyl glucosyl analogue 17 (CA IX Ki = 32.6 nM) was the best
triazole (1,4- or 1,5-disubstituted) with regard to selectivity for CA
IX over off-target CA I and II, it was 42-fold and 5-fold selective,
respectively. This selectivity is opposite to that observed with the
hydrophobic metallocene tail moieties.39 In these compounds the
1,4-disubstituted triazole regioisomer had better CA IX selectivity
than the 1,5-disubstituted triazole regioisomer.39 As the CA active
site encompasses two distinct regions to which the CA inhibitor tail
can potentially interact, one lined by hydrophobic amino acids (con-
sisting of Phe130, Val134, Leu203 and Pro201) and the other located di-
rectly opposite and lined by hydrophilic amino acids (primarily
Asn62, Asn67 and Gln92),2 it is logical that hydrophobic versus hydro-
philic tail groups may lead to differential isozyme selectivity.
In summary the new compounds of this study comprise a sugar
moiety tethered to an aromatic sulfonamide CA pharmacophore
through an intervening triazole ring. Compounds 22, 23, 25 and
26 each contain a free sugar moiety and so provide a selection of
likely membrane impermeable small molecule CA inhibitors with
selectivity for the extracellular active site CA IX over other (intra-
cellular) CA isozymes. The key step of our synthesis is the regiose-
lective Huisgen’s 1,3-DCR using RuAAC with [Cp⁄RuCl(cod)] as
catalyst. Our findings identified a number of 1,5-disubstituted tri-
azole inhibitors (compounds 18, 19, 21–23 and 26) that block CA
IX with inhibition constants less than 10 nM. One inhibitor (com-
pound 17) possessed very good selectivity for CA IX over off-target
CAs. Our results have demonstrated that subtle structural differ-
ences in the sugar tail can discriminate the CA isozyme active site
topology to influence enzyme inhibition characteristics. A compar-
ison of the CA IX inhibition of the new 1,5-disubstituted triazoles
(Kis 7.0–68.3 nM) with their 1,4-disubstituted counterparts
showed that nearly all were better CA IX inhibitors, a significant
step towards further building SAR with carbohydrate-based CA
inhibitors. The enzyme inhibition attributes of these compounds
are an important result for potential future biological studies or
17–26) associated with this article can be found, in the online ver-
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sulfonamide compounds.
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primary
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This research was financed in part by the Australian Research
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Supplementary data
Supplementary data (synthetic procedures; compound charac-
terisation data and the CA assay procedure for new compounds