Design and synthesis of mimics of S-Adenosyl-L-homocysteine as potential inhibitors of erythromycin methyltransferases

Article abstract of DOI:10.1016/S0960-894X(00)00021-4

A series of indanotriazine C-ribosides were prepared as SAH mimics, and tested for their ability to inhibit erythromycin resistance methylases Erm AM and Erm C'. A carbocyclic analogue derived from quinic acid was also synthesized and tested. (C) 2000 Elsevier Science Ltd. All rights reserved.

Full text of DOI:10.1016/S0960-894X(00)00021-4

Bioorganic & Medicinal Chemistry Letters 10 (2000) 433±437
Design and Synthesis of Mimics of S-Adenosyl-L-Homocysteine as
Potential Inhibitors of Erythromycin Methyltransferases
Stephen Hanessian* and Paulo W. M. Sgarbi
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Department of Chemistry, Universite de Montreal, PO Box 6128, Station Centre-ville, Montreal, QC, Canada H3C 3J7
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Received 23 November 1999; accepted 22 December 1999
AbstractÐA series of indanotriazine C-ribosides were prepared as SAH mimics, and tested for their ability to inhibit erythromycin
resistance methylases Erm AM and Erm C0. A carbocyclic analogue derived from quinic acid was also synthesized and tested.
# 2000 Elsevier Science Ltd. All rights reserved.
Erythromycin resistance methylase (Erm) is an enzyme
involved in the base-speci®c N-methylation of bacterial
23S ribosomal RNA, utilizing S-adenosylmethionine
as the methylating agent.1 Since this modi®cation of the
r-RNA takes place near or at the binding sites of
macrolide antibiotics, their interaction with the ribo-
some is rendered ine€ective with consequent loss of
antibacterial activity. This phenomenon of resistance
imparted by methyl transferases such as Erm AM and
Erm C0 extends to the macrolide±lincosamine±strepto-
gramin type B (MLS) group of antibiotics.2,3 The three-
dimensional (3-D) structure of Erm AM has been
determined by NMR spectroscopy.4 The crystal structure
of Erm C complexed with S-adenosylmethionine,
reveals binding interactions in the catalytic domain.5,6
drug±enzyme complexes. The triazine core compound 2
and the pyrimidine analogue 3 showed Ki values of 8
and 10 mM, respectively. Fesik and co-workers7 have
postulated speci®c interaction domains with the enzyme
Erm C0 based on a 3.0 A X-ray crystal structure of the
complex. The indane moiety was viewed as ®lling a
hydrophobic crevice composed of the side chains of
I185, L86, I106, D84 and D109. H-Bonding of the
amino triazine unit was proposed as another interaction
with Erm AM and Erm C0. The piperidine and aniline
side-chains in 2 and 3 respectively were found to only
partially ®ll the space occupied by the ribose ring in
SAH, while the amino acid portion of the latter had no
counterpart in the lead inhibitors.
These ®ndings prompted us to consider the design and
synthesis of mimics of SAH that would encompass some
of the bene®cial features of the Abbott compounds,
while adding complementary functionality.
In view of the importance of these enzymes, e€orts have
been made to develop inhibitors. Indeed such inhibitors
of Erm C0 can sensitize bacteria that are resistant to
MLS in vitro and in vivo. In this regard it is of interest
to point out that S-adenosyl-l-homocysteine (SAH, 1,
Fig. 1) is a naturally occurring inhibitor of methyl
transferases (Kiꢀ40 mM).
Fesik and co-workers7 have screened a library of small
heterocyclic molecules against Erm AM using SAR by
NMR. Some of the lead compounds such as 2 and 3
(Fig. 1), have shown binding to Erm AM similar to
SAH, as judged by their Ki values and chemical shift
changes for the amide NH groups in NMR spectra of
We report herein the synthesis of two prototypical SAH
mimics of generalized structures 4 and 5 (Fig. 1). We
envisaged hybrid structures that contain a common
indanotriazine sca€old as an adenine surrogate capable
of interacting with a hydrophobic side-chain and of
H-bonding. The diol groups in the anhydro sugar unit
in 4 and the cyclohexane ring in 5 were intended to
mimic the ribose ring in SAH. Functional diversity
would be provided by an ether or thioether type side-
chain that would correspond to the anilino appendage
in 3 and the amino acid unit in SAH, respectively.
Considering that diversi®cation was envisaged at the
hydroxymethyl group corresponding to the ribose unit
*Corresponding author. Tel.: +1-514-343-6738; fax: +1-514-343-
5728; e-mail: hanessia@ere.umontreal.ca
0960-894X/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(00)00021-4

434
S. Hanessian, P. W. M. Sgarbi / Bioorg. Med. Chem. Lett. 10 (2000) 433±437
Figure 1.
in SAH, the logical strategy was to prepare a core
anhydrosugar structure containing the indanotriazene
unit, then to conduct appropriate modi®cations at the
intended primary site (Scheme 1). This strategy, simple
as it appeared to be, had to be abandoned when it was
found that selective alkylation of the primary hydroxyl
group in the presence of the aminotriazine unit was not
possible. Temporary protection of the heterocycle as the
bis-N-Boc derivative was not entirely satisfactory, due
to the sensitivity of the urethane group to cleavage
under basic conditions, and the tendency for anomer-
ization via a base-catalyzed b-elimination and reclosure.
In view of the exploratory nature of the project, we
proceeded to reverse the order of substitution of the
anhydro sugar core (Scheme 1).
yields. Introduction of the indanotriazine was done
under basic conditions10,11 as shown in Scheme 1.
Unfortunately, this led to a mixture of anomers because
of the acidity of the methylene group in the resulting
triazine derivative and an inevitable b-elimination and
reclosure. Separation of the isomers and deprotection of
the acetal led to the intended prototypes 8 and 9 in each
case. Individual compounds as well as anomeric mix-
tures were tested for inhibition of Erm AM and Erm C0
(vide infra). A series of thioethers represented by 12
and 13 were also prepared by the same protocol
(Scheme 2). In order to avoid the isomerization issue,
we also prepared the extended-chain analogue 18 shown
in Scheme 3.
Finally, we used the readily available quinic acid 1912 as
a template to arrive at the intended carbocyclic SAH
mimic 5 as shown in Scheme 4. Deoxygenation13 of 20
Etheri®cation of the readily available hydroxyester 6,8,9
led to a series of aralkyl ethers expressed as 7 in excellent
Scheme 1. Conditions: (a) ArCH2Br, NaH, Bu4NI, DMF, rt, 12 h (85±90%); (b) indanyl-guanidine A, NaOMe, MePH, 80 ꢁC; (c) THF/H2O
9:1, p-TsOH, 40 ꢁC (54±78%).

S. Hanessian, P. W. M. Sgarbi / Bioorg. Med. Chem. Lett. 10 (2000) 433±437
435
Scheme 2. Conditions: (a) ArSH, NaH, DMF, rt, 6 h (75±88%); (b) indanyl-guanidine A (see Scheme 1), NaOMe, MeOH, 80 ꢁC; (c) THF/H2O 9:1,
p-TsOH, 40 ꢁC (56±87%).
Scheme 3. Conditions: (a) i. acetone, H2SO4, rt, 12 h (85%), ii. NaH, DMF, 0 ꢁC, 30 min; then 4-bromobenzyl bromide, 0 ꢁC to rt, 2 h (90%), iii.
DIBAL-H, PhCH3, 78 ꢁC, 12 h (91%); (b) i. phenyl disul®de, PBu3, PhCH3 (95%), ii. 5.0 eq allyltributyltin, 2.0 eq Bu3SnOTf, PhCH3, 110 ꢁC, 12 h
ꢁ
ꢁ
.
(82%); (c) i. BH3 Me2S, THF, 0 C; ii. EtOH, NaOH, H2O2 (80% over 2 steps), iii. Jones reagent, acetone, 0 C, iv. CH2N2, ether (95% over 2 steps);
(d) indanyl-guanidine A (see Scheme 1), NaOMe, MeOH, 80 ꢁC; f. THF/H2O 9:1, p-TsOH, 40 ꢁC (80% over 2 steps).
Scheme 4. Conditions: (a) i. p-TsOH, PhH, ii. Bu2SnO, iii. BnBr (75% over 3 steps); (b) i. K2CO3, MeOH (100%), ii. 2,2-DMP, CSA, THF, rt
(96%); (c) i. NaH, THF, ii. CS2, iii. Mel (94%); (d) Bu3SnH, AlBN, PhCH3 (75%); (e) indanyl-guanidine A (see Scheme 1), NaOMe, MeOH, 80 ꢁC;
f. THF/H2O 9:1, p-TsOH, 40 ꢁC (83% over 2 steps).
via its xanthate ester 21 led to the di€erentially pro-
tected cyclohexane carboxylic acid derivative 22, which
was transformed into 23.
extended aromatic ether group appears to be well toler-
ated (compare entries 1, 3 and 6 with 2, 4 and 8). A
methylene bridge between the anhydro sugar and the
indanotriazine seems better than an ethylene bridge
(entries 2 and 9). Finally, it appears that the anomeric
con®guration is not playing a crucial role in the inter-
action with Erm C0 and Erm AM (entries 2 and 8).
Table 1 shows the results of the inhibition studies on
Erm AM and Erm C0.14 Regrettably, only two com-
pounds (entries 2 and 8), showed weak but promising
activity at Ki values ranging from 40 to 80 mM. It is of
interest that even within this limited set of potential
inhibitors, some selectivity was observed based on subtle
functional changes. A p-substituted halogen or a chain
These preliminary observations could be useful in
designing more e€ective inhibitors of these important
enzymes in the future.

436
S. Hanessian, P. W. M. Sgarbi / Bioorg. Med. Chem. Lett. 10 (2000) 433±437
Table 1.
Entry
1
Erm AM est. Ki (mM)
Erm C0 est. Ki (mM)
>100 (16.9%@100)
>(5.5%@100)
2
3
4
5
ꢀ75
ꢀ40
>100 (15%@100)
>100 (0%@100)
ꢀ90
ꢀ60
>100 (3.4%@100)
>100 (28%@100)
6
7
>100 (10%@100)
>100 (18%@100)
>100 (10%@100)
50±100 (39.9%@100)
8
ꢀ55
ꢀ80
9
ꢀ50 (55%@100)
50±100 (37.5%@100)
>100 (17.7%@100)
10
>100 (9.9%@100)

S. Hanessian, P. W. M. Sgarbi / Bioorg. Med. Chem. Lett. 10 (2000) 433±437
437
Acknowledgement
7. Hajduk, P. J.; Dinges, J.; Schkeryantz, J. M.; Janowick, D.;
Kaminski, M.; Tufano, M.; Augeri, D. J.; Petros, A.; Nienaber,
V. L.; Zhong, P.; Hammond, R.; Coen, M.; Bentel, B.; Katz,
L.; Fesik, S. W. J. Med. Chem. 1999, 42, 3852.
8. Ohrui, H.; Jones, G. H.; Mo€att, J. G.; Maddox, M. L.;
Christensen, A. T.; Byran, S. K. J. Am. Chem. Soc. 1975, 97,
4602.
9. Hanessian, S.; Ogawa, T.; Guindon, Y. Carbohydr. Res.
1974, 38, C12.
10. For preparation of indanyl-guanidine, see Shapiro, S. L.;
Parrino, V. A.; Geiger, K.; Kobrin, S.; Freedman, L. J. Am.
Chem. Soc. 1957, 77, 5064.
11. For cyclization into a triazine, see Modest, E. J. In Het-
erocyclic Compounds; Elder®eld, R. C., Ed.; John-Wiley &
Sons, New York, 1961; Vol. 7, pp 627.
12. For a review on the utilization of quinic acid as a chiron in
synthesis, see Barco, A.; Benetti, S.; DeRisi, C.; Marchetti, P.;
Pollini, E. P.; Zanirato, V. Tetrahedron: Asymmetry 1997, 8,
3515.
13. Barton, D. H. R.; McCombie, S. W. J. Chem. Soc., Perkin
Trans. 1 1975, 1574
14. For details for the inhibition assay, see ref 7.
We thank Abbott Laboratoires for generous ®nancial
assistance and for biological testing.
References and Notes
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