Ring-constrained (N)-methanocarba nucleosides as adenosine receptor agonists: Independent 5′-uronamide and 2′-deoxy modifications

Article abstract of DOI:10.1016/S0960-894X(01)00213-X

Novel methanocarba adenosine analogues, having the pseudo-ribose northern (N) conformation preferred at adenosine receptors (ARs), were synthesized and tested in binding assays. The 5′-uronamide modification preserved [N⁶-(3-iodobenzyl)] or enhanced (N⁶-methyl) affinity at A₃ARs, while the 2′-deoxy modification reduced affinity and efficacy in a functional assay.

Full text of DOI:10.1016/S0960-894X(01)00213-X

Bioorganic & Medicinal Chemistry Letters 11 (2001) 1333–1337
Ring-Constrained (N)-Methanocarba Nucleosides as Adenosine
Receptor Agonists: Independent 50-Uronamide and 20-Deoxy
Modifications
Kyeong Lee,a Gnana Ravi,a Xiao-duo Ji,a Victor E. Marquezb
and Kenneth A. Jacobsona,*
aMolecular Recognition Section, LBC, NIDDK, National Institutes of Health, Bethesda, MD 20892, USA
bLaboratory of Medicinal Chemistry, National Cancer Institute, Frederick, MD 21702, USA
Received 12 January 2001; accepted 20 March 2001
Abstract—Novel methanocarba adenosine analogues, having the pseudo-ribose northern (N) conformation preferred at adenosine
receptors (ARs), were synthesized and tested in binding assays. The 50-uronamide modification preserved [N6-(3-iodobenzyl)] or
enhanced (N6-methyl) affinity at A3ARs, while the 20-deoxy modification reduced affinity and efficacy in a functional assay. Pub-
lished by Elsevier Science Ltd.
There are four subtypes of adenosine receptors (A1,
A2A, A2B, and A3), all of which are G protein-coupled
receptors (GPCRs). Modulation of adenosine receptors
by selective agonists and antagonists1,2 has the potential
for the treatment of a wide range of diseases, including
those of the cardiovascular, inflammatory, and central
nervous systems. For example, selective A1 and A3
receptor agonists protect cardiac myocytes from the
damaging effects of ischemia.3 Such agonists have also
been shown to be protective in models of cerebral
ischemia.4 In general, adenosine acts as a protective
local mediator, which responds to stress applied to a
system as a negative feedback control, leading to either
increased energy supply (usually via the A2A receptor)
to the organ or diminished energy demand (usually via
the A1 receptor). Recently, A2A receptor agonists have
been proposed as antiinflammatory agents and for use
in ischemia reperfusion.5
achieved through substitution at the 2-position. There
are currently no selective agonists of the A2B receptor.
Modifications of the ribose moiety of adenosine ago-
nists are less well tolerated and therefore less amenable
to extensive modifications. However, small alkyl 50-uro-
namide modification of the ribose often enhances affi-
nity of adenosine derivatives at multiple subtypes.
We have recently examined conformational require-
ments of the ribose moiety in adenosine agonists.7 In
general, the ribose rings of nucleosides and nucleotides
may adopt a range of conformations as described by the
‘pseudorotational cycle’.8 The northern [(N), 20-exo] and
southern [(S), 20-endo] conformations are the most rele-
vant to the biological activities observed for nucleosides
and nucleotides in association with DNA, RNA, and
various enzymes. We have defined a preference for the
(N) conformation of ribose at both adenosine7 and P2Y
receptors9 using methanocarba analogues in which a
cyclopropane moiety constrains a pseudosugar (cyclo-
pentane) ring of the nucleoside to either a (N)-, 1, or
(S)-, 2, envelope conformation (Fig. 1). Such analogues
Numerous structure–activity studies of adenosine deri-
vatives as receptor agonists2,6 conclude that selectivity
may be provided by specific substitutions of the adenine
ring. For example, N6-cycloalkyl groups favor selectiv-
ity for A1 versus A2A/A3 subtypes, and N6-benzyl sub-
stitutions favor selectivity for A3 versus A1/A2A
subtypes. Selectivity for the A2A receptor is often
*Corresponding author. Tel.: +1-301-496-9024; fax: +1-301-480-
8422; e-mail: kajacobs@helix.nih.gov
Figure 1.
0960-894X/01/$ - see front matter Published by Elsevier Science Ltd.
PII: S0960-894X(01)00213-X

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K. Lee et al. / Bioorg. Med. Chem. Lett. 11 (2001) 1333–1337
have helped to define the role of sugar puckering in
stabilizing the active adenosine receptor-bound con-
formation, and thereby have allowed identification of
the (N) conformation as the favored isomer.
In the present study, we have combined N6-substituted
adenosine agonists containing the (N)-methanocarba
modification with either 50-uronamide groups or the 20-
deoxy modification. The 20-deoxy modification is
Table 1. Affinities of methanocarba-adenosine analogues of the N-conformation and their 20-deoxy analogues in radioligand binding assays at rat
b
A1,a rat A2A
,
and human A3 receptors,c unless notedd
Ki (nM) or % displacement
a
b
c
Compd
R1
R2
R3
R4
rA1
rA2A
hA3
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
H
H
H
H
Cl
H
OH
OH
OH
OH
OH
OH
OH
H
CH2OH
CH2OH
CONHCH2CH3
CH2OH
CH2OH
CONHCH3
CH2OH
CH2OH
CH2OH
CH2OH
CH2OH
CONHCH3
CH2OH
CONHCH3
CH2OH
1680ꢀ80
273ꢀ36
22,500ꢀ100 (human)
1910ꢀ240
404ꢀ70e
84.7ꢀ18.7
29.9ꢀ6.8
126ꢀ18
31.8ꢀ6.9
1470ꢀ190
884ꢀ99
100ꢀ18
Me
Me
Me
CP
CP
CP
CP
IB
IB
IB
IB
IB
H
410% at 10 mM
410% at 10 mM
410% at 10 mM
6800ꢀ1800
Cl
Cl
H
22.5ꢀ7.4
6.19ꢀ0.42
170ꢀ51
805ꢀ197
5.06ꢀ0.51
5110ꢀ790
8.76ꢀ0.81
3600ꢀ780
69.2ꢀ9.8
52.7ꢀ5.2
141ꢀ22
H
15% at 100 mM
3390ꢀ520
2880ꢀ910
466ꢀ58
Cl
Cl
H
OH
H
45ꢀ5% at 100 mM
601ꢀ236
1090ꢀ190
4.13ꢀ1.76
2.39ꢀ0.54
2.24ꢀ1.45
1.51ꢀ0.23
912ꢀ29
OH
OH
OH
OH
H
H
548ꢀ115
Cl
Cl
Cl
732ꢀ207
83.9ꢀ10.3
8730ꢀ370
1660ꢀ260
25,400ꢀ3800
aDisplacement of specific [3H]R-PIA binding to A1 receptors in rat brain membranes, expressed as KiꢀSEM (n=3–5).
bDisplacement of specific [3H]CGS 21680 binding to A2A receptors in rat striatal membranes, expressed as KiꢀSEM (n=3–6), and at A2B receptors
expressed in HEK-293 cells versus [3H]ZM241,385, unless noted.
cDisplacement of specific [125I]AB-MECA binding at human A3 receptors expressed in CHO cells, in membranes, expressed as KiꢀSEM (n=3–4).
dMe, methyl; CP, cyclopentyl; IB, 3-iodobenzyl.
eMeasured in the absence of adenosine deaminase.
Scheme 1. (a) (i) BCl3, CH2Cl2, ꢁ78 ꢂC; (ii) p-TsOH, DMP, acetone; (b) NaIO4, RuO2, K2CO3, MeCN/CHCl3/H2O=2:2:3; (c) (i) EDAC, DMAP,
ꢂ
.
MeNH3, CH2Cl2/DMF=1:1; (ii) 10% CF3CO2H/MeOH, H2O; (d) 3-I-benzylamine HCl, TEA, MeOH; (e) (i) (COCl)2, 50 C, then MeNH2,
CH2Cl2; (ii) 10% CF3CO2H/MeOH, H2O; (f) NH3/2-propanol, 90 ꢂC; (g) (i) (COCl)2, 50 ꢂC, then EtNH2, CH2Cl2; (ii) 10% CF3CO2H/MeOH,
H2O, 60 ꢂC.

K. Lee et al. / Bioorg. Med. Chem. Lett. 11 (2001) 1333–1337
1335
Scheme 2. (a) (i) 2,6-Di-Cl-purine, DEAD, PPh3, THF; (ii) BCl3, CH2Cl2, 0 ꢂC; (b) cyclopentylamine (for 12) or 3-I-benzylamine.HCl, TEA (for 17),
MeOH; (C) H2/Pd–C, MeOH.
known to diminish agonist efficacy, to create partial
agonists.10
versus A1AR by 12- and 39-fold, respectively. Com-
pound 8 displayed a 4-fold increase in affinity at the
A3AR over 7, and consequently 130-fold selectivity
versus A1AR. The 50-uronamide-modified N6-(3-iodo-
benzyl) analogues, 14 and 16, maintained affinity at A1
and A3ARs and, therefore, selectivity for A3 receptors.
With an N6-methyl substituent, the 50-uronamide mod-
ification enhanced affinity at the A3AR. The 20-deoxy
modified N6-cyclopentyl analogues, 10 and 12, bound
weakly to adenosine receptors and were nonselective.
The 20-deoxy modified N6-(3-iodobenzyl) analogue, 17,
displayed greatly reduced affinity and selectivity for the
A3AR.
The structures of (N)-methanocarba adenosine analo-
gues (3–17) synthesized and tested in binding assays at
three subtypes of adenosine receptors11ꢁ13 are shown in
Table 1. We combined the (N)-methanocarba modifica-
tion of known potent adenosine agonists with either 50-
uronamide groups (5, 8, 14, and 16) or a 20-deoxy mod-
ification (10, 12, and 17). These adenosine agonists
contain methyl (6–8), cyclopentyl (9–12), or 3-iodo-
benzyl (13–17) substitution at the N6-position. Both 2-H
and 2-Cl analogues are included. Several of the com-
pounds, that is the triols 9, 11, 13, and 15, were reported
to be selective adenosine agonists in a previous study.7
Agonist efficacy of selected adenosine derivatives was
determined in a functional assay consisting of stimula-
tion of binding of [35S]GTP-g-S by activation of human
A1 and A3ARs.7,18 EC50 values for 10 and 12 at the
A1AR were 2.89ꢀ0.14 mM (30ꢀ1% efficacy) and
2.28ꢀ0.99 mM (40ꢀ8% efficacy), respectively. Thus
these two 20-deoxy analogues, 10 and 12, were weak,
partial agonists at the A1AR. EC50 values (nM) at the
A3AR were: 25.5ꢀ6.1 (8), 6.80ꢀ1.95 (14), 5.25ꢀ2.20
(16), and 303ꢀ93 (NECA), and all four derivatives
reached full agonist efficacy.
The synthetic methods used to prepare the new 50-uro-
namide analogues are shown in Scheme 1. Nucleoside
analogues, 20 and 21, containing a 6-Cl and a 50-OH
group, and protected as the 20,30-acetonides, were oxi-
dized using basic sodium periodate and ruthenium
tetraoxide. The resulting carboxylic acid derivatives,
23–25,14 were substituted at the 6-position by amine
treatment, converted to the acid chloride using oxalyl
chloride, and reacted immediately with methyl- or ethyl-
amine to form 50-uronamides.15 In the case of an N6-
methyl 50-uronamide derivative, the substitution of the
6-Cl and the formation of the uronamide from 22 were
carried out in a single step, using a carbodiimide con-
densing reagent, to yield, after deprotection, 8.16 20-
Deoxy analogues were synthesized by the methods
reported earlier9 via the (N)-methanocarba analogue of
2,6-dichloropurine-20-deoxyriboside, 28, as an inter-
mediate (Scheme 2).17
As reported previously,7 (N)-methanocarba analogues,
such as 9, 13, and 15, containing various N6-sub-
stituents, in which the parent compounds were potent
agonists at either A1 (e.g., cyclopentyl) or A3ARs (e.g.,
3-iodobenzyl), retained the selectivity of the parent
compound, especially at the A3AR. As before, the pre-
sent ‘ribose-like’ (N)-methanocarba analogues (20-OH)
had preserved or enhanced A3AR affinity. For example,
5 was 6-fold more potent than the ribose equivalent at
the A3AR and slightly less potent at A1 and A2AARs.
The efficacy in present compound was reduced at A1AR
for 20-deoxy analogues (10 and 12) and increased at
A3AR for 50-uronamides (14 and 16).
In binding assays at A1, A2A, and A3ARs, the (N)-
methanocarba analogue of 2-chloroadenosine, 4, in
comparison to the (N)-methanocarba adenosine, 3,
reported earlier,7 showed substantial enhancement of
affinity at all three subtypes and displayed mixed A1/
A3AR selectivity. The (N)-methanocarba analogue, 5,
of the potent, nonselective agonist NECA (50-N-ethyl-
uronamidoadenosine) was slightly selective for A1 and
A3ARs versus the A2AAR. For this 6-NH2 analogue,
the 50-uronamide, 5, enhanced affinity at the A1AR by
53-fold and at the A3AR by only 14-fold in comparison
to the triol, 3.
In this study, we have introduced a new synthetic route
for the oxidation of the 50-carbon in the (N)-methano-
carba series. This has allowed us to extend the SAR to
include a modification that is generally potency-enhan-
cing in the ribose series (i.e., 50-uronamide). With a
bulky N6-substituent (3-iodobenzyl), the A3AR affinity-
enhancing effects of (N)-methanocarba and 50-uron-
amide groups were not additive. Since the 50-uronamide
modification had either unchanged (for a large N6-sub-
stituent) or enhanced (for a small N6-substituent,
methyl) affinity at the A3AR, we may conclude that in
In the series of N6-methyl derivatives, binding at
A2AARs was absent, and the simple 40-CH2OH com-
pounds, 6 and 7, were selective in binding at the A3

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K. Lee et al. / Bioorg. Med. Chem. Lett. 11 (2001) 1333–1337
this series, requirements for N6- and 50-substitutions are
interrelated (i.e., non-independent in receptor binding).
Another small substituent at the N6-position (MeONH–),
when combined with modified 50-groups, resulted in
A3AR-selective agonists.19 Compound 8 (MRS 2346)
was 130-fold selective for the A3 versus A1AR, illus-
trating again that a bulky N6-substituent was not
required to achieve A3AR selectivity. Compound 16
(MRS 1898) was a potent and selective full agonist at
the human A3AR.
(M++1). 23: 1H NMR (CD3Cl, 300 MHz) d 8.74 (s, 1H), 8.21
(s, 1H), 5.91 (d, J=6.6 Hz, 1H), 5.05 (s, 1H), 4.79 (d, J=6.9
Hz, 1H), 2.35 (s, 1H), 1.86 (m, 1H), 1.67 (m, 1H). MS (NCI):
m/z 350 (Mꢁ).
15. General procedure for the 50-uronamide derivatives 5, 14,
and 16. A stirred mixture of the acid 22 (76.3 mg, 0.131 mmol)
and oxalyl chloride (1.4 mL) in CH2Cl2 (1 mL) was heated at
60 ꢂC for 2 h. After removal of the excess solvent and reagent
under N2, the residue was suspended in anhyd CH2Cl2 and
treated with methylamine (2 M in THF; in the case of 5, 2 M
ethylamine/THF). The resulting mixture was stirred at rt for 1
h and poured into ice-cold water, which was extracted with
CH2Cl2. After usual workup, the residue was purified on pre-
parative TLC (CH3Cl/MeOH=15:1) to provide the amide
intermediate (52.6 mg, 67.5%). The mixture of amide inter-
mediate (14.7 mg, 0.025 mmol) having an acetonide group,
10% trifluoroacetic acid/MeOH (3 mL), and H2O (0.3 mL)
was heated at 60 ꢂC for 4 h. The solvent was removed and
coevaporated with toluene. The residue was purified on silica
gel to give the free amide 14 (12.2 mg, 89%). 14: 1H NMR
(DMSO-d6, 300 MHz) d 8.21 (s, 1H), 8.08 (s, 1H), 7.74 (s, 1H),
7.58 (m, 1H), 7.36 (d, J=7.8 Hz, 1H), 7.13 (t, J=7.8 Hz, 1H),
4.93 (d, J=5.7 Hz, 1H), 4.66 (s, 1H), 4.60 (d, J=4.8 Hz, 1H),
3.89 (d, J=6 Hz, 1H), 3.38 (m), 2.67 (d, J=4.2 Hz, 3H), 1.82
(m, 1H), 1.60 (m, 1H), 1.29 (m, 1H). HRMS (FAB) calcd
555.0408, found 555.0418. 16: 1H NMR (CD3OD, 300 MHz) d
8.90 (t, 1H), 8.11 (s, 1H), 7.74 (s, 1H), 7.58 (m, 1H), 7.36 (d,
J=7.8 Hz, 1H), 7.13 (t, J=7.8 Hz, 1H), 4.93 (d, J=5.7 Hz,
1H), 4.66 (s, 1H), 4.60 (d, J=4.8 Hz, 1H), 3.89 (d, J=6 Hz,
1H), 3.38 (m), 2.67 (d, J=4.2 Hz, 3H), 1.82 (m, 1H), 1.60 (m,
1H), 1.29 (m, 1H). HRMS (FAB) calcd 521.0798, found
521.0814. 5: 1H NMR (CD3OD, 300 MHz) d 8.31 (s, 1H), 8.23
(s, 1H), 5.15 (d, J=6.6 Hz, 1H), 5.41–5.05 (m), 4.13 (d, J=6.3
Hz, 1H), 2.19 (m, 1H), 1.97 (m, 1H), 1.80 (m, 1H), 1.30 (t,
J=7.2 Hz, 3H). UV (MeOH) lmax 260.0 nm. HRMS (FAB)
calcd 319.1519, found 319.1510.
In conclusion, the (N)-methanocarba modification has
provided new analogues having A3AR selectivity, such
as 8, and mixed A1/A3AR selectivity. The pharmacol-
ogical properties of these analogues as agonists or par-
tial agonists of adenosine receptors may now be studied.
References and Notes
1. Fredholm, B. B.; Abbracchio, M. P.; Burnstock, G.;
Dubyak, G. R.; Harden, T. K.; Jacobson, K. A.; Schwabe, U.;
Williams, M. Trends Pharmacol. Sci. 1997, 18, 79.
2. Jacobson, K. A.; Knutsen, L. J. S. In Handbook of Experi-
mental Pharmacology; Abbracchio, M. P., Williams, M., Eds.;
Springer: Berlin, 2001; Vol. 151/I, pp 301–383.
3. Liang, B. T.; Jacobson, K. A. Proc. Natl. Acad. Sci. U.S.A.
1998, 95, 6995.
4. Von Lubitz, D. K. J. E.; Lin, R. C.-S.; Popik, P.; Carter,
M. F.; Jacobson, K. A. Eur. J. Pharmacol. 1994, 263, 59.
5. Okusa, M. D.; Linden, J.; Macdonald, T.; Huang, L. Am.
J. Physiol. 1999, 277, F404.
6. Muller, C. E. Curr. Med. Chem. 2000, 7, 1269.
¨
16. Procedure for the preparation of the N6-methylamino-50-
uronamide, 8. A mixture of the acid 23 (19.9 mg, 0.052 mmol),
DMAP (2.1 mg, 0.017 mmol), EDAC (1-[3-(dimethylamino)-
propyl]-3-ethylcarbodiimide.HCl, 13 mg, 0.068 mmol), and
methylamine (2 M in THF, 0.034 mL, 0.068 mmol) was stirred
for 2.5 h at rt. The reaction mixture was concentrated to dry-
ness and the residue was then washed with water. The organic
layer was dried, filtered and dried to dryness, which was pur-
ified on preparative TLC (CH3Cl/MeOH=15:1) to give the
amide intermediate (10 mg, 49%). 1H NMR (CD3Cl,
300 MHz) d 7.70 (s, 1H), 6.91 (br s, 1H), 6.26 (br s, 1H), 5.66
(d, J=7.5 Hz, 1H), 4.78 (m, 2H), 3.18 (d, 3H), 2.92 (d, J=5.1
Hz, 3H), 2.93 (s, 3H), 2.91 (s, 3H). HRMS (FAB) calcd
393.1442, found 393.1446. A mixture of amide intermediate
(5.2 mg, 0.013 mmol) having an acetonide group, 10% tri-
fluoroacetic acid/MeOH (1 mL), and H2O (0.1 mL) was
heated at 60 ꢂC for 4 h. The solvent was removed and coeva-
porated with toluene. The residue was purified on silica gel
(CH3Cl/MeOH=12:1) to give the free amide 8 (3.8 mg, 85%).
1H NMR (DMSO-d6, 300 MHz) d 8.06 (s, 1H), 5.43 (d, J=4.5
Hz, 1H), 4.93 (t, 6.3 Hz, 1H), 4.82 (d, J=7.8 Hz, 1H), 4.66 (s,
1H), 4.12 (m, 2H), 3.87 (m, 1H), 2.91 (d, 3H), 2.66 (d, J=4.2
Hz, 3H), 1.81 (m, 1H), 1.60 (m, 1H), 1.35 (m, 1H). UV
(MeOH) lmax 271.0 nm. HRMS (FAB) calcd 353.1129, found
353.1139.
7. Jacobson, K. A.; Ji, X.-D.; Li, A. H.; Melman, N.; Siddi-
qui, M. A.; Shin, K. J.; Marquez, V. E.; Ravi, R. G. J. Med.
Chem. 2000, 43, 2196.
8. Marquez, V. E.; Siddiqui, M. A.; Ezzitouni, A.; Russ, P.;
Wang, J.; Wagner, R. W.; Matteucci, M. D. J. Med. Chem.
1996, 39, 3739.
9. Nandanan, E.; Jang, S. Y.; Moro, S.; Kim, H.; Siddiqui,
M. A.; Russ, P.; Marquez, V. E.; Busson, R.; Herderwijn, P.;
Harden, T. K.; Boyer, J. L.; Jacobson, K. A. J. Med. Chem.
2000, 43, 829.
10. Van Der Graaf, P. H.; Van Schaick, E. A.; Matho t, R. A.;
ˆ
IJzerman, A. P.; Danhof, M. Pharmacol. Exp. Ther. 1997, 283,
809.
11. Schwabe, U.; Trost, T. Naunyn-Schmiedeberg’s Arch.
Pharmacol. 1980, 313, 179.
12. Jarvis, M. F.; Schutz, R.; Hutchison, A. J.; Do, E.; Sills,
M. A.; Williams, M. J. Pharmacol. Exp. Ther. 1989, 251, 888.
13. Olah, M. E.; Gallo-Rodriguez, C.; Jacobson, K. A.; Stiles,
G. L. Mol. Pharmacol. 1994, 45, 978.
14. General procedure for the 50-carboxylic acid derivatives
(22–23). To a solution of alcohol 20 (156 mg, 0.405 mmol) in
CH3CN/CHCl3/H2O (14 mL, 2:2:3) were added sodium peri-
odate (1.73 g, 8.1 mmol), ruthenium dioxide (40 mg), and
potassium carbonate (40 mg), and the mixture was stirred for
24 h and filtered through filter paper. The filtrate was diluted
with CH2Cl2 and H2O, and the water layer was separated. The
combined water layer was acidified with concd HCl to pH 5–6
at 0 ꢂC. The mixture was extracted with CH2Cl2 and the com-
bined organic layer was dried (MgSO4), filtered and con-
centrated to dryness to give the acid 22 as colorless oil (151.8
17. To a mixture of 2720 (0.25 g, 0.77 mmol), dichloropurine
(0.29 g, 1.54 mmol), and triphenylphosphine (0.4 g, 1.54
mmol) in anhydrous THF (10 mL) was added DEAD drop-
wise at 0 ꢂC with stirring for 6 h. Solvent was removed under
vacuum and the residue obtained was purified using flash
chromatography using 7:3 petroleum ether/ethyl acetate to
furnish 0.25 g of protected product. This compound (0.19 g,
0.38 mmol) was dissolved in CH2Cl2 (10 mL) and treated with
1
mg, 97.3%). 22: H NMR (CD3Cl, 300 MHz) d 8.11 (s, 1H),
5.87 (d, J=7.2 Hz, 1H), 4.98 (s, 1H), 4.72 (d, J=6.9 Hz, 1H),
2.29 (s, 1H), 1.88 (m, 1H), 1.66 (m, 1H). MS (FAB) m/z 385

K. Lee et al. / Bioorg. Med. Chem. Lett. 11 (2001) 1333–1337
1337
1 M BCl3 in CH2Cl2 (1.14 mL, 1.14 mmol) at 0 ꢂC and stirred
for 15 min for complete reaction. Solvent was removed under
vacuum and the residue obtained was purified by flash chro-
matography using 10% MeOH in CHCl3 to furnish 0.13 g of
product 28. To a solution of 28 (0.025 g, 0.08 mmol) in MeOH
(2 mL), was added cyclopentylamine (0.04 mL, 0.4 mmol) and
the mixture was stirred at rt for 8 h. Solvent was removed
under vacuum and the residue was purified by flash chroma-
tography using 5% MeOH in CHCl3 to furnish 0.023 g of
1.1–1.0 (m, 1H), 0.98–0.75 (m, 1H). HRMS (FAB) calcd
330.1930, found 330.1941. To a solution of 28 (0.025 g, 0.08
mmol) in MeOH (2 mL) was added 3-iodobenzylamine
hydrochloride (0.1 g, 0.4 mmol) and triethylamine (0.056 mL,
0.4 mmol), and the mixture was stirred at rt for 6 h. Solvent
was removed under vacuum and the residue was purified using
flash chromatography using 5% MeOH in CHCl3 to furnish
1
0.03 g of 17: H NMR (CD3OD) d 8.46 (s, 1H, C-8), 7.77 (s,
1H), 7.59 (d, 1H, J=7.81 Hz), 7.39 (d, 1H, J=7.81 Hz), 7.09
(t, 1H, J=7.81 Hz), 4.96 (d, 1H, J=5.86 Hz), 4.7 (s, 2H), 4.27
(d, 1H, J=11.72 Hz), 3.36 (d, 1H, J=11.72 Hz), 2.1–1.96 (m,
1H), 1.9–1.7 (m, 1H), 1.7–1.6 (m, 1H), 1.04–1.01 (m, 1H),
0.82–0.74 (m, 1H). HRMS (FAB) calcd 512.0350, found
512.0358.
1
product 12: H NMR (CDCl3) d 8.02 (s, 1H, C-8), 6.22 (bs,
1H), 5.16 (t, 1H, J=7.81 Hz), 4.58 (s, 1H), 4.25 (d, 1H,
J=11.72 Hz), 3.50 (d, 1H, J=11.72 Hz), 2.17–2.10 (m, 3H),
1.95–1.85 (m, 1H), 1.76–1.52 (m, 7H), 1.0–0.74 (m, 3H).
HRMS (FAB) calcd 364.1540, found 364.1549. To a solution
of 12 in MeOH (10 mL) was added 10% Pd/C (4 mg) and
stirred under H2 at atmospheric pressure. Solvent was
removed, and the residue was purified by preparative TLC
10% MeOH in CHCl3 to furnish 10 mg of 10: 1H NMR
(CD3OD) d 8.49 (s, 1H, C-8), 8.23 (s, 1H, C-2), 5.03 (d, 1H,
J=6 Hz) 4.58 (d, 1H J=12 Hz), 4.29 (d, 1H, J=11.53 Hz),
3.34 (d, 1H, J=11.53 Hz), 2.2–1.98 (m, 4H), 1.92–1.6 (m, 8H),
18. Lorenzen, A.; Guerra, L.; Vogt, H.; Schwabe, U. Mol.
Pharmacol. 1996, 49, 915.
19. Mogensen, J. P.; Roberts, S. M.; Bowler, A. N.; Thomsen,
C.; Knutsen, L. J. Bioorg. Med. Chem. Lett. 1998, 8, 1767.
20. Marquez, V. E.; Russ, P.; Alonso, R.; Siddiqui, M. A.;
Hernandez, S.; George, C.; Nicklaus, M. C.; Dai, F.; Ford, H.
Helv. Chim. Acta 1999, 82, 2119.