Synthesis of the Marine Natural Product Oroidin and Its Z-Isomer

Full text of DOI:10.1021/jo991395b

2806
J . Org. Chem. 2000, 65, 2806-2809
thesis of (E)-1 for the first time allows stable isotopic
Syn th esis of th e Ma r in e Na tu r a l P r od u ct
Or oid in a n d Its Z-Isom er †
labeling of the double bond protons 9-H and 10-H. (E)-1
is of ecological importance because of its function as a
chemical defendant in Caribbean sponges of the genus
Agelas.11
Thomas Lindel* and Matthias Hochgu¨rtel
Institute of Pharmaceutical Chemistry, University of
Heidelberg, Im Neuenheimer Feld 364,
D-69120 Heidelberg, Germany
The (Z)-vinyl double bond of the N-methylated ker-
amadine (2, Scheme 1) is stereochemically stable, but it
was unclear how the N-free (Z)-oroidin ((Z)-1) would
behave. To date, aplysinamisine I from the sponge
Aplysina aerophoba is the only natural product exhibiting
a (Z)-2-amino-5-vinylimidazole subunit.12 Our syntheses
of (Z)-oroidin ((Z)-1) and keramadine (2) from Agelas sp.
take advantage of the Sonogashira alkynylation13 of the
regiochemically pure 4-iodoimidazoles 414 and 10,15 re-
spectively (Scheme 1). Pd-catalyzed coupling of 4 resp.
10 with Boc-protected propargylic amine (3)16 gives the
alkynylimidazoles 5 and 11, respectively, in high yields.
After azidation of the imidazole 2-position employing
n-BuLi/tosyl azide17 and simultaneous removal of the Boc
and trityl protecting groups yielding the dihydrochloride
7, the pyrrole moiety was introduced via coupling with
the pyrrolyltrichloromethyl ketone 8.18 The overall se-
quence to (Z)-1 concludes with the double hydrogenation
of the 5-alkynyl-2-azidoimidazole 9, generating both the
(Z)-double bond and the 2-amino function. In the syn-
thesis of keramadine (2), the desired imidazole substitu-
tion pattern is achieved via treatment of the alkynylated
imidazole 12 with trimethyloxonium tetrafluoroborate,
yielding 12 after methanolysis, followed by azidation
providing 13. (Z)-Oroidin ((Z)-1) and keramadine (2) were
obtained in 30% (five steps) and 25% (six steps) overall
yields, respectively.
Received September 2, 1999
Pyrrole-imidazole alkaloids continue to be discovered
as biologically active natural products in marine sponges.1
The various modes of cyclization and dimerization of the
C11N5 skeleton of the major metabolite oroidin ((E)-1,
Scheme 1)2 give rise to a variety of natural products with
different geometries and functionalizations, economically
based on a common precursor. With respect to structural
diversity as a central issue of modern drug discovery,3 it
is an intriguing question if oroidin ((E)-1) itself or
structural analogues thereof can be used to find new
modes of cyclization and dimerization in advance to their
discovery from natural sources. In 1982, Foley and Bu¨chi
biomimetically cyclized 9,10-dihydrooroidin to racemic
dibromophakellin.4 Recent work on the preparation of
cyclized pyrrole-imidazole alkaloids includes the total
syntheses of hymenialdisine5 and agelastatin A6 and
incomplete approaches to palau’amine, styloguanidine,7
and phakellstatin.8
Four syntheses of the natural product oroidin ((E)-1)
have been reported to date,9 while its very interesting
(Z)-isomer (Z)-1 has not yet been characterized. Ahond,
Poupat, et al. prepared keramadine (2) as well as
imidazole-N-tritylated (Z)-oroidin, which isomerized to
(E)-1 under acidic deprotection conditions.9c In this
paper, we present an alternative synthetic approach to
(Z)-oroidin ((Z)-1), oroidin ((E)-1), and keramadine (2)10
employing alkyne intermediates (Scheme 1). Our syn-
Clean conversion of (Z)- to (E)-oroidin is observed under
acidic conditions (6 N aqueous HCl/MeOH (1:1) at 60 °C,
Scheme 2). When the analogous experiment was per-
formed in an NMR tube in DCl/D2O, no incorporation of
deuterium into positions 9 or 10 of the resulting (E)-
oroidin ((E)-1) was observed. This indicates that under
the chosen acidic conditions a 5-alkylidene-2-imino tau-
tomer such as 18 is not formed,9c,17b,19 because this
† This paper is dedicated to Professor Dr. Richard Neidlein on the
occasion of his 70th birthday.
(1) (a) For a review of the pyrrole-imidazole alkaloids, see: Gribble,
G. W. Fortschr. Chem. Org. Naturst.; Herz, W., Kirby, G. W., Moore,
R. E., Steglich, W., Tamm, C., Eds.; Springer: Vienna, 1996; Vol. 68,
pp 137ff. (b) Pettit, G. R.; McNulty, J .; Herald, D. L.; Doubek, D. L.;
Chapuis, J .-C.; Schmidt, J . M.; Tackett, L. P.; Boyd, M. R. J . Nat. Prod.
1997, 60, 180-183 and references cited therein. (c) Urban, S.; de
Almeida Leone, P.; Carroll, A. R.; Fechner, G. A.; Smith, J .; Hooper,
J . N. A.; Quinn, R. J . J . Org. Chem. 1999, 64, 731-735 and references
cited therein.
(10) (a) Nakamura, H.; Ohizumi, Y.; Kobayashi, J .; Hirata, Y.
Tetrahedron Lett. 1984, 25, 2475-2478. (b) Cafieri, F.; Fattorusso, E.;
Taglialatela-Scafati, O. J . Nat. Prod. 1998, 61, 122-125. Synthesis:
ref 9c and (c) Lindel, T.; Hochgu¨rtel, M. Tetrahedron Lett. 1998, 39,
2541-2544.
(11) Chanas, B.; Pawlik, J . R.; Lindel, T.; Fenical, W. J . Exp. Mar.
Biol. Ecol. 1996, 208, 185-196.
(12) Rodriguez, A. D.; Pin˜a, I. C. J . Nat. Prod. 1993, 56, 907-914.
(13) (a) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett.
1975, 16, 4467-4470. Direct alkynylation of 5-iodo-1-methylimidazole
proceeds in very low yields: (b) Sakamoto, T.; Nagata, H.; Yoshinori,
K.; Shiraiwa, M.; Yamanaka, H. Chem. Pharm. Bull. 1987, 35, 823-
828.
(14) Kirk, K. L. J . Heterocycl. Chem. 1985, 22, 57-59.
(15) Cliff, M. D.; Pyne, S. G. J . Org. Chem. 1995, 60, 2378-2383.
(16) Casara, P.; Danzin, C.; Metcalf, B.; J ung, M. J . Chem. Soc.,
Perkin Trans. 1 1985, 2201-2208.
(17) (a) Narasimham, N. S.; Ammanamanchi, R. Tetrahedron Lett.
1983, 23, 4733-4734. (b) For the first 2-azidation of N-protected
imidazoles, see: Daninos, S.; Al Mourabit, A.; Ahond, A.; Bedoya
Zurita, M.; Poupat, C.; Potier, P. Bull. Soc. Chim. Fr. 1994, 131, 590-
599.
(18) Bailey, D. M.; J ohnson, R. E. J . Med. Chem. 1973, 16, 1300-
1302.
(2) (a) Forenza, S.; Minale, L.; Riccio, R.; Fattorusso, E. J . Chem.
Soc., Chem. Commun. 1971, 1129-1130. (b) Garcia, E. E.; Benjamin,
L. E.; Fryer, R. I. J . Chem. Soc., Chem. Commun. 1973, 78-79.
(3) For
a definition of “structural diversity” in the context of
combinatorial chemistry, see: Balkenhohl, F.; von dem Bussche-
Hu¨nnefeld, C.; Lansky, A.; Zechel, C. Angew. Chem. Int. Ed. 1996, 108,
2288-2337.
(4) Foley, L. H.; Bu¨chi, G. J . Am. Chem. Soc. 1982, 104, 1776-1777.
(5) (a) Annoura, H.; Tatsuoka, T. Tetrahedron Lett. 1995, 36, 413-
416. (b) Xu, Y. Z.; Yakushijin, K.; Horne, D. A. J . Org. Chem. 1997,
62, 456-464.
(6) (a) Anderson, G. T.; Chase, C. E.; Koh, Y.-h..; Stien, D.; Weinreb,
S. M.; Shang, M. Y. J . Org. Chem. 1998, 63, 7594-7595. (b) Stien, D.;
Anderson, G. T.; Chase, C. E.; Koh, Y.-h.; Weinreb, S. M. J . Am. Chem.
Soc. 1999, 121, 9574-9579.
(7) Overman, L. E.; Rogers, B. N.; Tellew, J . E.; Trenkle, W. C. J .
Am. Chem. Soc. 1997, 119, 7159-7160.
(8) Lindel, T.; Hoffmann, H. Liebigs Ann./ Recueil 1997, 1525-1528.
(9) (a) de Nanteuil, G.; Ahond, A.; Poupat, C.; Thoison, O.; Potier,
P. Bull. Soc. Chim. Fr. 1986, 813-816. (b) Little, T. L.; Webber, S. E.
J . Org. Chem. 1994, 59, 7299-7305. (c) Daninos-Zeghal, S.; Al
Mourabit, A.; Ahond, A.; Poupat, C.; Potier, P. Tetrahedron 1997, 53,
7605-7614. (d) Olofson, A.; Yakushijin, K.; Horne, D. A. J . Org. Chem.
1998, 63, 1248-1253.
(19) A diazafulvene intermediate may occur in H2SO4: (a) Braun,
M.; Bu¨chi, G. J . Am. Chem. Soc. 1976, 98, 3049-3050. (b) Braun, M.;
Bu¨chi, G.; Bushey, D. F. J . Am. Chem. Soc. 1978, 100, 4208-4213.
See also: (c) Xu, Y.-z.; Yakushijin, K.; Horne, D. A. J . Org. Chem. 1996,
61, 9569-9571.
10.1021/jo991395b CCC: $19.00 © 2000 American Chemical Society
Published on Web 04/04/2000

Notes
J . Org. Chem., Vol. 65, No. 9, 2000 2807
Sch em e 1. Un ified Syn th etic Sch em e tow a r d (Z)-Or oid in ((Z)-1) a n d Ker a m a d in e (2)a
a
i
Key: (a) 4, Pd(PPh3)2Cl2, CuI, Bu2NH, THF, rt, 20 h, 85%; (b) n-BuLi (2.1 equiv), THF, -78 °C, TsN3, 10 min, 70%; (c) (1) TFA,
CH2Cl2, rt, 5 h; (2) HCl(g), Et2O/MeOH; (d) 8, DMF, Na2CO3, rt, 6 h, 69%; (e) H2/Pd-Lindlar, 1 atm, rt, 3 h; 9: MeOH, 74%; 15: THF/
i
MeOH (5:1), 12 h, 90%; (f) 6 N HCl/MeOH, 60 °C, 6 h, 56%; (g) 10, Pd(PPh3)2Cl2, CuI, Bu2NH, THF, rt, 24 h, 92%; (h) (CH3)3OBF4 (1
equiv), CH2Cl2, rt, 2 h, 87%; (i) n-BuLi (2.1 equiv), THF, -78 °C, TsN3, 10 min, 62%; (j) (1) TFA, CH2Cl2, rt, 3 h; (2) 14, DMF, rt, 6 h, 62%.
Sch em e 2. Isom er iza tion of (Z)-[9,10-D2]Or oid in
((Z)-16) u n d er Acid ic Con d ition sa
In conclusion, a convenient synthesis of both the
hitherto unknown (Z)-oroidin and the natural product
(E)-oroidin ((Z)-1, (E)-1)) has been developed. The use of
alkyne intermediates allows the selective isotopic labeling
of the vinyl double bond of both isomers. Our isomeriza-
tion study indicates that the deuterated derivatives 16
and 17 may be more suitable as advanced precursors for
biosynthetic studies than expected. Following a hypoth-
esis recently forwarded by Scheuer et al.,20 the putative
existence of (Z)-oroidin ((Z)-1) as a natural product would
explain the stereochemistry of the dimeric pyrrole-
imidazole alkaloid konbu’acidin.21
Exp er im en ta l Section
Gen er a l Meth od s. Melting points are uncorrected. NMR
spectra were acquired at 250 or 360 (1H) MHz and 62.9 or 90.6
(
a
13C) MHz. Chemical shifts refer to those of residual solvent
Key: (a) 6 N HCl/MeOH (1:1), 60 °C, 6 h, 80%.
signals based on δTMS ) 0. All measurements were carried out
at 300 K. Mass spectra were taken in EI or FAB (nitrobenzyl
alkohol as matrix) mode. Solvents were purified and dried
according to standard procedures.22 Column chromatography
was carried out on silica gel (silica gel 60 (60-200 mesh), Merck)
and on Sephadex LH20 (Pharmacia). Thin-layer chromatography
(TLC) was performed on silica gel (precoated silica gel plate F254
Merck).
Gen er a l P r oced u r e for th e Son oga sh ir a Alk yn e Cou -
p lin g. Under an argon atmosphere, Boc-protected propargy-
lamine (3, 1.5 equiv) was added to a solution of the protected
4-iodoimidazole (1 equiv), Pd(PPh3)2Cl2 (0.025 equiv), CuI (0.05
equiv), and diisobutylamine (3 equiv) in dry THF. After being
stirred at room temperature for 20 h, the reaction mixture was
filtered and concentrated in vacuo to yield a dark residue that
was chromatographed on silica gel with the eluent specified.
tautomerization would have led to the deuteration of C-9.
Our finding was confirmed on analysis of (Z)-[9,10-D2]-
oroidin (16), obtained by reduction of the alkyne 9 with
D2. The isomerization product 17 obtained by treatment
1
with HCl/H2O showed no signals in the H NMR spec-
trum for any double bond protons (Scheme 2). From the
absence of the monodeuterated oroidin 19 it can be
concluded that the tautomer 18 does not play a major
role, because otherwise exchange of 9-D of (E)-1 would
have occurred.
To our surprise, (Z)-oroidin ((Z)-1) is remarkably stable
and remains unchanged in an NMR solvent mixture of
DMSO-d6/TFA-d1 (1:1) at room temperature, while (E)-
oroidin ((E)-1) slowly decomposes to a very complex
product mixture under the same conditions. For kera-
madine (2), irradiation with a sunlamp (300 W) in
DMSO-d6/TFA-d1 (1:1) leads to a 3:1 mixture of (Z)- and
(E)-isomers, both of which are stable under the reaction
conditions.
(20) Kinnel, R. B.; Gehrken, H.-P.; Swali, R.; Skoropowski, G.;
Scheuer, P. J . J . Org. Chem. 1998, 63, 3281-3286.
(21) Kobayashi, J .; Suzuki, M.; Tsuda, M. Tetrahedron 1997, 53,
15681-15684. See also the Supporting Information.
(22) Perrin, D. D.; Armarego, W. L. F., Purification of Laboratory
Chemicals, 3rd ed.; Pergamon: Oxford, 1988.

2808 J . Org. Chem., Vol. 65, No. 9, 2000
Notes
[3-(1-Tr iph en ylm eth yl-1H-im idazol-4-yl)pr op-2-yn yl]car -
ba m ic Acid ter t-Bu tyl Ester (5). The iodoimidazole 4 (10 g,
23 mmol) and the alkyne 3 (7.1 g, 46 mmol) were coupled
according to the general procedure. Purification by column
chromatography (silica gel, petroleum ether/CH2Cl2/ether (5/4/
1)) afforded a pale yellow solid (9.0 g, 85%) that was recrystal-
lized from ethanol: mp 210 °C; 1H NMR (250 MHz, CDCl3) δ
7.39 (s, 1H), 7.36-7.31 (m, 9H), 7.16-7.08 (m, 6H), 7.00 (s, 1H),
4.88 (s, 1H), 4.10 (d, J ) 5.3 Hz, 2H), 1.43 (s, 9H); 13C NMR
(62.9 MHz, CDCl3) δ 155.2, 142.0, 138.9, 129.7, 128.3, 128.2,
125.6, 85.6, 79.7, 77.2, 75.7, 31.2, 28.3; IR (KBr) 3266, 1710, 1521
cm-1; EIMS m/z (rel intensity) 463 (0.4) [M+], 243 (100), 165
tion monitored by TLC (silica gel, CHCl3/MeOH/NH3 (40:10:1)),
the solvent was removed in vacuo. The crude product was
purified by column chromatography (Sephadex LH20, methanol).
Addition of gaseous HCl to a methanol/ether solution of the free
base, followed by filtration, yielded 7 as a colorless solid (0.61
1
g, 88%): mp 152 °C dec; H NMR (360 MHz, DMSO-d6) δ 8.66
(s, H), 7.38 (s, 1H), 6.38 (s), 3.93 (m, 2H); 13C NMR (91 MHz,
DMSO-d6) δ 145.5, 128.8, 122.8, 88.2, 84.2, 34.0; EIMS m/z (rel
intensity) 162 (4) [M+], 99 (57), 61 (10), 59 (51), 57 (100); IR
(KBr) 2889, 2153, 1620, 1564 cm-1; UV (MeOH) λmax (lg ꢀ) 252
nm (4.11) and 206 nm (3.75); HREIMS calcd for C6H6N6
162.0654, found 162.0654.
(43), 57 (14); HRMS (FAB, PEG) calcd for
486.2157, found 486.2171.
C
30H29N3O2Na
4,5-Dibr om o-1H-p yr r ole-2-ca r boxylic Acid [3-(2-Azid o-
3H-im id a zol-4-yl)p r op -2-yn yl]a m id e (9). 4,5-Dibromopyrrol-
2-yltrichloromethyl ketone (8, 1.57 g, 4.25 mmol) was added to
a solution of 7 (1 g, 4.25 mmol) and Na2CO3 (450 mg, 4.25 mmol)
in dry DMF (10 mL) at room temperature under argon. After
being stirred for 6 h, the reaction mixture was concentrated in
vacuo and suspended in water. The precipitate was filtered, dried
in vacuo, and purified by column chromatography (silica gel,
CHCl3/MeOH (20/1)) to yield 9 as a brownish solid (1.22 g,
69%): mp 132 °C dec; 1H NMR (360 MHz, DMSO-d6) δ 12.64 (s,
1H), 8.64 (t, J ) 5.4 Hz, 1H), 7.23 (s, 1H), 6.96 (s, 1H), 4.24 (d,
J ) 5.4 Hz, 2H). 13C NMR (90.6 MHz, CDCl3) δ 158.5, 139.9,
127.6, 120.9, 120.6, 113.0, 105.1, 98.0, 85.9, 76.4, 28.6; IR (KBr)
3287, 2145, 1638 cm-1; FABMS m/z (rel intensity) 412/414/416
(3/7/3) [M+ + H]; HRFABMS calcd for C11H8N7O79Br81Br
413.9137, found 413.9135.
4-Br om o-1H -p yr r ole-2-ca r b oxylic Acid [3-(2-Azid o-3-
m eth yl-3H-im id a zol-4-yl)p r op -2-yn yl]a m id e (15). A solution
of 13 (1.3 g, 4.7 mmol) in CH2Cl2 (20 mL) under argon was
treated with TFA (6 mL) and stirred at room temperature for 3
h. After complete deprotection was confirmed by TLC, the
solvents were evaporated. The residue was suspended in DMF
(10 mL) and neutralized with Na2CO3. To the stirred suspension
was added 4-bromopyrrol-2-yltrichloromethyl ketone (14, 2.05
g, 7.05 mmol) at room temperature under argon. After being
stirred for 6 h, the reaction mixture was concentrated in vacuo
and suspended in water. The precipitate was filtered, dried in
vacuo, and purified by column chromatography (silica gel, CHCl3/
MeOH (20/1)) to yield a pale brown solid (1.01 g, 62%): mp 112
°C dec; 1H NMR (360 MHz, DMSO-d6) δ 11.91 (s, 1H), 8.65 (t, J
) 5.9 Hz, 1H), 7.14 (s, 1H), 7.00 (m, 1H), 6.88 (m, 1H), 4.30 (s,
2H), 3.33 (s, 3H); 13C NMR (90.6 MHz, DMSO-d6) δ 159.2, 140.1,
131.5, 126.2, 121.6, 114.5, 111.8, 94.9, 94.3, 69.9, 29.8, 28.7;
FABMS m/z (rel intensity) 348/350 (23/22) [M+ + H]; HRFABMS
calcd for C12H11N7O79Br 348.0208, found 348.0222. Anal. Calcd
for C12H10N7O1Br C: 41.40; H, 2.89; N, 26.17. Found: C, 41.13;
H, 3.05; N, 26.37.
Gen er a l P r oced u r e for Dou ble Lin d la r Hyd r ogen a tion .
A solution of the alkynyl azido imidazole in THF/MeOH was
hydrogenated in the presence of Lindlar catalyst (5% Pd on
CaCO3, poisoned with Pb) at room temperature at atmospheric
pressure. After complete hydrogenation (monitored by TLC) the
reaction mixture was filtered and the solvent was removed.
Purification by column chromatography yielded the free base.
(Z)-Or oid in ((Z)-1). According to the general procedure
(Lindlar catalyst, 80 mg; MeOH, 40 mL), 9 (200 mg, 0.48 mmol)
was hydrogenated. Purification by column chromatography
(Sephadex LH20, methanol) afforded a colorless solid (140 mg,
74%, Z/E ≈ 16:1): 1H NMR (360 MHz, methanol-d4) δ 6.82 (s,
1H), 6.81 (s, 1H), 6.20 (d, J ) 11.5 Hz, 1H), 5.75 (dt, J ) 11.5,
6.5 Hz, 1H), 4.07 (dd, J ) 6.5, 1.5 Hz, 2H); 13C NMR (90.6 MHz,
DMSO-d6/TFA-d1 (1:1)) δ 162.7, 148.2, 130.6, 128.5, 124.4, 116.9,
114.9, 113.0, 105.6, 99.5, 39; 13C NMR (90.6 MHz, methanol-d4)
δ 162.3, 149.1, 131.0, 128.6, 125.3, 117.3, 114.9, 113.6, 106.8,
100.4, 39.5; UV (MeOH) λmax (log ꢀ) 208 (4.02), 278 nm (4.31);
FABMS m/z (rel intensity) 388/390/392 (17/35/20) [M+ + H];
HRFABMS calcd for C11H12N5O79Br81Br 389.9389, found 389.9401.
Ker a m a d in e (2). According to the general procedure (Lindlar
catalyst, 40 mg; THF/MeOH (5/1, 10 mL)), 15 (100 mg, 0.29
mmol) was hydrogenated. Purification afforded a colorless solid
(84 mg, 90%). Addition of TFA to the methanolic solution of the
free base, followed by concentration in vacuo yielded the tri-
fluoroacetate of 2 as a colorless solid: mp 180 °C; 1H NMR (360
MHz, DMSO-d6) δ 12.59 (s), 11.85 (s), 8.46 (t, J ) 5.9 Hz, 1H),
7.78 (s, 1H), 7.11 (s, 1H), 6.99 (m, 1H), 6.85 (m, 1H), 6.26 (d, J
[3-(1-Ben zen esu lfon yl-1H-im id a zol-4-yl)p r op -2-yn yl]ca r -
ba m ic Acid ter t-Bu tyl Ester (11). The iodoimidazole 10 (3 g,
9 mmol) and the alkyne 3 (3.5 g, 23 mmol) were coupled
according to the general procedure. Purification by column
chromatography (silica gel, petroleum ether/CH2Cl2/ether (5/10/
2)) afforded a colorless solid (2.99 g, 92%) that was recrystallized
1
from ethanol: mp 145 °C; H NMR (250 MHz, CDCl3) δ 7.95-
7.90 (m, 3H), 7.75-7.65 (m, 1H), 7.60-7.55 (m, 2H), 7.39 (d, J
) 1.2 Hz, 1H), 4.10 (d, J ) 5.6 Hz, 2H), 1.44 (s, 9H); 13C NMR
(62.9 MHz, CDCl3) δ 155.1, 137.5, 136.3, 135.1, 129.9, 127.3,
126.6, 120.3, 87.8, 78.0, 74.7, 31.00, 28.3; IR (KBr) 3352, 3141,
3119, 2987, 1679, 1511 cm-1; EIMS m/z (rel intensity) 361 (0.1)
[M+], 305 (14), 164 (100), 120 (12), 93 (14), 77 (42), 57 (43);
HREIMS calcd for C17H19N3O4S 361.1096, found 361.1095. Anal.
Calcd for C17H19N3O4S: C, 56.50; H, 5.30; N, 11.63. Found: C,
56.53; H, 5.34; N, 11.43.
[3-(3-Meth yl-3H-im idazol-4-yl)pr op-2-yn yl]car bam ic Acid
ter t-Bu tyl Ester (12). To a solution of 11 (830 mg, 2.3 mmol)
in dry CH2Cl2 (30 mL) was added (CH3)3OBF4 (340 mg, 2.3
mmol). After the mixture was stirred at room temperature for
2 h, methanol (10 mL) was added. The solvent was removed,
and the residue was purified by column chromatography (silica
gel, CHCl3/MeOH (20/1)) to yield 12 (468 mg, 87%) as a pale
yellow oil: 1H NMR (250 MHz, CDCl3) δ 7.41 (s, 1H), 7.22 (s,
1H), 4.93 (s, 1H), 4.18 (d, J ) 5.8 Hz, 2H), 3.64 (s, 3H), 1.47 (s,
9H); 13C NMR (90.6 MHz, CDCl3) δ 155.3, 138.2, 134.5, 115.7,
93.0, 80.2, 71.2, 31.6, 32.0, 28.4; IR (KBr) 3324, 2977, 1704 cm-1
;
EIMS m/z (rel intensity) 235 (11), 179 (77), 134 (100), 119 (51),
57 (70); HREIMS calcd for C12H17N3O2 235.1321, found 235.1320.
Gen er a l P r oced u r e for Azid a tion of th e Alk yn yl Im i-
d a zoles. A solution of the imidazole (5 or 12) in dry THF was
cooled to -78 °C, followed by addition of n-BuLi (2.1 equiv, 1.6
M solution in hexane). The cooling bath was removed for 5 min.
After the mixture was recooled to -75 °C, tosyl azide (1.5 equiv)
in THF was added to the stirred solution. After 10 min, aqueous
buffer (pH 7) was added, and the reaction mixture was extracted
three times with CH2Cl2. The combined organic layers were dried
(MgSO4), concentrated in vacuo, and purified by column chro-
matography.
[3-(2-Azid o-3-tr ip h en ylm eth yl-3H-im id a zol-4-yl)p r op -2-
yn yl]ca r ba m ic Acid ter t-Bu tyl Ester (6). Azidation of 5 (5.5
g, 11.9 mmol) yielded 6 as a pale yellow solid (4.2 g, 70%; silica
gel, petroleum ether/ethyl acetate (3/1)): mp 75-80 °C decomp;
1H NMR (250 MHz, CDCl3) δ 7.40-7.25 (m, 9H), 7.15-7.05 (m,
6H), 6.85 (s, 1H), 4.72 (s, 1H), 4.11 (d, J ) 5.5 Hz, 2H), 1.47 (s,
9H); 13C NMR (90.6 MHz, CDCl3) δ 157.8, 142.3, 141.3, 129.6,
128.0, 124.8, 119.6, 86.2, 76.4, 75.7, 60.4, 31.1, 28.4; IR (KBr)
2133, 1718 cm-1; FABMS m/z (rel intensity) 527 (100) [M + Na+],
477 (71), 421 (63); HRFABMS calcd for C30H28N6O2Na 527.2171,
found 527.2164.
[3-(2-Azid o-3-m eth yl-3H-im id a zol-4-yl)p r op -2-yn yl]ca r -
ba m ic Acid ter t-Bu tyl Ester (13). Azidation of 12 (420 mg,
1.8 mmol) yielded 13 (310 mg, 62%; silica gel, petroleum ether/
ethyl acetate (4/1)): mp 126 °C dec; 1H NMR (250 MHz, CDCl3)
δ 7.07 (s, 1H), 4.82 (s, 1H), 4.16 (d, J ) 5.4 Hz, 2H), 3.38 (s,
3H), 1.46 (s, 9H); 13C NMR (90.6 MHz, CDCl3) δ 155.3, 141.0,
132.3, 114.7, 93.0, 80.2, 71.3, 31.3, 30.0, 28.3; IR (KBr) 3324,
2979, 2146, 1682 cm-1; EIMS m/z (rel intensity) 276 (14) [M+],
193 (6), 192(52), 160 (15), 139 (25), 57 (100); HREIMS calcd for
C
12H16N6O2 276.1335, found 276.1334.
3-(2-Azid o-1H-im id a zol-4-yl)p r op -2-yn yla m in e Dih yd r o-
ch lor id e (7). TFA (6 mL) was slowly added to a solution of 7
(1.5 g, 2.98 mmol) in CH2Cl2 (20 mL). After complete deprotec-

Notes
J . Org. Chem., Vol. 65, No. 9, 2000 2809
) 11.7 Hz, 1H), 5.86 (dt, J ) 5.9, 11.7 Hz, 1H), 4.02 (m, 2H),
3.39 (s, 3H); 13C NMR (90.6 MHz, DMSO-d6) δ 159.5, 146.5,
133.4, 126.6, 123.7, 121.3, 113.7, 111.8, 111.5, 94.9, 37.6, 29.2;
IR (KBr) 3300, 3148, 1683, 1558 cm-1; UV (MeOH) λmax (log ꢀ)
222 (3.91), 272 nm (4.15); EIMS m/z (rel intensity) 323/324/325/
326 (62/9/60/5) [M+], 245 (8) [M+ - Br], 151 (100); HREIMS calcd
for C12H14N5O79Br 323.0382, found 323.0383.
Or oid in ((E)-1). (Z)-Oroidin (1) (200 mg, 0.51 mmol) was
dissolved in methanol (6 mL). After addition of aqueous HCl
(25%, 4 mL), the solution was heated for 6 h at 60 °C.
Purification by column chromatography (Sephadex LH20, metha-
nol) afforded a colorless solid (111 mg, 56%): 1H NMR (360 MHz,
methanol-d4) δ 6.82 (s, 1H), 6.74 (s, 1H), 6.30 (d, J ) 16.4 Hz,
1H), 6.01 (dt, J ) 16.4, 5.5 Hz, 1H), 4.04 (dd, J ) 5.5, 1.5 Hz,
2H); 13C NMR (90.6 MHz, methanol-d4) δ 161.6, 149.3, 128.6,
127.6, 127.0, 117.6, 114.3, 111.9, 106.3, 100.0, 41.6; UV
(MeOH) λmax (log ꢀ) 203 (4.30), 275 nm (4.33); FABMS m/z
(rel intensity) 388/390/392 (16/29/17); HRFABMS calcd for
C11H12ON579Br81Br 389.9389, found 389.9421.
intensity) 390/392/394 (50/100/49); HRFABMS calcd for C11H10D2-
ON579Br81Br 391.9514, found 391.9492.
Isom er iza tion of 16. (Z)-[9,10-D2]Oroidin (16) (40 mg, 0.10
mmol) was dissolved in 3 mL of methanol. After addition of 2
mL of aqueous HCl (25%), the solution was heated for 6 h at 60
°C. Purification by column chromatography (Sephadex LH20,
methanol) afforded 17 as a colorless solid (21 mg, 53%): 1H NMR
(360 MHz, methanol-d4) δ 6.82 (s, 1H), 6.73 (s, 1H), 4.04 (s, 2H);
FABMS m/z (rel intensity) 390/392/394 (12/19/10); HRFABMS
calcd for C11H10D2ON579Br81Br 391.9514, found 391.9514.
Ack n ow led gm en t. This work was supported in part
by a grant from the Deutsche Forschungsgemeinschaft
(Li 597/2-2). We appreciate the generous support of Prof.
Dr. Richard Neidlein. Dieter Holzmann and Damian
Kokot are thanked for their assistance.
Deu ter a tion of 9. According to the general procedure (Lind-
lar catalyst, 20 mg; MeOH, 10 mL), 9 (100 mg, 0.24 mmol) was
reacted with deuterium. Purification by column chromatography
(Sephadex LH20, methanol) afforded (Z)-[9,10-D2]oroidin (16)
as a colorless solid (47 mg, 50%): 1H NMR (360 MHz, methanol-
d4) δ 6.84 (s, 1H), 6.82 (s, 1H), 4.08 (s, 2H); FABMS m/z (rel
Su p p or tin g In for m a tion Ava ila ble: NMR spectra for
compounds (Z)-1, (E)-1, 2, 16, and 17; HPLC elution profiles
and mass spectra of 16 and 17. This material is available free
of charge via the Internet at http://pubs.acs.org.
J O991395B