Notes
Journal of Natural Products, 2006, Vol. 69, No. 1 127
then partitioned between n-BuOH (3 × 500 mL) and H2O (300 mL).
The resulting n-BuOH (15.9 mg) fraction from the solvent partitioning
scheme was purified by gel chromatography on Sephadex LH-20
(Pharmacia) using MeOH as mobile phase. Final purification of the
isolated compounds was achieved by preparative RP18 HPLC on a
Kromasil RP18 column (16 × 250 mm, 10 µm) applying a MeCN/
TFA (0.1% in H2O) gradient to afford 1 (8.9 mg, 0.009% of dry weight)
and 2 (10.3 mg, 0.011% of dry weight).
1-Fluoro-2,4-dinitrophenyl-5-L-alaninamide (FDAA) Derivati-
zation and Absolute Configuration of 2 (Marfey’s method7). To 10
µL (130 µg) of amino acid solution were added 100 µL of 0.1 M
NaHCO3 and 100 µL of 3 mM 1-fluoro-2,4-dinitrophenyl-5-L-alanine.
The solution was heated to 80 °C for 5 min. Then 50 µL of 0.2 M HCl
and 40 µL of 50% aqueous MeCN containing 0.1% formic acid were
added to the reaction mixture. Separation was achieved by a Waters
XTerra RP18 column (3.0 × 150 mm, 3.5 µm) applying an MeCN/
H2O/HCOOH gradient (0 min: 10% MeCN/90% HCOOH (0.1% in
H2O), 30 min: 60% MeCN/40% HCOOH (0.1% in H2O)) with a flow
rate of 0.4 mL/min. UV detection was performed with a DAD (Agilent)
at a wavelength of 340 nm. Retention times: natural product, 23.82
min; synthetic compound, 23.80 min.
HPLC (Prontosil Eurobond C18 (20 × 250 mm, 5 µm)) applying a
gradient containing MeCN/TFA (0.1% in H2O) to yield 1 as a colorless
oil (22 mg, 65.3%). The NMR data were identical to the natural product.
[R]2D3 -8 (c 0.15, MeOH); HRESI-(+)MS m/z 346.0501 [M + H]+
(calcd for C11H17N5O379Br, m/z 346.0509, ∆m ) 2.3 ppm).
(2S)-2-Amino-6-[1-(4-bromo-1H-pyrrole-2-ylmethanoyl)amino]-
hexanoic Acid Methyl Ester (7). To a solution of
L-lysine methyl
ester hydrochloride (100 mg, 0.40 mmol) in MeCN (3 mL) were added
4-bromopyrrole-2-yl trichloromethyl ketone (5, 159 mg, 0.55 mmol)
and N,N-diisopropylethylamine (150 µL, 0.91 mmol). After 6 h at room
temperature the solvent was evaporated. The crude residue was purified
by preparative HPLC (Prontosil Eurobond C18 (20 × 250 mm, 5 µm))
applying a gradient containing MeCN/TFA (0.1% in H2O) to yield 7
as a colorless oil (55.6 mg, 29.2%). For this compound no NMR data
were measured. HRESI-(+)MS: m/z 346.0745 [M + H]+ (calcd for
C13H21N3O379Br, m/z 346.0761, ∆m ) 4.5 ppm).
(2S)-2-Amino-6-[1-(4-bromo-1H-pyrrole-2-ylmethanoyl)amino]-
hexanoic Acid (2). A 55.6 mg portion of 7 was dissolved in HCl (32%).
After 22 h at room temperature the solvent was evaporated. The crude
residue was purified by preparative HPLC (Prontosil Eurobond C18
(20 × 250 mm, 5 µm)) applying a gradient containing MeCN/TFA
(0.1% in H2O) to yield 2 as a colorless oil (17.8 mg, 34.9%). The NMR
data were identical to the natural product. [R]D
4-Bromopyrrole-2-carboxyarginine (1): light yellow oil; [R]D23
-16 (c 0.25, MeOH); UV (DAD) λmax 271 nm; HPLC-
HRESI-(+)MS: tR ) 7.1 min, m/z 346.0487 [M + H]+ (calcd for
C11H17N5O379Br, m/z 346.0509, ∆m ) 6.4 ppm).
4-Bromopyrrole-2-carboxy-N(E)-lysine (2): light yellow oil;
[R]2D3 +5.2 (c 0.50, MeOH); UV (DAD) λmax 268 nm; HPLC-
HRESI-(+)MS: tR ) 8.1 min, m/z 318.0445 [M + H]+ (calcd for
C11H17N3O379Br, m/z 318.0448, ∆m ) 0.9 ppm).
23 +5.4 (c 0.41, MeOH);
HRESI-(+)MS m/z 318.0435 [M
+
H]+
(calcd for
C11H17N3O379Br, m/z 318.0448, ∆m ) 4.0 ppm).
Acknowledgment. The sponge collection was carried out by Dr.
M. Assmann during a scientific expedition to the Bahamas in 2000.
During this time the project was sponsored by the DFG (Ko1314/3-1
to 3-4). We would like to acknowledge the support of Prof. Dr. J. R.
Pawlik (University of North Carolina at Wilmington, NC), who gave
members of the Ko¨ck research group the opportunity to participate in
the scientific sojourns to the Bahamas in the years 1998, 1999, 2000,
2001, and 2003. We further thank Dr. H.-O. Burmeister (TU Braun-
schweig) for measuring the optical rotation.
4-Bromopyrrol-2-yl Trichloromethyl Ketone (5). Synthesis was
performed according to Kitamura et al.10c based on the method of Bailey
et al.10b A solution of Br2 (308 µL, 6 mmol) in 20 mL of glacial HOAc
was added slowly to a stirred solution of pyrrol-2-yl trichloromethyl
ketone (1266 mg, 6 mmol) in 5 mL of glacial HOAc. Pyrrol-2-yl
trichloromethyl ketone was synthesized according to Bailey et al.10a
from pyrrole and trichloroacetyl chloride. After 4 h 30 mL of H2O
was added and the solution was extracted twice with 50 mL of DCM.
The combined DCM solutions were dried (Na2SO4), and the solvent
was evaporated. The crude products were purified by preparative HPLC
(Prontosil Eurobond C18 (20 × 250 mm, 5 µm)) applying a gradient
containing MeCN/TFA (0.1% in H2O) to yield 5 as a white powder
(754 mg, 44%): 1H NMR (DMSO-d6, 400 MHz) δ 12.84 (1H, br s,
H-1), 7.54 (1H, dd, H-5), 7.32 (1H, dd, H-3); 13C NMR (DMSO-d6,
100.7 MHz) δ 171.6 (C-6), 129.0 (C-5), 122.0 (C-2), 121.5 (C-3), 97.6
(C-4), 94.5 (C-7); HRESI-(-)MS m/z 287.8364 [M - H]- (calcd for
C6H2NO35Cl379Br, m/z 287.8380, ∆m ) 5.6 ppm).
(2S)-2-{[1-(4-Bromo-1H-pyrrol-2-yl)methanoyl]amino}-5-[N-Pmc-
guanidino]pentanoic Acid (6). A 159 mg (0.55 mmol) amount of 5,
190 mg (0.43 mmol) of NG-2,2,5,7,8-pentamethylchroman-6-sulfonyl-
L-arginine, and 150 µL (0.91 mmol) of N,N-diisopropylethylamine were
suspended in MeCN (3 mL). After stirring for 6 h at room temperature
the solvent was evaporated. The crude residue was purified by
preparative HPLC (Prontosil Eurobond C18 (20 × 250 mm, 5 µm))
applying a gradient containing MeCN/TFA (0.1% in H2O) to yield 6
as a colorless oil (80 mg, 23.7%). For this compound no NMR data
were measured. HRESI-(+)MS: m/z 612.1464 [M + H]+ (calcd for
C25H35N5O6S79Br, m/z 612.1486, ∆m ) 3.5 ppm).
References and Notes
(1) (a) Forenza, S.; Minale, L.; Riccio, R.; Fattorusso, E. J. Chem. Soc.
D 1971, 1129-1130. (b) Garcia, E. E.; Benjamin, L. E.; Fryer, R. I.
J. Chem. Soc., Chem. Commun. 1973, 78-79. (c) Walker, R. P.;
Faulkner, D. J.; van Engen, D.; Clardy, J. J. Am. Chem. Soc. 1981,
103, 6772-6773.
(2) Al Mourabit, A.; Potier, P. Eur. J. Org. Chem. 2001, 237-243.
(3) Andrade, P.; Kerr, R. G.; Willoughby, R.; Pomponi, S. A. Tetrahe-
dron Lett. 1999, 40, 4775-4778.
(4) (a) Assmann, M.; Lichte, E.; Ko¨ck, M.; van Soest, R. W. M. Org.
Lett. 1999, 1, 455-457. (b) Lindel, T.; Hochgu¨rtel, M.; Assmann,
M.; Ko¨ck, M. J. Nat. Prod. 2000, 63, 1566-1569.
(5) Williams, D. E.; Patrick, B. O.; Behrisch, H. W.; van Soest, R.;
Roberge, M.; Andersen, R. J. J. Nat. Prod. 2005, 68, 327-330.
(6) Auterhoff, H.; Kovar, K.-A. Identifizierung Von Arzneistoffen;
Wissenschaftliche Verlagsgesellschaft mbH: Stuttgart, 1977.
(7) Marfey, P. Carlsberg Res. Commun. 1984, 49, 591-596.
(8) (a) Lehnert, H.; van Soest, R. W. M. Beaufortia 1998, 48, 71-103.
(b) Alvarez, B.; van Soest, R. W. M.; Ru¨tzler, K. Smithson. Contrib.
Zool. 1998, 598, 1-47
(9) Assmann, M.; van Soest, R. W. M.; Ko¨ck, M. J. Nat. Prod. 2001,
64, 1345-1347.
(10) (a) Bailey, D. M.; Johnson, R. E.; Albertson, N. F. Org. Synth. 1971,
51, 100-102. (b) Bailey, D. M.; Johnson, R. E. J. Med. Chem. 1973,
16, 1300-1302. (c) Kitamura, C.; Yamashita, Y. J. Chem. Soc.,
Perkin Trans. 1 1997, 10, 1443-1448.
(2S)-2-{[1-(4-Bromo-1H-pyrrol-2-yl)methanoyl]amino}-5-guani-
dinopentanoic Acid (1). A solution of 6 (60 mg, 0.098 mmol) in TFA
(98%, 3 mL) was stirred for 45 min at room temperature. The solvent
was evaporated, and the crude residue was purified by preparative
NP0502746