P. Herdewijn et al.
FULL PAPER
from Novabiochem (Switzerland). Tentagel-NH2 was obtained from
RAPP-Polymere (Tübingen, Germany). Dichloromethane, N,N-dimethyl-
formamide, acetic anhydride (Ac2O) and pyridine were obtained from
BDH (Poole, England). Piperidine, trifluoroacetic acid (TFA), diisopro-
pylcarbodiimide (DIC), 1-hydroxybenzotriazole (HOBt), 1-methylimida-
zole (NMI), dimethylaminopyridine (DMAP) and 1-(3-dimethylamino-
propyl)-3-ethylcarbodiimide hydrochloride (DEC) were supplied by AC-
ROS (Geel, Belgium).
NBA ± NaOAc) calcd for C18H17NO4Na [MNa] 334.1055, found
334.1054; elem. anal. for C18H17NO4 calcd C 69.44, H 5.50, N 4.50; found
C 69.42, H 5.58, N 4.70.
N-(9-fluorenylmethyloxycarbonyl)g-aminobutyric
acid
(Fmoc ± g-
Abu):[15, 16] Sodium carbonate (10 g), 1,4-dioxane (50 mL) and 9-fluorenyl-
methyloxycarbonyl chloride (5.72 g, 22 mmol, 1.1 equiv) were added to a
solution of g-amino butyric acid (2.1 g, 20 mmol) in H2O (100 mL). The
reaction mixture was stirred for 2.5 h and poured into H2O (200 mL). The
solution was extracted three times with diethyl ether; the aqueous layer was
acidified under vigorous stirring with a 2n solution of hydrochloric acid in
water. The white precipitate was isolated by filtration, washed with diethyl
ether and dried in vacuo. The name product was crystallised from ethyl
acetate to yield 6.3 g (19.2 mmol, 96%). Analytical data are in agreement
with ref. [16]. M.p. 1708C (ref. [16] 166 ± 1688C); elem. anal. for C19H19NO4
calcd C 70.14, H 5.89, N 4.30; found C 70.25, H 5.77, N 4.28.
Amino acids used in the libraries: For the assembly of the first library the
following building blocks were used: N-Fmoc-1-amino-1-cyclohexanoic
acid,[12] N-Fmoc-isonipecotic acid,[12] N-Fmoc-a-aminoisobutyric acid,[13] N-
Fmoc-sarcosine,[14] N-Fmoc-g-aminobutyric acid,[15,16] N-Fmoc-4-O-tert-
butylproline,[17] N-Fmoc-b-(uracil-1-yl)-a-d-alanine, N-Fmoc-b-(hypoxan-
thin-9-yl)-a-d-alanine,
Na-Fmoc-Nd-(2-thiophenecarbonyl)ornithine,[18]
Na-Fmoc-Nd-(p-toluenesulphonyl)ornithine,[18] Na-Fmoc-Nd-8-(quinoline-
sulfonyl)ornithine,[18] Nin-tert-butyloxycarbonyl-Na-Fmoc-tryptophan, Nd-
tert-butyloxycarbonyl-Na-Fmoc-ornithine and N-trityl-Na-Fmoc-gluta-
mine. The latter three were obtained from Advanced ChemTech, while
synthesis of the other building blocks was carried out as described.
Analytical data lacking in the literature are provided. During the course of
our work the building blocks Fmoc ± Sar, Fmoc ± g-Abu and Fmoc ± Hyp
(tBu) have become available from Advanced Chemtech or Novabiochem.
N-(9-fluorenylmethyloxycarbonyl)-4-O-tert-butyl proline [Fmoc ± Hyp(t-
Bu)]: The title compound was synthesised in 3 steps from hydroxyproline
as described.[17] 13C NMR ([D6]DMSO): d 28.15 (tBu, CH3), 37.74 (C-3),
46.48 (Fmoc, C-9'), 53.00, 53.99 (C-5), 58.62 (C-2), 66.51, 66.99 (Fmoc,
CH2O), 68.40, 69.20 (C-4), 73.44 (tBu, C ± O), 120.15 (Fmoc, C-4'), 125.14
(Fmoc, C-1'), 127.16 (Fmoc, C-2'), 127.75 (Fmoc, C-3'), 140.85 (Fmoc, C-
11'), 144.00 (Fmoc, C-10'), 154.07 (OCONH), 175.23 (COOH); exact mass
General procedure for fluorenylmethyloxycarbonylations: Protection of
the a-amino moiety with the fluorenylmethyloxycarbonyl group was
carried out as described here for the synthesis of Fmoc ± Hex.
(LSIMS, thioglycerol) calcd for C25H27NO4 [MH] 410.19673; found
410.19673.
Na-tert-butyloxycarbonyl-b-(uracil-1-yl)-a-d-alanine: This compound was
N-(9-fluorenylmethyloxycarbonyl)-1-aminocyclohexanecarboxylic
acid
synthesised before as
reaction[19] and as an enantiomerically pure compound by opening of
Boc-serine b-lactone.[20] To
suspension of uracil (5.04 g, 45 mmol,
a racemic mixture using a Michael addition
(Fmoc ± Hex):[12] Na2CO3 (25 g, 5 equiv), 1,4-dioxane (200 mL) and 9-
fluorenylmethyloxycarbonyl chloride (14.2 g, 55 mmol, 1.1 equiv) were
added to a solution of 1-aminocyclohexanecarboxylic acid hydrochloride
(8.9 g, 50 mmol) in H2O (250 mL). After stirring for 16 h, the reaction
mixture was poured into 300 mL of H2O and the solution was extracted
three times with diethyl ether. The aqueous layer was acidified with a 2n
solution of hydrochloric acid in water to pH 2 and the colourless suspension
was extracted three times with ethyl acetate. The combined organic layer
was dried on anhydrous MgSO4, filtered and evaporated. The obtained
white solid was crystallised from nitromethane to yield 11.68 g of Fmoc ±
Hex (32 mmol, 64%). M.p. 1788C; 13C NMR ([D6]DMSO): d 21.30 (C-3,
C-5), 25.28 (C-4), 32.09 (C-2, C-6), 47.00 (Fmoc, C-9'), 58.44 (C-1), 65.60
(Fmoc, CH2O), 120.32 (Fmoc, C-4'), 125.63 (Fmoc, C-1'), 127.31 (Fmoc, C-
2'), 127.87 (Fmoc, C-3'), 140.96 (Fmoc, C-11'), 144.12 (Fmoc, C-10'), 155.45
(OCONH), 176.22 (COOH); exact mass (LSIMS, thioglycerol) calcd for
a
1.1 equiv) in anhydrous DMF (170 mL), NaH (80% dispersion in oil,
1.8 g, 40 mmol, 1 equiv) was added. The suspension was stirred at room
temperature for 1 h and cooled to 788C. A solution of N-tert-Boc-d-
serine-b-lactone[21,22] (7.4 g 40 mmol) in anhydrous DMF (70 mL) was
added dropwise for 30 min. After stirring for 16 h at room temperature, the
solvent was evaporated to dryness. The obtained oil was dissolved in water
and acidified with a 2n solution of hydrochloric acid in water. The
colourless suspension was extracted three times with ethyl acetate. The
organic layer was dried on anhydrous MgSO4, filtered and evaporated to
dryness. The residual oil was purified by flash column chromatography on
silica gel (elution 93% DCM/6% MeOH/1% HOAc or TEA) yielding
8.03 g of the title compound (26.8 mmol, 67%). 13C NMR ([D6]DMSO):
d 8.71 (TEA, CH3), 28.21 (Boc, CH3), 45.01 (TEA, CH2), 50.87 (b-CH2),
53.19 (a-CH), 77.96 (Boc, C ± O), 100.04 (U, C-5), 146.33 (U, C-6), 151.08
(U, C-2), 155.21 (OCONH), 164.05 (U, C-4), 172.14 (COO ); exact mass
C22H24NO4 [MH] 366.1705, found 366.17160; elem. anal. for C22H23NO4
calcd C 72.32, H 6.34, N 3.83; found C 72.37, H 6.34, N 3.77.
N-(9-fluorenylmethyloxycarbonyl)isonipecotic acid (Fmoc ± Inp):[12] The
title compound was prepared according to the general procedure as
described for Fmoc ± Hex and was crystallised from nitromethane (80%).
M.p. 1828C; 13C NMR (CDCl3): d 28.06 (C-3), 41.06 (C-2), 43.64 (2 Â C-
4), 47.85 (Fmoc, C-9'), 67.84 (Fmoc, CH2O), 120.48 (Fmoc, C-4'), 125.43
(Fmoc, C-1'), 127.54 (Fmoc, C-2'), 128. 19 (Fmoc, C-3'), 141.84 (Fmoc, C-
11'), 144.48 (Fmoc, C-10'), 155.80 (OCONH), 180.44 (COOH); exact mass
(LSIMS, thioglycerol) calcd for C12H18N3O6 [MH] 300.1195; found
300.1198.
Na-(9-fluorenylmethyloxycarbonyl)-b-(uracil-1-yl)-a-d-alanine
(Fmoc ±
AlaU): A solution of Na-tert-Boc-b-uracil-1-yl)-a-alanine (8.00 g) in a
mixture of TFA/DCM 1:1 (100 mL) was stirred for 16 h. The solvent was
evaporated and the foam obtained was dissolved in a 10% aqueous
solution of sodium carbonate (200 mL). To this clear yellow solution was
added 1,4-dioxane (100 mL) and a solution of FmocCl (7.58 g, 29.4 mmol,
1.1 equiv). The reaction mixture was stirred for 16 h at room temperature,
poured into water (200 mL) and extracted three times with diethyl ether.
The aqueous phase was acidified by a 2n aqueous solution of hydrochloric
acid to pH 2 and extracted three times with ethyl acetate. The combined
organic layer was dried on anhydrous MgSO4, filtered and evaporated. The
title compound was crystallised from DCM yielding 8.42 g (20 mmol,
77%). M.p. 2218C; 13C NMR ([D6]DMSO): d 46.68 (Fmoc, C-9'), 48.65
(b-CH2), 52.24 (a-CH), 65.93 (Fmoc, CH2O), 100.65 (U, C-5), 120.67
(Fmoc, C-4'), 125.30 (Fmoc, C-1'), 127.20 (Fmoc, C-2'), 127.79 (Fmoc, C-3'),
140.83 (Fmoc, C-11'), 143.80 (Fmoc, C-10'), 146.16 (U, C-6), 150.99 (U, C-
2), 156.15 (OCONH), 163.83 (U, C-4), 171.23 (COOH); exact mass
(LSIMS, thioglycerol) calcd for C21H22NO4 [MH] 352.1548, found
352.1536; elem. anal. for C21H21NO4 calcd C 71.78, H 6.02, N 3.99; found
C 71.78, H 6.09, N 3.93.
N-(9-fluorenylmethyloxycarbonyl)-a-aminoisobutyric
acid
(Fmoc ±
Aib):[13] Following the general procedure, the title compound was
synthesised and crystallised from nitromethane in 83% overall yield.
M.p. 1788C (ref. [13] 179 ± 1808C); 13C NMR ([D6]DMSO): d 25.28 (2 Â
CH3), 46.79 (Fmoc, C-9'), 55.29 (a-C), 65.43 (Fmoc, CH2O), 120.21 (Fmoc,
C-4'), 125.42 (Fmoc, C-1'), 127.20 (Fmoc, C-2'), 127.75 (Fmoc, C-3'), 140.82
(Fmoc, C-11'), 143.96 (Fmoc, C-10'), 155.09 (OCONH), 175.98 (COOH);
exact mass (LSIMS, glycerol) calcd for C19H20NO4 [MH] 326.1392, found
326.1389; elem. anal. for C19H19NO4 calcd C 70.14, H 5.89, N 4.30; found C
69.89, H 5.92, N 4.48.
(LSIMS, thioglycerol) calcd for C22H20N3O6 [MH] 422.1352; found
422.1359; elem. anal. for C22H19N3O6 calcd C 62.70, H 4.54, N 9.97; found C
62.63, H 4.29, N 10.03.
N-(9-fluorenylmethyloxycarbonyl)sarcosine (Fmoc ± Sar):[14] The title com-
pound was crystallised from hexane ± EtOAc in 90% yield. M.p. 1138C
(ref. [14] 43 ± 458C); 13C NMR ([D6]DMSO): d 35.13, 35.78 (NCH3),
50.02, 50.40 (a-C), 67.18, 67.35 (Fmoc, CH2O), 120.39 (Fmoc, C-4'), 125.31
(Fmoc, C-1'), 127.39 (Fmoc, C-2'), 127.94 (Fmoc, C-3'), 141.00 (Fmoc, C-
11'), 127.94 (Fmoc, C-3'), 141.00 (Fmoc, C-12'), 144.04 (Fmoc, C-10'),
155.79, 156.17 (OCONH), 171.13, 171.28 (COOH); exact mass (LSIMS,
Na-tert-Butyloxycarbonyl-b-(6-chloropurin-9-yl)-a-d-alanine: Likewise,
this compound was synthesised as a racemic mixture by means of a
Michael addition reaction[19] and as an enantiomeric pure compound by
opening of Boc-serine b-lactone.[20] To a solution of 6-chloropurine (5.41 g,
35 mmol, 1.2 equiv) in anhydrous DMF (150 mL) was added NaH (80%
430
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Chem. Eur. J. 1998, 4, No. 3