X. Qi et al. / European Journal of Medicinal Chemistry 40 (2005) 805–810
809
was dissolved in 6 ml of DCM (THF was added in case of
poor solubility). The solution was cooled to –10 to 0 °C and
2 mmol of DDC was added. After 30 min at 0 °C, the mixture
was filtered directly into a vessel containing 1 g of the
polymer-bonund-4-hydroxy-3-nitrobenzophenone. Pyridine
(0.5 ml) was added, and the mixture was shaken for 1 h at
room temperature. The polymer was washed with six to eight
10-ml portions of chloroform. Active esters of Boc-glycine,
Boc-phenylalanine, and Boc-o-benzyl-tyrosine were thus pre-
pared. Determination of the loading by reacting the polymers
with an excess of benzylamine and weighing the resulting
amide showed that 70–80% of the available OH groups under-
went esterfication.
pressure). The rate of addition was adjusted so as to keep the
internal temperature below –70 °C.After of addition, the reac-
tion mixture was stirred for an additional 2.5 h at –78 °C
(under an N2 atmosphere) when the TLC showed the clean
formation of product 15. The reaction was quenched by slowly
adding 70 ml of cold (–78 °C) CH3OH(H2↑ evolution) to
keep the internal temperature below –65 °C. The resulting
white emulsion was slowly poured into 1000 ml of ice-cold
1 N HCl with swirling over 15 min, and the aqueous mixture
was then extracted with EtOAc (3 × 1000 ml), dried with
MgSO4, filtered and concentrated in vacuo to give crude prod-
uct 15 as a colorless oil, which was vacuum distilled to give
1
15 32.2 g (91.0%) as a colorless liquid. H NMR(CDCl3)
dppm: 1.42(s, 9H), 1.50–1.64 (br, m, 6H), 4.06–4.09 (m, 2H),
4.20–4.35 (m, 1H), 9.53 (br, s, H).
3.2. General procedure
3.2.1. Synthesis of [N-[(1,1-dimethylethoxy)
carbonyl]-serine, methyl ester] (13)
3.2.4. General procedure representative prexperimental
procedure for mitsunobu reaction bibenzyl phthalimidooxy
(18)
H-Ser-OMe-HCl (15 g, 96.5 mmol) was dissolved in
dichloromethane (200 ml) and 2.2 equiv of triethylamine
added, then tert-butylpyrocarbonate (23.2 g, 0.106 mol) were
slowly added with vigorous stirring and cooling in an ice bath.
After stirring at 0 °C for 30 min in the solution was stirred at
room temperature for 3 h. The reaction mixture was then
evaporated and partitioned between 200 ml of ethyl acetate
and 100 ml of KHSO4 (1 M) and washed with 1 M KHSO4
(100 ml, 1 M), NaHCO3 (100 ml) and brine (3 × 50 ml).After
drying over MgSO4, the extract was taken to dryness at
reduced pressure to give 13 20.1 g as oil (yield 95%).
1H NMR (acetic-d6) d ppm: 1.43 (s, 9H, CH3, Boc), 2.50
(br, s, H, exchanged with D2O), 3.76(s, 3H, CH3, OMe), 3.85–
4.98 (m, 2H, CH2, Ser), 4.39 (m, 1H, CH, ser), 5.49 (br, 1H,
NH, exchanged with D2O).
To a stirred solution of 17a (6.6 g, 36 mmol) PPh3
(12.3 g, 47.0 mmol, 1.3 equiv) and PhthNOH (7.0 g,
43.2 mmol,1.2 equiv) in THF (100 ml) was added DIAD
(9.5 g, 47.0 mmol, 1.3 equiv) dropwise over 30 min. The mix-
ture was stirred at r.t. for 6 h. TLC showed without of starting
material. The reaction mixture was concentrated and then the
residue was dissolved in ethanol (30 ml) to get 18a as a solid.
The solid was washed with ethanol to afford a pure 18a in
93% yield as a solid. 1H NMR(CDCl3) d ppm: 5.07 (s, 2H),
7.41–7.83 (m, 13H).
3.2.5. Preparation of compound 19a
To a stirred solution of 18a (7.2 g, 22 mmol) in CH2Cl2
(150 ml) was added dropwise NH2NH2 (1.4 ml, 44 mmol).
The reaction mixture was stirred at r.t. for 4 h. Lots of solid
appeared, the mixture was filtered through celite. The filtrate
was washed by 2 N NaOH, concentrated. The residue was
purified by flash column chromatography (1:1 hexane/EtOAc)
3.2.2. 3-(1,1-Dimethylethyl)4-methyl-2,2-dimethyl-3,4-
oxazolidinedicarboxylate (14)
To a stirred solution of Boc-Ser-OMe (13, 35.8 g,
163 mmol) in CH2Cl2 (200 ml) were added DMP (100 ml,
820 mmol) and p-toluenesulfonic acid monohydrate (p-
TsOH·H2O, 3.2 g, 16.4 mmol) at 0 °C. After stirring at r.t. for
12 h, the mixture was poured into statured aq. NaHCO3
(200 ml) and then the resulting solution was extracted with
Et2O (3 × 150 ml). The organic layer was washed with stat-
ured aq. NaHCO3 (3 × 100 ml), brine (3 × 100 ml), and then
dried (Na2SO4). Concentration in vacuo gave a crude oil,
which was distilled in vacuo to give 14 as a colorless oil 39.1 g
(90%), b.p. 110–112 °C per 4 Torr. 1H NMR (CDCl3) d ppm:
1.39(s, 9H), 1.48(br, s, 3H), 1.65(br, s, 3H), 3.74(s, 3H),
4.11(dd, J = 8.5 and 8.1 Hz, 1H), 4.35(dd, J = 8.5 and 3.5 Hz,
H), 4.47(m, H).
1
to give 19a 2.8 g (63.9%) as oil. H NMR (CDCl3) dppm:
4.74 (s, 2H), 5.43 (br, s, 2H), 7.33–7.61 (m, 9H).
To a solution of 19a (2.0 g, 10 mmol) in MeOH(50 ml)
was added 15 (2.3 g, 10 mmol). The resulting mixture was
heated at 50 °C for 12 h. TLC showed without of starting
materials. After concentration under reduced pressure, the
residue was dissolved in TFA (15 ml) and H2O (50 ml) and
the mixture was stirred at r.t. for 1 h. The solvent was evapo-
rated in vacuo and statured aq NaHCO3 was added. The mix-
ture was extracted with EtOAc, dried with Na2SO4 and con-
centrated in vacuo to give 9a 1.0 g (36.2% in two steps) as
yellow oil. 1H NMR(CDCl3) d ppm: 3.28 (br, s, 2H), 3.56–
3.76 (m, 3H), 5.08 (s, 2H), 7.34–7.57 (m, 10H).
3.2.6. Preparation of compound 2
3.2.3. 1,1-Dimethylethyl-4-formyl-2,2-dimethyl-3-oxazo-
lidinecarboxylate (15)
To a stirred –78 °C solution of 14 (40.2 g, 0.155 mol) in
dry toluene (300 ml) was add ed a –78 °C solution of 1.5 M
DIBAL-H in toluene (175 ml) via cannula (using positive N2
In a single 96-well microtiter plate to produce one product
per well. For the reaction, 0.014 mmol of 8 per well in DCM,
and compound 9 (1.1 equiv). The plate was capped for 48 h
at r.t. The products were removed from the resin, washed into