December 2001
1645
Chart 1
propyl-O-tert-butylisourea7) to give 2. Then the phenolic OH
group was silylated by tert-butyldimethylchlorosilane (TB-
DMSCl) to give a monosilylated compound (3). In the H-
NMR spectrum of 3, the singlet methyl signal due to Me–Si
appeared at 0.17 ppm. Irradiation of this signal in the nuclear
Overhauser effect (NOE) experiment induced 5.1% NOE on
the aromatic proton signal at 6.75 ppm. Thus, we deduced
that the TBDMS group was substituted on the phenolic OH.
After protection of OH group of 4-coumaric acid as TBDMS
(400 MHz) spectrometer. The following abbreviations are used: s, singlet; d,
doublet; t, triplet; dd, doublet of doublets; m, multiplet.
(؎)-tert-Butyl 3-(4-Hydroxyphenyl)lactate (2) N,NЈ-Diisopropyl-O-
tert-butylisourea (150 ml, 8.37 mmol) was added to a suspension of (Ϯ)-3-
(4-hydroxyphenyl)lactic acid (296 mg, 1.62 mmol) in tetrahydrofuran (THF)
(3.0 ml) and t-BuOH (2.5 ml) at 0 °C and stirred at room temperature for
14 h. The reaction mixture was diluted with AcOEt and washed with 10%
aqueous citric acid, 10% aqueous NaHCO3 and brine, dried over Na2SO4,
and concentrated in vacuo. The residue was chromatographed on SiO2
(hexane–AcOEt, 10 : 1—2 : 1) to give 2 (352 mg, 91%) as colorless oil. IR
(neat, cmϪ1): 3470, 3319 (OH), 1713 (CϭO). 1H-NMR (CDCl3) d: 1.45
1
ether, the resulting carboxylic acid (4) was condensed with (9H, s, O–C(CH3)3), 2.84 (1H, dd, Jϭ6.3, 14.1 Hz, CHaHb-Ph), 2.88 (1H, dd,
Jϭ4.6, 14.1 Hz, CHaHb-Ph), 4.27—4.31 (1H, m, OCH ), 6.68, 7.06 (each
3 in the presence of 1-(3-dimethylaminopropyl)-3-ethylcar-
2H, both d, Jϭ8.3 Hz, Ar-H). HR-EI-MS; m/z: 238.1208 [Mϩ] (Calcd for
bodiimide (EDCI), 4-dimethylaminopyridine (DMAP) and 1-
C13H18O4: 238.1205).
1
hydroxybenzotriazole (HBT) to give an ester (5). The H-
(؎)-tert-Butyl 3-(4-tert-Butyldimethylsilyloxyphenyl)lactate (3) To a
solution of 2 (98.1 mg, 0.41 mmol), DMAP (13.3 mg, 0.11 mmol) and tri-
ethylamine (Et3N) (125 ml, 0.89 mmol) in THF (2.0 ml), a solution of TB-
DMSCl (94.9 mg, 0.62 mmol) in THF (1.0 ml) was added in dropwise at
0 °C. The mixture was stirred at room temperature for 14 h, diluted with
AcOEt, washed with 5% aqueous citric acid, 5% aqueous NaHCO3 and
brine, dried over Na2SO4, and concentrated in vacuo. The residue was chro-
matographed on SiO2 (hexane–AcOEt, 100 : 1—9 : 1) to give 3 (103 mg,
NMR spectrum of 5 showed the methyne signal at 5.20 ppm,
downfield relative to that of 3. The FAB-MS spectrum also
supported the structure. The TBDMS groups of 5 were then
cleaved in the presence of tetrabutylammonium fluoride
1
(TBAF) to yield 6. The H-NMR spectrum of 6 showed no
methyl signals due to TBDMS group. Finally, 6 was treated
with trifluoroacetic acid (TFA) to give the desired ester (1).
The 1H-NMR spectrum indicated the presence of two sets of
para-substituted phenyl group, a trans-olefin and a CH–CH2
system. The high-resolution (HR)-FAB-MS spectrum also
supported the structure of 1.
As described above, (Ϯ)-2-O-(4-coumaroyl)-3-(4-hydrox-
yphenyl)lactic acid (1) was simply prepared from 4-coumaric
acid and (Ϯ)-3-(4-hydroxyphenyl)lactic acid. To our knowl-
edge, this is a first report about the preparation of a simple
1
72% yield) as colorless oil. IR (neat, cmϪ1): 3584 (OH), 1726 (CϭO). H-
NMR (CDCl3) d: 0.17 (6H, s, Si(CH3)2), 0.97 (9H, s, Si–C(CH3)3), 1.42
(9H, s, O–C(CH3)3), 2.88 (1H, dd, Jϭ6.1, 14.1 Hz, CHaHb-Ph), 3.00 (1H, dd,
Jϭ4.9, 14.1 Hz CHaHb-Ph), 4.26—4.30 (1H, m, OCH ), 6.75, 7.10 (each
2H, both d, Jϭ8.3 Hz, Ar-H). HR-EI-MS; m/z: 352.2071 [Mϩ] (Calcd for
C19H32O4Si: 352.2070).
4-O-tert-Butyldimethylsilylcoumaric Acid (4) TBDMSCl (1074 mg,
7.12 mmol) was added to
a solution of 4-coumaric acid (98.7 mg,
0.60 mmol) and imidazole (423 mg, 7.12 mmol) in N,NЈ-dimethylformamide
(DMF, 1.5 ml) at 0 °C, and the mixture was stirred at room temperature for
3 h. The reaction mixture was diluted with AcOEt and the solution was
but important phenyllactic acid possessing a cinnamate sub- washed with 10% aqueous NaHCO3 and brine, dried over Na2SO4, and con-
centrated in vacuo. The residue was chromatographed on SiO2 (hexane–
stituent on the OH at the a position of the carboxy group.
AcOEt, 9 : 1—1 : 1) to give 4 (164 mg, 98% yield) as amorphous powder. IR
Compound 1 would be useful for characterization of RA
(neat, cmϪ1): 1682 (CϭO). 1H-NMR (CDCl3) d: 0.23 (6H, s, Si(CH3)2),
biosynthesis.
0.99 (9H, s, Si–C(CH3)3), 6.32 (1H, d, Jϭ15.9 Hz, CO–CHϭCH), 6.86, 7.45
(each 2H, both d, Jϭ8.5 Hz, Ar-H), 7.74 (1H, d, Jϭ15.9 Hz, PhCHϭCH).
HR-EI-MS; m/z: 278.1340 [Mϩ] (Calcd for C15H22O3Si: 278.1339).
Experimental
(؎)-tert-Butyl 2-O-(4-O-tert-Butyldimethylsilylcoumaloyl)-3-(4-tert-
butyl-dimethylsilyloxyphenyl)lactate (5) To a solution of 4 (164 mg,
0.588 mmol), HBT (82.6 mg, 0.611 mmol), EDCI (195 mg, 1.02 mmol) and
DMAP (85.2 mg, 0.697 mmol) in CH2Cl2 (2.0 ml), a solution of 3 (185 mg,
General The electron impact (EI) and FAB-MS and HR-EI and FAB-
MS were measured with a JEOL JMS DX-505 or SX-102 mass spectrome-
ter. The IR spectra were recorded on a Shimadzu FTIR-8100 spectrometer.
The 1H-NMR spectra were measured with a JEOL JNM Lambda 400