Peptidoglycan Substrates for PBP5
(25 mL) was neutralized with Et3N (98 µL, 0.7 mmol) and was
stirred at rt for 15 min. p-Nitrophenyl ester 14 was added into
this amine solution, and the resultant mixture was stirred at
rt for 18 h. The solvent was removed in vacuo, and the residue
was suspended in water and was filtered. The residue was
purified by short-path column chromatography (CHCl3/MeOH,
5:1) to give 16, which was dissolved in 60% acetic acid (5 mL),
and the mixture was stirred at 50 °C for 1 h. After removal of
acetic acid in vacuo, the residue was dissolved with MeOH (10
mL), and 10% Pd/C was added. The mixture was refluxed for
5 h under an atmosphere of hydrogen. The reaction mixture
was treated with charcoal and was filtered through a layer of
Celite, which was washed with methanol. The filtrate was
concentrated prior to purification of the desired compound by
short-path column chromatography (MeOH/AcOH, 4:1) to give
the title compound (0.25 g, 65% from 13). 1H NMR (500 MHz,
D2O): δ 1.27 (d, J ) 7.3 Hz, 3H), 1.31 (d, J ) 7.3 Hz, 3H),
1.34 (d, J ) 6.5 Hz, 3H), 1.39 (d, J ) 7.3 Hz, 3H), 1.27-1.39
(m, 2H), 1.65 (m, 2H), 1.76 (m, 2H), 1.90 (m, 1H), 1.92 (s, 3H),
2.10 (m, 1H), 2.28 (t, J ) 7.3 Hz, 2H), 2.95 (t, J ) 8.1 Hz, 2H),
3.45 (s, 3H), 3.50 (m, 3H), 3.69-3.78 (overlapping dd, J )
11.35, 8.9, 5.7 Hz, 2H), 3.90 (d, J ) 10.5 Hz, 1H), 4.10-4.30
(overlapping dd and m, J ) 11.4, 7.3, 6.5, 5.7 Hz, 6H), 4.36 (d,
J ) 8.1 Hz, 1H, H-1). 13C NMR (125 MHz, D2O): δ 16.6, 17.0,
17.3, 18.8, 22.2, 22.3, 26.4, 28.1, 30.5, 31.8, 39.3, 49.7, 49.9,
54.2, 55.1, 57.3 (OCH3), 60.8 (C-6), 68.9, 75.8, 78.3 (O-CH-
CH3), 82.7, 102.1 (C-1), 174-176 (a total of 8 carbonyl signals).
HRMS (ESI) [M + H]+ calcd for C32H56N7O15+ 778.3829, found
778.3813.
ane/EtOAc, 3:1-1:1) to give the title compound (3.3 g, 72%)
as a single isomer. 1H NMR (400 MHz, CDCl3): δ 1.83 (brs,
6H, 2CH3), 3.63 (m, 1H, H-5), 3.77 (tapp, J ) 8.9 Hz, 1H, H-4),
3.80 (tapp, J ) 9.7 Hz, 1H, H-6), 3.92 (dd, J ) 10.1, 8.5 Hz, 1H,
H-2), 4.36 (dd, J ) 10.5, 3.2 Hz, 1H, H-6′), 4.37 (dd, J ) 10.5,
8.9 Hz, 1H, H-3), 4.50, 4.84 (2d, J ) 12.2 Hz, 2H, CH2Ph),
5.24 (t, J ) 8.5 Hz, 1H, H-1), 5.59 (s, 1H, CHPh), 7.11-7.52
(m, 10H). 13C NMR (100 MHz, CDCl3): δ 8.9 (CH3), 57.8 (C-
2), 66.5 (C-5), 68.9 (C-6), 74.4 (CH2Ph), 75.1 (C-3), 83.1 (C-4),
93.9 (C-1), 101.5 (CHPh), 126.3, 127.7, 128.5, 129.3, 137.3,
137.5, 138.5, 172.0. MS (ES) m/z 488.21 [M + Na]+, 504.18
[M + K]+.
Meth yl 2-Aceta m id o-3-O-a cetyl-6-O-ben zyl-2-d eoxy-â-
D-glu cop yr a n osid e (24). Compound 12 (3.2 g, 10 mmol) in
CH2Cl2 (10 mL) was stirred with pyridine (2.4 mL, 30 mmol)
and acetic anhydride (3.9 mL, 30 mmol) at rt overnight. The
reaction mixture was diluted with CH2Cl2 and was washed
with water and brine. The organic layer was concentrated to
dryness, and the sample was kept under vacuum for 1 h. The
residue was subjected to the regioselective benzylidene ring
opening reaction, which was reported by Deninno et al.10
Meth yl 2-Aceta m id o-3-O-ben zyl-4,6-O-ben zylid en e-2-
d eoxy-â-D-glu cop yr a n osyl-(1f4)-2-a ceta m id o-3-O-a cetyl-
6-O-ben zyl-2-d eoxy-â-D-glu cop yr a n osid e (26). This proce-
dure has to be carried out under scrupulously dry conditions
or else the reaction may fail entirely. Compound 22 (4.7 g, 10
mmol) in anhydrous CH2Cl2 (50 mL) was treated with 2,2,2-
trichloroacetonitrile (2.5 mL, 25 mmol) and a catalytic amount
of DBU. When the starting material was consumed completely
(2 h), the reaction mixture was filtered through a layer of silica
gel, which was washed with CH2Cl2. The filtrate was concen-
trated under scrupulously dry conditions, and the residue was
kept under high vacuum for 0.5 h. The residue (23) was
dissolved in anhydrous CH2Cl2 (50 mL) and was treated with
compound 24 (4.4 g, 12 mmol) and activated 4-Å molecular
sieves (5 g). After being stirred for 0.5 h at rt, the mixture
was cooled to -5 °C and was treated with a catalytic amount
of trimethylsilyl trifluoromethanesulfonate (0.1 mL). When the
starting material was consumed completely, a few drops of
Et3N were added and the solution was stirred at rt for 0.5 h.
The reaction mixture was concentrated to dryness, and the
resultant residue was dissolved in a small amount of ethyl
acetate, which was filtered through a small layer of silica gel.
Silica gel was washed with hexane/EtOAc (4:1), and the
combined filtrate was concentrated to dryness. The residue
was chromatographed (hexane to hexane/EtOAc, 4:1) to give
compound 25 (3.3 g, 40% from 22).
ter t-Bu tyld im eth ylsilyl 3-O-Ben zyl-4,6-O-ben zylid en e-
2-d im eth ylm a leim id o-2-d eoxy-â-D-glycop yr a n osid e (21).
This procedure has to be carried under scrupulously dry
condition, or else the reaction may fail entirely. To a solution
of 209 (4.6 g, 10 mmol) in anhydrous CH2Cl2 (20 mL) and
anhydrous cyclohexane (20 mL) were added benzyl 2,2,2-
trichloroacetimidate (3.7 mL, 20 mmol) and activated 4-Å
molecular sieves (5 g), and the mixture was stirred at rt for
0.5 h. Then, the mixture was cooled in an ice-water bath, and
a catalytic amount of trifluoromethanesulfonic acid was added
dropwise (0.1 mL). 2,2,2-Trichloroacetamide started to crystal-
lize from the reaction solution. The reaction was monitored
by TLC. When the starting material was consumed completely
(approximately 1 h), the reaction was quenched by a few drops
of Et3N and additional cyclohexane (20 mL) was added. After
the mixture was stirred for 0.5 h at rt, 2,2,2-trichloroacetamide
was filtered and washed with hexane/EtOAc (4:1). The filtrate
was concentrated to dryness, and the residue was chromato-
graphed (hexane to hexane/EtOAc, 8:1) to give 21 as a colorless
oil (3.9 g, 67%). 1H NMR (400 MHz, CDCl3): δ -0.07, 0.03,
0.75 (3s, 15H), 1.94 (s, 6H, 2CH3), 3.58 (m, 1H, H-5), 3.74 (dd,
J ) 10.5, 8.1 Hz, 1H, H-4), 3.86 (tapp, J ) 10.5 Hz, 1H, H-6),
3.94 (dd, J ) 10.5, 8.1 Hz, 1H, H-2), 4.29 (dd, J ) 10.5, 8.9
Hz, 1H, H-3), 4.33 (tapp, J ) 10.5 Hz, 1H, H-6′), 4.50, 4.82 (2d,
J ) 12.2 Hz, 2H, CH2Ph), 5.24 (d, J ) 8.1 Hz, 1H, H-1), 5.59
(s, 1H, CHPh), 7.12-7.52 (m, 10H). 13C NMR (100 MHz,
CDCl3): δ -5.4, -4.0, 8.9, 17.8, 25.6, 58.0 (C-2), 66.4 (C-5),
69.0 (C-6), 74.2 (CH2Ph), 74.9 (C-3), 83.3 (C-4), 94.3 (C-1), 101.5
(CHPh), 126.3, 127.6, 128.4, 128.5, 128.8, 129.2, 130.0, 134.7,
137.1, 137.6, 138.7, 172.1. MS (ES) m/z 580.26 [M + H]+,
602.23 [M + Na]+, 618.21 [M + K]+.
The mixture of 25 (3.3 g, 4 mmol) and sodium hydroxide
(1.44 g, 36 mmol) in a dioxane/water mixture (5:1, 70 mL) was
stirred at rt. After 4 h, the pH was adjusted to 3.5 by 1 N
HCl, and the solution was stirred for 12 h while pH was kept
between 3.0 and 3.5. The solution was concentrated to dryness,
and the residue was dissolved in anhydrous MeOH. The
precipitate was filtered, the filtrate was evaporated to dryness,
and the residue was kept under high vacuum for a while. The
residue in pyridine (2.4 mL, 30 mmol) was treated with acetic
anhydride (3.9 mL, 30 mmol) at rt overnight. Evaporation of
the volatiles gave the crude product (26), which was purified
by column chromatography (1.5 g, 49%). Compound 23. 1H
NMR (400 MHz, CDCl3): δ 1.81 (s, 6H, 2CH3), 3.78-3.90 (m,
3H, H-4, H-5, H-6), 4.29 (dd, J ) 9.7, 8.9 Hz, 1H, H-2), 4.44
(dd, J ) 10.5, 8.9 Hz, 1H, H-3), 4.46 (dd, J ) 6.5, 4.1 Hz, 1H,
H-6′), 4.53, 4.86 (2d, J ) 12.2 Hz, 2H, CH2Ph), 5.62 (s, 1H,
CHPh), 6.33 (d, J ) 8.9 Hz, 1H, H-1), 7.14-7.54 (m, 10H),
8.61 (s, 1H). 13C NMR (100 MHz, CDCl3): δ 8.9 (CH3), 54.8
(C-2), 67.1 (C-5), 68.8 (C-6), 74.5 (CH2Ph), 75.0 (C-3), 82.7
(C-4), 94.7 (C-1), 101.7 (CHPh), 126.3, 127.8, 128.5, 128.6,
129.3, 137.3, 137.4, 138.4, 161.0, 171.3. MS (ES): m/z 631.14
3-O-Ben zyl-4,6-O-ben zylid en e-2-d im eth ylm a leim id o-2-
d eoxy-â-D-glycop yr a n ose (22). Compound 21 (5.8 g, 10
mmol) in dry THF (80 mL) was treated by the dropwise
addition of tetrabutylammonium fluoride (12.5 mL, 1.0 M in
THF) at -20 °C. The mixture was stirred until starting
material was consumed (4 h). Subsequently, acetic acid (0.8
mL) was added, and the mixture was warmed to rt over 10
min. After the addition of a few drops of satd NaHCO3, the
solvent was removed in vacuo, the residue was taken up in
CH2Cl2 (50 mL) and washed with satd NaHCO3, and the
organic layer was dried over anhydrous MgSO4, filtered, and
concentrated. The crude product was chromatographed (hex-
1
[M + Na]+. Compound 26. H NMR (400 MHz, 5% CD3OD in
CDCl3): δ 1.71, 1.82, 1.91 (3s, 9H), 3.20 (m, 1H, H-5II), 3.36
(s, 3H, OCH3), 3.38 (m, 1H, H-5I), 3.48-3.62 (overlapping dd,
J ) 9.7, 8.9, 8.1 Hz, 6H, H-2II, H-4II, H-6I, H-6′I, H-6II, H-3II),
J . Org. Chem, Vol. 69, No. 3, 2004 783