An entry to 7-amino- and to 2-ethoxycarbonyl-5-dethia-5-oxa-cephams from 1,3-alkylidene-l-erythritol

Article abstract of DOI:10.1016/j.tet.2006.08.074

The alkoxyallene derived from 1,3-benzylidene-l-erythritol when treated with chlorosulfonyl isocyanate provided diastereomeric β-lactams with moderate stereoselectivity. After the intramolecular alkylation of the nitrogen atom, these afforded compounds ha

Full text of DOI:10.1016/j.tet.2006.08.074

Tetrahedron 62 (2006) 10928–10936
An entry to 7-amino- and to 2-ethoxycarbonyl-5-dethia-5-oxa-
cephams from 1,3-alkylidene-L-erythritol
Tong Thanh Danh,a Katarzyna Borsuk,a Jolanta Soleckab and Marek Chmielewskia,
*
aInstitute of Organic Chemistry of the Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
bNational Institute of Hygiene, 00-791 Warsaw, Poland
Received 30 May 2006; revised 9 August 2006; accepted 23 August 2006
Available online 18 September 2006
Abstract—The alkoxyallene derived from 1,3-benzylidene-L-erythritol when treated with chlorosulfonyl isocyanate provided diastereomeric
b-lactams with moderate stereoselectivity. After the intramolecular alkylation of the nitrogen atom, these afforded compounds having oxa-
cepham skeletons. The exo-isopropylidene group enabled the introduction of a variety of substituents to the C-7 carbon atom of the cepham,
whereas removal of the benzylidene protection followed by the oxidation of 3-OH to the ketone allowed carboxylation of the C-2 carbon atom.
Ó 2006 Elsevier Ltd. All rights reserved.
1. Introduction
the cephams thus formed. The introduction of the amino
function (13) was successfully performed for the cepham 5
only, having the (S) configuration at the bridgehead carbon
atom.2
Recently, we have demonstrated that the [2+2]cycloaddition
of chlorosulfonyl isocyanate (CSI) to alkoxyallene 1 derived
from the 1,2-O-isopropylidene-D-xylofuranose provided b-
lactams 2 and 3 with a moderate stereoselectivity.1 The intra-
molecular alkylation of the nitrogen atom in 2 and 3 afforded
cephams 4 and 5 having an exo-isopropylidene group
(Scheme 1). Compounds 4 and 5 were used as substrates
for a variety of transformations leading to the introduction
of isopropyl, hydroxyisopropyl, oxygen, and nitrogen func-
tions at the a position to the b-lactam carbonyl group (6–
13).2 These transformations followed, in part, Buynak and
co-workers3 study on the functionalization of 3-alkylidene-
azetidin-2-ones. Reactions described by us proceeded in
high stereoselectivity, with control of the configuration of
Due to the specific multifunctional character of the 1,2-
O-isopropylidene-D-xylofuranose scaffold, however, the
cephams obtained are of limited value, since the acid cata-
lyzed hydrolysis of the acetal center derived from the sugar
precursor could not be made without the opening of the
azetidinone ring. The successful opening of the furanoid
fragment was performed as a base induced b-elimination
process.4
The [2+2]cycloaddition of CSI to alkoxyallene 14 derived
from benzylidene erythritol provided azetidinones 15 and
TrO
TrO
TrO
H
O
O
O
H
O
O
H
H
H
H
N
H
H
N
H
O
O
O
O
O
O
H
O
H
O
O
O
NH
NH
O
O
O
O
O
O
O
O
O
O
O
H
5
H
3
1
2
4
HO
R2
H
N
H
R2
H
N
H
1
; R2=OH
; R2=H
1
HO
HO
O
H
H
; R2=
6: R =
R1
O
O
R1
O
O
11: R =OH
12: R1=H ; R2=OH
13: R1=H ; R2=AcHN
O
H
1
7: R =
H
O
O
H
H
; R2=
8: R1=
10: R1=H
9: R1=OH ; R2=H
; R2=H
Scheme 1.
Keywords: Alkoxyallenes; b-Lactams; 5-Oxacephams.
* Corresponding author. Tel.: +48 22 631 87 88; fax: +48 22 632 66 81; e-mail: chmiel@icho.edu.pl
0040–4020/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.08.074

T. T. Danh et al. / Tetrahedron 62 (2006) 10928–10936
10929
H
H
16, which were subjected to intramolecular alkylation
O
O
O
iii,iv
O
Ph
i
Ph
Ph
OH
OR2
ii
O
affording corresponding tricyclic cephams.5 Compounds
17 and 18 were synthesized with the intention to introduce
a carboxylic function to the C-2 atom and a variety of
substituents to the C-7 carbon atom of the 3,4-disubstituted
5-oxacepham skeleton (Chart 1).
O
O
O
R1O
20: R1=Tr
RO
HN
TrO
21: R2=Allyl
22: R2=(Z)-propenyl
23: R=Tr
24: R=Ts
H
H
H
H
H
H
H
N
H
N
O
O
O
N
v
OR3
OR3
O
Ph
O
CH2
O
O
O
H
H
26:R3=H
25
H
28
O
Ph
O
O
27:R3=Ac
Ph
O
O
O
HN
TrO
TrO
O
14
15
O
H
H
H
H
O
O
OR2
ii
Ph
Ph
Ph
O
O
+
O
O
O
R1O
29: R1=TBS; R2=H
TsO
H
4a
9a
H
5a
N8
HN
33
HN
TsO
O
O
O
4
H
O
O
TrO
5
3O
Ph
O
6
7
O
2
1
iv
24
9
O
Ph
30: R1=TBS; R2=Allyl
O
HN
H
O
S
31: R1=H; R2=(Z)-propenyl
32: R1=Ts; R2=(Z)-propenyl
H
H
H
N
O
O
17
16
+
25
CO2H
H
O
Ph
O
N
H
N
H
34
COHN
O
H2N
v
H
H
H
N
S
O
N
O
H
H
H
H
H
H
O
O
N
O
OR3
OR3
CO2
N
O
Ph
O
N
O
O
O
18
OCP-9-176 19
35:R3=H
37
36:R3=Ac
Chart 1.
Scheme 2. (i) (a) NaH/DMF, CH2]CHCH2Br; (b) t-BuOK/DMSO; (ii)
CSI, Na2CO3/Red-Al; (iii) (a) TsOH/MeOH; (b) TsCl/Py; (iv) K2CO3,
Bu4NBr/CH3CN; and (v) (a) Pd/C, H2; (b) Ac2O/Py.
2. Results and discussion
Introduction of the benzylidene grouping to the L-erythritol
is a crucial step for successful functionalization of the 5-
oxacepham skeleton, since the reductive removal of the
protection should be performed easily without any decom-
position of the b-lactam ring. The debenzylidation leaves
a free OH group at C-3 of the cepham, which after oxidation
to the ketone should allow us to introduce an alkoxycarbonyl
function to the C-2 carbon atom.6 Moreover, the cepham
obtained contains the hydroxymethyl group at C-4, which
may increase its biological activity. At the end of the eighties
the Merck and Meiji groups7 reported a new 4-methyl-ceph-
alosporin 19, which offers the stability toward b-lactamases
together with a significant antibacterial activity.
fragment caused the inversion in the conformation of the
six-membered oxazine ring. Consequently hydroxymethyl
and hydroxy groups switched from diequatorial geometry
coerced by the rigid trans decalin system to the distorted di-
axial geometry of the oxazine ring. This was demonstrated
by the change of coupling constants J3,4 from about 9.5 Hz
to 2.2 Hz. Similar conformation of the six-membered oxa-
zine ring has been found by us recently for cepham 28.10
Such a conformational switch demonstrates the angular
strain existing in 25. Contrary to that, the hydrogenation of
the alternative diastereomer 34, having syn protons at C-5a
and C-6a carbon atoms, provided cepham 36, which did
not show an inversion in the conformation of the six-mem-
bered oxazine ring in comparison with the decalin precursor
34. The coupling constant J3,4¼9.8 Hz remains large, prov-
ing the diaxial position of both protons. This shows that the
conformation of the oxacepham having the b-lactam ring
fused to the six-membered oxazine is well defined. The
bridgehead proton H-6 of the molecule must be located in
the pseudoaxial position. One can compare X-ray structures
of 28 and 37 reported by us recently.10 The reverse conforma-
tional arrangement can occur only if the cepham fragment
is a part of the bigger rigid molecule, for example, a trans
decalin system.
The usefulness of the benzylidene erythritol scaffold8 was
demonstrated using simple diastereomeric models 25 and
34 obtained by the standard reaction sequence developed
for the ethylidene congeners (Scheme 2).9,20 [2+2]Cyclo-
addition of chlorosulfonyl isocyanate to 20 proceeded with
excellent stereoselectivity, and provided, after intramolecular
alkylation of the b-lactam nitrogen atom, only one oxacep-
ham 25. Its diastereomer 34, having the (S) configuration
at the bridgehead carbon atom, was obtained by the same re-
action sequence, starting from the tosyloxymethyl propenyl
ether 32, which gave lower stereoselectivity in the cyclo-
addition. The minor product of the cycloaddition (33) after
the intramolecular alkylation provided the cepham 34. All
these reactions followed our earlier observations made for
ethylidene analogs.9
Readily available oxacepham 17 and its C-6 epimer 185 were
selected to demonstrate both functionalizations, i.e., intro-
duction of substituents at the C-7 carbon atom and alkoxy-
carbonylation of the C-2. The sodium in liquid ammonia
reduction of compound 17, which should remove the benzyl-
idene protection and reduce the double bond, led to the
As it was expected, hydrogenation of 25 over palladium gave
26 in a very good yield. Removal of the benzylidene

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T. T. Danh et al. / Tetrahedron 62 (2006) 10928–10936
mixture of three products 38, 39, and 40 in a ratio of about
1.3:1.2:1, respectively, whereas compound 18 under the
same conditions provided a corresponding mixture of 41,
42, and 43 in the ratio of about 2:2:1 (Scheme 3). The transfer
of the benzyl radical or anion to the a,b-unsaturated amide is
worth mentioning. Addition of acrylamide to the reaction
mixture in order to trap the reactive intermediate did not
change significantly the proportion of the reaction products.
Low stereoselectivity of reduction of the double bond was
another feature that differentiated reduction of 17 or 18
from that of 4, which proceeded exclusively to the trans
arrangementofprotonsatC-6andC-7ofthecephamskeleton.2
Since ozonolysis of the exo double bond in b-lactams led to
the decomposition of the azitidin-2-one ring,12 we used a cis
hydroxylation–glycolic cleavage sequence to split the dou-
ble bonds in 17 and 18. Introduction of substituents to the
C-3 carbon atom of the azetidin-2-one ring via 2,3-dione
stage has been reported recently.13 Oxidation of the cephams
17 and 18 independently with RuCl3/NaIO4 in H2O/CH3CN/
CHCl3 mixture, for 30 min,14 afforded corresponding mix-
tures of diols 47 and 48 in a good yields (Scheme 5). Gly-
colic cleavage of 4715, followed by reduction of unstable
ketone 49 with sodium borohydride provided a mixture of
alcohols in a very low yield, which were characterized as
acetates 50. This low yield could be explained by the
mentioned above strain, which exists in (6R) b-lactam ring
fused to the trans decalin system and is manifested by the
easy opening of the four-membered b-lactam ring.
H
H
H
N
O
O
O
Ph
O
17
i, ii
HO
H
H
H
H
OHH
N
HO
OH
H
N
H
O
O
O
iv
i
O
O
OBz
OBz
H
H
Bn
H
H
H
H
N
H
H
H
H
N
H
N
O
O
O
N
OAc
OAc
OAc
OAc
O
Ph
Ph
O
Ph
O
O
O
+
+
H
ii
H
17
OAc
OAc
47
51
O
O
O
H
H
H
H
H
38
39
40
H
H
H
H
AcO
O
O
O
O
O
O
iii
O
H
N
N
N
O
O
Ph
O
H
O
O
H
50
49
O
Ph
O
HO
H
H
H
H
H
H
HO
H
N
OH
OHH
N
18
O
O
i
iv
i, ii
O
O
OBz
OBz
N
O
Ph
Ph
O
O
O
O
H
H
H
Bn
H
H
H
H
N
H
N
H
H
O
O
O
OAc
OAc
OAc
OAc
18
48
52
+
+
N
OAc
OAc
O
O
O
Scheme 5. (i) RuCl3/NaIO4, H2O/CH3CN/CHCl3; (ii) H5IO6/AcOEt; (iii)
(a) NaBH4; (b) Ac2O/Py; and (iv) (a) H2, Pd/C; (b) BzCl/Py.
H
41
42
43
Scheme 3. (i) Na/NH3 and (ii) Ac2O/Py.
The hydrogenolysis of the benzylidene fragment in diol 47
released the conformational strain providing a tetraol, which
was protected at the primary and secondary hydroxyl groups
and gave compound 51. Glycolic cleavage performed on diol
51 proceeded in much better yield. Unstable 7-keto com-
pound 53 was thus obtained, which without purification was
immediatelyreducedtothecorresponding7-ol54. Subsequent
triflation of the hydroxyl group, followed by nucleophilic sub-
stitution with azide, provided 55 with the inversion in the con-
figuration at C-7 carbon atom. Hydrogenation of the azide 55
and acetylation of the resulting amino group ended the reac-
tion sequence affording 56. The same reaction sequence was
performed on 48, yielding the corresponding acetamide 60.
All transformations proceeded in good yield (Scheme 6).
The isopropylidene group in compound 17 can be easily
transformed into hydroxyisopropyl by the sequence of reac-
tions involving the bromohydrin formation followed by the
reductive removal of the bromine atom (Scheme 4).
HO
H
H
H
Br H
N
H
N
O
O
i
O
ii
O
O
Ph
O
Ph
O
O
H
44
17
HO
HO
H
H
H
H
H
N
H
O
O
O
O
+
N
O
Ph
O
Ph
O
O
Hydrogenation of compound 17 over palladium followed by
tritylation of the primary hydroxyl group provided only one
diastereomer 61 having cis located H-6 and H-7 protons.
Subsequent oxidation of the secondary hydroxyl group
afforded the ketone 62. Reaction of 62 with 1.1 equiv of
KHMDS at ꢀ78 ꢁC in toluene followed by the addition of
ethyl cyanoformate provided, after acetylation, the cepham
63 in 60% yield (Scheme 7). This relatively high yield
of ethoxycarbonylation was in contrast to our previous
observations.6
H
H
45
46
Scheme 4. (i) NBS/DMSO–H2O and (ii) Bu3SnH/AIBN/toluene.
The treatment of 17 with NBS in wet DMSO,11 according to
the known procedure,3f provided a mixture of bromohydrins
44, which upon treatment with tributyltin hydride gave
two diastereomers 45 and 46 in the ratio of 4.4:1, respec-
tively (Scheme 4). The relatively high stereoselectivity of
debromination, which did not depend upon the proportion
of bromohydrins, was in agreement with the previous
observations.2
Oxacephams 17, 18, 56, and 63 were tested for their biological
activity. An inhibition of the DD-carboxypeptidaseactivityand,

T. T. Danh et al. / Tetrahedron 62 (2006) 10928–10936
10931
recorded on a Perkin–Elmer FTIR Spectrum 200 spectro-
photometer. Mass spectra were recorded using AMD-604
Inectra GmbH and HPLC–MS with Mariner and API 356
detectors. Optical rotations were measured using JASCO P
3010 polarimeter at 22ꢂ3 ꢁC. Column chromatography
was performed using E. Merck Kiesel Gel (230–400 mesh).
H
N
H
H
N
O
HO
O
O
i
OBz ii
OBz
OBz
iii
51
OBz
O
O
53
54
H
H
N
H
H
N
AcHN
O
N3
O
OBz
OBz
OBz
OBz
iv
Compounds 21–25 and 30–34 were obtained according to
the procedures reported previously for ethylidene analogs.9
Detailed procedures, spectral and analytical data are pro-
vided in Supplementary data.20
O
O
O
55
56
H
H
N
H
N
HO
O
O
OBz
OBz
OBz
iii
ii
i
52
4.1.1. (3S,4R,6R,7S)-3-Hydroxy-4-hydroxymethyl-
7-methyl-5-oxa-cepham (26). Compound 25 (0.07 g,
0.25 mmol) dissolved in MeOH (10 mL) was hydrogenated
in the presence of 5% Pd/C (0.007 g) for 1.5 h. Subsequently
the mixture was filtered through Celite and evaporated. The
crude product was purified by chromatography using AcOEt/
MeOH, 4:1 v/v as an eluent to afford 26 (0.04 g, 83%). [a]D22
+21.7 (c 0.1, CH2Cl2). IR (film): 1740, 3367 cmꢀ1. HRMS
(ESI), m/z (M+H)+, calcd for C8H15O4N: 188.0917, found:
OBz
O
O
57
58
H
H
H
H
AcHN
N3
O
O
OBz
OBz
OBz
OBz
iv
N
N
O
O
59
60
Scheme 6. (i) H5IO6/AcOEt; (ii) NaBH4/H2O; (iii) (a) Tf2O/Py; (b) NaN3/
DMF; and (iv) (a) Pd/C, H2; (b) Ac2O, Py.
1
188.0922. H NMR (400 MHz, D2O) d: 1.24 (d, J¼7.5 Hz,
3H, CH3), 3.38 (ddd, J¼1.8, 2.9, 14.7 Hz, 1H, H-2), 3.50
(ddq, J¼1.8, 3.7, 7.5 Hz, 1H, H-7), 3.64 (ddd, J¼1.1, 2.0,
14.7 Hz, 1H, H-20), 3.77–3.85 (m, 2H, H-3, CHAHBOH),
4.06–4.14 (m, 2H, H-4, CHAHBOH), 5.29 (d, 1H, J¼3.7 Hz,
H-6). Acetate 27. [a]D22 +83.3 (c 0.5, CH2Cl2). IR (film):
1745, 1770 cmꢀ1. HRMS (ESI), m/z (M+Na)+, calcd for
C12H17O6NNa: 294.0948, found: 294.0953. 1H NMR
(500 MHz, C6D6) d: 1.19 (d, J¼7.5 Hz, 3H, CH3), 1.59, 1.67
(2s, 6H, 2Ac), 2.51 (ddd, J¼1.4, 3.0, 15.1 Hz, 1H, H-2), 2.86
(ddq, J¼1.4, 3.6, 7.5 Hz, 1H, H-7), 3.66 (dd, J¼4.9,
12.0 Hz, 1H, CHAHBOAc), 3.67 (dt, J¼1.3, 1.8, 15.1 Hz,
1H, H-20), 4.00 (m, 1H, H-4), 4.13 (dd, J¼7.7, 12.0 Hz, 1H,
CHAHBOAc), 4.25 (ddd, J¼1.8, 2.2, 3.0 Hz, 1H, H-3), 4.58
(d, J¼3.6 Hz, 1H, H-6).
H
H
H
N
H
N
O
O
O
i
OTr
OH
ii
O
Ph
O
O
H
17
61
H
H
N
H H
N
O
O
OTr
OTr
OAc
CO2Et
iii
O
O
O
62
63
˚
Scheme 7. (i) (a) Pd/C, H2; (b) TrCl, Py; (ii) PCC, MS 4 A, CH2Cl2, reflux;
and (iii) (a) KHMDS, NCCO2Et, toluene; (b) Ac2O, Py.
separately, an inhibition of b-lactamase was measured.16–19
Within studied series, all tested oxacephams showed low ac-
tivity of DD-peptidase. All tested compounds did not show
any significant activity as inhibitors of the b-lactamase either.
4.1.2. (3S,4R,6S,7R)-3-Hydroxy-4-hydroxymethyl-
7-methyl-5-oxa-cepham (35). Compound 34 was hydroge-
nated according to the procedure described above to afford
35 (85%). [a]2D2 ꢀ10.8 (c 0.5, CH2Cl2). IR (film): 1743,
3378 cmꢀ1
.
HRMS (ESI), m/z (M+H)+, calcd for
C8H15O4N: 188.0917, found: 188.0906. 1H NMR
(500 MHz, CDCl3) d: 1.20 (d, J¼7.5 Hz, 3H, CH3), 2.77
(ddd, J¼2.6, 9.7, 13.1 Hz, 1H, H-2), 3.36 (ddq, J¼1.7, 3.7,
7.5 Hz, 1H, H-7), 3.49 (m, 1H, CHAHBOH), 3.78 (m, 1H,
H-3), 3.91 (m, 2H, H-4, CHAHBOH), 4.11 (dd, J¼6.2,
13.1 Hz, H-20), 4.97 (d, J¼3.7 Hz, 1H, H-6). Acetate 36:
3. Conclusions
In summary, we have demonstrated that the [2+2]cyclo-
adducts of CSI to 2-O-allenyl-1,3-benzylidene-L-erythritol
are versatile intermediates for the preparation of a wide
range of 7-substituted-5-oxacephams and for the introduc-
tion of carboxylic function to the C-2 carbon atom. Except
the cycloaddition reaction that proceeded with a moderate
stereoselectivity, the other transformations offer high stereo-
selectivities, and therefore may provide substituents at C-7,
existing in many active b-lactam antibiotics.
[a]D22 ꢀ15.1 (c 0.1, CH2Cl2). IR (film): 1746, 1773 cmꢀ1
.
HRMS (ESI), m/z (M+Na)+, calcd for C12H17O6NNa:
294.0948, found: 294.0925. H NMR (500 MHz, C6D6) d:
1
1.08 (d, J¼7.5 Hz, 3H, CH3), 1.53, 1.61 (2s, 6H, 2Ac),
2.25 (ddd, J¼1.6, 9.5, 13.0 Hz, 1H, H-2), 2.79 (ddq, J¼1.6,
3.7, 7.5 Hz, 1H, H-7), 3.22 (ddd, J¼2.9, 4.6, 9.8 Hz, 1H,
H-4), 4.09 (dd, J¼2.9, 12.1 Hz, 1H, CHAHBOAc), 4.12 (dd,
J¼4.6, 12.1 Hz, 1H, CHAHBOAc), 4.17 (dd, J¼6.3,
13.0 Hz, 1H, H-20), 4.19 (d, J¼3.7 Hz, 1H, H-6), 4.66 (dt,
J¼6.4, 9.5, 9.8 Hz, 1H, H-3).
4.1.3. (3S,4R,6R,7R)-3-Acetoxy-4-(acetoxymethyl)-7-(10-
benzyl-10-methyl-ethyl)-5-oxa-cepham (38), (3S,4R,6R,7R)
and (3S,4R,6R,7S)-7-isopropyl-3-acetoxy-4-(10-acetoxy-
methyl)-5-oxa-cepham (39 and 40). To a stirring solution
4. Experimental
4.1. General remarks
Melting points were determined on a Koefler hot-stage appa-
ratus. NMR spectra were recorded using Bruker Avance 500
and Varian Mercury 400 instruments. IR spectra were

10932
T. T. Danh et al. / Tetrahedron 62 (2006) 10928–10936
of sodium (0.040 g, 1.7 mmol) in liquid ammonia (40 mL)
at 60 ꢁC, compound 17 (0.050 g, 0.166 mmol) in dry THF
(4 mL) was added dropwise. The temperature was maintained
for 40 min. Subsequently NH4Cl (0.5 g) was added and the
mixture was left until evaporation of ammonia. To the residue,
10 mL of water was added and the mixture was extracted with
AcOEt (3ꢃ20 mL). The extract was dried and evaporated. The
crude products were acetylated with Ac2O/pyridine mixture.
Standard workup and chromatographical separation using
hexane/AcOEt, 7:3 v/v as an eluent provided compound 38
(0.013 g, 20%) and a mixture 39/40 (0.017 g, 34%) in a ratio
of about 1.2:1, respectively.
7.19–7.29 (m, 5H, Ph). 13C NMR (CDCl3) d: 20.75, 21.00,
24.36, 25.23, 33.95, 39.62, 47.17, 60.92, 64.42, 69.01,
72.98, 75.61, 126.26, 127.87, 130.88, 137.45, 169.98,
170.34, 170.36.
Compounds 42 and 43, taken for the mixture. IR (film):
1732, 1772 cmꢀ1. HRMS (ESI), m/z (M+Na)+, calcd for
C14H21NO6Na: 322.1261, found: 322.1279. 1H NMR
(500 MHz, CDCl3) d: 42: 1.01 (d, J¼6.8, 3H, CH3), 1.06
(d, J¼6.7 Hz, 3H, CH3), 2.00 (m, 1H, CH–(CH3)2), 2.06
and 2.09 (2s, 6H, 2Ac), 2.77 (dd, J¼9.5, 13.0 Hz, 1H,
H-2), 2.96 (d, J¼6.7 Hz, 1H, H-7), 3.7 (m, 1H, H-4),
4.20 (dd, J¼2.4, 12.2 Hz, 1H, CHAHBOAc), 4.24 (m, 1H,
CHAHBOAc), 4.40 (dd, J¼6.4, 13.0 Hz, 1H, H-20), 4.72
(dt, J¼6.4, 9.5 Hz, 1H, H-3), 4.80 (s, 1H, H-6). 43: 0.95
(d, J¼6.5 Hz, 3H, CH3), 1.13 (d, J¼6.7 Hz, 3H, CH3),
2.06 and 2.08 (2s, 6H, 2 Ac), 2.15 (m, 1H, CH–(CH3)2),
2.75 (ddd, J¼1.6, 9.5, 13.0 Hz, 1H, H-2a), 2.94 (ddd,
J¼1.6, 3.6, 10.9 Hz, 1H, H-7), 3.75 (m, 1H, H-4), 4.23 (m,
2H, CH2OAc), 4.29 (dd, J¼6.4, 13.0 Hz, 1H, H-2b), 4.71
(m, 1H, H-3), 4.98 (d, J¼3.6 Hz, 1H, H-6).
Compound 38: [a]2D2 +44.2 (c 0.4, CH2Cl2). IR (film): 1745,
1769 cmꢀ1
.
HRMS (ESI), m/z (M+Na)+, calcd for
C21H27NO6Na: 412.1731, found: 412.1756. 1H NMR
(500 MHz, CDCl3) d: 0.97 and 1.03 (2s, 6H, 2CH3),
2.11 (s, 6H, 2Ac), 2.63 and 2.68 (2d, J¼13.2 Hz, 2H,
CH2Ph), 3.06 (s, 1H, H-7), 3.32 (dd, J¼3.51, 15.03 Hz,
1H, H-2), 3.87 (m, 1H, H-20), 4.20 (m, 1H, H-4), 4.25
(m, 1H, CHAHBOAc), 4.53 (dd, J¼6.12, 11.13 Hz, 1H,
CHAHBOAc), 4.70 (m, 1H, H-3), 4.95 (s, 1H, H-6), 7.18–
7.28 (m, 5H, Ph). 13C NMR (CDCl3) d: 20.76, 21.02,
24.35, 25.22, 33.95, 39.60, 47.14, 60.88, 64.39, 68.97,
72.96, 75.57, 126.25, 127.87, 128.32, 130.88, 137.43,
169.99, 170.36.
4.1.5. (2R,4aR,5aR,6R,9aS) and (2R,4aR,5aR,6S,9aS)-6-
Bromo-6-(10-hydroxy-10-methyl-ethyl)-2-phenyl-1,3,5-
trioxa-8-aza-cyclobuta[b]decalin-7-on (44). To a stirring
solution of 17 (0.040 g, 0.13 mmol) in water (0.01 mL,
0.55 mmol) and DMSO (5 mL) NBS (0.034 g, 0.19 mmol)
was added. Stirring was continued at room temperature for
12 h. Subsequently the mixture was poured into water
(10 mL) and extracted with Et2O (2ꢃ20 mL). Organic layer
was dried and evaporated. The residue was purified by chro-
matography using hexane/AcOEt, 1:1 v/v as an eluent to
afford 44 as a mixture of two diastereomers in a ratio of
about 10:1 (0.032 g, 62%). HRMS (ESI) taken for the mix-
ture, m/z (M+Na)+, calcd for C17H20BrNO5Na: 420.0417,
found: 420.0439. 1H NMR (500 MHz, CDCl3) d: the major
isomer: 1.42 and 1.54 (2s, 6H, 2CH3), 3.66 (dd, J¼7.2,
12.7 Hz, 1H, H-9), 3.78 (m, 2H, H-4, H-9a), 4.12 (m, 2H,
H-4a, H-90), 4.44 (dd, J¼2.1, 10.7 Hz, 1H, H-40), 5.31
(s, 1H, H-2), 5.55 (s, 1H, H-5a), 7.36–7.46 (m, 5H, Ph).
13C NMR (CDCl3) d: 26.27, 26.41, 41.82, 65.40, 68.74,
72.11, 73.97, 79.99, 80.26, 102.05, 126.14, 128.33,
128.39, 129.39, 136.64, 165.68.
Compounds 39 and 40, taken for the mixture. IR (film): 1745,
1769 cmꢀ1
.
HRMS (ESI), m/z (M+Na)+, calcd for
C14H21NO6Na: 322.1261, found: 322.1275. 1H NMR
(500 MHz, CDCl3) d: 39: 1.01 (d, J¼6.7 Hz, 3H, CH3),
1.06 (d, J¼6.7 Hz, 3H, CH3), 1.98 (m, 1H, CH–(CH3)2),
2.10 and 2.12 (2s, 6H, 2Ac), 2.98 (d, J¼6.7 Hz, 1H, H-7),
3.30 (dd, J¼3.4, 15.1 Hz, 1H, H-2), 3.86 (m, 1H, H-20),
4.22 (m, 1H, H-4), 4.30 (m, 1H, CHAHBOAc), 4.56 (dd,
J¼6.5, 11.2 Hz, 1H, CHAHBOAc), 4.70 (m, 1H, H-3), 4.95
(s, 1H, H-6). Compound 40: 0.96 (d, J¼6.6 Hz, 3H, CH3),
1.16 (d, J¼6.7 Hz, 3H, CH3), 2.10 and 2.11 (2s, 6H, 2Ac),
2.24 (m, 1H, CH–(CH3)2), 2.95 (ddd, J¼1.4, 3.5, 10.9 Hz,
1H, H-7), 3.30 (ddd, J¼1.4, 3.3, 15.0 Hz, 1H, H-2),
3.84 (m, 1H, H-20), 4.24 (m, 1H, H-4), 4.28 (dd, J¼5.5,
11.8 Hz, 1H, CHAHBOAc), 4.54 (dd, J¼6.7, 11.8 Hz, 1H,
CHAHBOAc), 4.70 (m, 1H, H-3), 5.18 (d, J¼3.5 Hz, 1H,
H-6).
4.1.6. (2R,4aR,5aR,6S,9aS) and (2R,4aR,5aR,6R,9aS)-6-
(10-Hydroxy-10-methyl-ethyl)-2-phenyl-1,3,5-trioxa-8-
aza-cyclobuta[b]decalin-7-on (45 and 46). A solution of
tri-n-butyltin hydride (0.37 mL, 0.14 mmol) and AIBN
(0.021 g, 0.16 mmol) in toluene (2 mL) was added to a hot
solution (95 ꢁC) of bromohydrins 44 (0.027 g, 0.07 mmol)
in toluene (3 mL). The stirring and temperature was main-
tained for additional 40 min. Subsequently the temperature
of the mixture was cooled to room temperature and the sol-
vent was evaporated. The residue was purified by chromato-
graphy using hexane/AcOEt, 1:1 v/v as an eluent to afford
a mixture of 45/46 in a ratio of about 4.4:1 (0.019 g, 85%).
IR (film): 1755, 3457 cmꢀ1. HRMS (ESI) taken for the
mixture, m/z (M+Na)+, calcd for C17H21NO5Na: 342.1312,
found: 342.1317. 1H NMR (500 MHz, CDCl3) d: major
component 45: 1.38 and 1.46 (2s, 6H, 2CH3), 3.23 (dd,
J¼1.9, 3.4 Hz, 1H, H-6), 3.59 (ddd, J¼1.9, 7.1, 12.0 Hz,
1H, H-9), 3.74 (dd, J¼8.7, 10.9 Hz, 1H, H-4), 3.76 (dd,
J¼9.5, 12.0 Hz, 1H, H-90), 4.05 (m, J¼4.9, 8.7, 9.5 Hz,
4.1.4. (3S,4R,6S,7S)-3-Acetoxy-4-(acetoxymethyl)-7-(10-
benzyl-10-methyl-ethyl)-5-oxa-cepham (41), (3S,4R,6S,7S)
and (3R,4R,6S,7R)-7-isopropyl-3-acetoxy-4-(10-acetoxy-
methyl)-5-oxa-cepham (42 and 43). Compound 41 (23%)
and a mixture 42/43 (32%) were obtained from compound
18 according to the procedure described for compounds
38–40.
Compound 41: [a]2D2 +36.4 (c 0.1, CH2Cl2). IR (film): 1746,
1765 cmꢀ1
.
HRMS (ESI), m/z (M+Na)+, calcd for
C21H27NO6Na: 412.1731, found: 412.1755. 1H NMR
(500 MHz, CDCl3) d: 0.98, 1.04 (2s, 6H, 2CH3), 2.17 (s,
6H, 2Ac), 2.61 and 2.73 (2d, J¼13.3 Hz, 2H, CH2Ph),
2.78 (dd, J¼9.5, 13.0 Hz, 1H, H-2a), 3.03 (s, 1H, H-7),
3.72 (ddd, J¼2.4, 5.1, 9.9 Hz, 1H, H-4), 4.19 (dd, J¼2.4,
12.2 Hz, 1H, CHAHBOAc), 4.25 (dd, J¼5.1, 12.2 Hz, 1H,
CHAHBOAc), 4.33 (dd, J¼6.3, 13.0 Hz, 1H, H-2b), 4.73
(dt, J¼6.5, 9.5, 9.9 Hz, 1H, H-3), 4.78 (s, 1H, H-6),

T. T. Danh et al. / Tetrahedron 62 (2006) 10928–10936
10933
1H, H-4a), 4.12 (dt, J¼7.1, 9.5, 9.5 Hz, 1H, H-9a), 4.34 (dd,
J¼4.9, 10.9 Hz, 1H, H-40), 5.37 (d, J¼3.4 Hz, 1H, H-5a),
5.55 (s, 1H, H-2), 7.36–7.45 (m, 5H, Ph). Compound 46 inter
alia: 1.34 and 1.40 (2s, 6H, 2CH3), 3.20 (s, 1H, H-6), 4.4
(dd, J¼5.0, 10.7 Hz, 1H, H-40), 5.24 (s, 1H, H-5a), 5.54 (s,
1H, H-2).
4.1.10. (3S,4R,6R,7R) and (3S,4R,6R,7S)-3-Benzoyloxy-4-
benzoyloxymethyl-7-hydroxy-7-(10-hydroxy-10-methyl-
ethyl)-5-oxa-cepham (51). Compound 47 (0.060 g,
0.18 mmol) in MeOH (10 mL) was treated with 10% Pd/C
(3 mg) and stirred under a hydrogen atmosphere for 2 h.
Subsequently the mixture was filtered and evaporated. The
residue was treated with BzCl/Py mixture. After standard
workup, compound 51 was obtained (0.063 g, 77%) in a ratio
6:1. IR (film): 3331, 1787, 1747, 1724 cmꢀ1. HRMS
(ESI), m/z (M+Na)+, calcd for C24H25NO8Na: 478.1472,
found: 478.1487. 1H NMR (500 MHz, CDCl3) major
isomer d: 1.33 and 1.45 (2s, 6H, 2CH3), 3.62 (dd, J¼3.3,
15.1 Hz, 1H, H-2), 4.00 (m, 1H, H-20), 4.60 (m, 2H, H-4,
CHAHBOBz), 4.80 (dd, J¼6.3, 12.0 Hz, 1H, CHAHBOBz),
5.08 (m, 1H, H-3), 5.28 (s, 1H, H-6), 7.19–8.02 (m, 10H,
2ꢃPh).
4.1.7. (2R,4aR,5aR,6S,9aS) and (2R,4aR,5aR,6R,9aS)-6-
Hydroxy-6-(10-hydroxy-10-methyl-ethyl)-2-phenyl-1,3,5-
trioxa-8-aza-cyclobuta[b]decalin-7-on (47). A solution of
17 (0.070 g, 0.23 mmol) in CH3CN (10 mL), CHCl3
(2 mL), and water (5 mL) was treated with NaIO4
(0.245 g, 1.15 mmol) and RuCl3$H2O (0.001 g). The stirring
was continued until disappearance of the substrate (TLC),
about 30 min. The mixture was treated with water (10 mL)
and extracted with AcOEt (3ꢃ20 mL). Organic layer was
dried and evaporated. The residue was purified by chromato-
graphy using hexane/AcOEt, 7:3 v/v as an eluent to afford 47
as a mixture of diastereoisomers in a ratio of about 2.8:1
(0.067 g, 87%). IR (film): 3293, 3222, 1755 cmꢀ1. HRMS
(ESI) taken for the mixture, m/z (M+Na)+, calcd for
C17H21NO6Na: 358.1261, found: 358.1271. 1H NMR
(500 MHz, CDCl3) d: major component: 3.63–3.82 (m,
3H, H-4, H-9, H-90), 3.92 (m, 1H, H-9a), 4.16 (m, 1H,
H-4a), 4.33 (dd, J¼5.0, 10.9 Hz, 1H, H-40), 5.15 (s, 1H,
H-2), 5.54 (s, 1H, H-5a), 7.34–7.46 (m, 5H, Ph). Minor
component inter alia: 4.43 (dd, J¼5.0, 10.9 Hz, 1H, H-4),
5.22 (s, 1H, H-2), 5.55 (s, 1H, H-5a).
4.1.11. (3S,4R,6S,7R) and (3S,4R,6S,7S)-3-Benzoyloxy-4-
benzoyloxymethyl-7-hydroxy-7-(10-hydroxy-10-methyl-
ethyl)-5-oxa-cepham (52). Compounds 52 (75%) in a ratio
2.1:1 were obtained from 48 according to the procedure
described for 51. IR (film): 1721, 1761, 3423, 3519 cmꢀ1
.
HRMS (ESI), m/z (M+Na)+, calcd for C24H25NO8Na:
478.1472, found: 478.1498. H NMR (500 MHz, CDCl3)
1
major isomer d: 1.35, 1.46 (2s, 6H, 2CH3), 3.08 (dd,
J¼9.5, 12.9 Hz, 1H, H-2), 4.26–4.34 (m, 1H, H-4), 4.53
(dd, J¼4.2, 12.3 Hz, 1H, CHAHBOBz), 4.56 (dd, J¼6.3,
12.3 Hz, 1H, CHAHBOBz), 4.67 (dd, J¼2.6, 12.9 Hz, 1H,
H-20), 5.10 (s, 1H, H-6), 5.18 (dt, J¼6.4, 9.5, 9.5 Hz, 1H,
H-3), 7.43–8.00 (m, 10H, 2ꢃPh).
4.1.8. (2R,4aR,5aS,6S,9aS) and (2R,4aR,5aS,6R,9aS)-6-
Hydroxy-6-(10-hydroxy-10-methyl-ethyl)-2-phenyl-1,3,5-
trioxa-8-aza-cyclobuta[b]decalin-7-on (48). Compound
48 (90%) in a ratio of about 4.5:1 was obtained from 18 fol-
lowing procedure described for 47. IR (film): 1756, 3220,
3292 cmꢀ1. HRMS (ESI), m/z, (M+Na)+, calcd for
C17H21NO6Na: 358.1261, found: 358.1271. 1H NMR
(500 MHz, CDCl3) major product d: 1.28 and 1.39 (2s,
6H, 2CH3), 3.04 (dd, J¼10.0, 12.6 Hz, 1H, H-9), 3.62
(ddd, J¼4.8, 9.1, 9.9 Hz, 1H, H-4a), 3.68–3.74 (m, 2H,
H-4, H-9a), 4.17 (dd, J¼5.7, 12.6 Hz, 1H, H-90), 4.30
(dd, J¼4.8, 10.7 Hz, 1H, H-40), 5.00 (s, 1H, H-2), 5.52
(s, 1H, H-5a), 7.18–7.38 (m, 5H, Ph).
4.1.12. (3S,4R,6R,7S)-3-Benzoyloxy-4-benzoyloxy-
methyl-7-hydroxy-5-oxa-cepham (54). A solution of com-
pound 51 (0.055 g, 0.12 mmol) in AcOEt (5 mL) was treated
with H5IO6 (0.027 g, 0.12 mmol) and stirred at room tem-
perature for 45 min. Subsequently the mixture was cooled
to ꢀ5 ꢁC and a solution of NaBH4 (0.01 g, 0.026 mmol) in
water (2 mL) was added. Stirring was continued for
30 min and then water (10 mL) was added and the mixture
was extracted with AcOEt (3ꢃ20 mL). Organic layer was
dried and evaporated. The residue was purified by chromato-
graphy using hexane/AcOEt, 3:2 v/v as an eluent to afford 54
(0.031 g, 65%). [a]2D2 +10.4 (c 0.2, CH2Cl2). IR (film): 1721,
1757, 3394 cmꢀ1. HRMS (ESI), m/z (M+Na)+, calcd for
C21H19NO7Na: 420.1054, found: 420.1072, 1H NMR
(500 MHz, CDCl3) d: 3.58 (m, 1H, H-2), 4.07 (m, 1H,
H-20), 4.63–4.70 (m, 2H, H-4, CHAHBOBz), 4.93–4.99
(m, 2H, H-7, CHAHBOBz), 5.13 (m, 1H, H-3), 5.44 (dd,
J¼3.2 Hz, 1H, H-6), 7.48–8.07 (m, 10H, 2ꢃPh). 13C NMR
(CDCl3) d: 39.55, 61.78, 65.59, 73.47, 74.80, 78.86,
128.56, 2ꢃ128.67, 128.97, 129.72, 129.92, 2ꢃ133.66,
165.57, 165.91, 172,39.
4.1.9. (2R,4aR,5aR,6S,9aS) and (2R,4aR,5aR,6R,9aS)-6-
Acetoxy-2-phenyl-1,3,5-trioxa-8-aza-cyclobuta[b]deca-
lin-7-on (50). A solution of 47 (0.065 g, 0.19 mmol) in
AcOEt (5 mL) was treated with H5IO6 (0.043 g,
0.19 mmol). Upon stirring at temperature 0–5 ꢁC, NaBH4
(0.01 g, 0.026 mmol) in water (2 mL) was added. After
20 min, 10 mL of water was added and the mixture was
extracted with AcOEt (3ꢃ20 mL). The extract was dried
and evaporated. The crude product was acetylated with
Ac2O/Py mixture to afford, after standard workup, com-
pound 50 in a ratio of about 5.5:1 (0.003 g, 5%). IR (film):
1755, 1782 cmꢀ1. HRMS (ESI), m/z (M+Na)+, calcd for
C16H17NO6Na: 342.0948, found: 342.0953. 1H NMR
(500 MHz, C6D6) major isomer (6S) d: 3.00 (ddd, J¼1.2,
7.6, 12.4 Hz, 1H, H-9), 3.32 (m, 1H, H-90), 3.44 (dd,
J¼9.9, 10.3 Hz, 1H, H-4), 3.80 (m, 2H, H-9a, H-4a), 4.19
(dd, J¼5.1, 10.3 Hz, 1H, H-40), 4.79 (d, J¼2.5 Hz, 1H,
H-5a), 5.25 (s, 1H, H-2), 5.31 (dd, J¼1.7, 2.5 Hz, 1H,
H-6), 7.27–7.62 (m, 5H, Ph). Minor isomer (6S) inter alia:
4.86 (s, 1H, H-5a), 5.19 (s, 1H, H-2), 5.54 (s, 1H, H-6).
4.1.13. (3S,4R,6R,7R)-7-Azido-3-benzoyloxy-4-benzoyl-
oxymethyl-5-oxa-cepham (55). Tf2O (0.047 g, 0.17 mmol)
was added to pyridine (2 mL) at ꢀ20 ꢁC under argon. After
5 min a solution of 54 (0.056 g, 0.14 mmol) in pyridine
(2 mL) was added and the mixture was left for 30 min.
Subsequently the solvent was removed under diminished
pressure. The residue was dissolved in DMF (10 mL),
treated with NaN3 (0.065 g, 1.0 mmol) and heated to 70 ꢁC
for 30 min until disappearance of the triflate (TLC). Subse-
quently, the mixture was cooled to room temperature, treated

10934
T. T. Danh et al. / Tetrahedron 62 (2006) 10928–10936
with water (20 mL) and extracted with AcOEt (3ꢃ20 mL).
Organic layer was dried and evaporated. The crude product
was purified by chromatographyusing hexane/AcOEt, 9:1 v/v
as an eluent to afford 55 (44 mg, 75%). [a]2D2 +69.4 (c 1.8,
CH2Cl2). IR (film): 1722, 1782, 2114 cmꢀ1. HRMS (ESI),
m/z (M+Na)+, calcd for C21H18N4O6Na: 445.1119, found:
4.1.17. (3S,4R,6S,7R)-7-Acetamino-3-benzoyloxy-4-ben-
zoyloxymethyl-5-oxa-cepham (60). Compound 60 was ob-
tained from 59 (92%) according to the procedure described
for 56. [a]2D2 +17.9 (c 0.4, CH2Cl2). IR (film): 1722, 1777,
3313 cmꢀ1
.
HRMS (ESI), m/z (M+Na)+, calcd for
C23H22N2O7Na: 461.1319, found: 461.1338. 1H NMR
(500 MHz, CDCl3) d: 2.02 (s, 3H, Ac), 3.08 (dd, J¼9.4,
13.0 Hz, 1H, H-2), 4.14 (ddd, J¼2.7, 5.4, 9.7 Hz, 1H, H-
4), 4.42 (dd, J¼5.4, 12.2 Hz, 1H, CHAHBOBz), 4.52 (dd,
J¼6.4, 13.0 Hz, 1H, H-20), 4.62 (d, J¼7.35 Hz, 1H, H-7),
4.66 (dd, J¼2.7, 12.2 Hz, 1H, CHAHBOBz), 5.07 (dt,
J¼6.4, 9.7, 1H, H-3), 5.24 (s, 1H, H-6), 5.20 (d, J¼7.4 Hz,
1H, NH), 7.34–8.05 (10H, m, 2ꢃPh). 13C NMR (CDCl3)
d: 22.78, 42.28, 63.33, 64.07, 64.32, 75.49, 84.04, 128.41,
128.58, 128.74, 129.47, 129.76, 129.79, 133.24, 133.72,
164.06, 164.93, 166.20, 170.64.
1
445.1133. H NMR (500 MHz, CDCl3) d: 3.65 (dd, J¼3.1,
15.0 Hz, 1H, H-2), 4.08 (m, 1H, H-20), 4.58 (s, 1H, H-7),
4.61 (m, 2H, H-4, CHAHBOBz), 4.86 (m, 1H, CHAHBOBz),
5.10 (m, 1H, H-3), 5.29 (s, 1H, H-6), 7.47–8.06 (m, 10H,
2ꢃPh). 13C NMR (CDCl3) d: 40.70, 60.02, 64.74, 72.39,
73.62, 79.65, 128.65, 128.73, 128.98, 128.99, 129.73,
129.82, 133.72, 133.74, 163.80, 165.48, 165.89.
4.1.14. (3S,4R,6R,7R)-7-Acetamino-3-benzoyloxy-4-
benzoyloxymethyl-5-oxa-cepham (56). Compound 55
(0.030 g, 0.07 mmol) and 5% Pd/C in AcOEt (10 mL)
were hydrogenated for 2 h. Subsequently the mixture was
filtered through Celite and evaporated. The residue was acet-
ylated with Ac2O/Py mixture. Subsequently the mixture was
evaporated and purified by chromatography using AcOEt to
afford 56 (0.028 g, 90%). [a]2D2 +38.6 (c 0.4, CH2Cl2). IR
4.1.18. (3S,4R,6R,7S)-7-Isopropyl-3-hydroxy-4-trityl-
oxymethyl-5-oxa-cepham (61). Compound 17 (0.13 g,
0.43 mmol) in MeOH (10 mL) was hydrogenated in the
presence of a catalytic amount of 10% Pd/C for 4 h. Subse-
quently the mixture was filtered and evaporated. The crude
product was treated with TrCl in pyridine at 70 ꢁC for 2 h.
After standard workup and chromatographical purification,
compound 61 was obtained (0.176 g, 90%). [a]2D2 +44.1
(c 0.4, CH2Cl2). IR (film): 1748, 3431 cmꢀ1. HRMS (ESI),
m/z (M+Na)+, calcd for C29H31NO4Na: 480.2145, found:
480.2154. 1H NMR (500 MHz, CDCl3) d: 0.97 (d, J¼
6.5 Hz, 3H, CH3), 1.15 (d, J¼6.7 Hz, 3H, CH3), 2.20 (m,
1H, CH(CH3)2), 2.86 (ddd, J¼1.4, 3.5, 11.3 Hz, 1H, H-7),
3.04 (dd, J¼1.4, 3.1, 14.1 Hz, 1H, H-2), 3.41 (dd, J¼6.4,
10.1 Hz, 1H, CHAHBOTr), 3.51 (dd, J¼5.6, 10.1 Hz, 1H,
CHAHBOTr), 3.64 (dt, J¼1.3, 14.1 Hz, 1H, H-20), 3.74 (m,
1H, H-3), 4.15 (m, 1H, H-4), 5.00 (d, J¼3.5 Hz, 1H, H-6),
7.27–7.44 (m, 15H, OTr).
(film): 1722, 1775, 3300 cmꢀ1
. HRMS (ESI), m/z
(M+Na)+, calcd for C23H22N2O7Na: 461.1319, found:
461.1341. 1H NMR (500 MHz, CDCl3) d: 2.04 (s, 3H,
Ac), 3.68 (dd, J¼3.2, 14.9 Hz, 1H, H-2), 4.08 (m, 1H,
H-20), 4.60 (m, 1H, H-4), 4.64 (m, 1H, CHAHBOBz), 4.82
(dd, J¼5.2, 11.0 Hz, 1H, CHAHBOBz), 4.86 (d, J¼7.6 Hz,
1H, H-7), 5.10 (m, 1H, H-3), 5.38 (s, 1H, H-6), 6.01 (d,
J¼7.6 Hz, 1H, NH), 7.46–8.05 (m, 10H, 2ꢃPh). 13C NMR
(CDCl3) d: 22.86, 40.62, 62.10, 64.99, 65.68, 73.40, 80.72,
128.60, 128.67, 2ꢃ129.08, 129.76, 129.85, 133.60, 133.65,
165.52, 165.64, 165.95, 170.20.
4.1.15. (3S,4R,6S,7R)-3-Benzoyloxy-4-benzoyloxy-
methyl-7-hydroxy-5-oxa-cepham (58). Compound 58
was obtained from the mixture 52 (74%) according to the
procedure described for 54. [a]2D2 +46.7 (c 3, CH2Cl2). IR
4.1.19. (3S,4R,6R,7S)-7-Isopropyl-3-oxo-4-trityloxy-
methyl-5-oxa-cepham (62). Compound 61 (0.1 g,
0.22 mmol) in CH2Cl2 (10 mL) was treated with PCC
(film): 1722, 1759, 3424 cmꢀ1 1H NMR (500 MHz,
.
˚
CDCl3) d: 3.03 (m, 1H, H-2), 4.27 (ddd, J¼2.7, 5.6,
9.8 Hz, 1H, H-4), 4.50 (m, 2H, CHAHBOBz, H-7), 4.69
(dd, J¼2.7, 12.2 Hz, 1H, CHAHBOBz), 4.93 (ddd, J¼1.2,
3.2, 11.8 Hz, 1H, H-20), 5.12 (dt, J¼6.3, 9.5, 9.8 Hz, 1H,
H-3), 5.14 (d, J¼3.2 Hz, 1H, H-6), 7.42–8.02 (m, 10H,
2ꢃPh). 13C NMR (CDCl3) d: 41.59, 63.37, 63.99, 75.17,
78.19, 79.48, 128.47, 128.59, 128.74, 129.4, 129.75,
129.81, 133.33, 133.74, 164.84, 166.22, 171.12.
(0.056 g, 0.26 mmol) and molecular sieves MS 4 A
(0.02 g). The reaction mixture was stirred under reflux until
disappearance of the substrate (4 h, TLC). Subsequently it
was filtered by Celite and concentrated. The residue was fil-
tered by chromatography using hexane/AcOEt, 7:3 v/v as an
eluent to afford 62 (0.09 g, 90%). [a]2D2 +77.13 (c 0.3,
CH2Cl2). IR (film): 1763, 1778 cmꢀ1. HRMS (ESI), m/z
(M+Na)+, calcd for C29H29NO4Na: 478.1989, found:
478.2009. 1H NMR (500 MHz, CDCl3) d: 0.99 (d, J¼
6.4 Hz, 3H, CH3), 1.18 (dd, J¼6.7 Hz, 3H, CH3), 2.55 (m,
1H, CH(CH3)2), 3.06 (ddd, J¼1.6, 3.5, 11.6 Hz, 1H, H-7),
3.56 (dd, J¼2.3, 10.4 Hz, 1H, CHAHBOTr), 3.69 (dd,
J¼4.7, 10.4 Hz, 1H, CHAHBOTr), 3.84 (dt, J¼1.6, 19.5 Hz,
1H, H-2), 4.41 (m, 1H, H-4), 4.47 (d, J¼19.5 Hz, 1H, H-
20), 5.74 (d, J¼3.5 Hz, 1H, H-6), 7.27–7.38 (m, 15H, OTr).
13C NMR (CDCl3) d: 20.49, 21.48, 24.51, 60.34, 62.33,
65.66, 77.52, 79.80, 87.78, 127.36, 128.00, 128.52, 143.08,
172.51, 201.37.
4.1.16. (3S,4R,6S,7R)-7-Azido-3-benzoyloxy-4-benzoyl-
oxymethyl-5-oxa-cepham (59). Compound 59 was ob-
tained from 58 (85%) according to the procedure
described for compound 55. [a]2D2 ꢀ15.43 (c 0.3, CH2Cl2).
IR (film): 1732, 1783, 2113 cmꢀ1. HRMS (ESI), m/z
(M+Na)+, calcd for C21H18N4O6Na: 445.1119, found:
445.1130. 1H NMR (500 MHz, CDCl3) d: 3.06 (dd, J¼9.4,
13.1 Hz, 1H, H-2), 4.16 (ddd, J¼2.6, 5.5, 9.8 Hz, 1H,
H-4), 4.41 (dd, J¼5.5, 12.3 Hz, 1H, CHAHBOBz), 4.53
(dd, J¼6.4, 13.1 Hz, 1H, H-20), 4.56 (s, 1H, H-7), 4.70
(dd, J¼2.6, 12.3 Hz, 1H, CHAHBOBz), 5.02 (s, 1H, H-6),
5.08 (dt, J¼6.4, 9.8, 1H, H-3), 7.42–8.02 (m, 10H, 2ꢃPh).
13C NMR (CDCl3) d: 42.37, 63.13, 63.70, 70.92, 75.62,
83.14, 128.40, 128.50, 128.56, 129.26, 129.68, 129.73,
133.284, 133.77, 161.94, 164.73, 166.00.
4.1.20. (4R,6R,7S)-3-Acetoxy-7-isopropyl-2-ethoxycar-
bonyl-4-trityloxymethyl-5-oxa-2-cephem (63). Com-
pound 62 (0.017 g, 0.038 mmol) in toluene (5 mL) at
ꢀ45 ꢁC under argon was treated with KHMDS
(0.045 mmol, 0.091 mL, 0.5 M in toluene). After 30 min

T. T. Danh et al. / Tetrahedron 62 (2006) 10928–10936
10935
ethyl cyanoformate (0.045 mmol, 0.004 mL) was added.
Stirring was continued for 30 min and then the solution
was treated with Ac2O (0.5 mL) in pyridine (5 mL) with cat-
alytic amount of DMAP. The mixture was stirred for 4 h at
room temperature and then brine (10 mL) was added. The
mixture was extracted with AcOEt (3ꢃ20 mL). The extract
was dried and evaporated. The residue was purified by chro-
matography using hexane/AcOEt, 95:5 v/v as an eluent to
afford 63 (0.012 g, 60%). [a]2D2 ꢀ54.3 (c 0.1, CH2Cl2). IR
(film): 1727, 1776 cmꢀ1. HRMS (ESI), m/z (M+Na)+, calcd
7.0 and 10 mL solution of oxacephams in methanol. The
samples were incubated for 30 min at 37 ꢁC. Then 30 mL
of nitrocephin and 430 mL, 0.1 M phosphate buffer pH 7.0
were added, and all the samples were incubated for 10 min
at 37 ꢁC. Absorption was measured at 482 nm.
The following oxacephams were tested for both activities:
17, 18, 56, and 63.
Acknowledgements
1
for C34H35NO7Na: 592.2306, found: 592.2329. H NMR
(500 MHz, CDCl3) d: 1.02 (d, J¼6.4, 3H, CH3), 1.14 (d,
J¼6.7 Hz, 3H, CH3), 1.32 (t, J¼7.1 Hz, 3H, OCH2CH3),
2.04 (s, 3H, OAc), 2.25 (m, 1H, CH(CH3)2), 3.10 (dd,
J¼3.9, 11.8 Hz, 1H, H-7), 3.31 (dd, J¼2.6, 10.6 Hz, 1H,
CHAHBOTr), 3.39 (dd, J¼4.7, 10.6 Hz, 1H, CHAHBOTr),
4.24 (dq, J¼10.7, 7.1 Hz, 1H, OCHAHBCH3), 4.34 (dq,
J¼10.8, 7.1 Hz, 1H, OCHAHBCH3), 4.59 (m, 1H, H-4),
5.44 (d, J¼3.9 Hz, 1H, H-6), 7.25–7.43 (15H, m, OTr). 13C
NMR (CDCl3) d: 14.07, 20.36, 20.46, 21.64, 24.20, 60.37,
61.43, 61.63, 63.57, 72.89, 76.19, 87.15, 119.49, 127.26,
127.93, 128.65, 143.26, 159.74, 167.32, 169.18.
This work was supported by the Ministry of Education and
Science, Grant PBZ-KBN-126/T09/08/2004.
Supplementary data
Supplementary data including spectral and analytical data
for compounds 21–25 and 31–34 are available on the www
under http://www.sciencedirect.com or from the authors.
Supplementary data associated with this article can be found
in the online version, at doi:10.1016/j.tet.2006.08.074.
4.1.21. Assay of DD-carboxypeptidase activity. The en-
zyme activity was measured as described previously.16,17
Samples for the assay of the DD-carboxypeptidase activity
consisted of 10 mL of DD-carboxypeptidase from Saccharo-
polyspora erythraea PZH TZ 64-575 (40 units/mg), 20 mL
of substrate solution containing 4.52 mg/mL Na,N3-diace-
tyl-L-lysyl-D-alanyl-D-alanine in 0.1 M phosphate buffer,
pH 8.0 and 10 mL of 0.1 M phosphate buffer, pH 8.0. Stan-
dard sample contained 20 mL of D-alanine in distilled water.
References and notes
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