Synthesis of penicillin N and isopenicillin N

Article abstract of DOI:10.1016/S0040-4020(00)00673-6

Enantiomeric 2-(N-allyloxycarbonyl)aminoadipic acid 1-allyl esters were obtained from the corresponding 2-(N-trityl)aminoadipic acid diallyl esters following selective hydrolysis of the allyl 6-ester group and subsequent exchange of the trityl group by the allyloxycarbonyl function. The resulting monoacids were used to acylate 6-aminopenicillanic acid allyl ester using a carbodiimide-mediated coupling. The products, the L- and D-isomers of 6-[6-(2-(N-allyloxycarbonyl) aminoadipyl)]aminopenicillanic acid diallyl ester were deprotected in one step by catalytic allyl transfer using tetrakis-(triphenylphosphine)palladium(0), to afford isopenicillin N and penicillin N, respectively. The presented straightforward route to penicillin N and isopenicillin N is uniquely compatible with the sensitive nature of the condensation products and gives entry to a new and high yielding procedure that is superior to existing approaches. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4020(00)00673-6

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 7601–7606
Synthesis of Penicillin N and Isopenicillin N
Rute Madeira Lau,a Jacques T. H. van Eupen,b Dick Schipper,a Godefridus I. Tesser,c
Jan Verweija and Erik de Vrooma,
*
aDSM Anti-Infectives, P.O. Box 1, 2600 MA Delft, The Netherlands
bSynthon B.V., Nijmegen, The Netherlands
cUniversity of Nijmegen, Nijmegen, The Netherlands
Received 7 April 2000; revised 12 July 2000; accepted 27 July 2000
Abstract—Enantiomeric 2-(N-allyloxycarbonyl)aminoadipic acid 1-allyl esters were obtained from the corresponding 2-(N-trityl)amino-
adipic acid diallyl esters following selective hydrolysis of the allyl 6-ester group and subsequent exchange of the trityl group by the
allyloxycarbonyl function. The resulting monoacids were used to acylate 6-aminopenicillanic acid allyl ester using a carbodiimide-mediated
coupling. The products, the l- and d-isomers of 6-[6-(2-(N-allyloxycarbonyl) aminoadipyl)]aminopenicillanic acid diallyl ester were
deprotected in one step by catalytic allyl transfer using tetrakis-(triphenylphosphine)palladium(0), to afford isopenicillin N and penicillin
N, respectively. The presented straightforward route to penicillin N and isopenicillin N is uniquely compatible with the sensitive nature of the
condensation products and gives entry to a new and high yielding procedure that is superior to existing approaches. ᭧ 2000 Elsevier Science
Ltd. All rights reserved.
Introduction
media.2 The method of choice seemed to be the application
of protecting groups of the benzyl-type which are removable
under neutral conditions, i.e. catalytic hydrogenolysis, and
is used in all previously described procedures. However, a
severe disadvantage of catalytic hydrogenolysis is the very
large amount of catalyst that is required to obtain complete
hydrogenolysis, which is due to catalyst poisoning effects of
the sulfur atom present in the penicillin nucleus.8 Moreover,
this phenomenon leads to a drastic reduction in yield due to
degradation of the penicillin nucleus. We reasoned that this
problem could be avoided by employing allyl-type protect-
ing groups9 that can be easily removed under neutral condi-
tions. A well-known procedure is catalytic allyl-transfer to a
suitable allyl acceptor, e.g. 5,5-dimethyl-1,3-cyclohexane-
dione (dimedone), offering an essentially neutral reaction
medium. The usual catalyst is tetrakis-(triphenylphos-
phine)palladium(0), which is readily soluble in the majority
of organic solvents. Since the central palladium atom is
protected by its ligands against complexation with thio-
compounds, it can catalyze allyl transfer even in sulfur-
containing solvents (e.g. dimethylsulfoxide).
Isopenicillin N (1b, Fig. 1) is an intermediate common to
the biosynthesis of penicillins and cephalosporins.1 In
cephalosporin producing organisms isopenicillin N is
converted to penicillin N (1a) by an enzyme referred to as
isopenicillin N/penicillin N epimerase. Small amounts of 1a
and 1b are of pivotal importance in laboratory studies
related to the biosynthesis of penicillins and cephalosporins
and play a central role in molecular pathway engineering
studies.
Several syntheses of these compounds have been published
during the last two decades.2–7 The choice of the protecting
groups in these syntheses is restricted due to the fact that 1a
and 1b are highly unstable in both acidic and alkaline
A further drawback of the currently recommended routes is
the absence of a general and simple route to 2-aminoadipic
acid 1-esters, suitable for condensation with the amino-
penicillanic acid moiety. The appropriately protected
aminoadipic acid derivatives are obtained from multi-step
sequences frequently including laborious chromatography
isolation procedures. Itoh10 developed a procedure in
which the 2-benzyloxycarbonylamino- and the 1-carboxylic
functions in benzyloxycarbonylaspartic and glutamic acids
Figure 1. Penicillin N (1a: R0ˆH, R00ˆNHϩ3 ) and isopenicillin N (1b:
R0ˆNHϩ3 , R00ˆH).
Keywords: allyl protection; 2-aminoadipic acid; catalytic allyl transfer;
isopenicillin N; penicillin N.
* Corresponding author. Tel.: ϩ31-15-2792993; fax: ϩ31-15-2793286;
e-mail: erik.vroom-de@dsm-group.com
0040–4020/00/$ - see front matter ᭧ 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(00)00673-6

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R. M. Lau et al. / Tetrahedron 56 (2000) 7601–7606
are protected simultaneously by formation of oxazolidine
derivatives, by reaction with paraformaldehyde under acidic
conditions, thereby leaving the 6-carboxylic group free for
further reaction. Lal and Kulkarni7 applied this method
successfully in the partial protection of 2-aminoadipic
acid, but they also had to face the slow rate of the final
hydrogenolysis. Allyl protection of the b-lactam nucleus
of our target molecules has already been reported by
Manhas et al., who published a convenient method for the
preparation of 6-aminopenicillanic acid (6-APA) allyl ester
4-toluenesulfonate.11 The required 2-aminoadipic acid
derivatives, however, have not yet been described.
2-aminoadipic acid was realized using transient protec-
tion12–14of the amino group with the triphenylmethyl (trityl)
function. It is well known that the trityl group deactivates
the 1-carboxylic function towards both hydrolysis and trans-
esterification.13 Thus, for the preparation of the desired
2-aminoadipic acid derivatives, the appropriate enantiomer
of the amino dicarboxylic acid 2 was esterified with allyl
alcohol and then tritylated using standard procedures.
Attempts to replace benzene by toluene in the esterification
reaction failed. It was noted that at the higher temperature of
the allyl alcohol–toluene azeotrope (92ЊC) some starting
material was converted into a cyclic six-membered amide
ring, a phenomenon that was not observed at the boiling
point of the allyl alcohol–benzene azeotrope (77ЊC).
Furthermore, a significant amount of allyl alcohol is with-
drawn from the reaction mixture in the allyl alcohol–
toluene azeotrope (50:50) compared to that of allyl alcohol–
benzene (17:83).
An alternative high yielding procedure for the preparation of
1a and 1b, using allyl protection of both the 1-carboxyl
group in the side chain and the carboxyl group of the peni-
cillin nucleus, and allyloxycarbonyl for protection of the
amino group, is presented in this paper (Scheme 1).
2-(N-Trityl)aminoadipic acid 1-allyl ester (4) was readily
obtained by alkaline hydrolysis in aqueous ethanol. It was
noted that unwanted formation of the 6-ethyl ester took
place as a function of the amount of water present in the
Results and Discussion
Discrimination between the two carboxylic acid functions in
Scheme 1. Synthesis of isopenicillin N (1b, Fig. 1) from l-2-aminoadipic acid and 6-aminopenicillanic acid using allyl type protective groups (the synthesis of
penicillin N encompasses the same steps, only us using d-2-aminoadipic acid as starting material).

R. M. Lau et al. / Tetrahedron 56 (2000) 7601–7606
7603
hydrolysis reaction. Addition of 10% of water appeared to
be the correct amount to suppress ethyl ester formation on
the one hand whilst maintaining solubility on the other. This
selective hydrolysis of Na-tritylaminodicarboxylic acid
diesters was further generalized with experiments to obtain
1-esters of aspartic and glutamic acid. In these experiments
(experimental details not given), it appeared that the a-ester
function of N-tritylaspartic acid diallyl ester was consider-
ably more susceptible towards base-catalyzed hydolysis
than those of N-tritylaminoadipic acid diallyl ester and
N-tritylglutamic acid diallyl ester. In our view, this phenom-
enon is due to anchimeric assistance by the b-carboxylate
function of aspartic acid, once it is liberated.
conditions that are incompatible with the maintenance of
the penicillin skeleton, its formation should be suppressed.
A good alternative to dimedone as a neutral allyl acceptor
may be N,N0-dimethylbarbituric acid16–18 (DMBS,
pKaˆ4.7), a compound that hardly possesses diketone char-
acter. The use of DMBS for this specific application is
currently under investigation.
Isolation of the end products 1 as lyophilized disodium salts
needs to be performed carefully by keeping temperatures
low and pH-values close to neutral or slightly acidic. By
nature, these penicillins are extremely susceptible towards
degradation, a process that can readily occur, e.g. during
NMR analysis.
Subsequent acid-catalyzed hydrolysis of the trityl group in 4
using acetic acid readily afforded 2-aminoadipic acid 1-allyl
ester (5).
Conclusion
Acylation with allyl succinimidyl carbonate gives the
required 2-(N-allyloxycarbonyl)aminoadipic acid 1-allyl
ester (6). For the l-isomer the sequence of steps from 4b
was performed in an excellent 76% yield. During the synth-
esis of the d-isomer an unexpected hydrolysis problem
forced us to purify extensively crude valuable 5a thereby
making a fair comparison of yields impossible. We noted
that this intermediate, upon prolonged storage at low
temperatures, slowly hydrolyzes to give aminoadipic acid
(approx. 0.05% hϪ1 at 0–5ЊC), a phenomenon which can be
easily circumvented by avoiding prolonged storage of
monoester 5a.
N-Tritylamino acid 1-esters behave as deactivated esters
while, simultaneously, remote ester functions in bivalent
ester molecules retain their normal reactivity13 (i.e. they
can selectively undergo hydrolysis or base-catalyzed trans-
esterification). Furthermore they resist base-induced race-
mization.14 These features provide a general route to
selectively protected 2-aminodicarboxylic acid esters and
are applied here successfully in a straightforward synthesis
of l- and d-2-(N-allyloxycarbonyl)aminoadipic acid 1-allyl
esters (6). The latter are used to acylate 6-aminopenicillanic
acid allyl ester resulting in the efficient formation of the two
fully protected penicillin N diastereoisomers. Removal of
the two allyl- and allyloxycarbonyl protecting groups can be
performed smoothly in one operation using catalytic allyl
transfer. During this process, the catalyst, tetrakis-(triphe-
nylphosphine)palladium(0), is not poisoned by thioethers, a
phenomenon that often occurs in b-lactam chemistry.
Activation with dicyclohexylcarbodiimide, DCC, was found
to be effective for acylation of the free amino function in
6-APA-allyl ester (8). The 4-nitrophenyl and 1-succinimidyl
esters of 6 were ineffective: even after prolonged reaction
times, only starting material was recovered. Thus, DCC
mediated coupling of 8 with the appropriate isomer of
aminoadipic acid derivative 6 afforded the fully protected
penicillin N (7a) and isopenicillin N (7b) in quantitative
yield as judged by TLC. Upon purification by flash chroma-
tography, a necessary step prior to the deprotection
sequence, the isolated yields of 7a and 7b were 66% and
68%, respectively. These yields may be considered good
since it is well known that silica gel chromatography of
hydrophobic b-lactam derivatives is a low yield purification
process (due to product degradation and irreversible attach-
ment to the column material).
Application of dimedone as the recommended allyl receptor
is to be further investigated, since this diketone can slowly
produce a very stable Schiff-base with the 2-amino group of
the aminoadipic moiety once it is released. Preliminary
experiments employing N,N0-dimethylbarbituric acid as
allyl acceptor have shown that this alternative for dimedone
leads to improved deprotection results.
The present route to penicillin N and isopenicillin N exploit-
ing allyl-type protecting groups combines an efficient
derivatization of the rare and expensive 2-aminoadipic
acid enantiomers to partially protected acids, ready for
acylation of the amino group of 6-aminopenicillanic acid
allyl ester, with effective deprotection compatible with the
sensitive nature of the two diastereoisomeric condensation
products affording the two scientifically highly interesting
and hitherto laboriously accessible compounds.
Removal of the three protective functions by allyl transfer to
dimedone was performed satisfactorily in THF. Although
the deprotection also occurs smoothly in dichloromethane,
this solvent should not be used in conjunction with penicil-
lin derivatives. It has been shown that minute amounts of
acid are formed during the deprotection reaction in
dichloromethane, which catalyze the complete hydrolysis
of the b-lactam ring if trace amounts of water are present
in the solvent.15 Dimedone (pKaˆ5.2) has been recom-
mended as a neutral nucleophile in allyl transfer reactions9
and has been applied here successfully. However, dimedone
can also react as a diketone to give a Schiff-base. Indeed, the
slow formation of this compound was, in some cases,
observed during our experiments. Since the Schiff base is
a stable by-product, which can only be hydrolyzed using
Experimental
General
Allyl alcohol, l- and d-2-aminoadipic acid, dimedone,
potassium hydrogen sulfate, tetrakis-(triphenylphosphine)-
˚
palladium(0), triethyl amine (stored on 3 A molecular
sieve), and trityl chloride were purchased from Aldrich.

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R. M. Lau et al. / Tetrahedron 56 (2000) 7601–7606
4-Dimethylaminopyridine (DMAP) was purchased from
Merck. Benzene, N,N0dicyclohexylcarbodiimide (DCC),
4-toluenesulfonic acid monohydrate, and the extra dry
quality solvents acetonitrile, CH2Cl2 and THF were
purchased from Acros Organics. Allylsuccinimidyl
carbonate was obtained as a low melting solid (mp 12ЊC)
by reacting 1-hydroxysuccinimide with allyl chloro-
formate19 and triethylamine (1 equiv.) in acetonitrile
(yield 92%). 6-APA-allyl ester 4-toluenesulfonate was
prepared according to a literature procedure.11
and triethylamine (18.5 ml, 132 mmol) was treated with
trityl chloride (17.0 g, 61 mmol). The reaction mixture
was left at room temperature for 4 h and concentrated in
vacuo. The residue was diluted with EtOAc (200 ml),
filtered and the filtrate washed with water, dried (Na2SO4)
and concentrated in vacuo. Column chromatography (silica-
60, 600 g, column л 50 mm, elution with EtOAc–hexane
1:4) gave a colorless syrup.
l-Isomer (3b): TLC, one spot Rfˆ0.35, EtOAc–hexane
(1:4); yield 26 g (86%); purity 83%; [a]2D2ˆϩ39.6 (cˆ1,
1
In extraction procedures, organic phases were dried solely
with Na2SO4 since magnesium ions derived from MgSO4,
often cause complications due to the formation of intract-
able complex salts.
CHCl3). H NMR (CDCl3): dˆ1.5–1.9 (m, 4H, H3ϩH4);
2.34 (t, Jˆ6.5 Hz, 2H, H5); 3.34 (m, 1H, H2); 3.9 (m, 2H,
CH2vCHCH2–); 4.7 (d, Jˆ5.8 Hz, 2H, CH2vCHCH2–);
5.0–5.5 (m, 4H, CH2vCHCH2–); 5.5–6.3 (m, 2H,
CH2vCHCH2–); 7.0–7.6 (m, 15H, Ph). 13C NMR
(CDCl3): dˆ20.7 (C-3); 33.9 (C-5); 35.1 (C-4); 55.6
(C-2); 64.8 (CH2vCHCH2–); 118.0 (CH2vCHCH2–);
118.2 (CH2vCHCH2–); 126.3, 127.7, 128.7 (Ph (tert));
131.7 (CH2vCHCH2–); 132.1 (CH2vCHCH2–); 145.8
(Ph (quat)); 172.6 and 174.3 (carboxyl carbons). m/z (%):
484.2 [Mϩ], calculated for C31H34NO4: 484.2488.
Thin layer chromatography was performed on pre-coated
silica plates (Merck Silicagel 60 F254); column chromato-
graphy was on silica (Lichroprep silica 60). Detection was
by UV-fluorescence and by spraying with MeOH/H2SO4
(4:1, v/v) for trityl derivatives, with ninhydrin for free
amines, or with chlorine–TDM20 for amines and N-acylated
compounds. Optical rotations were measured at room
temperature using a Perkin–Elmer 241 polarimeter. 1H
NMR and 13C NMR spectra were obtained using a Bruker
AM 360 spectrometer (TMS as internal standard) for solu-
tions in CDCl3 as the solvent. The 13C NMR spectra of 1
were recorded on a Bruker AM 300 NMR spectrometer (in
CDCl3).
d-Isomer (3a, using as starting material 5 g of 2): TLC one
spot, Rfˆ0.36, EtOAc–hexane (1:4); yield 10.4 g (69.5%);
purity 83%; [a]2D2ˆϪ39.7 (cˆ1, CHCl3). 1H NMR (CDCl3):
dˆ1.5–1.9 (m, 4H, H3ϩH4); 2.35 (t, Jˆ6.5 Hz, 2H, H5);
3.36 (m, 1H, H2); 4.09 (m, 2H, CH2vCHCH2–); 4.6 (d,
Jˆ5.8 Hz, 2H, CH2vCHCH2–); 5.1–5.4 (m, 4H,
CH2vCHCH2–); 5.5–6.0 (m, 2H, CH2vCHCH2–); 7.1–
7.6 (m, 15H, Ph). 13C NMR (CDCl3): dˆ20.65 (C-3);
33.90 (C-5); 35.1 (C-4); 55.6 (C-2); 64.87
(CH2vCHCH2–); 118.06 (CH2vCHCH2–); 118.24
(CH2vCHCH2–); 126.41, 127.79, 128.75 (Ph (tert));
131.76 (CH2vCHCH2–); 132.11 (CH2vCHCH2–);
145.81 (Ph (quat)); 172.65 and 174.31 (carboxyl carbons).
m/z (%): 484.3 [Mϩ], 506.4 [MϩNa], calculated for
C31H34NO4: 484.2488.
Quantitative 1H NMR experiments were performed in dupli-
cate at 600 MHz on a Bruker AMX 600 spectrometer. To an
accurately weighed quantity of 1 was added a known quan-
tity of internal standard (maleic acid, in phosphate buffer pH
6.4); the mixture was lyophilized and then dissolved in D2O.
Spectra were determined using 90Њ pulses (8.5 ms); the FID
was multiplied with an exponential function causing line-
broadening of 0.2 Hz. The integral of the H5 proton and the
internal standard were measured and the purity of 1 was
calculated. The accuracy of this absolute method is con-
sidered to be better than 0.5% according to validation
studies on similar compounds. Similar quantifications
were used for intermediate products.
2-(N-Trityl)aminoadipic acid 1-allyl ester (4). A stirred
solution of compound 3 (25.5 g, 52.1 mmol) in 125 ml
EtOH/water (9:1, v/v), maintained at 50ЊC, was treated
slowly with aqueous NaOH (1 M, 58 ml, 1.1 equiv.); the
mixture was left for 2 h at 50ЊC and was then concentrated
in vacuo and diluted with water (50 ml). The aqueous
concentrate was neutralized with acetic acid (1 M, 58 ml)
and the precipitated oil was taken up in CH2Cl2 (100 ml);
the aqueous layer was extracted with CH2Cl2 (2×25 ml) and
the combined organic phases were washed successively
with water (25 ml) and with a saturated NaCl solution
(2×25 ml). The organic phase was dried (Na2SO4), concen-
trated and dried in vacuo to remove residual CH2Cl2, to give
a sticky colorless syrup.
Low resolution molecular masses were obtained using
Liquid Secondary Ion Mass Spectroscopy (LSIMS), a
method that is particularly suitable for the measurement of
highly labile products, using an AMD 604 high field mass
spectrometer and were recorded on a Kratos Mach3 data
system.
2-(N-Trityl)aminoadipic acid diallyl ester (3). 2-Amino-
adipic acid (2, 10 g, 62 mmol) was heated under reflux in
freshly distilled allyl alcohol (100 ml), benzene (250 ml)
and 4-toluenesulfonic acid monohydrate (13 g, 68 mmol).
The distillate was collected in a Dean–Stark trap and heat-
ing was continued until formation of water ceased and TLC
indicated the absence of free aminoadipic acid (approx.
48 h). Volatile constituents were removed by concentration
in vacuo; the residue crystallized very slowly to give waxy,
low melting material of 2-aminoadipic acid diallyl ester
4-toluenesulfonate. A stirred,cooled (0ЊC) solution of this
material (25.2 g, 61 mmol) in CH2Cl2 extra-dry (200 ml)
l-Isomer (4b): TLC one spot, Rfˆ0.14, EtOAc–hexane
(1:4), Rfˆ0.7, EtOAc–hexane (1:1); yield 23 g (98%);
purity 80.5%; [a]D22ˆϩ35.05Њ (cˆ2, CH2Cl2). 1H NMR
(CDCl3): dˆ1.5–2.0 (4H, H3ϩH4); 2.36 (t, Jˆ6.9 Hz, 2H,
H5); 3.37 (t, Jˆ5.0 Hz,1H, H2); 3.8–4.25 (m, 2H,
CH2vCHCH2–); 5.10–5.25 (m, 3H, NH and
CH2vCHCH2–); 5.55–5.8 (m, 1H, CH2vCHCH2–); 7.0–
7.6 (m, 15H, Ph). m/z (%): 444.2 [Mϩ], calculated for
C28H30NO4: 444.2175.

R. M. Lau et al. / Tetrahedron 56 (2000) 7601–7606
7605
d-Isomer: (4a, using as starting material 10.4 g of 3):
TLC one spot, Rfˆ0.15, EtOAc–hexane (1:4); yield
10.1 g as crude extract (quantitative); [a]2D2ˆϪ30.2 (cˆ2,
CH2Cl2).
solution of compound 6 (4.6 g, 16.1 mmol) and 6-amino-
penicillanic acid allyl ester 4-toluenesulfonate (7.24 g,
16.9 mmol) in dry acetonitrile (150 ml), containing tri-
ethylamine (2.48 ml, 17.7 mmol) and a catalytic amount
of DMAP was treated with DCC (3.65 g, 17.7 mmol), set
aside at 4ЊC for 24 h and was then allowed to attain room
temperature gradually. The suspension was cooled again to
Ϫ20ЊC, filtered and the filtrate was evaporated in vacuo.
The solid residue was dissolved in pure anhydrous EtOAc
(30 ml), washed with ice-water (2×10 ml), ice-cold aqueous
0.05 M KHSO4 solution (5 ml), saturated NaHCO3 solution
(pH 7–8, 10 ml) and saturated NaCl solution (2×10 ml),
then dried (Na2SO4) and concentrated in vacuo. Column
chromatography (silica 60, EtOAc–hexane 2:1 v/v) of the
residue followed by evaporation of solvent gave the
expected compound as a white foam.
2-(N-Allyloxycarbonyl)aminoadipic acid 1-allyl ester (6).
A stirred solution of compound 4 (22.2 g, 50 mmol) in a
mixture of AcOH/water/2 M HCl (200 ml, 160:15:25
v/v/v) was heated to 60ЊC for 30 min and subsequently
cooled down to room temperature. The precipitated tri-
phenylmethanol was collected by filtration. Ether (150 ml)
and water (20 ml) were added to the filtrate. The two phases
were re-extracted, to remove triphenylmethanol completely;
the combined aqueous phases were concentrated in vacuo,
to yield pale yellow syrup of 2-aminoadipic acid 1-allyl
ester hydrochloride (5) which solidified. This product,
dissolved in a mixture of acetonitrile and water (60 ml,
4:1 v/v) was treated with triethylamine (6.2 ml, 44 mmol)
to give pH 9.3. Subsequently, a solution of allyl succini-
midyl carbonate (5.33 g, 26.8 mmol, 1.27 equiv.) in aceto-
nitrile (10 ml) was added, the apparent pH being controlled
with a pH-stat. The pH of the mixture decreased immedi-
ately and further triethylamine was added to restore the pH
to 9. The almost clear solution was filtered and concentrated
to remove organic solvent. Water (40 ml) was added and the
product was precipitated by the addition of a small excess of
1.5 M hydrochloric acid (20 ml), to give pH Ͻ2. The
decanted water phase was then extracted with ether
(4×20 ml) and the ether phases were combined with the
main product. The obtained extract of the crude product
was washed with 10% aqueous NaCl (3 times), dried
(Na2SO4) and concentrated in vacuo to leave clear syrup.
Protected isopenicillin N (7b): TLC Rfˆ0.65, EtOAc–
hexane (2:1); yield 6.6 g (68%); purity 56%; [a]2D0ˆϩ144
(cˆ1.5, CHCl3). IR (KBr): nˆ1780 cmϪ1 (b-lactam car-
0
1
00
bonyl). H NMR (CDCl3): dˆ1.52 (s, 3H, H2 ); 1.66 (s,
3H, H2 ); 1.74 (m, 2H, H11); 1.74–1.90 (m, 2H, H12);
2.29–2.34 (m, 2H, H10); 4.38 (m, 1H, H13); 4.44 (s, 1H,
H3); 4.58–4.67 (m, 6H, CH2vCHCH2–); 5.22–5.39 (m,
6H, CH2vCHCH2–); 5.40 (s, 1H, NH); 5.55 (d, 1H,,
Jˆ4.0 Hz, H5); 5.69 (d, 1H,, Jˆ4.0 Hz, H6); 5.91–5.92
(m, 3H, CH2vCHCH2–); 6.26 (s, 1H, NH). 13C NMR
(CDCl3): dˆ21.5 (C-11); 27.5 (C-20); 31.9 (C-200); 32.4
(C-12); 35.5 (C-10); 53.8 (C-13); 58.9 (C-6); 65.3 (C-2);
66.4, 66.5, 66.7 (CH2vCHCH2–); 68.4 (C-5); 70.9 (C-3);
118.3, 119.5, 120.3 (CH2vCHCH2–); 131.4, 132.9, 133.0
(CH2vCHCH2); 156.2 (allyloxycarbonyl); 167.7, 172.0,
172.2 (carboxyl carbons); 174.2 (C-7).
l-Isomer (6b): TLC Rfˆ0.8, BuOH–AcOH–water (4:1:1);
yield 12.9 g (90%); purity 75%; [a]2D0ˆϩ6.0 (cˆ1, CHCl3).
1H NMR (CDCl3): dˆ1.6–2.0 (m, 4H, H3ϩH4); 2.40 (m,
2H, H5); 4.40 (m, 1H, H2); 4.57ϩ4.65 (2×d, Jˆ5.4 Hz, 4H,
CH2vCHCH2–); 5.2–5.5 (m, 4H, CH2vCHCH2–); 5.85–
6.0 (m, 2H, CH2vCHCH2–); 6.1 (bs, 1H, NH). The acid
was crystallized as the dicyclohexylammonium salt by
dissolving the syrup in ether and adding dicyclohexylamine.
TLC two spots, Rfˆ0.8 (acid) and 0.57 (amine), BuOH–
AcOH–Water (4:1:1); mp 117.5ЊC; [a]2D0ˆϪ1.9 (cˆ1,
CHCl3). Anal. calcd for C25H42N2O6 (466.61): C 64.35, H
9.07, N 6.00. Found: C 63.93, H 8.85, N 5.90.
Protected penicillin N (7a): starting from 2.5 g of 6a: TLC
Rfˆ0.69, EtOAc–Hexane (2:1); yield 3.5 g (66%); purity
50%; [a]2D0ˆϩ87.8 (cˆ1.5, CH2Cl2). IR (KBr):
nˆ1780 cmϪ1 (b-lactam carbonyl).00 1H NMR (CDCl3):
0
dˆ1.52 (s, 3H, H2 ); 1.67 (s, 3H, H2 ); 1.72–1.90 (m, 2H,
H12); 1.76 (m, 2H, H11); 2.27–2.38 (m, 2H, H10); 4.39 (m,
1H, H13); 4.44 (s, 1H, H3); 4.57–4.67 (m, 6H,
CH2vCHCH2–); 5.08–5.44 (m, 6H, CH2vCHCH2–);
5.41 (s, 1H, NH); 5.55 (d, 1H,, Jˆ4.0 Hz, H5); 5.70 (d,
1H, Jˆ4.0 Hz, H6); 5.91–5.92 (m, 3H, CH2vCHCH2–);
6.34 (s, 1H, NH). 13C NMR (CDCl3): dˆ21.5 (C-11);
27.5 (C-20); 31.9 (C-200); 32.5 (C-12); 35.5 (C-10); 53.8
(C-13); 58.9 (C-6); 65.2 (C-2); 66.3, 66.6, 66.6
(CH2vCHCH2–); 68.5 (C-5); 70.9 (C-3); 118.3, 119.5,
d-Isomer (6a, using 3.63 g of crude 5a as starting material;
as explained in the text, this crude material contained d-2-
aminoadipic acid and was extensively purified by silicagel
chromatography using hexane–EtOAc (9:1) prior to further
reaction): TLC Rfˆ0.75, BuOH–AcOH–Water (4:1:1);
yield 2.6 g (approx. 50% based on crude 5a); purity 70%;
[a]2D0ˆϪ1.7 (cˆ1, CH2Cl2). 1H NMR (CDCl3): dˆ1.6–2.0
(m, 4H, H3ϩH4); 2.40 (m, 2H, H5); 4.37 (m, 1H, H2);
4.57ϩ4.65 (2×d, Jˆ5.4 Hz, 4H, CH2vCHCH2–); 5.15–
5.5 (m, 4H, CH2vCHCH2–); 5.68 (bs, 1H, NH); 5.85–6.0
(m, 2H, CH2vCHCH2–). 13C NMR (CDCl3): dˆ21.0
(C-4); 31.6 (C-3); 33.7 (C-5); 54.1 (C-2); 66.3
120.3
(CH2vCHCH2–);
131.4,
131.8,
132.9
(CH2vCHCH2); 156.4 (allyloxycarbonyl); 167.7, 172.1,
172.2 (carboxyl carbons); 174.2 (C-7).
(Iso)penicillin N disodium salt (1). To a stirred solution of
compound 7b (2.45 g, 4.7 mmol) in peroxide-free THF
(25 ml) and maintained under argon, dimedone (3.29 g,
23.5 mmol) and tetrakis-(triphenylphosphine)palladium(0)
(0.36 g, 0.3 mmol) were added. The solution was kept for
16 h at room temperature, during which time a precipitate
was gradually formed. The solid material was collected by
filtration, washed with THF (2×5 ml), dissolved in ice-cold
water (25 ml) and the pH was carefully adjusted to 7 by
addition of an aqueous solution of 10% NaHCO3 (w/w).
The solution was extracted with EtOAc (3×5 ml), the
(CH2vCHCH2–);
119.2
(CH2vCHCH2–);
131.9
(CH2vCHCH2–); 169.3 and 176.3 (carboxyl carbons).
6-[6-(2-(N-Allyloxycarbonyl)aminoadipyl)]aminopeni-
cillanic acid diallyl ester (7). A stirred, cooled (Ϫ20ЊC)

7606
R. M. Lau et al. / Tetrahedron 56 (2000) 7601–7606
3. Usher, J. J.; Loder, B.; Abraham, E. P. Biochem. J. 1975, 151,
729–739.
aqueous layer was decolorized with active charcoal and
subjected to lyophilization.
4. Baldwin, J. E.; Herchen, S. R.; Singh, P. D. Biochem. J. 1980,
186, 881–887.
5. Jensen, S. E.; Westlake, D. W. S.; Bowers, R. J.; Wolfe, S.
J. Antibiot. 1982, 35, 1351–1360.
6. Huffman, G. W. Org. Prep. Proc. 1988, 20, 497–503.
7. Lal, B.; Kulkarni, B. K. Indian . J. Chem. B 1991, 30, 230–232.
8. Stedman, R. J.; Swered, K.; Hoover, J. R. E. J. Med. Chem.
1964, 7, 117–119.
9. Kunz, H.; Unverzagt, C. Angew. Chem., Int. Ed. Engl. 1984, 96,
426–427.
10. Itoh, Z. Chem. Pharm. Bull. (Japan) 1969, 17, 1679–1684.
11. Manhas, M. S.; Gala, K.; Bari, S. S.; Bose, A. K. Synthesis
1983, 549–552.
12. Helferich, B.; Moog, L.; Ju¨nger, A. Ber. Dtsch. Chem. Ges.
1925, 58, 872–886.
13. Amiard, G.; Heymes, R. Bull. Soc. Chim. Fr. 1956, 97–101.
14. Barlos, K.; Papaioannou, D.; Patrianakou, S.; Tsegenidis, T.
Liebigs Ann. Chem. 1986, 1950–1955.
15. Personal communication of Professor Dr F. Albericio,
Barcelona, Spain.
Isopenicillin N sodium salt (1b). Yield 1.22 g (75%);
purity 82%; [a]2D0ˆϩ145 (cˆ0.5, H2O); IR (KBr)
1
nˆ1775 cmϪ1 (b-lactam carbonyl). H NMR (600 MHz,
0
00
D2O): dˆ1.52 (s, 3H, H2 ); 1.63 (s, 3H, H2 ); 1.73–1.92
(m, 4H, H11ϩH12); 2.40 (t, 2H, Jˆ6.4 Hz, H10); 3.73 (t,
1H, Jˆ6.0 Hz, H13); 4.24 (s, 1H, H3); 5.46 (d, 1H,
Jˆ4.0 Hz, H6); 5.56 (d, 1H, Jˆ4.0 Hz, H5). NMR chemical
shifts are in accordance with those published by Huffman.6
Chemical shifts, J-, and IR-values are in accordance with
those published by Vanderhaeghe et al.2
Penicillin N sodium salt (1a): starting from 0.46 g of 7a:
yield 0.16 g (43%); purity 72%; [a]2D0ˆϩ254 (cˆ0.5, H2O);
IR (KBr) nˆ1780 cmϪ1 (b-lactam carbonyl). 1H NMR
0
00
(600 MHz, D2O): dˆ1.52 (s, 3H, H2 ); 1.63 (s, 3H, H2 );
1.73–1.92 (m, 4H, H11ϩH12); 2.40 (t, 2H, Jˆ6.4 Hz, H10);
3.73 (t, 1H, Jˆ6.0 Hz, H13); 4.24 (s, 1H, H3); 5.46 (d, 1H,
Jˆ4.0 Hz, H6); 5.56 (d, 1H, Jˆ4.0 Hz, H5). NMR chemical
shifts are in accordance with those reported by Huffman.6
Chemical shifts, J-, and IR-values are in complete agree-
ment with those published by Vanderhaeghe et al.,2 Baldwin
et al.4 and Lal and Kulkarni.7
¨
16. Kunz, H.; Marz, J. Angew. Chem., Int. Ed. Engl. 1988, 100,
1424–1425.
´
17. Kimbonguila, M.; Merzouk, A.; Guibe, F.; Loffet, A. In:
Peptides 1994, Proceedings of the 23rd European Peptide
Symposium; Maia, H.L.S., Ed.; Escom: Leiden, 1995, pp 159–
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