Structure-based design of nonpeptidic thrombin inhibitors: Exploring the D-pocket and the oxyanion hole

Article abstract of DOI:10.1002/1522-2675(200205)85:5<1210::AID-HLCA1210>3.0.CO;2-T

Structure-activity relationships for new members of a class of nonpeptidic, low-molecular-weight inhibitors of thrombin, a key serine protease in the blood coagulation cascade, are described. These compounds, which originate from X-ray-structure-based design, feature a conformationally rigid, bi- or tricyclic core from which side chains diverge into the four major binding pockets (distal D, proximal P, recognition or specificity Sl, and oxyanion hole O) at the thrombin active site (Fig. 1). Phenylamidinium is the side chain of choice for the S1 pocket, while the most active inhibitors orient an i-Pr group into the P-pocket (Table 1). The key step in the synthesis of the inhibitors is the construction of the central bi- or tricyclic scaffold by 1,3-dipolar cycloaddition of an in situ prepared azomethine ylide and an N-substituted maleimide (Schemes 1-3, and 8-10). One series of compounds was designed to explore the binding features of the large hydrophobic D pocket. This pocket provides space for lipophilic residues as bulky as benzhydryl groups. A new strategy was developed, allowing introduction of these sterically demanding substituents very late in the synthesis (Schemes 5 and 6). Benzhydryl derivative (±)-2 was found to be the most selective member (K_i (trypsin)/K_i (thrombin) = 1200) of this class of nonpeptidic thrombin inhibitors, while the 'dipiperonyl' analog (±)-3 (K_i = 9 nM, 7.60-fold selectivity) displays the highest potency of all compounds prepared so far (Table 1). A second series of inhibitors features side chains designed to orient into the oxyanion hole and to undergo H-bonding with the backbone NH groups lining the catalytic site of the enzyme. Unfortunately, neither activity nor selectivity could be substantially improved by introduction of these substituents (Table 2), Presumably, the high degree of pre-organization and the rigidity of the tightly bound scaffolds prevents the new substituents from assuming a position that would allow favorable interactions in the oxyanion hole. However, the oxyanion hole and the S1' pocket next to it were found to be capable of accommodating quite large groups, which leaves much room for further exploration.

Full text of DOI:10.1002/1522-2675(200205)85:5<1210::AID-HLCA1210>3.0.CO;2-T

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Helvetica Chimica Acta Vol. 85 (2002)
Structure-Based Design of Nonpeptidic Thrombin Inhibitors: Exploring
the D-Pocket and the Oxyanion Hole
by Patrick Betschmann, Stefan Sahli, and FranÁois Diederich*
Laboratorium f¸r Organische Chemie der Eidgenˆssischen Technischen Hochschule, ETH-Hˆnggerberg, HCI,
CH-8093 Z¸rich
and Ulrike Obst
Pharma Division, Pr‰klinische Forschung, F. Hoffmann-La Roche AG, CH-4070 Basel
and Volker Gramlich
Laboratorium f¸r Kristallographie der Eidgenˆssischen Technischen Hochschule, ETH-Zentrum,
Sonneggstrasse 5, CH-8092 Z¸rich
Structure-activity relationships for new members of a class of nonpeptidic, low-molecular-weight inhibitors
of thrombin, a key serine protease in the blood coagulation cascade, are described. These compounds, which
originate from X-ray-structure-based design, feature a conformationally rigid, bi- or tricyclic core from which
side chains diverge into the four major binding pockets (distal D, proximal P, recognition or specificity S1, and
oxyanion hole O) at the thrombin active site (Fig. 1). Phenylamidinium is the side chain of choice for the S1
pocket, while the most active inhibitors orient an i-Pr group into the P-pocket (Table 1). The key step in the
synthesis of the inhibitors is the construction of the central bi- or tricyclic scaffold by 1,3-dipolar cycloaddition of
an in situ prepared azomethine ylide and an N-substituted maleimide (Schemes 1 3, and 8 10). One series of
compounds was designed to explore the binding features of the large hydrophobic D pocket. This pocket
provides space for lipophilic residues as bulky as benzhydryl groups. A new strategy was developed, allowing
introduction of these sterically demanding substituents very late in the synthesis (Schemes 5 and 6). Benzhydryl
derivative (Æ)-2 was found to be the most selective member (Ki (trypsin)/Ki (thrombin) ˆ 1200) of this class of
nonpeptidic thrombin inhibitors, while the −dipiperonyl× analog (Æ)-3 (Ki ˆ 9 nm, 7.60-fold selectivity) displays
the highest potency of all compounds prepared so far (Table 1). A second series of inhibitors features side chains
designed to orient into the oxyanion hole and to undergo H-bonding with the backbone NH groups lining the
catalytic site of the enzyme. Unfortunately, neither activity nor selectivity could be substantially improved by
introduction of these substituents (Table 2). Presumably, the high degree of pre-organization and the rigidity of
the tightly bound scaffolds prevents the new substituents from assuming a position that would allow favorable
interactions in the oxyanion hole. However, the oxyanion hole and the S1' pocket next to it were found to be
capable of accommodating quite large groups, which leaves much room for further exploration.
1. Introduction. Controlling the delicate balance of blood coagulation, which is
responsible for vital hemostasis on the one side, but for undesired formation of blood
clots within intact blood vessels (thrombosis) on the other, continues to be in the focus
of pharmaceutical research, since thrombotic disorders are among the major causes of
mortality in the developed world [1]. Thrombin is a trypsin-like serine protease and one
of the key enzymes regulating blood coagulation. It catalyzes the conversion of the
soluble blood constituent fibrinogen into insoluble and polymerizable fibrin and
activates platelet aggregation, as well as enzymes within the coagulation cascade [2].
X-Ray crystal structures of thrombin-inhibitor complexes show a fairly rigid protein

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with a number of well-defined binding pockets at the active site [3][4]. Not
surprisingly, the central position of thrombin as a target in the blood coagulation
process, the availability of structural information, and the rigidity of its active site have
led to a significant number of structure-based-inhibitor design programs [5 8].
Fig. 1 shows inhibitor (‡)-1 (Ki ˆ 7 nm, selectivity over trypsin Ki(trypsin)/
Ki(thrombin) ˆ 740) developed in our laboratory and its binding mode in the thrombin
active site according to an X-ray crystal structure of the protein complex [9][10]. The
thrombin active site features four pockets: The distal (D) pocket is a large hydrophobic
pocket that preferentially accommodates lipophilic residues such as aromatic rings; it is
occupied by a Phe side chain in the case of the natural substrate fibrinogen. The
proximal (P) pocket binds small hydrophobic residues; in the complex with fibrinogen,
this pocket is occupied by a Val side chain. The specificity pocket S1 features an Asp
carboxylate at the bottom and prefers incorporation of a positively charged group; the
natural substrate directs an Arg side chain into this pocket. Finally, the catalytic site
with the oxyanion hole (O), lined with H-bond donor centers, is another potential
pocket for occupation by parts of an inhibitor.
Fig. 1. Inhibitor (‡)-1 in the active site of thrombin [10]. D ˆ distal pocket, P ˆ proximal pocket, S1 ˆ specificity
pocket, O ˆ oxyanion hole.

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Here, we describe our efforts to improve binding potency and specificity of our class
of inhibitors (such as (‡)-1; Fig. 1) [9 11] through modification of the substituent
extending into the D-pocket and by anchoring new side chains to the central bi- and
tricyclic scaffolds for reaching into the oxyanion hole (for a preliminary communication
of parts of this work, see [12]; for some recent reports on thrombin inhibitors, see [13]).
2. Results and Discussion. 2.1. Optimization of the Substituent to Fill the D-Pocket.
2.1.1. Design. The majority of synthetic low-molecular-weight thrombin inhibitors fill
the large hydrophobic D-pocket with lipophilic residues, often Ph rings [5 8]. Quite a
few of them employ even larger aromatic residues as D-pocket substituents. Within a
series of peptidomimetic d-PheÀProÀArg-type inhibitors, it was discovered by
researchers at Merck that
a
change from d-Phe to d-diphenylalanine
(H2NÀCH(CHPh2)ÀCO2H) boosted the activity by as much as a factor of 160
(Fig. 2) [14]. Several other large lipophilic residues, even nonaromatic ones such as the
dicyclohexylmethyl group could be easily placed into the D-pocket as well [15][16].
Fig. 2. Thrombin inhibitors reported by the Merck group: increased activity upon changing from the benzyl to the
benzhydryl group
We had introduced the piperonyl (ˆ(1,3-benzodioxol-5-yl)methyl) group as a D-
pocket substituent in our inhibitors sich as (‡)-1. Expecting a similar increase in affinity
as reported in the Merck study, a second aromatic ring was to be introduced into our
systems. Therefore, we planned the synthesis of the N-benzhydryl derivative (Æ)-2 and,
for comparison purposes, N-benzyl-substituted (Æ)-3 (Fig. 3). The additional Ph ring
(a) in (Æ)-2 (Fig. 3) was predicted by computer modeling [17] to undergo aromatic
edge-to-face interactions with the indole ring of Trp60D, which was expected to
compensate for the loss of the H-bond between the piperonyl residue and Tyr60A in
(‡)-1. The second Ph ring (b) of the active enantiomer of (Æ)-2 was predicted to adopt
a location in the D-pocket similar to that of the piperonyl residue in (‡)-1. As a
difference, however, Ph ring b in (Æ)-2 was expected to undergo parallel p-p stacking
with the indole ring of Trp215, whereas the piperonyl residue in (‡)-1 prefers an edge-
to-face orientation [9][10]. Finally, the active enantiomer of compound (Æ)-4 combines
the recognition features of both piperonyl and diarylmethyl residues.
2.1.2. Synthesis. Synthesis of the N-benzyl-substituted inhibitor (Æ)-3 was accom-
plished according to the method used for (Æ)-1 [10]. N-Benzylmaleimide (5) [18] was
reacted in a 1,3-dipolar cycloaddition with the azomethine ylide [19], generated in situ

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Fig. 3. Large aromatic residues for filling the D-pocket at the thrombin active site. The active enantiomers of
compounds (Æ)-2, (Æ)-3, and (Æ)-4 are shown.
from l-proline (6) and 4-bromobenzaldehyde (7), to yield nearly equal amounts of the
desired endo-cycloadduct (Æ)-8a (42%) and the undesired exo-derivative (Æ)-8b (40%;
Scheme 1). Regio- and stereoselective reduction (Li[Et3BH], THF) of (Æ)-8a afforded
hydroxy lactam (Æ)-9, which was converted to sulfone (Æ)-10 [10]. Nucleophilic

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Scheme 1. Synthesis of the N-Benzylated Inhibitor (Æ)-3
a) MeCN, D, 7 h; 42% ((Æ)-8a), 40% ((Æ)-8b). b) Li[Et3BH], THF, À788, 30 min. c) 4-MeÀC6H4SO2H, CaCl2,
CH2Cl2, r.t., 5 d; 74% (from (Æ)-8a). d) (i-Pr)MgCl, ZnCl2, CH2Cl2, r.t., 23 h; 78%. e) CuCN, DMF, D, 10 h;
66%. f) 1. HCl (g), MeOH, CHCl3, 48, 3 d; 2. NH3, MeOH, 658, 3 h; 86%.
displacement of the arylsulfonyl group according to the protocol (ZnCl2/i-PrMgCl)
introduced by Ley and co-workers [20] gave under retention of configuration
isopropyl derivative (Æ)-11. Finally, bromide/nitrile exchange to (Æ)-12 and the Pinner
reaction [21] provided target compound (Æ)-3.
The synthesis of N-benzhydryl derivative (Æ)-2 was planned along a similar route
(Scheme 2). The preparation of the required dipolarophile, N-benzhydrylmaleimide
(13), required rather harsh conditions compared with the formation of derivatives with
less bulky N-substituents such as 5. Cycloaddition of 13 with the azomethine ylide
formed from l-proline (6) and 4-formylbenzonitrile (14) also turned out to be more
problematic than expected. For the first time in our thrombin-inhibitor project [9 11],
all four possible diastereoisomers (Æ)-15a d were formed in significant amounts

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during the cycloaddition. Apparently, the steric bulk of the benzhydryl group reduces
the reactivity of dipolarophile 13, slowing down the cycloaddition considerably and
allowing isomerization of the initially formed (E)-azomethine ylide [22] to the (Z)-
configured 1,3-dipole, from which the exo,cis and endo,cis-isomers, (Æ)-15b and (Æ)-
15c, respectively, arise (endo,exo refer to the orientation of the 4-cyanophenyl ring at
C(4) with respect to the bicyclic perhydropyrrolo[3,4-c]pyrrole scaffold, and cis,trans to
the position of this ring with respect to the configuration of C(8a) at the fusion of the
two pentagons in the perhydropyrrolizine bicycle; for numbering, see Scheme 2). In
cycloadditions with sterically less-hindered, highly reactive maleimides (such as 5;
Scheme 1), only the exo,trans- and endo,trans-diastereoisomers, resulting from addition
of the (E)-configured 1,3-dipole, are obtained.
Scheme 2. Cycloadditions with N-Benzhydrylmaleimide (13) and Synthesis of Inhibitor (Æ)-17
a) RˆCN: DMF, 808, 3.5 h. b) RˆBr: MeCN, D, 3.5 h. c) CuCN, DMF, D, 22 h; 45%. d) 1. HCl (g), MeOH,
CHCl3, 48, 2 d; 2. NH3, MeOH, 658, 6 h; 35%.

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Assignment of the correct relative configuration of the trans-isomers (Æ)-15a and
1
(Æ)-15d was possible through comparison with the H-NMR spectra of other pairs of
endo/exo-cycloadducts such as (Æ)-8a and (Æ)-8b. An X-ray crystal-structure analysis
(Fig. 4) of (Æ)-15c revealed its endo,cis-configuration; therefore, (Æ)-15b had to be the
exo,cis-diastereoisomer.
Fig. 4. X-Ray crystal structure of endo,cis-(Æ)-15c. Arbitrary numbering. Atomic displacement parameters
obtained at 293 K are drawn at the 50% probability level.
The use of 4-bromobenzaldehyde (7) instead of the benzonitrile 14 under
optimized cycloaddition conditions allowed suppression of the formation of the two
undesired isomers (Æ)-exo,cis-16b and (Æ)-endo,cis-16c (Scheme 2), which greatly
facilitated workup and purification. The desired endo,trans-diastereoisomer (Æ)-16d
was converted to carbonitrile (Æ)-15d and eventually to amidinium salt (Æ)-17.
Since preparation and purification of larger amounts of cycloadduct (Æ)-16d were
tedious and low-yielding, this route seemed impractical for the synthesis of target
molecule (Æ)-2, which would require several additional steps. Hence, it was decided to
replace proline (6) by achiral a-aminoisobutyric acid (18) as the amine component in
the azomethine ylide formation [10]. This would eliminate one stereogenic center in
the cycloadducts, while ultimately leading to bicyclic inhibitors close in potency to their
tricyclic congeners.
DMF had previously been used in the 1,3-dipolar cycloadditions since the desired
endo-cycloadduct was always formed preferentially in this solvent [10]. While the
reaction with N-benzhydrylmaleimide (13), a-aminoisobutyric acid (18), and 4-
formylbenzonitrile in this environment also yielded a mixture of endo ((Æ)-19a, 35%)
and exo ((Æ)-19b, 13%) cycloadducts, the corresponding conversion with 4-bromo-

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benzaldehyde (7) turned out to be exo-selective ((Æ)-endo-20a: 20% and (Æ)-exo-20b:
51%; Scheme 3). Fortunately, this selectivity could be reversed by using less polar and
higher-boiling solvents such as chlorobenzene, an observation that still warrants a good
explanation. Both endo-cycloadducts (Æ)-19a and (Æ)-20a were N-methylated under
Eschweiler-Clarke conditions [10][23] to yield (Æ)-21 and (Æ)-22, respectively. Finally,
carbonitrile (Æ)-21 was converted to the corresponding amidinium salt (Æ)-23.
Scheme 3. Synthesis of Inhibitor (Æ)-23
a) DMF, 808, 12 h; 35% ((Æ)-19a), 13% ((Æ)-19b). b) DMF, 808, 24 h; 20% ((Æ)-20a), 51% ((Æ)-20b). c) PhCl,
D, 24 h; 53% ((Æ)-20a), 12% ((Æ)-20b). d) RˆCN: HCHO, HCO2H, D, 12 h; 71% ((Æ)-21). e) HCHO,
HCO2H, D, 6 h; 87% ((Æ)-22). f) from ((Æ)-21): 1. HCl (g), MeOH, CHCl3, 48, 2 d; 2. NH3, MeOH, D, 6 h;
76%.
The relative configuration of (Æ)-endo-19a was confirmed by X-ray crystallography
(Fig. 5,a). In the crystal packing (Fig. 5,b), the major interactions among enantiomers
are both parallel-shifted p-p stacking as well as edge-to-face CÀH ¥¥¥ p interactions [24]
between their aromatic rings. Another notable short contact (3.47 ä) is observed
between the cyano N-atom and an aromatic benzhydryl CÀH group. Since this CÀH
group is orthogonal to the CꢀN bond, the contact is best viewed as a weak H-bond
to the p-system of the CN group [25]. The cyanophenyl moieties of two enantiomers
stack in an antiparallel way, thereby favorably compensating their local dipole
moments.
Reduction of (Æ)-22 was surprising in its unfavorable regioselectivity, as the major
product was the undesired constitutional isomer (Æ)-24 (55%), with the desired (Æ)-25

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Fig. 5. a) X-Ray crystal structure of carbonitrile (Æ)-19a. Arbitrary numbering. Atomic displacement
parameters obtained at 293 K are drawn at the 50% probability level. b) Crystal packing of (Æ)-19.
formed in only 31% yield (Scheme 4). Again, this was in sharp contrast to the reduction
of N-benzyl (Scheme 1) or N-piperonyl derivatives [10], which all yielded predom-
inately the desired regioisomer. The rather unexpected exo-orientation of the OH
group in hydroxy lactam (Æ)-25 was confirmed by X-ray crystallography (Fig. 6).

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Scheme 4. Introduction of the i-Pr Side Chain into (Æ)-22
a) Li[Et3BH], CH2Cl2, 08, 90 min; 55% ((Æ)-24), 31% ((Æ)-25). b) 1. Ac2O, 4-(dimethylamino)pyridine
(DMAP), r.t., 3 h; 2. i-PrMgCl, ZnCl2, CH2Cl2, r.t., 15 h; 9%.
Fig. 6. X-Ray crystal structure of hydroxy lactam (Æ)-25. Arbitrary numbering. Atomic displacement
parameters obtained at 293 K are drawn at the 50% probability level.

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The subsequent introduction of the Ts group or less bulky sulfonyl groups into (Æ)-
25 failed, apparently due to steric hindrance by the benzhydryl residue. The use of AcO
instead of sulfonyl as a leaving group for introducing the i-Pr side chain gave the desired
lactam (Æ)-26; however, in very low yield at best.
The harsh conditions required for the preparation of maleimide 13, the lack of
diasteroselectivity in the cycloaddition (Scheme 2), the wrong regioselectivity in the
imide reduction, and the failure to form the aryl sulfone from (Æ)-25 (Scheme 4) are
obviously due to the increased steric bulk of the benzhydryl compared with the benzyl
or piperonyl group. It was, therefore, decided to follow a different strategy to prepare
(Æ)-2. In this new route, the imide moiety in the tricyclic cycloadduct is N-protected,
then the i-Pr side chain is introduced, followed by N-deprotection and introduction of
the bulky benzhydryl residue late in the synthesis.
We chose the piperonyl group as N-protecting group, since the synthesis of the key
intermediate lactam (Æ)-27 had been established in our previous work [10]. Removal
of the piperonyl group, however, proved to be quite challenging. Among the many
published methods for N-dealkylating an amide or lactam [26], only the treatment with
molten phosphoric acid or benzylic oxidation with CrO3, followed by hydrolysis [27],
gave isolable quantities of the desired N-unsubstituted lactam (Æ)-28 (Scheme 5).
Successful N-re-alkylation of (Æ)-28 required considerable experimentation as well.
Deprotonation or activation of the lactam to improve its nucleophilicity in a
Scheme 5. Synthesis of Inhibitor (Æ)-2
a) 1. H3PO4, PhOH, 1508, 1 h; 2. aq. NaOH soln., D, 1 h; 32%. b) Ph2CHCl, AgOSO2CF3, CH2Cl2, sealed tube,
1008, 1 h; 65%. c) CuCN, DMF, D, 20 h; 40%. d) 1. HCl (g), MeOH, CHCl3, 48, 24 h; 2. NH3, MeOH, 658, 3.5 h;
42%.

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substitution reaction with benzhydryl bromide produced only trace amounts of (Æ)-29,
but the use of better electrophiles, such as diazodiphenylmethane and benzhydryl
triflate [28], gave higher yields of (Æ)-29 (Scheme 5). Bromide (Æ)-29 was then
converted to carbonitrile (Æ)-30 and, finally, to amidinium salt (Æ)-2.
The synthesis of inhibitor (Æ)-4 was performed according to a similar protocol
(Scheme 6). Lithiation of 5-bromo-2H-benzo[d][1,3]dioxole (31) and addition to
piperonal (32) gave the secondary alcohol 33, which was converted to chloride 34 [29].
N-Alkylation of (Æ)-28 with the triflate generated in situ from 34 provided lactam (Æ)-
35, which was transformed into nitrile (Æ)-36 and finally into target compound (Æ)-4.
Scheme 6. Synthesis of Inhibitor (Æ)-4
a) BuLi, À788, 15 min; 98%. b) HCl (g), Et2O, r.t., 2 h; 97%. c) AgOSO2CF3, CH2Cl2, sealed tube, 1008, 3 h;
44%. d) CuCN, DMF, D, 2 d; 52%; e) 1. HCl (g), MeOH, CHCl3, 48, 2 d; 2. NH3, MeOH, 658, 4 h; 54%.
2.1.3. Biological Activity. All newly synthesized inhibitors were tested for their
activity against thrombin, trypsin, and related enzymes (coagulation factors VIIa and
Xa). Their potency was compared with that of some of the previously described,
structurally related inhibitors (Æ)-37 (Æ)-39 and (Æ)-1 [10] (Table 1). In the series of
imides with a bicyclic scaffold, the benzhydryl derivative (Æ)-23 showed an inhibitory
potency similar to that of the piperonyl analog (Æ)-37. Assuming similar overall
enzyme-inhibitor binding geometries, the loss of the H-bond to Tyr60A (in the complex
of (Æ)-37) is fully compensated for by the interactions gained by inclusion of the second
Ph ring in the complex of (Æ)-23.
A comparison in the series of imides with a tricyclic scaffold ((Æ)-38, (Æ)-39, and
(Æ)-17) also shows that the introduction of the benzhydryl moiety is as profitable for
potency as the introduction of the piperonyl group. It is noteworthy, however, that
undesired inhibition of trypsin by the benzhydryl derivative (Æ)-17 is ca. six times
weaker than by (Æ)-39. This is an indicator for the predicted interactions (see
Sect. 2.1.1) between one of the Ph rings and the Tyr60A-Pro60B-Pro60C-Trp60D loop,
which is unique to thrombin. Compound (Æ)-17 is the most selective of all inhibitors
with a CˆO group occupying the P-pocket [10].
The same trend reappears in the tricyclic lactam series (Æ)-1 (Æ)-4. Although it is
slightly less active than the piperonyl reference (Æ)-1, the benzhydryl derivative (Æ)-2

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Table 1. Activities of Thrombin Inhibitors and Selectivities with Respect to Trypsin
Inhibitor
R
Ki [mm]
Selectivitya)
Thrombin
Trypsin
(Æ)-23
Ph2CH
Piperonyl
0.61
0.5
1.1
1.1
1.8
2.2
(Æ)-37b)
(Æ)-38b)
(Æ)-39b)
(Æ)-17
PhCH2
Piperonyl
Ph2CH
0.22
0.090.7
0.11
2.6
7.8
4.8
12
44
(Æ)-1b)
(Æ)-3
(Æ)-2
(Æ)-4
Piperonyl
PhCH2
Ph2CH
0.013
0.065
0.028
0.0097.0 0
9.9
25
35
760
380
1200
dipipc)
79
a) Ki(Trypsin)/Ki(Thrombin). b) From [10]. c) dipip ˆ

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is the most selective so far within this family of nonpeptidic thrombin inhibitors. Finally,
the −dipiperonyl× inhibitor (Æ)-4 displays only a very modest increase in activity and a
small decrease in selectivity (as compared with (Æ)-2). With its biological data
resembling those of the monopiperonyl derivative (Æ)-1, the second aryl ring seems
ineffective.
2.2. Reaching into the Oxyanion Hole. 2.2.1. Side Chains Attached to the Pyrrolidine
N-Atom. The negatively charged tetrahedral intermediates (and the corresponding
transition states) formed during thrombin-catalyzed fibrinogen cleavage are stabilized
by ionic H-bonding to NH residues of the peptidic enzyme backbone inside the so-
called oxyanion hole. Placing a suitable substituent, which is capable of H-bonding with
these groups, into this pocket could substantially increase binding strength of a
thrombin inhibitor. In choosing such a substituent, it was our clear objective to avoid
formation of a covalently binding inhibitor, which would contain an electrophilic
residue that is attacked by Ser195 of the catalytic triade (for examples of −covalent×
thrombin inhibitors, see [8][30 35].
In a first approach, side chains designed to reach the oxyanion hole were attached to
the pyrrolidine N-atom. The CˆO groups of nonactivated carboxylate (Æ)-37,
carboxylic acid (Æ)-38, and dione (Æ)-39 (Scheme 7) were to serve as H-bond
acceptors in the oxyanion hole. Cycloadduct (Æ)-40, originating from an azomethine
ylide generated from a-aminoisobutyric acid (18), was alkylated with glyoxylic acid in a
Leuckart-Wallach reaction [23], and the crude product was esterified with MeOH to
give ester (Æ)-41, which was converted to (Æ)-37 and, by hydrolysis, to (Æ)-38
(Scheme 7). Another Leuckart-Wallach reaction with phenylglyoxal afforded (Æ)-42
and, subsequently, target compound (Æ)-39.
Inhibitor (Æ)-43 with an ester side chain and, for comparison, (Æ)-44 were also
prepared, since the endo-Me group in (Æ)-37 (Æ)-39 was suspected to conflict
sterically with the indole ring of Trp60D [36]. Their syntheses started from cycloadduct
(Æ)-45 and proceeded in the usual way via (Æ)-46 and (Æ)-47, respectively.
Compared with (Æ)-48 [10], carboxylate (Æ)-37 was only slightly more active but
significantly more selective for thrombin over trypsin (Table 2). The corresponding
carboxylic acid (Æ)-38 and dione (Æ)-39, however, were bound much more weakly.
Unfavorable complexation-induced desolvation of the carboxy group in (Æ)-38 and
steric hindrance of the Ph group in bound (Æ)-39 are possible reasons for the loss of
activity. The removal of the endo-Me group in inhibitors (Æ)-43 and (Æ)-44 did not
provide much advantage in potency over the corresponding geminal dimethyl
derivatives (Æ)-48 and (Æ)-37, respectively. However, both inhibitors (Æ)-43 and (Æ)-
44 were significantly more selective than (Æ)-37 and (Æ)-48, respectively, which was
rather unexpected.
It can be concluded from these biological results that the chosen N-substituents do
not significantly benefit from new interactions within the oxyanion hole.
2.2.2. Side Chains Attached to the C(1)-Atom of the Octahydropyrrolo[3,4-c]pyrrole
Scaffold. Molecular-modeling examinations indicated that the C(1)-atom of the
octahydropyrrolo[3,4-c]pyrrole scaffold (for numbering, see Fig. 7) in our family of
inhibitors would be another possible point of attachment for oxyanion-hole-binding
substituents, such as propionate (in (Æ)-49) and hydroxamate (in (Æ)-50) (Table 2).
Fig. 7 depicts the binding mode predicted for the active enantiomer of hydroxamic acid

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Helvetica Chimica Acta Vol. 85 (2002)
Scheme 7. Synthesis of Inhibitors with a Side Chain at the Pyrrolidine N-Atom
a) 1). HCOCO2H, HCO2H, D, 1 d; 2. MeOH, cat. H2SO4, D, 2 d; 40% ((Æ)-41), 48% ((Æ)-46). b) HCOCOPh,
HCO2H, 1008, 10 h; 22% ((Æ)-42). c) 1. HCl (g), MeOH, CHCl3, 48, 24 h; 2. NH3, MeOH, 658, 3.5 h; 75% ((Æ)-
37); 97% ((Æ)-39); 37% ((Æ)-43); 56% ((Æ)-44). d) 3n HCl, D, 17 h; 36%. e) HCHO, HCO2H, D, 20 h; 9 1%
((Æ)-47).
(Æ)-50. The modeling suggested for the hydroxamic acid residue of (Æ)-50 to interact
with both the NH group of Gly193 and the CˆO group of Leu41. For the carboxy
residue of (Æ)-49, both H-bonding to the NH group of Gly193 in the oxyanion hole and
ion pairing with the side chain of Lys60F were predicted. Obviously, a compound such
as (Æ)-50 would hardly be a selective serine protease inhibitor, since hydroxamic acids
are well-known metalloprotease inhibitors [37], but our objective was primarily to
verify binding predictions based on modeling in an isolated in vitro test.
Our initial synthetic strategy towards inhibitors (Æ)-49 and (Æ)-50 started with the
1,3-dipolar cycloaddition between N-piperonylmaleimide (51) and the azomethine
ylide formed from l-glutamine (52) and 4-formylbenzonitrile (14) to yield the desired
bicyclic central scaffold. Its exo-propionamide side chain would be transformed into the
desired carboxylic and hydroxamic acid residues afterwards. However, only one
diastereoisomer of the desired cycloadduct (Æ)-53 was isolated in poor yield (5.1%)

Helvetica Chimica Acta Vol. 85 (2002)
1225
Table 2. Activities of Thrombin Inhibitors with Side Chains Designed to Reach into the Oxyanion Hole and
Selectivities with Respect to Trypsin
Inhibitor
R
Ki [mm]
Selectivitya)
Thrombin
Trypsin
(Æ)-48b)
(Æ)-37
(Æ)-38
(Æ)-39
Me
0.5
0.27
7.4
1.1
3.8
3.2
32
2.2
14
0.4
6.3
CH2COOMe
CH2COOH
COCH2Ph
5.1
(Æ)-44
(Æ)-43
Me
CH2COOMe
0.20
0.53
4.924.3
1936
(Æ)-49
(Æ)-58
(Æ)-50
(Æ)-59
OH
OMe
NHOH
NHOCH2Ph
18
57
3.2
7.2
11.6
4.5
0.17
0.43
0.57
1.2
5.0
2.6
a) Ki(Trypsin)/Ki(Thrombin). b) From [10].

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Helvetica Chimica Acta Vol. 85 (2002)
Fig. 7. Schematic representation of the expected interactions between thrombin and the active enantiomer of
hydroxamic acid (Æ)-50
with the major product fraction containing the four diastereoisomeric tricyclic lactams
(Æ)-54a d (total yield of 49.1%; Scheme 8). Although amide CˆO groups are poor
electrophiles, intramolecular attack by the secondary pyrrolidine N-atom had led to the
formation of five-ring lactams. These lactams were probably formed after and not
before the cycloaddition, since pyroglutamic acid, the intramolecular cyclization
product of l-glutamine (52), would not form an azomethine ylide with aldehyde 14.
Scheme 8. 1,3-Dipolar Cycloaddition with an Azomethine Ylide Formed from l-Glutamine
a) PhCl, D, 45 h.

Helvetica Chimica Acta Vol. 85 (2002)
1227
Fig. 8. X-Ray crystal structure of lactam (Æ)-54d. Arbitrary numbering. Atomic displacement parameters
obtained at 293 K are drawn at the 50% probability level.
The relative configurations of diastereoisomers (Æ)-54a d were assigned on the
1
basis of the 1D-NOE difference H-NMR spectra; these assignments were further
supported by the X-ray crystal structure of (Æ)-54d (Fig. 8). We decided not to proceed
any further with these lactams, since an earlier study [11] had shown that N-acetylated
pyrrolidine inhibitors of this type display strongly reduced activity.
We finally succeeded in introducing the desired substituents by using l-glutamic
acid derivative 55 with the side-chain carboxy group protected as tert-butyl ester [38].
Steric hindrance by the bulky ester residue prevented intramolecular lactamization
effectively during the 1,3-dipolar cycloaddition. Under optimized conditions, cyclo-
adduct (Æ)-56 with the desired propionate side chain was obtained with a remarkable
endo,trans-selectivity and in good yield (56%; Scheme 9). N-Methylation of (Æ)-56
under Eschweiler-Clarke conditions also led to cleavage of the tert-butyl ester. The
intermediate was, therefore, re-esterified with MeOH to give (Æ)-57, and Pinner
reaction provided methyl propionate (Æ)-58. Hydrolysis gave the target carboxylic acid
(Æ)-49.
Attempts to prepare hydroxamic acid (Æ)-50 by reacting (Æ)-58 with hydroxyl-
amine hydrochloride [39] or by transforming the methyl ester into the Bn-protected
precursor (Æ)-59 failed. Fortunately, benzyloxy amide (Æ)-60 could be prepared at the
stage of the nitrile [40] and subsequently transformed into the amidinium salt (Æ)-59.
Catalytic hydrogenolysis of the O-Bn group finally afforded hydroxamic acid (Æ)-50
(Scheme 9) [37].
Biological studies showed propionic acid (Æ)-49 to be the weakest of the inhibitors
with the C(1) side chain (Table 2). A similar result had been obtained in the series of
inhibitors with side chains departing from the pyrrolidine N-atom ((Æ)-38). Probably,
no interaction in the oxyanion hole can compensate for the energy necessary to
desolvate the carboxylate.
Ester (Æ)-58 is slightly more active than hydroxamic acid (Æ)-50 or Bn-protected
(Æ)-59. Unfortunately, there is no supporting evidence that the side chain CˆO groups

1228
Helvetica Chimica Acta Vol. 85 (2002)
Scheme 9. Synthesis of Inhibitors (Æ)-49 and (Æ)-50
a) MeCN, 908, 16 h; 56%. b) 1. HCO2H, CH2O, 1008, 14 h; 2. MeOH, conc. H2SO4, D, 18 h; 76%. c) 1. HCl,
MeOH, CHCl3, 48, 24 h; 2. NH3, MeOH, 3 h, 658; 54% ((Æ)-58); 21% ((Æ)-59). d) KOH, MeOH, r.t., 24 h;
74%. e) NH2OH ¥ HCl, KOH, MeOH. f) Me3Al, BnONH2 ¥ HCl, CH2Cl2, r.t., 20 h, 24% ((Æ)-60). g) H2, Pd/C,
MeOH, r.t., 7 h; 99%.
of these compounds actually participate in the predicted H-bonding in the oxyanion
hole. It is possible that the conformational rigidity of the bicyclic scaffold prevents their
optimal positioning in this newly targeted pocket.
2.2.3. Side Chains Attached to the Tricyclic Scaffold: Preliminary Results. Molecular-
modeling studies indicated that a tetrazole ring, attached to the tricyclic scaffold in (Æ)-

Helvetica Chimica Acta Vol. 85 (2002)
1229
61, could favorably interact at the catalytic site of thrombin. As a precursor to (Æ)-61,
the tricyclic derivatives 62a and 62b were synthesized by 1,3-dipolar cycloaddition with
l-(4R)-hydroxyproline (63; Scheme 10) as the amine component to form the
azomethine ylide. The latter, formed in situ, is no longer CS-symmetrical, as in the
other cases reported in this study. With a C1-symmetrical azomethine ylide, no
racemates are formed in the cycloaddition, but up to eight different, optically active
diastereoisomers are possible.
The reaction was carried out in MeCN or DMF, leading to only three diastereoisom-
ers, including 62a and 62b (Scheme 10). The latter two could not yet be separated by
chromatography; they even crystallize together, forming a mixed crystal, whose
structure was solved by X-ray-analysis (Fig. 9,a). This behavior is reminiscent of
Scheme 10. Synthesis of the Two Diastereoisomers 62a and 62b
a) MeCN, 908, 28 h; 14% (62a), 14% (62b).

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Helvetica Chimica Acta Vol. 85 (2002)
Fig. 9. a) X-Ray crystal structure of hydroxy derivatives 62a and 62b. Arbitrary numbering. Atomic displace-
ment parameters obtained at 293 K are drawn at the 50% probability level. b) H-Bonding between two
diastereoisomers 62a and 62b in the crystal. c) View of the packing in the mixed crystal. Distances in ä.

Helvetica Chimica Acta Vol. 85 (2002)
1231
racemate formation by a pair of enantiomers, and we propose that the two
diastereoisomers 62a and 62b can be viewed as pseudoenantiomers. Pseudoenantio-
meric behavior is well-established for some members of the cinchona alkaloid family.
Thus, quinine and quinidine (or cinchonine and cinchonidine) are pairs of diaster-
eoisomers, but they usually behave like enantiomers when used as ligands in
asymmetric catalysis or as components of chiral stationary phases [41][42].
The crystal lattice shows pairwise alignment of the two diastereoisomers with a
short H-bond (O ¥¥¥ O distance: 2.74 ä) between their OH groups (Fig. 9,b). H-
Bonding between imide CˆO and OH groups, as well as parallel-shifted p-p stacking,
are additional intermolecular contacts seen in the crystal packing (Fig. 9,c). Con-
version of these compounds to the desired tetrazole is now in progress.
3. Conclusions. Consistent with literature reports, the D-pocket of the thrombin
active site is capable of accommodating very large, lipophilic groups, providing high
activity and selectivity (over trypsin; Table 1). Thus, the benzhydryl derivative (Æ)-2 is
the most selective member (Ki(trypsin)/Ki(thrombin) ˆ 1200) of our class of non-
peptidic thrombin inhibitors with a bicyclic or a tricyclic central scaffold, constructed by
1,3-dipolar cycloaddition of in situ prepared azomethine ylides to N-substituted
maleimides. Also, the −dipiperonyl× analog (Æ)-4 (Ki ˆ 9 nm, 760-fold selectivity) is the
most potent inhibitor in this class prepared so far. In contrast to the findings within a
series of peptidomimetic inhibitors reported by the Merck group (Fig. 2) [14], however,
we did not observe a dramatic increase in binding upon changing the D-pocket
substituent from a benzyl ((Æ)-3; Ki ˆ 65 nm) to a benzhydryl group ((Æ)-2; Ki ˆ
28 nm). Presumably, the rigid, phenylamidinium-substituted bi- and tricyclic central
scaffolds do not allow the benzhydryl group to adopt the most favorable binding mode
in the D-pocket. Additional, more in-depth exploration of the binding characteristics of
the D-pocket is clearly warranted. Our new approach, which allows incorporation of
the D-pocket substituent very late in the synthesis, should greatly facilitate such study.
Our first attempts to enhance binding potency and selectivity by directing a side
chain of the inhibitor into the oxyanion hole for H-bonding to the backbone NH groups
of the enzyme have not yet been very successful. The biological results (Table 2) do not
provide evidence for additional noncovalent interactions being picked up at this site.
Again, the high degree of preorganization and the rigidity of the central scaffold may
not allow the new side chains to assume a position required to undergo the predicted
interactions. However, the unexpectedly high residual activity of the large N-
benzyloxyamide (Æ)-59 (Ki ˆ 570 nm) indicates that the catalytic site and its
neighborhood, the S1'-pocket, are capable of accommodating quite large groups. This
also leaves room for further exploration, which we will continue with the synthesis of
tetrazole-substituted (Æ)-61.
Although we have experienced difficulties in successfully predicting and establish-
ing new host-guest interactions in the thrombin active site, we continue to recognize
structural information as a very useful piece of knowledge in guiding a medicinal-
chemistry project.
This work was supported by F. Hoffmann-La Roche AG. We thank David W. Banner and Allan D×Arcy for
protein X-ray crystallographic analyses and Heidi Hoffmann Maiocchi, Pascale Blond, and Thomas Tschopp for
the measurement of enzyme inhibitor constants. We also thank Holger Gohlke for his contributions towards the
design of some inhibitors described.

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Helvetica Chimica Acta Vol. 85 (2002)
Experimental Part
General. Solvents and reagents were reagent-grade, purchased from commercial suppliers, and used
without further purification unless otherwise stated. The following compounds were prepared according to
literature procedures: 5 [9][10], 4-toluenesulfinic acid [43], and (Æ)-27 [10]. THF and Et2O were freshly
distilled from sodium benzophenone ketyl, CH2Cl2 from CaH2. HCl Gas was dried with conc. H2SO4, NH3 gas
with KOH (s). Molecular sieves were activated at 10À2 Torr and 5008. Evaporation in vacuo was conducted at
H2O aspirator pressure. If not mentioned otherwise, all products were dried under high vacuum (10À2 Torr)
before anal. characterization. Column chromatography (CC): SiO2 60 (40 63 mm) from Fluka or Merck, 0
0.4 bar pressure. TLC: SiO2 60 F245, Merck, visualization by UV light at 245 nm. M.p.: B¸chi SMP 20 apparatus;
uncorrected. IR Spectra [cmÀ1]: Perkin-Elmer 1600-FT spectrometer. NMR spectra (1H, 13C, 19F, NOE): Varian
Gemini-200, Varian Gemini-300, and Bruker AMX-500, spectra were recorded at r.t. with solvent peak as
reference. In some 1H- and 13C-NMR spectra ((Æ)-2, (Æ)-4, (Æ)-16a, (Æ)-17, (Æ)-20b, (Æ)-21, (Æ)-23, (Æ)-30,
(Æ)-38, (Æ)-39, (Æ)-42, (Æ)-43, (Æ)-49, (Æ)-50, (Æ)-60, 62a, 62b), individual resonances overlap or are buried
under the solvent peak. MS (m/z (%)): FAB: VG-ZAB2-SEQ (3-nitrobenzyl alcohol matrix); EI, DEI: VG-
‡
TRIBRID at 70 eV; MALDI: IonSpec Ultima (2,5-dihydroxybenzoic acid (DHB) matrix); molecular ions (M )
reported for phenylamidinium salts refer to the corresponding phenylamidine derivatives. Elemental analyses
were performed by the Mikrolabor at the Laboratorium f¸r Organische Chemie, ETH-Z¸rich.
Determination of Inhibition Constants. The affinities of thrombin inhibitors were determined according to
[44][45] (chromogenic substrate S-2238). An exhaustive protocol of the binding assay identical to the one used
in this study is provided in [44].
General Procedure A for the 1,3-Dipolar Cycloaddition. A mixture of a-amino acid (1 mmol), 4-
formylbenzonitrile, or 4-bromobenzaldehyde (1 mmol), and N-substituted maleimide (1 mmol) in MeCN
(3 ml) was heated to 808 for 16 48 h. The solvent was evaporated in vacuo, and the residue was purified by CC
(AcOEt/Et3N 99 :1 or hexane/AcOEt/Et3N 59 :40 :1 or 33 :66 :1).
General Procedure B for the Eschweiler-Clarke Methylation. A mixture of cycloadduct (9mmol), 85% aq.
HCO2O soln. (100 mmol), and 35% aq. HCHO soln. (36 mmol) was heated to 1008 for 6 20 h. After cooling,
sat. aq. NaHCO3 soln. was added, and the mixture was extracted with CH2Cl2. The org. phase was dried
(Na2SO4) and evaporated, and the residue was purified by CC (hexane/AcOEt/Et3N 74 :25 :1 or 49.5 :49.5 :1).
General Procedure C for the Preparation of Amidinium Salts by the Pinner Reaction. Dry HCl was bubbled
at 08 for 10 min into a soln. of nitrile (2 mmol) in dry CHCl3 (5 ml) and dry MeOH (1 ml). The mixture was
stored at 48 for 24 h, then Et2O was added. The precipitate formed was isolated by filtration, dried in high
vacuum, and redissolved in MeOH (5 ml). A methanolic soln. of NH3 was slowly added until the NH3 odor
persisted; then the mixture was stirred for 3.5 h at 658. After cooling, NH4Cl was precipitated with acetone and
removed by filtration. The solvent was evaporated in vacuo, the residue was dissolved in EtOH, and the
amidinium salt was slowly precipitated with Et2O.
General Procedure D for the Conversion of an Aryl Bromide to the Corresponding Aryl Nitrile. A
suspension of the aryl bromide (1 mmol) and CuCN (5 mmol) in DMF (5 ml, purged with Ar) was heated to
reflux under Ar for 12 48 h. The solvent was partially removed, and CH2Cl2 and conc. aq. NH4OH soln. were
added. The mixture was stirred at r.t. for 1 h, the blue aq. phase removed, and the org. phase washed with conc.
aq. NH4OH soln. and H2O. The combined aq. phases were extracted with CH2Cl2. The combined org. phases
were dried (Na2SO4), the solvent removed in vacuo, and the resulting residue purified by CC (hexane/AcOEt/
Et3N 49.5 :49.5 :1 or 66 :33 :1 or CH2Cl2/Et3N 9 9 :1).
(3aSR,4RS,8aSR,8bRS)- and (3aSR,4SR,8aRS,8bRS)-4-(4-Bromophenyl)-2,3,3a,4,5,6,7,8,8a,8b-decahy-
dro-2-(phenylmethyl)-1H-pyrrolo[3,4-a]pyrrolizine-1,3-dione ((Æ)-8a and (Æ)8b, resp.). General Procedure A,
starting from 5, 6, and 7, gave endo- and exo-adducts ((Æ)-8a and (Æ)-8b, resp.) adducts after CC (CH2Cl2/Et3N
99 :1).
Data of (Æ)-8a: 42%. Colorless solid. M.p. 172 1758. IR (CHCl3): 3025, 3013, 2971, 1775, 1705, 1399, 1346,
1
1072, 1011. H-NMR (300 MHz, CDCl3): 1.61 1.82 (m, 2 H); 1.96 2.17 (m, 2 H); 2.58 2.67 (m, 1 H); 2.79
2.89( m, 1 H); 3.27 (d, J ˆ 8.1, 1 H); 3.46 (dd, J ˆ 8.1, 8.6, 1 H); 3.77 (dd, J ˆ 7.3, 9.8, 1 H); 4.01 (d, J ˆ 8.6, 1 H);
4.53 (s, 1 H); 4.54 (s, 1 H); 7.07, 7.34 (AA'BB', J ˆ 8.4, 4 H); 7.26 7.30 (m, 5 H). 13C-NMR (75 MHz, CDCl3):
23.4; 29.6; 42.6; 49.2; 50.6; 50.8; 68.0; 68.4; 121.8; 128.1; 128.8; 129.2; 130.0; 131.5; 136.0; 137.3; 175.4; 178.2.
‡
‡
‡
FAB-MS: 849.1 (2, M2H ), 425.0 (100, MH ), 237.0 (17), 90.8 (8, PhCH2 ). Anal. calc. for C22H21BrN2O2
(425.33): C 62.13, H 4.98, N 6.59, Br 18,79; found: C 62.00, H 5.05, N 6.59, Br 18.73.
Data of (Æ)-8b: 40%. Colorless crystals. M.p. 122 1248 (MeOH). IR (CHCl3): 2969, 1773, 1704, 1487, 1434,
1395, 1344, 1072, 1011. 1H-NMR (300 MHz, CDCl3): 1.50 1.60 (m, 1 H); 1.63 1.74 (m, 2 H); 1.88 1.9 7 (m, 1 H);

Helvetica Chimica Acta Vol. 85 (2002)
1233
2.37 2.46 (m, 1 H); 2.88 2.96 (m, 1 H); 3.29( dd, J ˆ 5.7, 9.1, 1 H); 3.52 (t, J ˆ 9.1, 1 H); 3.87 (m, 1 H); 4.05 (d,
J ˆ 5.7, 1 H); 4.65 (s, 2 H); 7.26 7.49( m, 9 H). 13C-NMR (75 MHz, CDCl3): 24.4; 26.3; 42.7; 48.0; 52.1; 55.6;
‡
66.5; 69.2; 121.5; 128.4; 128.9; 128.9; 129.3; 132.0; 135.7; 141.5; 176.9; 178.0. FAB-MS: 849.0 (10, M2H ), 425.1
‡
‡
(100, MH ), 237.0 (22), 90.8 (31, PhCH2 ). Anal. calc. for C22H21BrN2O2 (425.33): C 62.13, H 4.98, N 6.59,
Br 18.79; found: C 62.19, H 5.13, N 6.58, 18.65.
(1RS,3aSR,4RS,8aSR,8bRS)-4-(4-Bromophenyl)-2,3,3a,4,5,6,7,8,8a,8b-decahydro-1-[(4-methylphenyl)sul-
fonyl]-2-(phenylmethyl)-1H-pyrrolo[3,4-a]pyrrolizin-3-one ((Æ)-10). A 1m soln. of Li[Et3BH] in THF (240 ml,
240 mmol) was added to (Æ)-8a (59.54 g, 140 mmol) in dry THF (500 ml) at À788 under Ar. After 30 min, the
mixture was warmed to r.t., and sat. aq. NaHCO3 soln. was added. Extraction with CH2Cl2, drying of the org.
phase (MgSO4), and evaporation in vacuo gave crude hydroxy lactam (Æ)-9. A CH2Cl2 soln. containing (Æ)-9, 4-
toluenesulfinic acid (65.6 g, 420 mmol), and suspended H2O-free, powdered CaCl2 (46.6 g, 420 mmol) was
stirred at r.t. for 5 d. Sat. aq. NaHCO3 soln. was added, the extracted org. phase was washed several times with
sat. aq. NaHCO3 soln. and dried (Na2SO4), and the solvent was removed in vacuo. The crude sulfone (Æ)-10 was
purified by dissolution in a small amount of boiling AcOEt and subsequent precipitation. Redissolving in
CH2Cl2 and evaporation of the solvent in vacuo removed traces of AcOEt to yield (Æ)-10 (58.6 g, 74%).
Colorless solid. M.p. 186 1888. IR (CHCl3): 3018, 1712, 1487, 1400, 1318, 1303, 1135, 1082. 1H-NMR (300 MHz,
CDCl3): 1.53 1.71 (m, 2 H); 1.85 1.92 (m, 1 H); 1.94 2.05 (m, 1 H); 2.43 2.58 (m, 2 H); 2.48 (s, 3 H); 2.82
2.91 (m, 1 H); 2.96 2.99 (m, 1 H); 3.03 3.09( m, 1 H); 3.91 (d, J ˆ 6.5, 1 H); 4.08, 5.14 (AB, J ˆ 14.8, 2 H); 4.30
(s, 1 H); 7.16 7.24 (m, 4 H); 7.29 7.43 ( m, 7 H); 7.72 (d, J ˆ 8.1, 2 H). 13C-NMR (75 MHz, CDCl3): 21.9; 24.5;
31.8; 43.1; 45.2; 51.1; 51.9; 69.7; 71.3; 81.1; 121.1; 127.9; 128.5; 128.8; 129.4; 129.7; 130.5; 130.9; 132.3; 135.2; 137.2;
‡
146.2; 172.6. DEI-MS: 565.1 (0.2, MH ), 409.0 (18), 304.0 (25), 212.1 (52), 156.0 (20), 139.0 (40), 91.1 (100,
‡
PhCH2 ). Anal. calc. for C29H29BrN2O3S (565.53): C 61.59, H 5.17, N 4.95, S 5.67, Br 14.13; found: C 61.40,
H 5.31, N 4.99, S 5.77, Br 14.12.
(1RS,3aSR,4RS,8aSR,8bRS)-4-(4-Bromophenyl)-2,3,3a,4,5,6,7,8,8a,8b-decahydro-1-(1-methylethyl)-2-
(phenylmethyl)-1H-pyrrolo[3,4-a]pyrrolizin-3-one ((Æ)-11). (i-Pr)MgCl (89ml of 2 m soln. in THF/Et2O,
188 mmol) was added to a soln. of ZnCl2 (103 ml of 1m soln. in Et2O, 103 mmol) in dry CH2Cl2 (400 ml) under
Ar. After 30 min, a soln. of (Æ)-10 (53.29g, 94 mmol) in dry CH 2Cl2 (400 ml) was slowly added while cooling
with an ice bath. The mixture was stirred at r.t. for 23 h, then 1n HCl was added. After 15 min, the mixture was
neutralized with sat. aq. NaHCO3 soln. and extracted with CH2Cl2. The org. phase was dried (Na2SO4), the
solvent was removed, and the product was purified by CC (hexane/AcOEt/Et3N 66 :33 :1) to provide (Æ)-11
(33.19g, 78%). Colorless crystals. M.p. 135 138 8 (AcOEt). IR (CHCl3): 3007, 2964, 1675, 1486, 1441, 1071, 835.
1H-NMR (300 MHz, CDCl3): 0.71 (d, J ˆ 6.8, 3 H); 0.90 (d, J ˆ 7.2, 3 H); 1.51 1.67 (m, 1 H); 1.68 1.78
(m, 1 H); 1.89 2.01 ( m, 2 H); 2.03 2.14 (m, 1 H); 2.48 (dt, J ˆ 2.8, 8.6, 1 H); 2.58 2.66 (m, 1 H); 2.89 2.98
(m, 1 H); 3.23 3.25 (m, 2 H); 3.31 (dd, J ˆ 7.8, 8.6, 1 H); 3.79, 4.90 (AB, J ˆ 15.3, 2 H); 4.09( d, J ˆ 7.8, 1 H);
7.15 7.18 (m, 2 H); 7.24 7.35 (m, 3 H); 7.31, 7.44 (AA'BB', J ˆ 8.4, 4 H). 13C-NMR (75 MHz, CDCl3): 14.7;
18.5; 24.6; 28.0; 31.4; 41.5; 44.0; 52.5; 52.8; 67.3; 70.2; 73.2; 120.8; 127.3; 128.1; 128.5; 129.9; 130.9; 136.6; 138.8;
‡
‡
‡
172.5. FAB-MS: 905.4 (2, M2H ),453.2 (100, MH ), 297.2 (5), 237.1 (9), 90.8 (9, PhCH2 ). Anal. calc. for
C25H29BrN2O (453.43): C 66.22, H 6.45, N 6.18, Br 17.62; found: C 66.05, H 6.44, N 6.17, Br 17.63.
4-[(1RS,3aSR,4RS,8aSR,8bRS)-1-(1-Methylethyl)-2,3,3a,4,5,6,7,8,8a,8b-decahydro-3-oxo-2-(phenylmeth-
yl)-1H-pyrrolo[3,4-a]pyrrolizin-4-yl]benzonitrile ((Æ)-12). General Procedure D, starting from (Æ)-11, afforded
nitrile (Æ)-12 in 66% yield. Colorless crystals. M.p. 143 1468 (AcOEt). IR (CHCl3): 3010, 2966, 2230, 1677,
1
1440, 1241, 844. H-NMR (300 MHz, CDCl3): 0.72 (d, J ˆ 6.7, 3 H); 0.91 (d, J ˆ 7.0, 3 H); 1.54 1.64 (m, 1 H);
1.70 1.80 (m, 1 H); 1.89 2.03 ( m, 2 H); 2.09( dqq, J ˆ 3.4, 6.7, 7.0, 1 H); 2.49( dt, J ˆ 2.8, 8.4, 1 H); 2.54 2.63
(m, 1 H); 2.91 3.00 (m, 1 H); 3.22 3.29( m, 2 H); 3.35 (dd, J ˆ 7.8, 8.4, 1 H); 3.79, 4.88 (AB, J ˆ 14.9, 2 H);
4.16 (d, J ˆ 7.8, 1 H); 7.16 7.18 (m, 2 H); 7.25 7.36 (m, 3 H); 7.40, 7.60 (AA'BB', J ˆ 8.4, 4 H). 13C-NMR
(75 MHz, CDCl3): 14.9; 18.5; 24.7; 28.1; 31.5; 41.6; 44.0; 52.7; 53.1; 67.4; 70.7; 73.5; 110.8; 119.6; 127.6; 128.2;
‡
‡
128.8; 129.1; 131.8; 136.8; 146.1; 172.5. EI-MS: 799.2 (4, M2H ), 400.3 (100, MH ), 184.2 (46), 90.8 (38,
‡
PhCH2 ). Anal. calc. for C26H29N3O (399.54): C 78.16, H 7.32, N 10.52; found: C 78.12, H 7.41, N 10.46.
4-[(1RS,3aSR,4RS,8aSR,8bRS)-1-(1-Methylethyl)-2,3,3a,4,5,6,7,8,8a,8b-decahydro-3-oxo-2-(phenylmeth-
yl)-1H-pyrrolo[3,4-a]pyrrolizin-4-yl]benzamidine Hydrochloride ((Æ-3). General Procedure C, starting from
(Æ)-12, afforded (Æ)-3 in 86% yield. Orange solid. M.p. 190 1958. IR (CHCl3): 3281, 2967, 1672, 1614, 1493,
1
1448. H-NMR (300 MHz, (CD3)2SO): 0.66 (d, J ˆ 6.5, 3 H); 0.88 (d, J ˆ 6.9, 3 H); 1.55 1.70 (m, 2 H); 1.86
1.97 (m, 2 H); 2.06 2.11 (m, 1 H); 2.42 2.51 (m, 1 H); 2.55 (d, J ˆ 8.1, 1 H); 2.79 2.85 ( m, 1 H); 3.16 3.19
(m, 2 H); 3.35 3.41 (m, 1 H); 3.87, 4.63 (AB, J ˆ 14.9, 2 H); 4.20 (d, J ˆ 7.2, 1 H); 7.20 7.39( m, 5 H); 7.57, 7.78
(AA'BB', J ˆ 8.4, 4 H); 9.19 (br. s, 2 H), 9.37 (br. s, 2 H). 13C-NMR (125 MHz, (CD3)2SO): 14.5; 18.0; 24.2; 27.4;
30.6; 40.6; 42.8; 52.0; 52.2; 66.7; 69.6; 73.0; 125.5; 127.0; 127.1; 127.6; 128.4; 128.6; 136.9; 147.3; 165.4; 171.6. DEI-

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‡
‡
‡
MS: 416.3 (30, M ), 399.3 (17), 201.2 (49), 184.2 (100), 91.1 (23, PhCH2 ). HR-EI-MS: 416.2588 (M ,
C26H32N4O; calc. 416.2576).
1-(Diphenylmethyl)-2,5-dihydro-1H-pyrrole-2,5-dione (N-Benzhydrylmaleimide) (13). A soln. of benzhy-
drylamine (35.5 ml, 36.7 g, 200 mmol) in abs. Et2O (50 ml) was slowly added to a vigorously stirred, ice-cold
soln. of maleic anhydride (19.6 g, 200 mmol) in abs. Et2O (300 ml). The insoluble maleamic acid was filtered off,
repeatedly washed with Et2O, and dried. It was then dissolved in Ac2O (91.4 ml, 98.69 g, 965 mmol) together
with AcONa (13.34 g, 193 mmol) and stirred for 1 h at 1008. After cooling to r.t., H2O (300 ml) was added, and
the mixture was stirred for 12 h. The resulting precipitate was filtered off and purified by CC (CH2Cl2) to give 13
(22.37, 42%). Colorless crystals. M.p. 139 141 8 (MeOH) ([46]: 147 1518). 1H-NMR (300 MHz, CDCl3): 6.52
(s, 1 H); 6.71 (s, 2 H); 7.27 7.38 (m, 10 H). 13C-NMR (75 MHz, CDCl3): 57.8; 128.0; 128.7; 128.8; 134.5; 138.4;
170.7.
4-[(3aSR,4SR,8aRS,8bRS)-, (3aSR,4SR,8aSR,8bRS)-, (3aSR,4RS,8aRS,8bRS)-, and (3aSR,4R-
S,8aRS,8bRS)-2-(Diphenylmethyl)-2,3,3a,4,5,6,7,8,8a,8b-decahydro-1,3-dioxo-1H-pyrrolo[3,4-a]pyrrolizin-4-
yl]benzonitrile ((Æ)-15a 15d, resp.). General Procedure A, starting from 6, 13, and 14 in DMF as the solvent,
gave exo,trans-, exo,cis, endo,cis, and endo,trans adducts, (Æ)-15a (Æ15d, resp., after CC (hexane/AcOEt/Et3N
79:20 :1, then CH 2Cl2/Et3N 99 :1, then CH2Cl2/hexane/Et3N 79:20 :1).
Data of (Æ)-15a: 45%. Colorless oil. 1H-NMR (200 MHz, CDCl3): 1.52 1.76 (m, 3 H); 1.87 2.00 (m, 1 H);
2.36 2.49( m, 1 H); 2.92 3.04 (m, 1 H); 3.34 (dd, J ˆ 9.1, 5.4, 1 H); 3.57 (dd, J ˆ 9.1, 8.7, 1 H); 3.92 (m, 1 H);
‡
4.22 (d, J ˆ 5.4, 1 H); 6.57 (s, 1 H); 7.29 7.38 ( m, 10 H); 7.64 (s, 4 H). FAB-MS: 448.2 (100, MH ), 167.1 (71,
‡
PhCH2 ).
Data of (Æ)-15b: 3.7%. Colorless oil. 1H-NMR (200 MHz, CDCl3): 1.94 1.98 (m, 3 H); 2.17 2.31
(m, 2 H); 2.49 2.59( m, 1 H); 3.32 (dd, J ˆ 9.5, 7.1, 1 H); 3.54 (m, 1 H); 3.77 (dd, J ˆ 9.5, 8.3, 1 H); 4.29 (d, J ˆ
‡
8.3, 1 H); 6.52 (s, 1 H); 7.32 7.33 (m, 10 H); 7.66, 7.74 (AA'BB', J ˆ 8.3, 4 H). FAB-MS: 448.2 (100, MH ), 167.1
‡
(24, Ph2CH ), 149.0 (55).
Data of (Æ)-15c: 4.2%. Colorless crystals. 1H-NMR (300 MHz, CDCl3): 1.83 2.00 (m, 3 H); 2.04 2.14
(m, 1 H); 2.17 2.28 (m, 1 H); 2.82 (dt, J ˆ 8.4, 2.2, 1 H); 2.90 2.97 (m, 1 H); 3.14 3.18 (m, 1 H); 3.65 3.66
‡
(m, 2 H); 6.43 (s, 1 H); 7.13, 7.42 (AA'BB', J ˆ 8.4, 4 H); 7.26 7.36 (m, 10 H). FAB-MS: 448.2 (83, MH ), 391.2
‡
(100), 167.1 (43, Ph2CH ), 149.0 (55). X-Ray: see Fig. 4.
Data of (Æ)-15d: 11%. Colorless oil. IR (CHCl3): 3056, 2944, 2226, 1774, 1708, 1605, 1497, 1451, 1360, 1113,
1077. 1H-NMR (300 MHz, CDCl3): 1.61 1.88 (m, 2 H); 1.98 2.20 (m, 2 H); 2.59 2.67 ( m, 1 H); 2.89 2.98
(m, 1 H); 3.33 (d, J ˆ 8.2, 1 H); 3.55 (dd, J ˆ 8.6, 8.2, 1 H); 3.84 (dd, J ˆ 9.7, 7.5, 1 H); 4.13 (d, J ˆ 8.6, 1 H); 6.41
(s, 1 H); 7.21 7.34 (m, 12 H); 7.45 (d, J ˆ 8.4, 2 H). 13C-NMR (75 MHz, CDCl3): 23.5; 29.7; 49.0; 50.3; 51.0; 58.7;
68.4; 68.8; 111.6; 119.2; 128.0; 128.1; 128.5; 128.6; 128.6; 129.1; 129.3; 132.1; 137.5; 137.7; 143.8; 175.0; 177.9.
‡
‡
‡
FAB-MS: 448.2 (100, MH ), 167.1 (53, Ph2CH ). HR-FAB-MS: 448.2032 (MH , C29H25N3O2; calc. 448.2025).
An alternative synthesis of (Æ)-15d according to General Procedure D, starting from (Æ)-16d, afforded
nitrile (Æ)-15d in 45% yield.
(3aSR,4SR,8aRS,8bRS)- and (3aSR,4RS,8aRS,8bRS)-4-(4-Bromophenyl)-2,3,3a,4,5,6,7,8,8a,8b-decahy-
dro-2-(diphenylmethyl)-1H-pyrrolo[3,4-a]pyrrolizine-1,3-dione ((Æ)-16a and (Æ)-16d, resp.). General Proce-
dure A, starting from 6, 7, and 13, gave exo,trans- and endo,trans adducts, (Æ)-16a and (Æ)-16d, resp., after CC
(CH2Cl2/Et3N 9 9 :1).
Data of (Æ)-16a: 55%. Oil. IR (CHCl3): 2968, 1708, 1487, 1384, 1359, 1172, 1074, 1011. 1H-NMR (200 MHz,
CDCl3): 1.46 1.74 (m, 3 H); 1.85 1.97 (m, 1 H); 2.37 2.50 (m, 1 H); 2.89 3.04 ( m, 1 H); 3.35 (dd, J ˆ 9.1, 5.4,
1 H); 3.57 (dd, J ˆ 9.6, 8.7, 1 H); 3.85 3.97 (m, 1 H); 4.12 (d, J ˆ 5.0, 1 H); 6.56 (s, 1 H); 7.28 7.38 (m, 12 H);
7.45 7.50 (m, 2 H). 13C-NMR (75 MHz, CDCl3): 24.5; 26.2; 47.8; 52.2; 55.5; 58.8; 66.8; 69.4; 121.5; 128.2; 128.6;
‡
‡
128.7; 128.7; 128.9; 129.0; 131.9; 137.5; 141.5; 176.8; 177.9. FAB-MS: 501.1 (100, MH ), 167.1 (74, Ph2CH ). HR-
FAB-MS: 501.1185 (MH , C28H26N2O2; calc. 501.1178).
‡
Data of (Æ)-16d: 20%. Colorless crystals. M.p. 171 1738 (MeOH). IR (KBr): 2958, 1705, 1486, 1384, 1367,
1172, 1078, 1009, 698. 1H-NMR (300 MHz, CDCl3): 1.64 1.83 (m, 2 H); 1.99 2.14 (m, 2 H); 2.62 2.69
(m, 1 H); 2.86 2.95 (m, 1 H); 3.29( d, J ˆ 8.1, 1 H); 3.49( t, J ˆ 8.4, 1 H); 3.80 (m, 1 H); 4.04 (d, J ˆ 8.7, 1 H);
6.42 (s, 1 H); 7.11 (d, J ˆ 8.1, 2 H); 7.26 7.33 (m, 12 H). 13C-NMR (75 MHz, CDCl3): 23.4; 29.6; 49.0; 50.3; 50.9;
58.6; 68.3; 68.6; 121.7; 127.8; 128.0; 128.5; 128.5; 128.7; 129.3; 130.0; 131.5; 137.1; 137.7; 137.8; 175.2; 178.2. FAB-
‡
‡
‡
MS: 1001.0 (3, M2H ), 501.1 (100, MH ), 167.1 (56, Ph2CH ). Anal. calc. for C28H25BrN2O2 (501.43): C 67.07,
H 5.03, N 5.59, Br 15.94; found: C 67.03, H 5.11, N 5.60, Br 16.05.
4-[(3aSR,4RS,8aSR,8bRS)-2-(Diphenylmethyl)-2,3,3a,4,5,6,7,8,8a,8b-decohydro-1,3-dioxo-1H-pyrro-
lo[3,4-a]pyrrolizin-4-yl]benzamidine Hydrochloride ((Æ)-17). General Procedure C, starting from (Æ)-15d,
afforded amidinium salt (Æ)-17 after CC (CH2Cl2/MeOH 95 :5, 90 :10) in 35% yield. Yellowish solid. Dec.

Helvetica Chimica Acta Vol. 85 (2002)
1235
>1658. IR (CHCl3): 1708, 1676, 1588, 1366, 909. 1H-NMR (300 MHz, (CD3)2SO): 1.69 1.72 ( m, 2 H); 1.98
(m, 2 H); 2.66 2.84 (m, 2 H); 3.49 3.61 ( m, 2 H); 3.80 (t, J ˆ 8.4, 1 H); 4.25 (d, J ˆ 8.7, 1 H); 6.28 (s, 1 H);
7.13 7.19( m, 4 H); 7.29 7.39 ( m, 6 H); 7.43, 7.67 (AA'BB', J ˆ 8.4, 4 H); 8.99 (s, 4 H). 13C-NMR (125 MHz,
(CD3)SO): 23.0; 29.0; 48.3; 50.0; 50.4; 57.4; 67.5; 67.7; 126.6; 127.4; 127.5; 128.1; 128.1; 128.2; 128.4; 128.6; 137.6;
‡
‡
137.6; 145.3; 165.1; 175.2; 177.0. FAB-MS: 465.2 (100, MH ), 338.3 (38). HR-FAB-MS: 465.2285 (MH ,
C29H29N4O2; calc. 465.2291).
4-[(1RS,3aRS,6aSR)-5-(Diphenylmethyl)-1,2,3,3a,4,5,6,6a-octahydro-3,3-dimethyl-4,6-dioxopyrrolo[3,4-
c]pyrrol-1-yl]benzonitrile ((Æ)-19a). General Procedure A, starting from 13, 14, and 18 in DMF as the solvent,
yielded 35% of (Æ)-19a after CC (hexane/Et2O/Et3N 40 :59:1). Colorless crystals. M.p. 170 172 8 (MeOH). IR
(CHCl3): 3320, 2966, 2226, 1698, 1382, 1358, 871, 612. 1H-NMR (300 MHz, CDCl3): 1.39( s, 3 H); 1.46 (s, 3 H);
2.92 (d, J ˆ 7.8, 1 H); 3.45 (dd, J ˆ 7.8, 8.1, 1 H); 4.77 (d, J ˆ 8.1, 1 H); 6.40 (s, 1 H); 7.23 7.36 (m, 12 H); 7.44
7.47 (m, 2 H). 13C-NMR (75 MHz, CDCl3): 26.5; 28.4; 49.9; 53.4; 58.6; 60.6; 61.2; 111.7; 119.1; 128.0 (2Â); 128.4;
‡
‡
128.5; 128.6; 128.7; 129.2; 132.1; 137.6; 137.7; 144.1; 174.9; 176.0. FAB-MS: 871.6 (13, M2H ), 436.3 (100, MH ),
420.2 (26). Anal. calc. for C28H25N3O2 (435.53): C 77.22, H 5.79, N 9.65; found: C 77.21, H 5.68, N 9.60. X-Ray:
see Fig. 5. A small amount (13%) of the (1SR,3aRS,6aSR)-cycloadduct (Æ)-19b was also formed.
(3aRS,6RS,6aSR)- and (3aRS,6SR,6aSR)-6-(4-Bromophenyl)-2-(diphenylmethyl)-1,2,3,3a,4,5,6,6a-octahy-
dro-4,4-dimethylpyrrolo[3,4-c]pyrrole-1,3-dione ((Æ)-20a and (Æ)-20b, resp.). General Procedure A, starting
from 7, 13, and 18, was applied in PhCl as the solvent. Addition of MeOH to the crude isolated mixture of
diastereoisomers led to crystallization of the endo-isomer (Æ)-20a, which was purified by CC (Et2O/Et3N 9 9 :1).
The remaining exo-isomer (Æ)-20b was purified by CC (hexane/Et2O/Et3N 66 :33 :1).
Data of (Æ)-20a: 53%. Colorless crystals. M.p. 191 1938 (MeOH). IR (CHCl3): 2966, 1770, 1699, 1486,
1364, 1195, 1008, 699. 1H-NMR (200 MHz, CDCl3): 1.38 (s, 3 H); 1.45 (s, 3 H); 2.89( d, J ˆ 7.9, 1 H); 3.41
(dd, J ˆ 7.9, 7.9, 1 H); 4.71 (d, J ˆ 7.9, 1 H); 6.43 (s, 1 H); 7.11 (d, J ˆ 8.3, 2 H); 7.26 7.34 (m, 12 H). 13C-NMR
(125 MHz, CDCl3): 26.4; 28.7; 49.9; 53.5; 58.4; 60.3; 61.0; 121.5; 127.6; 127.7; 128.2; 128.3; 128.5; 129.0; 129.0;
‡
‡
131.2; 137.1; 137.5; 137.6; 174.8; 175.9. FAB-MS: 977.3 (2, M2H ), 489.2 (100, MH ), 391.3 (16), 167.1 (54,
‡
Ph2CH ). Anal. calc. for C27H25BrN2O2 (489.41): C 66.26, H 5.15, N 5.72, Br 16.33; found: C 66.15, H 5.15,
N 5.69, Br 16.42.
Data of (Æ)-21b: 12%. Colorless foam. M.p. 70 808 (MeOH). IR (CHCl3): 2965, 1771, 1704, 1488, 1355,
1
1170, 698. H-NMR (200 MHz, CDCl3): 1.03 (s, 3 H); 1.46 (s, 3 H); 3.16 (d, J ˆ 9.6, 1 H); 3.33 (dd, J ˆ 9.5, 6.6,
1 H); 4.51 (d, J ˆ 6.6, 1 H); 6.55 (s, 1 H); 7.33 7.46 (m, 14 H). 13C-NMR (125 MHz, CDCl3): 23.0; 30.5; 54.8;
55.7; 58.6; 61.5; 62.2; 121.3; 127.8; 127.9; 128.3; 128.3; 128.4; 128.5; 128.8; 131.6; 137.4; 141.0; 175.8; 177.4. FAB-
‡
MS: 489.1 (100, MH ), 338.3 (40), 289.1 (51). Anal. calc. for C27H25BrN2O2 (489.41): C 66.26, H 5.15, N 5.72,
Br 16.33; found: C 66.25, H 5.24, N 5.72, Br 16.23.
4-[(1RS,3aRS,6aSR)-5-(Diphenylmethyl)-1,2,3,3a,4,5,6,6a-octahydro-2,3,3-trimethyl-4,6-dioxopyrrolo[3,4-
c]pyrrol-1-yl]benzonitrile ((Æ)-21). General Procedure B, starting from (Æ)-19a, afforded tertiary amine (Æ)-21
in 71% yield. Colorless crystals. M.p. 219 222 8 (MeOH/Et2O). IR (KBr): 2974, 2225, 1768, 1701, 1364, 1191,
1172, 837, 700. 1H-NMR (200 MHz, CDCl3): 1.12 (s, 3 H); 1.48 (s, 3 H); 2.00 (s, 3 H); 2.94 (d, J ˆ 8.3, 1 H);
3.43 3.48 (m, 1 H); 4.00 (d, J ˆ 9.1, 1 H); 6.36 (s, 1 H); 7.11 7.36 (m, 14 H). 13C-NMR (75 MHz, CDCl3): 18.9;
24.4; 32.2; 48.3; 53.8; 58.6; 63.4; 68.8; 111.7; 119.1; 128.0; 128.1; 128.5; 128.7; 129.1; 129.5; 132.3; 137.6; 137.9;
‡
‡
143.6; 175.2; 176.1. DEI-MS: 449.2 (0.4, M ),434.2 (40), 167.1 (100, Ph2CH ). Anal. calc. for C29H27N3O2
(449.56): C 77.48, H 6.05, N 9.35; found: C 77.43, H 6.02, N 9.29.
(3aRS,6RS,6aSR)-6-(4-Bromophenyl)-2-(diphenylmethyl)-1,2,3,3a,4,5,6,6a-octahydro-4,4,5-trimethylpyr-
rolo[3,4-c]pyrrol-1,3-dione ((Æ)-22). General Procedure B, starting from (Æ)-20a, afforded tertiary amine (Æ)-
22 in 87% yield. Colorless crystals. M.p. 227 2318 (AcOEt). IR (KBr): 2969, 1692, 1602, 1484, 1365, 1190, 1006,
1
699. H-NMR (300 MHz, CDCl3): 1.10 (s, 3 H); 1.45 (s, 3 H); 1.9 8 (s, 3 H); 2.89( d, J ˆ 8.1, 1 H); 3.38 (dd, J ˆ
9.0, 8.1, 1 H); 3.91 (d, J ˆ 9.0, 1 H); 6.38 (s, 1 H); 6.92 (d, J ˆ 7.5, 2 H); 7.20 7.36 (m, 12 H). 13C-NMR (75 MHz,
CDCl3): 18.8; 24.5; 32.2; 48.3; 53.8; 58.5; 63.1; 68.6; 121.7; 127.9; 128.0; 128.5; 128.6; 128.7; 129.5; 130.0; 131.6;
‡
‡
136.9; 137.7; 138.0; 175.4; 176.3. EI-MS: 502.2 (1, M ), 487.1 (74), 167.2 (100, Ph2CH ). Anal. calc. for
C28H27BrN2O2 (503.44): C 66.80, H 5.41, N 5.56, Br 15.87; found: C 66.60, H 5.40, N 5.51, Br 15.99.
4-[(1RS,3aRS,6aSR)-5-(Diphenylmethyl)-1,2,3,3a,4,5,6,6a-octahydro-2,3,3-trimethyl-4,6-dioxopyrrolo[3,4-
c]pyrrol-1-yl]benzamidine Hydrochloride ((Æ)-23). General Procedure C, starting from (Æ)-21, afforded
amidinium salt (Æ)-23 in 76% yield. Yellowish solid. M.p. 200 2028. IR (KBr): 3059, 1705, 1491, 1359, 1194, 843,
700, 613. 1H-NMR (200 MHz, (CD3)2SO): 1.09( s, 3 H); 1.29( s, 3 H); 1.89( s, 3 H); 3.16 (d, J ˆ 7.9, 1 H); 3.63
3.71 (m, 1 H); 4.13 (d, J ˆ 8.7, 1 H); 6.26 (s, 1 H); 7.17 7.39( m, 12 H); 7.64 (d, J ˆ 7.9, 2 H); 9.20 (s, 2 H); 9.34
(s, 2 H). 13C-NMR (75 MHz, (CD3)2SO): 18.6; 24.2; 32.1; 48.0; 53.2; 56.0; 62.5; 67.8; 126.5; 127.5; 127.5; 128.1;

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Helvetica Chimica Acta Vol. 85 (2002)
‡
‡
128.1; 128.2; 128.5; 137.6; 137.7; 144.9; 165.2; 175.1; 179.9. FAB-MS: 933.5 (3, M2H ), 467.3 (100, MH ). HR-
FAB-MS: 467.2453 (MH , C29H31N4O2; calc. 467.2447).
‡
(3RS,3aRS,6RS,6aSR)-6-(4-Bromophenyl)-2-(diphenylmethyl)-1,2,3,3a,4,5,6,6a-octahydro-3-hydroxy-
4,4,5-trimethylpyrrolo[3,4-c]pyrrol-1-one ((Æ)-25) and (3aSR,4RS,6aRS)-4-(4-Bromophenyl)-2-(diphenylmeth-
yl)-1,2,3,3a,4,5,6,6a-octahydro-3-hydroxy-5,6,6-trimethylpyrrolo[3,4-c]pyrrol-1-one ((Æ)-24). A 1m soln. of
Li[Et3BH] in THF (24 ml, 24 mmol) was added to (Æ)-22 (6.04 g, 12 mmol) in dry CH2Cl2 (100 ml) at 08
under Ar. After 90 min, the mixture was warmed to r.t. and 1n NaOH was added. Separation of the phases,
extraction of the aq. phase with CH2Cl2, drying of the combined org. phases (Na2SO4), evaporation in vacuo,
and CC (CH2Cl2/AcOEt/Et3N 97 :2 :1) gave a mixture of (Æ)-25 and (Æ)-24.
Data of (Æ)-25: 1.91 g (31%). Colorless crystals. Dec. >2158 (AcOEt). IR (KBr): 3167, 2960, 1659, 1485,
1448, 1244, 1205, 1111, 1077, 1009, 820, 699. 1H-NMR (200 MHz, CDCl3): 1.04 (s, 3 H); 1.20 (s, 3 H); 1.98
(s, 3 H); 2.41 (dd, J ˆ 8.7, 4.6, 1 H); 3.39( dd, J ˆ 10.0, 8.7, 1 H); 3.84 (d, J ˆ 10.0, 1 H); 5.06 (m, 1 H); 6.12
(s, 1 H); 7.07 (d, J ˆ 8.3, 2 H); 7.22 7.27 (m, 8 H); 7.40 7.45 (m, 4 H). 13C-NMR (75 MHz, CDCl3): 18.3; 22.5;
32.1; 49.2; 57.6; 59.5; 61.1; 69.0; 84.2; 111.2; 121.5; 127.3; 128.0; 128.4; 128.4; 129.0; 130.2; 131.6; 138.0; 138.5;
‡
‡
140.3; 171.7. EI-MS: 504.2 (0.1, M ); 289.1 (11), 262.0 (14), 196.0 (14), 167.1 (100, Ph2CH ). Anal. calc. for
C28H29BrN2O2 (505.46): C 66.54, H 5.78, N 5.54, Br 15.81; found: C 66.53, H 5.83, N 5.49, Br 15.68. X-Ray: see
Fig. 6.
Data of (Æ)-24: 3.33 g (55%). Colorless crystals. Dec. >2308 (AcOEt). IR (KBr): 3411, 1654, 1444, 1389,
1256, 1044, 811, 700. 1H-NMR (300 MHz, CDCl3): 1.07 (s, 3 H); 1.43 (s, 3 H); 2.03 (s, 3 H); 2.83 (dd, J ˆ 8.7, 8.7,
1 H); 2.94 (d, J ˆ 8.7, 1 H); 3.84 (d, J ˆ 8.4, 1 H); 4.20 (s, 1 H); 6.17 (s, 1 H); 7.02 7.32 (m, 14 H). 13C-NMR
(75 MHz, CDCl3): 19.5; 23.9; 32.4; 48.4; 54.1; 60.8; 63.1; 68.4; 82.6; 121.1; 127.6; 128.0; 128.5; 128.7; 128.8; 129.3;
‡
‡
129.9; 131.9; 138.4; 138.6; 139.7; 174.0. EI-MS: 503.1 (1, [M À H] ), 489.1 (12), 167.1 (100, Ph2CH ). Anal. calc.
for C28H29BrN2O2 (505.46): C 66.54, H 5.78, N 5.54, Br 15.81; found: C 66.64, H 5.84, N 5.55, Br 15.93.
(3RS,3aSR,6RS,6aSR)-6-(4-Bromophenyl)-2-(diphenylmethyl)-1,2,3,3a,4,5,6,6a-octahydro-4,4,5-trimethyl-
3-(1-methylethyl)pyrrolo[3,4-c]pyrrol-1-one ((Æ)-26). Ac2O (0.09ml, 102 mg) was added to ( Æ)-25 (101 mg,
0.2 mmol) and DMAP (122 mg, 1 mmol) in CH2Cl2 (2 ml) at À208. After stirring for 3 h at r.t., the solvent was
removed in vacuo, and the residue was purified by CC (hexane/AcOEt/Et3N 89:10 :1) and washed with Et 2O to
yield acetoxylactam intermediate (57 mg, 52%). Colorless crystals. Dec. >1458 (hexane/AcOEt). IR (CHCl3):
3008, 1707, 1600, 1482, 1405, 1364, 1005. 1H-NMR (300 MHz, CDCl3): 1.03 (s, 3 H); 1.31 (s, 3 H); 1.59( s, 3 H);
2.00 (s, 3 H); 2.42 (dd, J ˆ 8.7, 1.9, 1 H); 3.31 (dd, J ˆ 8.7, 8.4, 1 H); 3.84 (d, J ˆ 8.4, 1 H); 6.14 (s, 1 H); 6.33
(d, J ˆ 1.9, 1 H); 7.00 (d, J ˆ 8.4, 2 H); 7.20 7.41 (m, 12 H). 13C-NMR (75 MHz, CDCl3): 19.3; 20.8; 23.7; 32.2;
48.7; 54.6; 60.3; 61.9; 69.1; 85.3; 111.2; 127.5; 128.0; 128.3; 128.7; 129.1; 129.4; 130.3; 131.3; 137.3; 138.6; 139.1;
‡
169.8; 173.3. FAB-MS: 547.6 (100, MH ), 531.9(76), 471.5 (50). Anal. calc. for C 30H31BrN2O3 (547.49): C 65.81,
H 5.71, N 5.12, Br 14.59; found: C 65.90, H 5.92, N 5.13, Br 14.43.
(i-Pr)MgCl (0.2 ml of 2m soln. in Et2O, 0.4 mmol) was added to ZnCl2 (0.44 ml of 0.5m soln. in Et2O,
0.22 mmol) in dry CH2Cl2 (1 ml) under Ar. After 1 h, a soln. of the acetoxylactam (109.5 mg, 0.2 mmol) in dry
CH2Cl2 (1 ml) was slowly added while cooling with an ice bath. After stirring at r.t. for 15 h, 1n HCl was added,
and, 15 min later, the mixture was neutralized with sat. aq. NaHCO3 soln. and extracted with CH2Cl2. The org.
phase was dried (Na2SO4), the solvent was removed, and the product was purified by CC (hexane/AcOEt/Et3N
79:20 :1, then 66 :33 :1) to yield ( Æ)-26 (17.6 g, 17%; 9% based on (Æ)-25). Colorless oil. IR (CHCl3): 3027,
2968, 1678, 1492, 1451, 1395, 1072, 1011, 831. 1H-NMR (300 MHz, CDCl3): 0.55 (d, J ˆ 6.8, 3 H); 0.75 (d, J ˆ 6.8,
3 H); 1.02 (s, 3 H); 1.12 (s, 3 H); 1.65 (dsept., J ˆ 6.8, 2.8, 1 H); 1.99 (s, 3 H); 2.20 (dd, J ˆ 9.3, 2.3, 1 H); 3.11
(dd, J ˆ 9.3, 7.8, 1 H); 3.73 (dd, J ˆ 2.8, 2.3, 1 H); 3.82 (d, J ˆ 7.8, 1 H); 6.00 (s, 1 H); 6.97 (d, J ˆ 8.7, 2 H); 7.22
(m, 10 H); 7.46 7.49( m, 2 H). 13C-NMR (75 MHz, CDCl3): 14.5; 18.9; 20.4; 24.9; 29.7; 32.7; 45.3; 50.6; 62.2;
62.7; 64.8; 69.7; 120.7; 127.2; 127.5; 127.9; 128.3; 129.0; 129.6; 130.5; 130.6; 137.6; 138.9; 140.0; 172.7. FAB-MS:
‡
‡
‡
531.1 (100, MH ), 515.0 (60), 167.1 (51, Ph2CH ). HR-MALDI-MS: 529.1849 ([M À H] , C31H34BrN2O; calc.
529.1855).
(1RS,3aSR,4RS,8aSR,8bSR)-4-(4-Bromophenyl)-2,3,3a,4,5,6,7,8,8a,8b-decahydro-1-(1-methylethyl)-1H-
pyrrolo[3,4-a]pyrrolizin-3-one ((Æ)-28).
A
mixture of (Æ)-27 (379mg, 0.76 mmol), phenol (120 mg,
1.28 mmol), and orthophosphoric acid (3.73 g, 38 mmol) was homogenized with CH2Cl2 (5 ml) and then
stirred at 1508 for 1 h. After cooling to r.t., H2O was added, and the mixture was extracted with Et2O. The
combined org. phases were extracted with H2O. The combined aq. phases were rendered alkaline with NaOH,
heated to reflux for 1 h, and extracted with CH2Cl2. The combined org. phases were dried (Na2SO4), and the
solvent was evaporated in vacuo. The brownish residue was washed with AcOEt and purified by CC (hexane/
AcOEt/Et3N 49.5 :49.5 :1) to afford (Æ)-28 (90 mg, 32%). Colorless crystals. M.p. 191 1938 (hexane/AcOEt)).
1
IR (CHCl3): 3436, 3018, 2965, 1694, 1486, 1072, 1010. H-NMR (300 MHz, CDCl3): 0.84 (d, J ˆ 6.9, 3 H); 0.89

Helvetica Chimica Acta Vol. 85 (2002)
1237
(d, J ˆ 6.5, 3 H); 1.48 1-63 (m, 2 H); 1.71 1.83 (m, 1 H); 1.94 2.08 (m, 2 H); 2.59( ddd, J ˆ 8.7, 3.9, 1.6, 1 H);
2.64 2.70 (m, 1 H); 2.87 2.97 (m, 1 H); 3.20 (t, J ˆ 8.7, 1 H); 3.20 (dd, J ˆ 6.5, 3.9, 1 H); 3.37 3.43 (m, 1 H);
3.96 (d, J ˆ 8.7, 1 H); 6.64 (s, 1 H); 7.29, 7.42 (AA'BB', J ˆ 8.6, 4 H). 13C-NMR (75 MHz, CDCl3): 18.3; 18.3;
‡
24.1; 30.4; 34.0; 47.5; 51.9; 52.0; 66.2; 69.5; 72.9; 120.9; 130.0; 131.0; 139.1; 175.7. FAB-MS: 363.2 (94, MH ),
‡
239.1 (7), 167.2 (9), 149.1 (100), 115.0 (16). HR-FAB-MS: 363.1078 (MH , C18H24BrN2O; calc. 363.1072).
(1RS,3aSR,4RS,8aSR,8bRS)-4-(4-Bromophenyl)-2-(diphenylmethyl)-2,3,3a,4,5,6,7,8,8a,8b-decahydro-1-
(1-methylethyl)-1H-pyrrolo[3,4-a]pyrrolizin-3-one ((Æ)-29). Benzhydryl chloride (0.36 ml, 811 mg, 2 mmol)
was added to a suspension of (Æ)-28 (727 mg, 2 mmol) and AgOSO2CF3 (514 mg, 2 mmol) in a sealed tube. A
gray precipitate formed instantly. After stirring at 1008 for 1 h and cooling to r.t., sat. aq. NaHCO3 soln. was
added, and the mixture was extracted with CH2Cl2. The org. phase was dried (Na2SO4), the solvent was removed
in vacuo, and the residue was purified by CC (hexane/AcOEt/Et3N 82.5 :16.5 :1) to yield (Æ)-29 (693 mg, 65%).
Yellowish oil. IR (CHCl3): 3028, 2966, 1681, 1590, 1487, 1410, 1073, 1011. 1H-NMR (300 MHz, CDCl3): 0.63
(d, J ˆ 6.5, 3 H); 0.75 (d, J ˆ 6.9, 3 H); 1.43 1.51 (m, 1 H); 1.56 1.68 (m, 1 H); 1.71 1.82 (m, 1 H); 1.89 2.07
(m, 2 H); 2.46 (dd, J ˆ 3.3, 7.7, 1 H); 2.56 2.66 (m, 1 H); 2.94 3.03 (m, 1 H); 3.29( dd, J ˆ 6.9, 7.7, 1 H); 3.34
3.39( m, 2 H); 4.07 (d, J ˆ 6.9, 1 H); 6.14 (s, 1 H); 7.23 7.41 (m, 14 H). 13C-NMR (75 MHz, CDCl3): 15.1; 19.0;
24.9; 29.8; 32.0; 41.9; 52.5; 53.6; 61.5; 69.5; 71.0; 73.7; 120.8; 127.5; 127.6; 128.4; 128.5; 129.2; 129.3; 130.2; 131.0;
‡
‡
‡
138.7; 139.5; 140.1; 173.1. FAB-MS: 529.1 (100, MH ); 167.1 (45, Ph2CH ). HR-FAB-MS: 527.1699 ([M À H] ,
C31H32BrN2O; calc. 527.1698).
4-[(1RS,3aSR,4RS,8aSR,8bRS)-2-(Diphenylmethyl)-2,3,3a,4,5,6,7,8,8a,8b-decahydro-1-(1-methylethyl)-3-
oxo-1H-pyrrolo[3,4-a]pyrrolizin-4-yl]benzonitrile ((Æ)-30). General Procedure D, starting from (Æ)-29, afford-
ed (Æ)-30 in 40% yield. Yellowish oil. IR (CHCl3): 3020, 2966, 2229, 1677, 1610, 1497, 1415. 1H-NMR (300 MHz,
CDCl3): 0.63 (d, J ˆ 6.6, 3 H); 0.76 (d, J ˆ 6.6, 3 H); 1.40 1.60 (m, 1 H); 1.50 2.09( m, 4 H); 2.46 2.65
(m, 2 H); 2.95 3.08 (m, 1 H); 3.32 3.45 (m, 3 H); 4.15 (d, J ˆ 6.6, 1 H); 6.07 (s, 1 H); 7.19 7.38 ( m, 10 H);
7.46, 7.51 (AA'BB', J ˆ 8.5, 4 H). 13C-NMR (75 MHz, CDCl3): 15.1; 18.9; 25.0; 29.8; 32.0; 42.0; 52.7; 53.8; 61.7;
69.8; 71.3; 73.9; 110.6; 119.7; 127.6; 127.6; 128.4; 128.5; 129.1; 129.2; 131.7; 139.4; 139.9; 145.8; 172.8. FAB-MS:
‡
‡
‡
‡
951.5 (10, M2H ), 476.3 (100, MH ), 167.1 (82, Ph2CH ). HR-FAB-MS: 476.2704 (MH , C32H34N3O; calc.
476.2702).
4-[(1RS,3aSR,4RS,8aSR,8bRS)-2-(Diphenylmethyl)-2,3,3a,4,5,6,7,8,8a,8b-decahydro-1-(1-methylethyl)-3-
oxo-1H-pyrrolo[3,4-a]pyrrolizin-4-yl]benzamidine Hydrochloride ((Æ)-2). General Procedure C, starting from
(Æ)-30, afforded amidinium salt (Æ)-2 in 42% yield. Yellowish solid. Dec. >1758. IR (CHCl3): 2968, 1675, 1614,
1
1494, 1448. H-NMR (300 MHz, (CD3)2SO): 0.59( d, J ˆ 6.9, 3 H); 0.81 (d, J ˆ 6.9, 3 H); 1.60 1.74 (m, 2 H);
1.86 2.04 (m, 3 H); 2.41 2.56 (m, 2 H); 2.83 2.96 (m, 1 H); 3.32 3.46 (m, 1 H); 3.50 3.59( m, 1 H); 3.62
3.65 (m, 1 H); 4.19( d, J ˆ 6.2, 1 H); 5.79( s, 1 H); 7.18 7.35 (m, 10 H); 7.52, 7.64 (AA'BB', J ˆ 8.4, 4 H); 9.02
(br. s, 2 H); 9.19 (br. s, 2 H). 13C-NMR (125 MHz, CD3OD): 15.6; 19.2; 26.0; 31.2; 32.6; 43.1; 54.1; 55.4; 63.8;
71.8; 72.5; 75.6; 127.9; 128.3; 128.7; 128.7; 129.4; 129.4; 129.8; 130.2; 130.4; 140.9; 141.0; 168.3; 174.6. FAB-MS:
‡
‡
‡
‡
985.3 (7, M2H ), 493.1 (100, MH ), 167.1 (26, Ph2CH ). HR-FAB-MS: 493.2966 (MH , C32H37N4O; calc.
493.2967).
(1,3-benzodioxol-5-yl)-1,3-benzodioxole-5-methanol (33). A soln. of 31 (7.41 ml, 12.06 g, 60 mmol) in dry
THF (100 ml) was treated at À788 with 1.6m BuLi in hexane (38.6 ml, 61.8 mmol) and, after 5 min, with a soln.
of 32 (9.01 g, 60 mmol) in dry THF (10 ml). After 10 min, MeOH (10 ml) was added, and, after warming to r.t.,
the solvent was removed in vacuo. The residue was redissolved in CH2Cl2 and extracted with sat. aq. NaHCO3
soln. The org. phase was dried (Na2SO4), and the solvent was removed to yield 33 (16.07 g, 98%). Colorless
solid. M.p. 82 858. IR (CHCl3): 3601, 3023, 2892, 1504, 1487, 1443, 1243, 1041, 934. 1H-NMR (300 MHz, CDCl3):
2.24 (d, J ˆ 3.1, 1 H); 5.66 (d, J ˆ 3.1, 1 H); 5.93, 5.93 (AB, J ˆ 1.6, 4 H); 6.74 6.77 (m, 2 H); 6.82 6.85
(m, 4 H). 13C-NMR (75 MHz, CDCl3): 75.8; 101.1; 107.0; 108.1; 119.8; 138.0; 147.0; 147.8. MALDI-MS: 273.0
‡
(10, MH ), 255.1 (100). Anal. calc. for C15H12O5 (272.26): C 66.17, H 4.44; found: C 66.00, H 4.60.
(1RS,3aSR,4RS,8aSR,8bRS)-4-(4-Bromophenyl)-2-[di(1,3-benzodioxol-5-yl)methyl]-2,3,3a,4,5,6,7,8,8a,8b-
decahydro-1-(1-methylethyl)-1H-pyrrolo[3,4-a]pyrrolizin-3-one ((Æ)-35). A soln. of 33 (599 mg, 2.2 mmol) in
Et2O (10 ml) was stirred for 2 h under HCl atmosphere. After a quick extraction with sat. aq. NaHCO3 soln., the
org. phase was dried (Na2SO4), and the solvent was removed in vacuo. The resulting crude diarylmethyl chloride
34 (618 mg, 97%) was redissolved in CH2Cl2 (20 ml) and added to a suspension of (Æ)-28 (691 mg, 1.9 mmol)
and AgOSO2CF3 (489mg, 1.9mmol) in CH 2Cl2 (20 ml) in a sealed tube. A gray precipitate formed instantly.
After stirring at 1008 for 3 h and cooling to r.t., sat. aq. NaHCO3 soln. was added, and the mixture was extracted
with CH2Cl2. The org. phase was dried (Na2SO4), the solvent was removed in vacuo, and the residue was
purified by CC (hexane/AcOEt/Et3N 79:20 :1) to yield ( Æ)-35 (520 mg, 44%) besides recovered starting
material (Æ)-28 (259 mg, 38%). Yellowish crystals. M.p. 191 1938 (hexane/AcOEt). IR (CHCl3): 3012, 1676,

1238
Helvetica Chimica Acta Vol. 85 (2002)
1504, 1488, 1442, 1247, 1042, 937. 1H-NMR (300 MHz, CDCl3): 0.62 (d, J ˆ 6.9, 3 H); 0.80 (d, J ˆ 7.2, 3 H); 1.54
1.68 (m, 2 H); 1.70 1.82 (m, 1 H); 1.89 2.08 ( m, 2 H); 2.47 (dd, J ˆ 8.1, 2.2, 1 H); 2.58 2.66 (m, 1 H); 2.94
3.03 (m, 1 H); 3.25 (dd, J ˆ 8.1, 6.7, 1 H); 3.34 3.42 (m, 2 H); 4.05 (d, J ˆ 6.7, 1 H); 5.83 (s, 1 H); 5.94 (s, 2 H);
5.95 (s, 2 H); 6.66 6.78 (m, 4 H); 6.81 6.85 (m, 1 H); 6.95 (d, J ˆ 1.6, 1 H); 7.23, 7.35 (AB, J ˆ 8.4, 4 H).
13C-NMR (75 MHz, CDCl3): 15.0; 19.0; 24.7; 29.9; 31.8; 41.6; 52.2; 53.5; 61.4; 70.0; 70.9; 73.8; 101.2; 101.2; 108.0;
108.1; 109.6; 109.8; 120.8; 122.3; 122.5; 130.1; 131.0; 133.7; 134.1; 138.5; 147.0; 147.1; 147.8; 148.0; 172.9. MALDI-
‡
‡
‡
MS: 639.1 (24, [M ‡ Na] ), 617.2 (11, MH ), 255.1 (100, [di(benzodioxolyl)methyl] ). MALDI-HR-MS:
‡
639.1465 ([M ‡ Na] , C33H33BrN2NaO5; calc. 639.1471). Anal. calc. for C33H33BrN2O5 (617.54): C 64.18, H 5.39,
N 4.54, Br 12.94; found: C 64.27, H 5.58, 4.25; Br 13.07.
2-[(1RS,3aSR,4RS,8aSR,8bRS)-Di(1,3-benzodioxol-5-yl)methyl]-2,3,3a,4,5,6,7,8,8a,8b-decahydro-1-(1-
methylethyl)3-oxo-1H-pyrrolo[3,4-a]pyrrolizin-4-yl]benzonitrile ((Æ)-36). General Procedure D, starting from
(Æ)-35, afforded (Æ)-36 in 52% yield. Yellowish oil. IR (CHCl3): 2965, 2882, 2226, 1686, 1504, 1489, 1442, 1247,
1042, 936. 1H-NMR (300 MHz, CDCl3): 0.63 (d, J ˆ 6.9, 3 H); 0.81 (d, J ˆ 6.9, 3 H); 1.55 1.67 (m, 2 H); 1.73
1.82 (m, 1 H); 1.86 2.09( m, 2 H); 2.49( dd, J ˆ 7.8, 2.8, 1 H); 2.54 2.63 (m, 1 H); 2.97 3.07 (m, 1 H); 3.33
(dd, ˆ 7.8, 7.2, 1 H); 3.38 3.43 (m, 2 H); 4.15 (d, J ˆ 7.2, 1 H); 5.77 (s, 1 H); 5.93 (s, 2 H); 5.95 (s, 2 H); 6.63
6.74 (m, 4 H); 6.78 6.81 (m, 1 H); 6.91 (d, J ˆ 1.6, 1 H); 7.46, 7.51 (AB, J ˆ 8.2, 4 H). 13C-NMR (75 MHz,
CDCl3): 15.0; 19.0; 24.8; 29.8; 31.8; 41.6; 52.3; 53.7; 61.4; 70.1; 71.0; 73.8; 101.1; 101.1; 107.8; 107.9; 109.3; 109.5;
110.4; 119.5; 122.0; 122.1; 128.8; 131.5; 133.4; 133.6; 145.4; 146.8; 146.9; 147.6; 147.7; 172.4. MALDI-MS: 586.2
‡
‡
‡
(100, [M ‡ Na] ), 562.2 (9, MH ), 255.1 (66, [di(benzodioxolyl)methyl] ). HR-MALDI-MS: 586.2310 ([M ‡
‡
Na] , C34H33N3NaO5; calc. 586.2312).
4-{(1RS,3aSR,4RS,8aSR,8bRS)-2-[Di(1,3-benzodioxol-5-yl)methyl]-2,3,3a,4,5,6,7,8,8a,8b-decahydro-1-(1-
methylethyl)-3-oxo-1H-pyrrolo[3,4-a]pyrrolizin-4-yl}benzamidine Hydrochloride ((Æ)-4). General Procedure C,
starting from (Æ)-36, afforded (Æ)-4 in 54% yield. Yellowish solid. Dec. >2008. IR (CHCl3): 3020, 2966, 1675,
1
1504, 1489, 1442, 1247, 1041, 936. H-NMR (300 MHz, CD3)2SO): 0.55 (d, J ˆ 6.9, 3 H); 0.85 (d, J ˆ 6.9, 3 H);
1.61 1.73 (m, 2 H); 1.78 2.02 (m, 3 H); 2.42 2.55 (m, 2 H); 2.87 2.95 (m, 1 H); 3.30 3.37 (m, 1 H); 3.39
3.43 (m, 1 H); 3.50 3.51 (m, 1 H); 4.18 (d, J ˆ 6.5, 1 H); 5.55 (s, 1 H); 5.97 (s, 2 H); 6.03, 6.04 (AB, J ˆ 0.9, 2 H);
6.52 (dd, J ˆ 8.1, 1.2, 1 H); 6.74 6.85 (m, 4 H); 6.93 (d, J ˆ 1.6, 1 H); 7.52, 7.65 (AA'BB', J ˆ 8.4, 4 H); 8.65 (br. s,
4 H). 13C-NMR (125 MHz, CDCl3): 15.5; 19.1; 25.4; 29.8; 32.3; 42.0; 52.8; 54.1; 61.9; 70.0; 70.9; 73.6; 101.2;
101.4; 107.8; 108.1; 108.6; 108.8; 121.4; 121.9; 125.3; 127.9; 128.3; 132.5; 146.3; 146.7; 147.1; 147.6; 147.9; 165.3;
‡
‡
‡
173.1. MALDI-MS: 603.2 (38, [M ‡ Na] ), 581.2 (14, MH ), 255.1 (100, [di(benzodioxolyl)methyl] ). HR-
‡
MALDI-MS: 581.2766 (MH , C34H37N4O5; calc. 581.2764).
(1RS,3aRS,6aSR)-4-{5-[(1,3-Benzodioxol-5-yl)methyl]-1,2,3,3a,4,5,6,6a-octahydro-3,3-dimethyl-4,6-dioxo-
1H-pyrrolo[3,4-c]pyrrol-1-yl]benzonitrile ((Æ)-40). General Procedure A, starting from 14, 18, and 51, gave (Æ)-
40 in 34% yield. Colorless solid. M.p. 172 1738 (MeOH). IR (KBr): 2230, 1770, 1698, 1608, 1490, 1443, 1400,
1369, 326, 1249, 1170, 1099, 1034. 1H-NMR (200 MHz, CDCl3): 1.37 (s, 3 H); 1.43 (s, 3 H); 1.50 (s, 1 H); 2.89
(d, J ˆ 7.9, 1 H); 3.45 (m, 1 H); 4.38, 4.45 (AB, J ˆ 13.9, 2 H); 4.75 (d, J ˆ 8.7, 1 H); 5.96, 5.99 (AB, J ˆ 1.2, 2 H);
6.74, 6.79( AB, J ˆ 7.9, 2 H); 6.77 (s, 1 H); 7.32, 7.53 (AA'BB', J ˆ 8.3, 4 H). 13C-NMR (50 MHz, CDCl3): 26.3;
28.8; 42.1; 50.2; 53.8; 60.4; 61.0; 101.3; 108.3; 109.7; 111.8; 119.1; 122.7; 128.4; 129.9; 132.0; 144.1; 147.5; 147.9;
‡
‡
‡
175.0; 176.0. FAB-MS: 807.2 (23, M2H ), 404.1 (100, MH ), 388.1 (11, [M À Me] ). Anal. calc. for C23H21N3O4
(403.44): C 68.47, H 5.25, N 10.42; found: C 68.32, H 5.30, N 10.55.
Methyl (3RS,3aSR,6aRS)-{5-[(1,3-Benzodioxol-5-yl)methyl]-3-(4-cyanophenyl)-1,2,3,3a,4,5,6,6a-octahy-
dro-1,1-dimethyl-4,6-dioxopyrrolo[3,4-c]pyrrol-2-yl}acetate ((Æ)-41). HCO2H (1.73 g, 37.5 mmol), glyoxylic
acid monohydrate (0.83 g, 9.0 mmol), and (Æ)-40 (3.03 g, 7.5 mmol) were mixed at 08 and then heated to reflux
for 24 h. The solvent was evaporated in vacuo, and the residue was redissolved in MeOH (11.5 ml). Conc. H2SO4
(0.15 g) was added, and the mixture was stirred at 908 for 48 h. After cooling, sat. aq. NaHCO3 soln. was added,
and the mixture was extracted with CH2Cl2. The org. phase was dried (Na2SO4), evaporated, and the residue
was purified by CC (hexane/AcOEt/Et3N 66 :33 :1, then 49.5 :49.5 :1) to give (Æ)-41 (1.42 g, 40%). Colorless
solid. M.p. 134 1368 (MeOH). IR (KBr): 2229, 1763, 1730, 1702, 1610, 1508, 1488, 1444, 1400, 1372, 1326, 1247,
1
1175, 1034. H-NMR (200 MHz, CDCl3): 1.17 (s, 3 H); 1.46 (s, 3 H); 2.92 (d, J ˆ 7.9, 1 H); 3.04, 3.16 (AB, J ˆ
17.2, 2 H); 3.40 (dd, J ˆ 7.9, 9.1, 1 H); 3.55 (s, 3 H); 4.34, 4.48 (AB, J ˆ 13.9, 2 H); 4.63 (d, J ˆ 9.1, 1 H); 5.97, 6.01
(AB, J ˆ 1.25, 2 H); 6.81 (m, 3 H); 7.21, 7.44 (AA'BB', J ˆ 7.9, 4 H ) . 13C-NMR (75 MHz, CDCl3): 21.2; 24.2; 42.2;
46.5; 48.2; 51.8; 54.1; 63.4; 66.2; 101.4; 108.4; 110.0; 112.2; 119.0; 123.0; 129.5; 129.7; 132.3; 142.8; 147.6; 147.9;
‡
‡
172.1; 175.0; 175.8. FAB-MS: 951.3 (9, [M2H] ), 476.1 (100, MH ), 416.1 (34), 402.1 (20), 135.1 (69,
‡
[piperonyl] ). Anal. calc. for C26H25N3O6 (475.50): C 65.68, H 5.30, N 8.84; found: C 65.70, H5.29, N 8.80.
(1RS,3aRS,6aSR)-4-{5-[(1,3-Benzodioxol-5-yl)methyl]-1,2,3,3a,4,5,6,6a-octahydro-3,3-dimethyl-4,6-dioxo-
2-(2-oxo-2-phenylethyl)pyrrolo[3,4-c]pyrrol-1-yl}benzonitrile ((Æ)-42). HCO2H (4.6 g, 100 mmol), phenyl-

Helvetica Chimica Acta Vol. 85 (2002)
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glyoxal monohydrate (3.65 g, 24 mmol), and (Æ)-40 (8.07 g, 20 mmol) were mixed at 08 and then stirred for 10 h
at 1008. After cooling, sat. aq. NaHCO3 soln. was added, and the mixture was extracted with CH2Cl2. The org.
phase was dried (Na2SO4), evaporated, and the residue was purified by CC (hexane/AcOEt/Et3N 49.5 :49.5 :1)
to give (Æ)-42 (2.25 g, 22%). Colorless solid. M.p. 176 1778 (hexane/AcOEt). IR (KBr): 2222, 1767, 1699, 1608,
1597, 1503, 1491, 1446, 1399, 1344, 1310, 1246, 1172, 1040. 1H-NMR (200 MHz, CDCl3): 1.25 (s, 3 H); 1.52
(s, 3 H); 2.99 (d, J ˆ 8.3, 1 H); 3.48 (m, 1 H); 3.63, 3.92 (AB, J ˆ 17.4, 2 H); 4.38, 4.52 (AB, J ˆ 13.9, 2 H); 4.74
(d, J ˆ 9.1, 1 H); 6.00, 6.03 (AB, J ˆ 1.2, 2 H); 6.80 6.92 (m, 3 H); 7.15 (d, J ˆ 8.3, 2 H); 7.31 7.58 (m, 3 H); 7.36,
7.70 (AA'BB', J ˆ 7.1, 4 H ) . 13C-NMR (75 MHz, CDCl3): 21.8; 24.7; 42.2; 48.5; 51.6; 54.2; 63.9; 67.1; 101.4; 108.5;
110.1; 112.1; 119.0; 123.0; 127.9; 128.8; 129.7; 132.2; 133.5; 136.0; 142.9; 147.6; 147.9; 175.2; 175.9; 197.8. FAB-
‡
‡
‡
MS: 1043.4 (7, M2H ), 522.2 (100, MH ), 416.2 (59), 135.0 (47 [piperonyl] ). Anal. calc. for C31H27N3O5
(521.56): C 71.39, H 5.22, N 8.06; found: C 71.40, H 5.39, N 8.17.
Methyl
(3RS,3aSR,6aRS)-(3-{4-[Amino(imino)methyl]phenyl}-5-[(1,3-benzodioxol-5-yl)methyl]-
1,2,3,3a,4,5,6,6a-octahydro-1,1-dimethyl-4,6-dioxopyrrolo[3,4-c]pyrrol-2-yl)acetate Hydrochloride ((Æ)-37).
General Procedure C, starting from (Æ)-41, gave (Æ)-37 in 97% yield. Slightly pink foam. M.p. >1438 (dec.).
IR (KBr): 1704, 1675, 1614, 1539, 1490, 1445, 1400, 1370, 1342, 1248, 1172, 1102, 1036. 1H-NMR (200 MHz,
(CD3)2SO): 1.14 (s, 3 H); 1.32 (s, 3 H); 2.85, 3.33 (AB, J ˆ 17.0, 2 H); 3.12 (d, J ˆ 8.3, 1 H); 3.46 (s, 3 H); 3.60
(m, 1 H); 4.35 (s, 2 H); 4.54 (d, J ˆ 8.7, 1 H); 6.06 (s, 2 H); 6.76 (s, 1 H); 6.77 (m, 2 H); 7.36, 7.65 (AA'BB', J ˆ
7.7, 4 H); 9.26 (br., 4 H). 13C-NMR (75 MHz, (CD3)2SO): 19.9; 24.0; 41.0; 47.2; 48.1; 51.3; 53.6; 62.8; 66.4; 101.1;
108.2; 108.5; 121.3; 126.9; 127.6 (2 Â); 129.9; 144.7; 146.7; 147.4; 165.4; 172.0; 175.3; 176.2. DEI-MS: 492.3 (10,
‡
‡
‡
M ), 477.2 (15, [M À Me] ), 433.3 (12), 416.2 (28), 402.2 (14), 135.1 (100, [piperonyl] ). HR-DEI-MS:
‡
492.2005 (M , C26H28N4O6, calc. 492.2002).
(3RS,3aSR,6aRS)-(3-{4-[Amino(imino)methyl]phenyl}-5-[(1,3-benzodioxol-5-yl)methyl]-1,2,3,3a,4,5,
6,6a-octahydro-1,1-dimethyl-4,6-dioxopyrrolo[3,4-c]pyrrol-2-yl)acetic Acid Hydrochloride ((Æ)-38). Ester (Æ)-
37 (793 mg, 1.5 mmol) was dissolved in 3n HCl (5 ml, 15 mmol) and stirred for 15 h at 1008. After cooling, the
mixture was evaporated and dried under high vacuum. The residue was redissolved twice in EtOH and
precipitated with Et2O to give 721 mg (93%) crude product, from which 270 mg were further purified by CC
(RP18-SiO2; H2O, then H2O/MeOH 2 :1, then 1 :1) to give (Æ)-38 (99.6 mg, 36%). Yellowish crystals. M.p.
>1708 (dec.). IR (KBr): 1771, 1698, 1617, 1490, 1445, 1402, 1248, 1172, 1036. 1H-NMR (200 MHz, (CD3)2SO):
1.16 (s, 3 H); 1.34 (s, 3 H); 2.76, 3.14 (AB, J ˆ 17.2, 2 H); 3.10 (d, J ˆ 7.9, 1 H); 3.59 (m, 1 H); 4.35 (s, 2 H); 4.60
(d, J ˆ 8.7, 1 H); 6.03 (s, 2 H); 6.77 (s, 1 H); 6.79, 6.90 (AB, J ˆ 7.5, 2 H); 7.45, 7.61 (AA'BB', J ˆ 7.7, 4 H); 9.10
(br. s, 2 H); 9.60 (br. s, 2 H). 13C-NMR (300 MHz, (CD3)2SO): 19.9; 24.0; 41.0; 46.6; 48.1; 53.6; 62.6; 65.9; 101.1;
108.2; 108.3; 120.9; 126.8; 127.6; 129.8; 145.0; 146.6; 147.4; 165.5; 173.1; 175.4; 176.3. FAB-MS: 479.2 (100,
‡
MH ), 433.2 (7). Anal. calc. for C25H26N4O6 ¥ HCl (514.96): C 58.31, H 5.28, N 10.88, Cl 6.88; found: C 58.58,
H 5.25, N 11.02, Cl 7.18.
(1RS,3aRS,6aSR)-4-{5-[(1,3-Benzodioxol-5-yl)methyl]-1,2,3,3a,4,5,6,6a-oxtahydro-3,3-dimethyl-4,6-dioxo-
2-(2-oxo-2-phenylethyl)pyrrolo[3,4-c]pyrrol-1-yl}benzamidine Hydrochloride ((Æ)-39). General Procedure C,
starting from (Æ)-42 gave (Æ)-39 in 75% yield. Yellowish solid. M.p. 1668. IR (KBr): 1772, 1702, 1675, 1613,
1539, 1490, 1446, 1399, 1247, 1172, 1037. 1H-NMR (200 MHz, (CD3)2SO): 1.17 (s, 3 H); 1.24 (s, 3 H); 3.10 (d, J ˆ
7.9, 1 H); 3.59 (m, 1 H); 3.53, 4.09( AB, J ˆ 18.3, 2 H); 4.32 (s, 2 H); 4.61 (d, J ˆ 9.1, 1 H); 6.02 (m, 2 H); 6.76
(d, J ˆ 1.24, 1 H); 6.81, 6.92 (AB, J ˆ 7.9, 2 H); 7.31 7.58 (m, 5 H); 7.37, 7.75 (AA'BB', J ˆ 7.1, 4 H); 9.03 (br. s,
2 H); 9.21 (br. s, 2 H). 13C-NMR (50 MHz, (CD3)2SO): 18.2; 22.5; 46.5; 50.2; 52.0; 61.2; 65.0; 99.3; 106.4; 106.7;
119.4; 124.9; 125.7; 126.0; 126.9; 127.5; 128.0; 131.4; 134.0; 143.3; 144.9; 145.6; 163.5; 173.7; 174.5; 195.9. FAB-
‡
‡
‡
MS: 1077.4 (20, M2H ), 539.1 (100, MH ), 433.1 (14), 135.0 (14, [piperonyl] ).
4-{(1RS,3SR,3aRS,6aSR)-5-[(1,3-Benzodioxol-5-yl)methyl]-1,2,3,3a,4,5,6,6a-octahydro-3-methyl-4,6-diox-
opyrrolo[3,4-c]pyrrol-1-yl}benzonitrile ((Æ)-45). General Procedure A, starting from (Æ)-alanine, 14, and 19,
gave (Æ)-45 in 38% yield. Colorless crystals. M.p. 175 1788 (MeOH). IR (CHCl3): 2968, 2230, 1708, 1495, 1404,
1
1048, 941. H-NMR (300 MHz, CDCl3): 1.32 (d, J ˆ 6.5, 3 H); 1.60 (s, 1 H); 3.00 (d, J ˆ 7.8, 1 H); 3.42 (dd, J ˆ
8.7, 7.8, 1 H); 4.06 (q, J ˆ 6.5, 1 H); 4.36, 4.42 (AB, J ˆ 13.8, 2 H); 4.80 (d, J ˆ 8.7, 1 H); 5.95, 5.99 (AB, J ˆ 1.4,
2 H); 6.71 6.78 (m, 3 H); 7.24, 7.47 (AB, J ˆ 8.2, 4 H). 13C-NMR (75 MHz, CDCl3): 20.8; 42.3; 49.0; 52.4; 55.7;
61.1; 101.2; 108.1; 109.7; 111.5; 118.9; 122.7; 128.1; 129.5; 131.9; 143.8; 147.3; 147.6; 175.0; 177.9. FAB-MS: 390.1
‡
‡
(100, MH ), 135.0 (46, [piperonyl] ). Anal. calc. for C22H19N3O4 (389.41): C 67.86, H 4.92, N 10.79; found:
C 67.70, H 4.98, N 10.80.
Methyl 2-{(1RS,3SR,3aRS,6aSR)-5-[(1,3-Benzodioxol-5-yl)methyl]-1-(4-cyanophenyl)-1,2,3,3a,4,5,6,6a-
octahydro-3-methyl-4,6-dioxopyrrolo[3,4-c]pyrrol-2-yl}acetate ((Æ)-46). A soln. of (Æ)-45 (779mg, 2 mmol)
and glyoxylic acid monohydrate (276 mg, 3 mmol) in HCO2H (0.38 ml, 460 mg, 10 mmol) was heated to reflux
for 24 h. The solvent was evaporated, the residue was redissolved in MeOH (5 ml), and H2SO4 (0.08 ml) was