Novel spirocyclic pyrrolidones as P2/P1 mimetics in potent inhibitors of HIV-1 protease.

Article abstract of DOI:10.1016/S0960-894X(02)00733-3

We have developed concise and efficient syntheses of novel spirocyclic pyrrolidones 1-3, which involve the alkylation of pyrrolidone precursor 13 with 1,5-dibromopentane, 16 and 15, followed by an in situ lactamization. Conjugates of 1 and 2 with P1'/P2' hydroxy-indanolamine moiety resulted in novel and potent inhibitors of HIV-1 protease 25 and 26, suggesting that 1 and 2 are novel P2/P1 HIV-PI mimetics.

Full text of DOI:10.1016/S0960-894X(02)00733-3

Bioorganic & Medicinal Chemistry Letters 12 (2002) 3431–3433
Novel Spirocyclic Pyrrolidones as P2/P1 Mimetics in Potent
Inhibitors of HIV-1 Protease
Wieslaw M. Kazmierski,* Eric Furfine, Andrew Spaltenstein and Lois L. Wright
GlaxoSmithKline, 5 Moore Drive, Research Triangle Park, NC 27709, USA
Received 10 May 2002; accepted 20 August 2002
Abstract—We have developed concise and efficient syntheses of novel spirocyclic pyrrolidones 1–3, which involve the alkylation of
pyrrolidone precursor 13 with 1,5-dibromopentane, 16 and 15, followed by an in situ lactamization. Conjugates of 1 and 2 with P10/
P20 hydroxy-indanolamine moiety resulted in novel and potent inhibitors of HIV-1 protease 25 and 26, suggesting that 1 and 2 are
novel P2/P1 HIV-PI mimetics.
# 2002 Elsevier Science Ltd. All rights reserved.
Highly Active Antiretroviral Therapy (HAART)
employs various cocktails of reverse transcriptase and
HIV-1 protease inhibitors (PI). Although several PIs,
including Amprenavir1 and Indinavir2 have been
deployed in HAART, there is a continued need for new
entities with improved physical properties, potency,
viral resistance, and safety.
fragment yielded potent HIV-1 protease inhibitors 7
(Ki=0.05 nM, Fig. 2),
(Ki=0.8 nM) and
respectively.3ꢀ5
8
Based on the known monoalkylation of N-benzyl-pyr-
rolidone and bisalkylation of N-alkyl pyrrolidone 8,9 we
attempted to bis-alkylate the (5R)-5-benzylpyrrolidin-2-
one with 1,5-dibromopentane, but detected no desired
product 1. We also attempted to synthesize 1–3 by
alkylating Boc-protected lactam 93 with 1,5-dibromo-
pentane (Fig. 3) under the conditions we successfully
developed towards the benzyl-derivative 5,4 but the
resulting mixture of mostly intractable products
contained no desired spirocyclic pyrrolidone 10.
Our laboratory has been involved in syntheses of such
PIs, and in this Letter we would like to describe novel
and potent HIV-protease inhibitors, which are based on
an unprecedented spirocyclic pyrrolidone scaffold,
exemplified by 1–3 (Fig. 1). We have designed this scaf-
fold to incorporate hybrid features of the two other,
recently disclosed P2/P1 PI mimetics 4 and 5.3ꢀ7 The
spirocyclic morpholinone 4, when combined with a sul-
fonamide P10/P20 fragment, yielded a potent HIV-pro-
tease inhibitor 6 (Ki=1.7 nM, Fig. 2).3,6,7 Similarly, the
combination of pyrrolidone 5 with a sulfonamide P10/P20
fragment as well as with a hydroxy-indane P10/P20
Figure 1. Spirocyclic pyrrolidone P2/P1 mimetics 1–5.
*Corresponding author. Tel.: +1-919-483-9462; fax +1-919-483-
6053; e-mail: wieslaw.m.kazmierski@gsk.com
Figure 2. Structures of the sulfonamide- and hydroxy-indane based
inhibitors 6–8.
0960-894X/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(02)00733-3

3432
W. M. Kazmierski et al. / Bioorg. Med. Chem. Lett. 12 (2002) 3431–3433
amounts of the desired spiro-pyrrolidinones 2 and 3
were formed, but we also isolated Boc-protected 17 and
18, and their uncyclized precursors 19 and 20. In addi-
tion, variable amounts (0–40%) of the cross-linked 21
and 22 were isolated. Products 18 and 20, obtained from
16, as well as products 17 and 19, obtained from 15,
afforded additional quantities of 2 and 3, respectively,
upon workup.13 The use of diiodopentane (entry 4, Fig.
5) as the alkylating agent met with even greater success,
Figure 3. (a) LHMDS ꢀ78 ꢁC, 1,5-dibromopentane.
Since bis-alkylation of N-acyl pyrrolidones has only
been described for reactive benzylic electrophiles,10 in
conjunction with our own results we concluded that
more reactive nucleophile was required. We envisioned
that the anion of methyl (4R)-4-[(tert-butoxy-
carbonyl)amino]-5-phenylpentanoate 11 (Fig. 4) might
serve as a highly reactive pyrrolidone precursor. Further
chemical plans, following successful bis-alkylation with
1,5-dibromopentane, included the deprotection of Boc
group with acids and cyclization of products to target
lactam 1 under basic conditions. Accordingly, we syn-
thesized 11 and then generated its lithium anion and
subjected it to alkylation with 1,5-dibromopentane. We
observed a complete consumption of starting materials,
but careful examination of a complex mixture of pro-
ducts revealed formation of only minor amounts (5%)
of the target spiro-pyrrolidone 1. The major product in
this reaction was identified as the methyl ester 12 (40%
yield, Fig. 4), possibly arising from intramolecular attack
of the enolate on the tert-butylcarboxy protecting group.11
affording a 70% combined yield of the desired
spirocycle 1, after quantitative conversion of 23 into 1.
While further optimization of this chemistry is beyond
the scope of this report, yields of the desired products 1–3
can in principle be improved by adjusting reaction times
and temperatures. Formation of the undesired cross-
linked products 14, 21, and 22 might be minimized
under high dilution or by further increasing the reactivity
of electrophile.
In summary, we discovered a novel, one-pot procedure
towards the previously unreported spiro-lactams 1–3.
When coupled to epoxide-indolamine P1/P2 24, both 1
and 2 resulted in potent HIV-1 PIs 25 and 26 (Ki=50
and 23 nM, respectively, Fig. 6).14 N-Benzyl substituted
spiro-pyrrolidinone 3 produced a weak inhibitor 27
(Ki=2.5 uM), presumably due to steric interactions of
N-Bn with the S2 site in HIV-1 protease. Molecular
modeling of these inhibitors docked to HIV-PRactive
site suggests that P2 moiety in spirolactams 1 and 2 may
be further chemically manipulated in order to improve
the HIV-1 protease inhibitory potency.
Based on this result, we decided to increase the steric
bulk in the hope of favoring the alkylation over cycli-
zation to carboxy-lactam of the type 12. Using similar
chemistry we developed towards 11, we then designed
and synthesized the tert-butyl (4R)-4-[(tert-butoxy-
carbonyl) amino]-5-phenylpentanoate 13 as substrate
for bis-alkylation (Fig. 5).12 Rewardingly, the alkylation
of 13 with the 1,5-dibromopentane resulted in the for-
mation of the desired pyrrolidone 1 in 50% yield (Fig. 5,
entry 3), which was consistent with the proposed design
rationale. The only other major byproduct identified
was the cross-linked bis-lactam 14 (40%).13
Encouraged by this result, we subjected 13 to additional
alkylations with N-benzyl-bis-N-(iodoethyl) amine 15
and bis-O-(iodoethyl) ether 16 (entries 1 and 2, Fig. 5),
in order to synthesize the spirocycles 2 and 3. These
analogues incorporated predictions from molecular
modeling, that heteroatoms in the six-membered ring in
2 and 3 might develop additional H-bonding interac-
tions with the S2 pocket of HIV-1 protease, while
improving overall solubility. In both cases, significant
Figure 5. (a) THF, 3 equiv LHMDS ꢀ78 ꢁC, 1 equiv alkylating agent
45 min at ꢀ78 ꢁC, then 17 h at rt.
Figure 4. (a) LHMDS, 1 equiv 13 at ꢀ78 ꢁC, 45 min. Then continue
Figure 6. (a) NaH/DMF, 80 ꢁC; (b) 4 M HCl/dioxane.
overnight at ambient temperature.

W. M. Kazmierski et al. / Bioorg. Med. Chem. Lett. 12 (2002) 3431–3433
3433
Acknowledgements
12. Synthesis of 13: tert-butyl diethylphosphonoacetate (16.9
g, 80.22 mM) in 20 mL of THF was cooled to 0 ꢁC and added
NaH (2.11 g, 88.2 mM) portion-wise. After 30 min. at rt, the
solution was cooled down to 0 ꢁC and added Boc-Phe(al) (20.0
g, 80.2 mM). The reaction was then continued for 1.5 h at rt,
We would like to thank Drs. Frank Salituro and
Roger Tung of Vertex Pharmaceuticals for stimulating
discussions.
added 200 mL of dioxane and Pd.C (10%, 0.5 g), and hydro-
1
genated for 24 h at 30 psi. H NMR(CDCl ) d 7.20 (m, 5H),
3
4.42 (m, 1H), 3.79 (m, 1H), 2.79 (m, 2H), 2.24 (t, 2H, J=7.4
Hz), 1.78 (m, 1H), 1.57 (m, 1H), 1.42 (s, 9H), 1.38 (s, 9H); 13
C
References and Notes
NMR(CDCl ) d 169.8, 152.3, 134.8, 126.4, 125.2, 123.2, 77.3,
3
76.0, 48.6, 38.8, 29.3, 25.9, 25.3, 25.0. MS: m/z 372.2 (M+Na).
13. Synthesis of 1. Intermediate 13 (1.228 mM, 0.377 g) in
THF (8 mL) was added 3 equiv of LHMDS (1 M in THF, 3.68
mM, 3.68 mL) at ꢀ78 ꢁC. After 45 min at ꢀ78 ꢁC, 1 equiv of
1,5-dibromopentane (1.228 mM, 0.282 g) in THF (5 mL) was
added, and the reaction was allowed to proceed at room tem-
perature for 17 h, and then quenched with 10% aqueous citric
acid. Aqueous work-up, followed by C18 RP-HPLC purifica-
1. Kim, E. E.; Baker, C. T.; Dwyer, M. D.; Murcko, M. A.;
Rao, B. G.; Tung, R. D.; Navia, M. A. J. Am. Chem. Soc.
1995, 117, 1181.
2. Askin, D.; Eng, K. K.; Rossen, K.; Purick, R. M.; Wells,
K. M.; Volante, R. P.; Reider, P. J. Tetrahedron Lett. 1994, 35,
673.
3. Tung, R. D.; Salituro, F. G.; Deininger, D. D.; Bhisetti,
G. R.; Baker, C. T.; Spaltenstein, A.; Kazmierski, W. M. WO
9727180. CAN 132:322087.
4. Salituro, F. G.; Baker, C. T.; Court, J. J.; Deininger, D. D.;
Kim, E. E.; Li, B.; Novak, P. M.; Rao, B. G.; Pazhanisamy,
S.; Porter, M. D.; Schairer, W. C.; Tung, R. D. Bioorg. Med.
Chem. Lett. 1998, 8, 3637.
5. Spaltenstein, A.; Cleary, D.; Bock, B.; Kazmierski, W.;
Furfine, E.; Wright, L.; Hazen, R.; Andrews, W.; Almond, M.;
Tung, R.; Salituro, F. Bioorg. Med. Chem. Lett. 2000, 10, 1159.
6. Fritch, P. C.; Kazmierski, W. M. Synthesis 1999, 1, 112.
7. Fritch, P. C.; Kazmierski, W. M. Peptidomimetics Protocols
Humana: Totowa, 1999; p 281.
8. Padwa, A.; Hertzog, D. L.; Nadler, W. R.; Osterhout,
M. H.; Price, A. T. J. Org. Chem. 1994, 59, 1418.
9. Nakagawa, Y.; Kanai, M.; Nagaoka, Y.; Tomioka, K.
Tetrahedron 1998, 54, 10295.
10. Charrier, J.-D.; Duffy, J. E. S.; Hitchcock, P. B.; Young,
D. W. Tetrahedron Lett. 1998, 39, 2199.
11. Related transformations of cyclic carbamates from
b-hydroxy-N-Boc amines have been described, e.g. Pihko,
A. J.; Nicolaou, K. C.; Koskinen, A. M. P. Tetrahedron:
Asymmetry 2001, 12, 937.
1
tion afforded 149 mg of 1 (0.614 mmol, yield 50%). H NMR
(CDCl3) d 7.23 (m, 5H), 3.87 (m, 1H), 2.81 (m, 2H), 2.26 (m,
1H), 1.8–1.2 (11H); 13C NMR(CDCl ) d 184.2, 136.9, 129.0,
128.9, 127.1, 54.2, 46.0, 43.0, 37.7, 33.9, 31.9, 25.2, 22.1, 22.0.
3
MS m/z 244.2 (M+H+).
Synthesis of 2. Synthesized as above except that bis-O-
1
iodoethyl ether was used (1.26 g, 1 equiv). H NMR(DMSO-
d6, 300 MHz) d 7.79 (s, 1H), 7.22 (m, 5H), 3.73 (m, 3H), 3.24
(m, 2H), 2.88 (dd, 1H, J=4.8, 13.4 Hz), 2.57 (dd, 1H, J=8.4,
13.4 Hz), 2.03 (m, 1H), 1.76 (m, 1H), 1.55 (m, 2H), 1.22 (m,
1H), 1.01 (m, 1H). MS m/z 246.2 (M+H+).
Synthesis of 3. Synthesized as above, except that additional
treatment with 1:1 (v/v) DCM/TFA (40 mL) was needed to
convert 17 into 3. N-benzyl-N-bis-iodoethane (5.5 g, 13.25
mmol) was prepared from the N-benzyl-N-bis-chloroethane
via Finkelstein reaction. 1H NMR(CDCl 3, 300 MHz) of 3
(TFA salt) d 7.30 (m, 10H), 5.85 (m, 1H), 4.16 (m, 2H), 3.86
(m, 1H), 3.68 (m, 1H), 3.36 (m, 3H), 2.88 (dd, 1H), 2.62 (dd,
1H), 1.7–2.2 (m, 6H). MS m/z 335.2 (M+H+).
14. Maschera, B.; Darby, G.; Palu, G.; Wright, L. L.; Tisdale,
M.; Myers, R.; Blair, E. D.; Furfine, E. S. J. Biol. Chem. 1996,
271, 33231.