Thalidomide metabolites and analogs. Part 2: Cyclic derivatives of 2-N-phthalimido-2S,3S (3-hydroxy) ornithine

Article abstract of DOI:10.1016/S0040-4039(00)01204-1

E-(5-N-phthaloyl)-2-pentenoic acid benzyl ester was dihydroxylated by a Sharpless AD-mix protocol followed by mononosylation of the resultant 2R,3S diol. Azide displacement of the mononosylate followed by protection with the TBDMS group gave the ε-N-phthaloyl-substituted-β-tert-butyldimethylsilyloxy-α-azidocarboxylic acid benzylester. Hydrazinolysis resulted in removal of the phthalimide group with concomitant lactamization to the 4-silyloxy-3-azidopiperidinones. Staudinger reduction of the azidopiperidinones followed by N-phthaloylation and hydrolysis of the silyl group afforded the 4'-hydroxylated-6'-deoxythalidomide derivatives. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4039(00)01204-1

Tetrahedron Letters 41 (2000) 7151±7155
Thalidomide metabolites and analogs. Part 2: Cyclic
derivatives of 2-N-phthalimido-2S,3S (3-hydroxy) ornithine
Frederick A. Luzzio,a,* Elizabeth M. Thomasa and William D. Figgb
aDepartment of Chemistry, University of Louisville, Louisville, Kentucky 40292, USA
bMedicine Branch, National Cancer Institute, Bethesda, Maryland 20892, USA
Received 4 May 2000; revised 10 July 2000; accepted 12 July 2000
Abstract
E-(5-N-phthaloyl)-2-pentenoic acid benzyl ester was dihydroxylated by a Sharpless AD-mix protocol
followed by mononosylation of the resultant 2R,3S diol. Azide displacement of the mononosylate followed
by protection with the TBDMS group gave the e-N-phthaloyl-substituted-b-tert-butyldimethylsilyloxy-a-
azidocarboxylic acid benzylester. Hydrazinolysis resulted in removal of the phthalimide group with
concomitant lactamization to the 4-silyloxy-3-azidopiperidinones. Staudinger reduction of the azidopiper-
idinones followed by N-phthaloylation and hydrolysis of the silyl group a€orded the 40-hydroxylated-60-
deoxythalidomide derivatives. # 2000 Elsevier Science Ltd. All rights reserved.
Keywords: amino acids and derivatives; azides; hydroxylation; imides; lactams.
The teratogenic and antiangiogenic properties of thalidomide (1) may be attributed to a prior
metabolic activation step which produces hydroxylated derivatives of either the phthalimide or
glutarimide rings.1 The disposition of 1 and its hydroxylated analogs may also be traced through
hydrolytic pathways in vivo which can operate to produce acyclic derivatives, namely the 2-N-
phthalimidoglutamine, -isoglutamine, -glutamic acid and the carboxybenzamidic (phthalamic
acid) derivatives of glutamine, isoglutamine and glutamic acid.2 The tendency of thalidomide to
racemize under physiological conditions3 together with the sensitivity of the compound and its
metabolites toward hydrolysis have complicated the task of identifying the active components
and elucidating the pathway of their formation. Moreover, details regarding the molecular
mechanism of thalidomide and its putative metabolites have remained elusive. Current studies in
our laboratory have involved the synthesis of hydroxylated metabolites and analogs of thalidomide
and its hydrolysis products4 with a particular emphasis on two fronts: (1) stereoselective
preparation of hydroxylated products of the glutarimide ring and their analogs; and (2)
preparation of deoxygenated analogs in which a carbonyl has been removed from either the
glutarimide ring or the phthalimide ring thereby enhancing the biological activity of the molecule
as an angiogenesis inhibitor.1b,5a
* Corresponding author. Tel: 502 852-7323; fax: 502 852-8249; e-mail: faluzz01@athena.louisville.edu
0040-4039/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(00)01204-1

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This letter details our progress in the synthesis of hydroxythalidomides 2 and 3. Analog 2 is a
putative metabolic product of 40-oxidation of the glutarimide ring, or if considering the ultimate
hydrolysis products, oxidation of the b-position of glutamine, isoglutamine or glutamic acid. We
designed the synthesis of 2 to include the deoxygenated analog 3 since the piperidinone analogs,
as in the case of the phthalimidine analog EM-12 (4),5 may o€er increased activity due to the
resistance of the lactams to hydrolysis in vivo. As in the synthesis of 50-hydroxythalidomide
derivatives (5),6 a subject of previous reports from our laboratory,7,8 the common objective is the
development and evaluation of methods for the stereoselective synthesis of b-and g-hydroxylated
a-amino acids and their derivatives.
Wittig ole®nation of 3-(N-phthalimido)propionaldehyde 69 with (benzyloxycarbonylmethyl)-
triphenylphosphonium bromide in the presence of NaOH/triethylamine in a two-phase system of
dichloromethane/H2O a€orded the E-5-N-phthalimido-a,b-unsaturated benzyl ester 710 in
99% yield (Scheme 1). Sharpless asymmetric dihydroxylation of a,b-unsaturated ester 711 gave
the 2R,3S-diol ester 812 in 82% yield.13 Azido ester 10 was prepared through a displacement of
the sensitive nosylate 9 by a two-step sequence which did not necessitate rigorous puri®cation of
intermediate 9. Treatment of diol ester 8 with 4-nitrobenzenesulfonyl chloride followed by rapid
silica gel ®ltration (hexane/EtOAc) provided the sensitive a-nosyl ester 9 which was immediately
exposed to sodium azide in dimethylformamide to a€ord the 2S,3S-N-phthalimido azido ester 10.14,15
Scheme 1. Conditions: (a) BnOCOCH2PPh3+Br^, NaOH, Et3N, CH2Cl2, H2O, 12 h, rt (99%); (b) AD mix-a,
CH3SO2NH2, (CH3)3COH, H2O, 48 h, 5ꢀC (82%); (c) 4-NO2PhSO2Cl, pyr, CH2Cl2, 72 h, 5ꢀC; (d) NaN3/DMF, 12 h,
60ꢀC (59% from 8); (e) (CH3)3C(CH3)2SiOSO2CF3, 2,4,6-collidine, CH2Cl2, 12 h, 5ꢀC (89%); (f) N2H4, EtOH, 12 h, rt
(90%, 14a:14b=3:1); (g) PPh3, THF, H2O, 16 h, rt; (h) o-C6H4(COCl)2, DMAP, CH2Cl2, 16 h, 0ꢀC (53% from 10); (i)
H2, Pd-C, EtOH, 7 atm, 72 h, rt (78%)

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Staudinger reduction of the azido ester 10 followed by direct N-phthaloylation furnished the
2S,3S-bis-N-phthalimido-b-hydroxyester 12 (53% from 10). Submission of 12 to catalytic
hydrogenation with palladium on charcoal facilitated cleavage of the benzyl group thereby
a€ording the bis-N-phthalimido-b-hydroxyornithine derivative 13 (78%) (Scheme 2).16
Scheme 2. Conditions: (a) PPh3, CH3CN, 12 h, rt; then H2O, Et3N, 5 h, rt (68%); (b) o-C6H4(COCl)2, DMAP,
CH2Cl2, 12 h, 0ꢀC (99%); (c) R-(+)-MTPA-Cl, DMAP, CH2Cl2, 24 h, 0ꢀC to rt; (d) TFA:H2O (9:1), CH2Cl2, 3 h, 0ꢀC
to rt (70%)
The alcohol function of azido ester 10 was silylated with tert-butyldimethylsilyl tri¯ate17 to give
the a-azido-b-silyloxy benzyl ester 11 (89%).18 Hydrazinolysis of the benzyl ester 11 resulted in
smooth removal of the phthalimide group and cyclization to provide the epimeric 3-azido-4-silyl-
oxypiperidinones 14a19 and 14b (90% in 3:1 ratio).20 Staudinger reduction/hydrolysis converted
the 3S,4S-3-azido-4-silyloxypiperidinone 14a to the corresponding 3-amino-4-silyloxypiper-
idinone 1521 in 68% yield. The enantiomeric composition of the 3-amino-4-silyloxypiperidinone
15 was determined by Mosher amide analysis.22 Treatment of 15 with R-(+)-a-methoxy-a-(tri-
¯uoromethyl)phenylacetyl chloride provided the chromatographically homogeneous corresponding
MTPA amide 16. 19F NMR analysis of 16 revealed >96% enantiomeric purity [ꢀ 7.13 (major); ꢀ
7.46 (minor), 470 MHz, CDCl3/TFA]. Phthaloylation of the 3-amino-4-silyloxypiperidinone 15
proceeded smoothly to deliver the 60-deoxy-40-silyloxythalidomides 17a23 and 17b (99%) as a
mixture (17a:17b=2:1) of epimers. Desilylation of 17a and 17b under acidic conditions24
provided the 60-deoxy-40-hydroxythalidomides 2S,3S-3a25 and 2R,3S-3b in 70% yield. The
oxidation of the 40-silyloxy-60deoxythalidomides 17a and 17b at C-60 to a€ord the corresponding
glutarimides is currently under examination. The employment of peroxide/metal oxidants such as
tert-butylhydroperoxide and MnIIIacac systems, although fruitful in many lactam to imide
oxidations,26 have been largely unsuccessful in our application. Recently, Takeuchi27 has
reported the oxidation of 30-¯uoro-60-deoxythalidomide analog to the corresponding glutarimide
using a ruthenium dioxide/metaperiodate system. These new results have given us impetus and
encouragement in our pursuit of a suitable oxidation system for the silyloxylactam substrates. In
summary we have detailed a novel route to b-hydroxyl-substituted 60-deoxythalidomide analogs
via the lactamization of a pivotal hydroxyornithine derivative. Prior to lactamization to the
cycloornithine derivatives, a key functionalization was introduced using the Sharpless asymmetric
dihydroxylation method.
References
1. (a) Braun, A. G.; Harding, F. A.; Weinreb, S. L. Toxicol. Appl. Pharmacol. 1986, 82, 175±179. (b) Bauer, K. S.;
Dixon, S. C.; Figg, W. D. Biochem. Pharmacol. 1998, 55, 1827±1934. (c) Figg, W. D.; Reed, E.; Green, S.; Pluda,

7154
J. M. In Antiangiogenic Agents in Cancer Chemotherapy; Teicher, B. A., Ed.; Humana Press: Totowa, NJ, 1999;
Chapter 24, pp. 407±422. (d) Udagawa, T.; Verheul, H. M. W.; D'Amato, R. J. In Antiangiogenic Agents in Cancer
Chemotherapy; Teicher, B. A., Ed.; Humana Press: Totowa, NJ, 1999; Chapter 16, pp. 263±269.
2. Schumacher, H.; Smith, R. L.; Williams, R. T. Brit. J. Pharmacol. 1965, 25, 324±337.
3. Nishimura, K.; Hashimoto, Y.; Iwasaki, S. Chem. Pharm. Bull. 1994, 42, 1157±1159.
4. Helm, F.; Frankus, E. F.; Friderichs, E.; Graudums, I.; Flohe, L. Arzneim.-Forsch./Drug Res. 1981, 31, 941±949.
See also Ref. 1d, pp. 265±266.
5. (a) Luzzio, F. A.; Piatt Zacherl, D.; Figg, W. D. Tetrahedron Lett. 1999, 40, 2087±2090. (b) Winckler, K.;
Klinkmuller, K. D.; Schmal, H.-J. J. Chromatogr. 1989, 488, 417±425. (c) Merker, H.-J.; Heger, E.; Sames, K.;
Sturge, H.; Neubert, D. Arch. Toxicol. 1988, 61, 165±179.
6. Eriksson, T.; Bjorkman, S.; Roth, B.; Bjork, H.; Hoglund, P. J. Pharm. Pharmacol. 1998, 50, 1409±1416.
7. Luzzio, F. A.; Mayorov, A. V.; Figg, W. D. Tetrahedron Lett. 2000, 41, 2275±2278.
8. (a) Luzzio, F. A.; Thomas, E. M.; Figg, W. D. Abstracts of Papers, 218th National Meeting of the American
Chemical Society, New Orleans, LA; August 22, 1999 (ORGN 164). (b) Luzzio, F. A.; Mayorov, A. V.; Figg,
W. D. Abstracts of Papers, 219th National Meeting of the American Chemical Society, San Francisco, CA; March
20 and 22, 2000 (ORGN 780).
9. Luzzio, F. A.; Adams, L. L. J. Org. Chem. 1989, 54, 5387±5390. Luzzio, F. A.; O'Hara, L. C. Synth. Commun.
1990, 20, 3223±3224.
10. For 7: IR (KBr) ꢁmax 3475, 3083, 2921, 2251, 1773, 1687, 1426 cm^1; 1H NMR (CDCl3, 500 MHz) ꢀ 7.82±7.81 (m,
2H), 7.34±7.29 (m, 5H), 6.95 (dt, 1H, J=15.7, 7.0 Hz), 5.92 (dt, 1H, J=15.7, 0.7 Hz), 5.14 (s, 2H), 3.81 (t, 2H,
J=7.0 Hz), 2.60 (dd, 2H, J=7.0, 7.0 Hz); 13C NMR (CDCl3, 125 MHz) ꢀ 168.1, 166.1, 144.8, 136.0 134.1, 132.0,
128.6, 128.2, 123.5, 123.4, 109.2, 66.2, 36.3, 31.3. HRMS (EI): calcd for C20H17O4 [M+]: 335.1157; found:
335.1170.
11. (a) Lohray, B. B.; Kalantar, T. H.; Kim, B. M.; Park, C. Y.; Shibata, T.; Wai, J. S.; Sharpless, K. B. Tetrahedron
Lett. 1989, 30, 2041±2044. (b) Fleming, P. R.; Sharpless, K. B. J. Org. Chem. 1991, 56, 2869±2875. (c) Sharpless,
K. B.; Amberg, W.; Bennani, W. L.; Crispino, G. A.; Hartung, J.; Jeong, K.; Kwong, H.; Morikawa, K.; Wang,
Z.; Xu, D.; Zhang, X. J. Org. Chem. 1992, 57, 268±271. (d) For speci®c conditions see: Boger, D. L.; Schule, G.
J. Org. Chem. 1998, 63, 6421±6424.
25
12. For 8: ‰ꢂŠ ^29.2 (c=1.08, CHCl3); IR (KBr) ꢁmax 3501, 3317, 2940, 2359, 2111, 1715, 1397 cm^1; 1H NMR
D
(CDCl3, 500 MHz) 7.84±7.82 (m, 2H), 7.72±7.70 (m, 2H), 7.32±7.24 (m, 5H), 5.24±5.19 (m, 2H), 4.12±4.07 (m,
1H), 3.95±3.88 (m, 2H), 3.86±3.78 (m, 1H), 3.04 (d, 1H, J=11.2 Hz), 2.88 (d, 1H, J=7.4 Hz), 2.4 (m, 1H), 1.88±
1.85 (m, 1H); 13C NMR (CDCl3, 125 MHz) ꢀ 172.8, 168.7, 134.1, 132.0, 128.6, 128.5, 128.4, 128.2, 123.4, 73.6,
69.7, 67.6, 34.6, 32.5. HRMS (EI): calcd for C20H19O6 [M+]: 369.1212; found: 369.1216.
13. Based on the Sharpless model for E-ole®n enantioselectivity with AD mix-a, the con®guration of diol 8 is assumed
to be 2R,3S; however, low ee's have been reported in cases of e-substituted-E-2-pentenoate esters (Ref. 11a) and E-
ole®ns bearing carbamate substituents (Shirota, O.; Nakanishi, K.; Berova, N. Tetrahedron 1999, 55, 13643±
13658). For purposes of relating absolute con®guration, the isopropylidene derivative of 8 was prepared from the
O-benzylbenzoate derivative of known (2R,3S) con®guration: Maier, M. E.; Hermann, C. Tetrahedron 2000, 56,
557±561 (shown below) and the con®guration of 2R,3S-8 was con®rmed. The enantioselectivity of the AD reaction
as applied to e-substituted-E-2-pentenoate benzyl esters has been under examination in these laboratories (Ref. 8a).
These results will be reported in a separate communication with full experimental details.
14. Attempted derivatization of the b-hydroxyl function of 10, for assay of chiral purity, with R-(+)-MTPA chloride
(DMAP/CH2Cl2/0ꢀC) resulted in facile elimination to the corresponding a,b-unsaturated ester (b-H, t, 6.23 ꢀ, 500
MHz, CDCl3). See Ref. 22 for the use of R-(+)-MTPA chloride.
25
D
1
15. For 10: ‰ꢂŠ ^45.11 (c=1.74, CHCl3); IR (Kbr) ꢁmax 3466, 3349, 2114, 1769, 1703, 1404, 1199 cm^1; H NMR
(CDCl3, 500 MHz) ꢀ 7.84±7.82 (m, 2H), 7.72±7.70 (m, 2H), 7.32±7.24 (m, 5H), 5.24±5.17 (m, 2H), 4.11±4.09 (m,
1H), 4.02±4.01 (d, 1H, J=5.5 Hz), 3.93±3.91 (br m, 1H), 3.82±3.82 (m, 2H), 1.86±1.83 (m, 2H); 13C NMR (CDCl3,

7155
125 MHz) ꢀ 172.8, 168.7, 134.1, 132.0, 128.6, 128.5, 128.4, 128.2, 123.4, 73.6, 69.7, 67.6, 34.6, 32.5. MS: [ES+] m/z
395.3 ([M+1], 100%).
16. Bis-phthalimide 13 was inactive when evaluated for inhibition of angiogenesis in the rat aortic ring and human
aortic endothelial cell (HAEC) bioassays (see Ref. 1b).
17. Corey, E. J.; Cho, H.; Rucker, C.; Hua, D. H. Tetrahedron Lett. 1981, 22, 3455±3458.
25
D
18. For 11: ‰ꢂŠ +8.28 (c=1.98, CHCl3); IR (KBr) ꢁmax 3033, 2945, 2858, 2112, 1715, 1443, 1398, 775 cm^1; 1H NMR
(CDCl3, 500 MHz) ꢀ 7.82±7.80 (m, 2H), 7.70±7.67 (m, 2H), 7.33±7.28 (m, 5H), 5.28±5.11 (m, 2H), 4.19±4.14 (m,
1H), 3.81±3.75 (m, 1H), 3.73±3.66 (m, 1H), 2.08±1.99 (m, 1H), 1.91±1.84 (m, 1H), 0.88 (s, 9H), 0.12 (s, 3H), 0.08 (s,
3H); 13C NMR (CDCl3, 125 MHz) ꢀ 167.8, 135.2, 134.2, 131.8, 128.8, 123.5, 72.2, 71.3, 67.9, 66.6, 64.6, 34.6, 32.0,
26.0, 18.0. MS: [ES+] m/z 509.4 ([M+1], 100%).
25
D
1
19. For 14a: ‰ꢂŠ ^24.06 (c=1.65, CHCl3); IR (KBr) ꢁmax 3350, 3311, 3199, 2929, 2247, 2105, 1680, 1255 cm^1; H
NMR (CDCl3, 500 MHz) 6.65 (br s, 1H), 4.27 (br m, 1H), 3.72 (d, 1H, J=2.8 Hz), 3.59±3.63 (m, 1H), 3.23±3.19
(m, 1H), 1.96 (m, 1H), 1.90 (m, 1H), 0.88 (s, 9H), 0.14 (s, 3H), 0.09 (s, 3H); 13C NMR (CDCl3, 125 MHz) ꢀ 168.7,
68.4, 63.1, 37.7, 28.6, 25.7, 16.5, ^5.0.
20. The hydrazinolysis of 11 to 14a/14b is the most facile conversion of an ornithine derivative to the corresponding
d-valerolactam that we have observed. For example, see: Toshima, H.; Maru, K.; Saito, M.; Ichiara, A.
Tetrahedron 1999, 55, 593±5808. Alternatively, the N-phthaloyl-3-azidoalcohol 10 could be lactamized with
hydrazine to the corresponding 4-hydroxy-3-azidopiperidinone 18 (below); however, the yields of the cyclization
and subsequent silylation of the hydroxyl group to a€ord 14a and 14b were lower. In addition, a remarkable
tendency for the 4-hydroxy-3-azidopiperidinone to undergo elimination to the 2-azido-2,3-didehydrocyclo-
ornithine 19 (Yonezowa, Y.; Hirosaki, T.; Hayashi, T.; Shin, C. Synthesis 2000, 1, 144±148) was observed when
attempting thionoformylation (below) of the alcohol function (phenylthionochloroformate, DMAP, CH2Cl2, 0ꢀC)
en route to a N-R-(+)-MPTA-cycloornithine amide derivative 20, by a Barton deoxygenation/reduction/MTPA
amide derivatization sequence (shown retrosynthetically).
25
D
1
21. For 15: ‰ꢂŠ +12.58 (c=1.2, CHCl3); IR (KBr) ꢁmax 3246, 3202, 2973, 2960, 1672, 1488, 1255 cm^1; H NMR
(CDCl3, 500 MHz) ꢀ 6.65 (br s, 1H), 4.27±4.26 (br m, 1H), 3.72 (d, 1H, J=2.8 Hz), 3.56 (dt, 1H, J=4.9, 6.2, 16.0
Hz), 3.23±3.19 (m, 1H), 1.96±1.92 (m, 1H), 1.90±1.84 (m, 1H), 0.88 (s, 9H), 0.14 (s, 3H), 0.09 (s, 3H); 13C NMR
(CDCl3, 125 MHz) ꢀ 168.7, 68.4, 63.2, 37.7, 28.7, 25.8, 18.1, ^5.0. MS: [ES+] m/z 245.3 ([M+1], 100%).
22. Dale, J. A.; Dull, D. L.; Mosher, H. S. J. Org. Chem. 1969, 34, 2543±2549.
23. For 17a: ‰ꢂŠ2D5+39.0 (c=1.1, CHCl3); IR (KBr) ꢁmax 3219, 3098, 2956, 2860, 1772, 1715, 1687, 1393, 767 cm^1; H
1
NMR (CDCl3, 500 MHz) ꢀ 7.80 (br s, 2H), 7.67 (dd, 2H, J=3.0, 5.3 Hz), 6.79 (br s, 1H), 4.75 (d, 1H, J=4.5 Hz),
4.31±4.29 (m, 1H), 3.79±3.73 (m, 1H), 3.25±3.20 (m, 1H), 2.0±1.98 (m, 2H), 0.72 (s, 9H), ^0.08 (s, 3H), ^0.31 (s,
3H); 13C NMR (CDCl3, 125 MHz) ꢀ 168.0, 134.1, 132.0, 123.4, 67.7, 57.4, 38.3, 32.0, 25.4, 17.6, ^4.7, ^5.2. MS:
m/z 375 [M]+ (82%), 145 (100%).
24. While tetra-N-butylammonium ¯uoride (TBAF) facilitated cleavage of the tert-butyldimethylsilyl (TBDMS)
group, the quaternary ammonium by-products complicated the chromatographic puri®cation of the 60-
deoxythalidomides 3a/3b thereby necessitating the employment of the easily-removable TFA.
25
25. For 3a: ‰ꢂŠ +16.6 (c=1.0, MeOH); IR (KBr) ꢁmax 3346, 2930, 2860, 1713, 1666, 1399, 1082, 717 cm^1; 1H NMR
D
(CDCl3, 500 MHz) ꢀ 7.87 (br d, 2H, J=3.0 Hz), 7.83 (br d, J=2.2 Hz), 4.90 (d, 1H, J=4.5 Hz), 4.31 (m, 1H),
3.76±3.70 (m, 1H), 3.32±3.29 (m, 1H), 2.12±2.11 (m, 2H); 13C NMR (CDCl3, 125 MHz) ꢀ 170.2, 169.5, 136.1,
135.5, 133.4, 124.3, 67.7, 58.5, 39.4, 31.9. MS: [ES+] m/z 261.3 ([M+1], 100%).
26. Doumaux Jr., A. R.; Trecker, D. J. J. Org. Chem. 1970, 35, 2121±2125.
27. Takeuchi, Y.; Shiragami, T.; Kimura, K.; Suzuki, E.; Shibata, N. Organic Lett. 1999, 1, 1571±1573.