Total synthesis of an antitumor agent RA-VII via an efficient preparation of cycloisodityrosine

Article abstract of DOI:10.1021/jo990432w

Details of efficient syntheses of (9S, 12S)-cycloisodityrosine (6) and a concise total synthesis of RAVII (1) were described. An intramolecular S(N)Ar-based cycloetherification reaction was employed as the key ring- closure step for construction of the illusive 14-membered m,p-cyclophane. Treatment of methyl N-[N-(tert-butyloxycarbonyl)-L-(3-hydroxy-4- methoxyphenylalanyl]-L-4-fluoro-3-nitrophenylalaninate ((9S,12S)-10) with potassium carbonate in DMSO at room temperature provided a mixture of two atropdiastereomers 20a and 20b in 75% yield that were transformed into cycloisodityrosine 6 in good overall yield. Furthermore, a size-selective ring-forming process was established for methyl N-[N-(tert-butyloxycarbonyl)- L-(3,4-dihydroxyphenylalanyl)]-L-4-fluoro-3-nitrophenylalaninate ((9S,12S)- 11). Thus, cyclization of 11 (K₂CO₃, DMSO, rt), followed by in situ methylation, gave exclusively the 14-membered m,p-cyclphane 20a and 20b without competitive formation of the alternative 15-membered p,p-cyclophane. The selective ring-forming process allowed us to develop one of the shortest and the most efficient synthesis of cycloisodityrosine to date. Computational studies have shown that it was the elimination, but not the addition, step that determined the ring-size selectivity observed in the cyclization of substrate 11. Coupling of 6 with L-N-Boc-Ala (51) proceeded efficiently to provide the corresponding tripeptide 52 that, after removal of the N-Boc function, was allowed to react with another tripeptide 53 to afford the hexapeptide 50 in good overall yield. Saponification followed by liberation of amino function from 50 gave the seco-acid, whose cyclization (DPPA, DMF, NaHCO₃) afforded the natural product RA-VII (1).

Full text of DOI:10.1021/jo990432w

J . Org. Chem. 1999, 64, 6283-6296
6283
Tota l Syn th esis of a n An titu m or Agen t RA-VII via a n Efficien t
P r ep a r a tion of Cycloisod ityr osin e†
Antony Bigot, Marie Elise Tran Huu Dau, and J ieping Zhu*
Institut de Chimie des Substances Naturelles, CNRS, 91198 Gif-sur-Yvette, France
Received March 10, 1999
Details of efficient syntheses of (9S,12S)-cycloisodityrosine (6) and a concise total synthesis of RA-
VII (1) were described. An intramolecular SNAr-based cycloetherification reaction was employed
as the key ring-closure step for construction of the illusive 14-membered m,p-cyclophane. Treatment
of methyl N-[N-(tert-butyloxycarbonyl)-L-(3-hydroxy-4-methoxyphenylalanyl]-L-4-fluoro-3-nitrophe-
nylalaninate ((9S,12S)-10) with potassium carbonate in DMSO at room temperature provided a
mixture of two atropdiastereomers 20a and 20b in 75% yield that were transformed into
cycloisodityrosine 6 in good overall yield. Furthermore, a size-selective ring-forming process was
established for methyl N-[N-(tert-butyloxycarbonyl)-L-(3,4-dihydroxyphenylalanyl)]-L-4-fluoro-3-
nitrophenylalaninate ((9S,12S)-11). Thus, cyclization of 11 (K2CO3, DMSO, rt), followed by in situ
methylation, gave exclusively the 14-membered m,p-cyclphane 20a and 20b without competitive
formation of the alternative 15-membered p,p-cyclophane. The selective ring-forming process allowed
us to develop one of the shortest and the most efficient synthesis of cycloisodityrosine to date.
Computational studies have shown that it was the elimination, but not the addition, step that
determined the ring-size selectivity observed in the cyclization of substrate 11. Coupling of 6 with
L-N-Boc-Ala (51) proceeded efficiently to provide the corresponding tripeptide 52 that, after removal
of the N-Boc function, was allowed to react with another tripeptide 53 to afford the hexapeptide 50
in good overall yield. Saponification followed by liberation of amino function from 50 gave the seco-
acid, whose cyclization (DPPA, DMF, NaHCO3) afforded the natural product RA-VII (1).
In tr od u ction a n d Ba ck gr ou n d
RA-VII (1) is a bicyclic hexapeptide (Figure 1) isolated
from the plants Rubia akane and Rubia cordifolia
(Rubiaceae)1 whose structure is closely related to
bouvardin (NSC 259968, 2) isolated from Bouvardia
ternifolia.2 To date, 16 congeners (RA-I-RA-XVI) have
been identified, and their relative and absolute configu-
rations have been determined.3 A characteristic struc-
tural feature of this family of natural products is the
presence of an 18-membered peptide ring and a bridged
14-membered cycloisodityrosine unit with an endo aryl-
aryl ether linkage. Both RA-VII (1) and bouvardin (2)
show potent antitumor activity by inhibiting protein
synthesis through eukaryotic 80S ribosomal binding.4,5
Mechanistic studies using purified elongation factors and
ribosomes have identified RA-VII as a peptidyltrans-
ferase inhibitor. RA-VII has been selected for clinic
F igu r e 1.
† Dedicated with affection to Professor Yulin Li on the occasion of
his 65th birthday.
evaluations in J apan as an anticancer agent.3 Extensive
structure-activity relationship (SAR) studies carried out
in Itokawa6 and Boger’s7 groups elucidated that the 14-
membered cycloisodityrosine moiety is the pharmacoph-
ore for this class of natural products.
(1) (a) Itokawa, H.; Takeya, K.; Mihara, K.; Mori, N.; Hamanaka,
T.; Sonobe, T. Chem. Pharm. Bull. 1983, 31, 1424-1427. (b) Itokawa,
H.; Takeya, K.; Mori, N.; Hamanaka, T.; Sonobe, T.; Mihara, K. Chem.
Pharm. Bull. 1984, 32, 284-290.
(2) (a) J olad, S. D.; Hoffman, J . J .; Torrance, S. J .; Wiedhopf, R. M.;
Cole, J . R.; Arora, S. K.; Bates, R. B.; Gargiulo, R. L.; Kriek, G. R. J .
Am. Chem. Soc. 1977, 99, 8040-44. (b) Bates, R. B.; Cole, J . R.;
Hoffmann, J . J .; Kriek, G. R.; Linz, G. S.; Torrance, S, J . J . Am. Chem.
Soc. 1983, 105, 1343-1347.
(3) (a) Itokawa, H.; Takeya, K. Heterocycles 1993, 35, 1467-1501.
(b) Itokawa, H.; Takeya, K.; Hitotsuyanagi, Y.; Morita, H. In The
Alkaloids; Cordell, G. A., Ed.; Academic Press: New York, 1997; Vol.
49, pp 301-387.
(4) (a) Zalacain, M.; Zaera, E.; Vazquez, D.; J imenez, A. FEBS Lett.
1982, 148, 95. (b) Morita, H.; Yamamiya, T.; Takeya, K.; Itokawa, H.;
Sakuma, C.; Yamada, J .; Suga, T. Chem. Pharm. Bull. 1993, 41, 781-
783.
(6) Selected examples: (a) Morita, H.; Kondo, K.; Hitotsuyanagi, Y.;
Takeya, K.; Itokawa, H.; Tomioka, N.; Itai, A.; Iitaka, Y. Tetrahedron
1991, 47, 2757-2772. (b) Hitotsuyanagi, Y.; Kondo, K.; Takeya, K.;
Itokawa, H. Tetrahedron Lett. 1994, 35, 2191-2194. (c) Hitotsuyanagi,
Y.; Lee, S.; Takeya, K.; Itokawa, H. J . Chem. Soc., Chem. Commun.
1996, 503-504. (d) Hitotsuyanagi, Y.; Matsumoto, Y.; Sasaki, S.-I.;
Suzuki, J .; Takeya, K.; Yamaguchi, K.; Itokawa, H. J . Chem. Soc.,
Perkin Trans. 1 1996, 1749-1755. (e) Hitotsuyanagi, Y.; Anazawa, Y.;
Yamagishi, T.; Samata, K.; Ichihara, T.; Nanaumi, K.; Okado, N.;
Nakaike, S.; Mizumura, M.; Takeya, K.; Itokawa, H. Biorg. Med. Chem.
Lett. 1997, 7, 3125-3128 and references therein.
(5) Sirdeshpande, B. V.; Toogood, P. L. Bioorg. Chem. 1995, 23, 460-
470.
10.1021/jo990432w CCC: $18.00 © 1999 American Chemical Society
Published on Web 07/28/1999

6284 J . Org. Chem., Vol. 64, No. 17, 1999
Bigot et al.
Sch em e 1
ditions including polymer-supported agents, ring closure
via C3-O2 bond formation based on Ullmann ether
synthesis,9 and intramolecular oxidative phenol cou-
pling11 have failed to give the elusive 14-membered ring.
Alternatively, Inoue and co-workers10 have devised an
ingenious synthesis of 6 based on thallium trinitrate
(TTN)-promoted intramolecular phenolic oxidative cou-
pling of tetrahalogenated dipeptide followed by reductive
dehalogenation,14 but the key cyclization step proceeded
in only 5% yield. Boger and co-workers7,9,13 have success-
fully implemented an intramolecular Ullmann ether
synthesis to reach directly the cycloisodityrosine 6 by
formation of the C1-O2 bond. However, the yield of this
cyclization methodology was still low to moderate and
the harsh reaction conditions used were far from ideal.
In fact, it has recently been disclosed that epimerization
had occurred during the Ullmann ether synthesis and
that the synthetic product thus obtained was in fact an
epi-6.15,16
In connection with our research project on the total
synthesis of vancomycin and related glycopeptide anti-
biotics, we have developed a novel cycloetherification
methodology based on intramolecular SNAr reaction.8,17
The power of this ring-forming process has been demon-
strated in the synthesis of a variety of complex biologi-
cally important macrocycles with an endo aryl-aryl18 or
aryl-alkyl ether19 linkage, which were otherwise dif-
ficultly accessible. We20 and Boger’s group16,21 have
independently applied this technology to the synthesis
of cycloisodityrosine by way of cyclization of the linear
dipeptide (9S,12S)-8 (route a, Scheme 2). Although the
synthesis was relatively efficient, partial epimerization
Strongly promoted by RA-VII’s significant biological
activity, great potential as a chemotherapeutic agent, and
its unique structural features, total synthesis of RA-VII
and its congeners has attracted a number of research
groups, and a variety of synthetic approaches have been
investigated.3,8-10 From the viewpoint of synthetic design,
three strategies, namely, (1) transannulation,7,9 (2) bot-
tom-up,11 and (3) top-down approaches7,9,10 were the most
evident for the synthesis of the bridged bicyclic system
of RAs, and indeed all of them have been investigated.
While the first two strategies failed to give the target
molecules, the “top-down” approach (Scheme 1) was found
to be more operative. Realizing that ring closure of the
bottom 18-membered macrocycle from seco-acid was
relatively easy,12 synthetic efforts have thus far concen-
trated on the synthesis of the key subunit, L,L-N,N-
dimethylcycloisodityrosine methyl ester 6. However, an
efficient synthesis of such compound is far from being a
trivial problem despite its simple structure. Cyclization
via macrolactamization13 under different activating con-
(14) (a) Nishiyama, S.; Yamamura, S. Tetrahedron Lett. 1982, 23,
1281-84. (b) Yamamura, S.; Nishiyama, S. In Studies in Natural
Products Chemistry Atta-ur-Rahman, Ed.; Elsevier: New York, 1992;
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Chem. J pn. 1997, 55, 1029-1039.
(15) Inoue, T.; Sazaki, T.; Takayanagi, H.; Harigara, Y.; Hoshino,
O.; Hara, H.; Inaba, T. J . Org. Chem. 1996, 61, 3936-3937.
(16) (a) Boger, D. L.; Zhou, J . J . Org. Chem. 1996, 61, 3938-3939.
(b) Boger, D. L. Zhou, J .; Borzilleri, R. M.; Nukui, S.; Castle, S. L. J .
Org. Chem. 1997, 62, 2054-2069.
(17) (a) For a highlight, see: Burgess, K.; Lim, D.; Martinez, C. I.
Angew. Chem., Int. Ed. Engl. 1996, 35, 1077-1078. (b) For a short
account, see: Zhu, J . Synlett 1997, 133-144.
(18) Selected examples: (a) Bois-Choussy, M.; Neuville, L.; Beugel-
mans, R.; Zhu, J . J . Org. Chem. 1996, 61, 9309-9322. (b) Boger, D. L.
Zhou, J .; Borzilleri, R. M.; Nukui, S. Biorg. Med. Chem. Lett. 1996, 6,
1089-1092. (c) Evans, D. A.; Barrow, J . C.; Watson, P. S.; Ratz, A.
M.; Dinsmore, C. J .; Evrard, D. A.; DeVries, K. M.; Ellman, J . A.;
Rychnovsky, S. D.; Lacour, J . J . Am. Chem. Soc. 1997, 119, 3419-
3420. (d) Nicolaou, K. C.; Boddy, C. N. C.; Natarajan, S.; Yue, T.-Y.;
Li, H.; Bra¨se, S.; Ramanjulu, J . M. J . Am. Chem. Soc. 1997, 119, 3421-
3422. (e) J anetka, J . W.; Rich, D. H. J . Am. Chem. Soc. 1997, 119,
6488-6495. (f) Pearson, A. J .; Zhang, P.; Bignan, G. J . Org. Chem.
1997, 62, 4536-4538. (g) Rama Rao, A. V.; Gurjar, M. K.; Lakshmi-
pathi, P.; Reddy, M. M.; Nagarajan, M.; Pal, S.; Sarma, B. V. N. B. S.;
Tripathy, N. K. Tetrahedron Lett. 1997, 38, 7433-7436. (h) Carrington,
S.; Fairlamb, A. H.; Blagbrough, I. S. J . Chem. Soc., Chem. Commun.
1998, 2335-2336. (i) Evans, D. A.; Wood, M. R.; Trotter, B. W.;
Richardson, T. I.; Barrow, J . C.; Katz, J . L. Angew. Chem., Int. Ed.
Engl. 1998, 37, 2700-2704; 2704-2708. (j) Nicolaou, K. C.; Natarajan,
S.; Li, H.; J ain, N. F.; Hughes, R.; Solomon, M. E.; Ramanjulu, J . M.;
Boddy, C. N. C.; Takayanagi, M. Angew. Chem., Int. Ed. Engl. 1998,
37, 2708-2714; 2714-2716; 2717-2719 and references therein.
(19) (a) Zhu, J .; La¨ıb, T.; Beugelmans, R. Angew. Chem., Int. Ed.
Engl. 1996, 35, 2517-2519. (b) La¨ıb, T.; Zhu, J . Tetrahedron Lett. 1999,
40, 83-86.
(7) Selected examples: (a) Boger, D. L.; Yohannes, D.; Meyers, J .
B., J r. J . Org. Chem. 1992, 57, 1319-1321. (b) Boger, D. L.; Patane,
M. A.; J in, Q.; Kitos, P. A. Biorg. Med. Chem. 1994, 2, 85-100. (c)
Boger, D. L.; Zhou, J .; Winter, B.; Kitos, P. A. Biorg. Med. Chem. 1995,
3, 1579-1593. (d) Boger, D. L.; Patane, M. A.; Zhou, J . J . Am. Chem.
Soc. 1995, 117, 7357-7363. (e) Boger, D. L.; Zhou, J . J . Am. Chem.
Soc. 1995, 117, 7364-7378. (f) Boger, D. L.; Zhou, J . Biorg. Med. Chem.
1996, 4, 1597-1603 and references therein.
(8) Rao, A. V. R.; Gurjar, M. K.; Reddy, L.; Rao, A. S. Chem. Rev.
1995, 95, 2135-2167.
(9) D. L.; Yohannes, D. Y. J . Am. Chem. Soc. 1991, 113, 1427-1429.
(b) Boger, D. L.; Yohannes, D.; Zhou, J .; Patane, M. A. J . Am. Chem.
Soc. 1993, 115, 3420-3430. (c) Boger, D. L.; Patane, M. A.; Zhou, J . J .
Am. Chem. Soc. 1994, 116, 8544-8556.
(10) (a) Inaba, T.; Umezawa, I.; Yuasa, M.; Inoue, T.; Mihashi, S.;
Itokawa, H.; Ogura, K. J . Org. Chem. 1987, 53, 2957-2958. (b) Inoue,
T.; Inaba, T.; Umezawa, I.; Yuasa, M.; Itokawa, H.; Ogura, K.;
Komatsu, K.; Hara, H.; Hoshino, O. Chem. Pharm. Bull. 1995, 43,
1325-1335.
(11) Bates, R. B.; Gin, S. L.; Hassen, M. A.; Hruby, V. J .; J anda, K.
D.; Kriek, G. R.; Michaud, J . P.; Vine, D. B. Heterocycles 1984, 22,
785-790.
(12) (a) Boger, D. L.; Yohannes, D. J . Org. Chem. 1988, 53, 487-
499. (b) Boger, D. L.; Meyers, J . B., J r. J . Org. Chem. 1991, 56, 5385-
5390.
(20) (a) Beugelmans, R.; Bigot, A.; Zhu, J . J . Org. Chem. 1996, 61,
771-774. In this paper, two epimers were erronously assigned as two
atropisomers: (b) Bigot, A.; Beugelmans, R.; Zhu, J . Tetrahedron 1997,
53, 10753-10764.
(21) Boger, D. L.; Borzilleri, R. M. Biorg. Med. Chem. Lett. 1995, 5,
1187-1190. (b) Boger, D. L.; Borzilleri, R. M. Nukui, S. Biorg. Med.
Chem. Lett. 1995, 5, 3091-94. (c) Boger, D. L.; Borzilleri, R. M. Nukui,
S. Biorg. Med. Chem. Lett. 1996, 6, 1089-1092.
(13) Boger, D. L.; Yohannes, D. J . Org. Chem. 1991, 56, 1763-1767.

Total Synthesis of an Antitumor Agent RA-VII
J . Org. Chem., Vol. 64, No. 17, 1999 6285
Sch em e 2
the replacement of nitro by a hydroxy function (7 to 6,
Scheme 2), especially in a larger scale preparation.
Furthermore, we also planned to investigate the cycliza-
tion of dipeptide 11 (R ) H), which contains two nucleo-
philic phenols and thus raises an interesting issue of ring-
size selectivity during the cyclization.25 The merit of this
route is that it would allow the use of commercially
available L-Dopa instead of the side-chain selectively
protected L-Dopa derivatives for which five steps are
required in the until now shortest syntheses.26 Full
details of the successful implementation of these strate-
gies, highlighted by efficient syntheses of cycloisodity-
rosine (6) and, subsequently, a total synthesis of RA-VII
(1) are reported in the present paper.
Resu lts a n d Discu ssion
Cycliza tion of Dip ep tid e (9S,12S)-10. Several syn-
theses of L-Dopa derivatives bearing a selectively pro-
tected catechol have been described.26 The most direct
route involving selective protection of unsymmetric cat-
echol of L-Dopa was unfortunately inefficient due to the
similar reactivity of the two phenol groups.27 Among
numerous reported approaches, the shortest syntheses
were that developed by Boger and J ung starting from
L-tyrosine.26 Our synthesis based on Evans’ asymmetric
azidation methodology28,29 is shown in Scheme 3. Conver-
sion of acid 12 into the mixed anhydride with pivaloyl
chloride followed by reaction with the lithium salt of (4S)-
4-benzyl-2-oxazolidinone (13) afforded the imide 14.
Treatment of 14 with KHMDS followed by trisyl azide
according to Evans gave the R-azido derivative 15. The
desired diastereoisomer was obtained after flash chro-
matography in 83% yield. Transesterification of 15 with
MeOMgBr30 furnished azido ester 16 in 90% yield with
concomitant recovery of the chiral auxiliary 13. Hydro-
genolysis of 16 afforded L-methyl 3-isopropyloxy-4-meth-
oxyphenylalaninate 17, which was coupled directly with
L-N-Boc-4-fluoro-3-nitrophenylalanine (18)31 to give the
dipeptide 19 in 90% overall yield. Deprotection of iso-
propyloxy ether with BCl332 caused partial removal of the
N-Boc moiety. However, treatment of the crude product
with Boc2O under classic conditions reinstalled the N-Boc
function, affording the cyclization precursor (9S,12S)-10
in excellent overall yield (99% for two steps).
of the C9 chiral center was encountered even under
optimized reaction conditions. While it was surprising to
observe facile epimerization under such mild conditions
(K2CO3, DMF), we were intrigued by the fact that
epimerization occurred exclusively at the C9 chiral center
rather than at C12. This preference of epimerization site
is uncommon, as it is well-known that derivatives of
N-methylamino acids are more prone to racemization (C-
12) than the corresponding amino acid derivatives (C-
9).22 To account for the configurational instability of C9
chiral center, we hypothesized that the presence of a nitro
group para to the benzylic position of the dipeptide 7 and/
or 8 was responsible for the facile epimerization at C-9.20b
Thus, both resonance contribution of the nitro group and
the inductive effect of the electron-deficient aromatic ring
increased the kinetic acidity of the C-9 proton and,
consequently, the opportunity of facile enolization and
hence epimerization at this chiral center.23 Based on this
assumption, we reasoned that an alternative strategy
based on cyclization of dipeptide 10 wherein the nitro
group was positioned meta to the benzylic carbon might
overcome this problem (route b, Scheme 2).24 An added
bonus to this approach is that the access to natural
products would now be achieved by reductive removal of
nitro group (9 to 6). Previous experiences have shown
that this transformation can be realized much easier than
In searching for cycloetherification conditions of com-
pound 10, a dramatic solvent effect was observed. Treat-
ment of (9S,12S)-10 with potassium carbonate (K2CO3)
in DMF at room temperature for 24 h did not afford any
cyclic compound. However, an efficient macrocyclization
occurred when the solvent was switched to DMSO18i,25
(25) Part of this work was published as a preliminary communica-
tion; see: Bigot, A.; Zhu, J . Tetrahedron Lett. 1998, 39, 551-554.
(26) (a) J ung, M. E.; Lazarova, T. I. J . Org. Chem. 1997, 62, 1553-
1555. (b) Boger, D. L.; Yohannes, D. J . Org. Chem. 1987, 52, 5283-
5286 and references therein.
(27) Konda, M.; Takayuki, S.; Yamada, S.-I. Chem. Pharm. Bull.
1975, 23, 1063-76.
(28) (a) Evans, D. A.; Britton, T. C.; Ellman, J . A.; Dorow, R. L. J .
Am. Chem. Soc. 1990, 112, 4011-4030. (b) Evans, D. A.; Evrard, D.
A.; Rychnovsky, S. D.; Fru¨h, T.; Whittingham, W. G.; Devries, K. M.
Tetrahedron Lett. 1992, 33, 1189-1192.
(29) Pearson, A. J .; Zhang, P.; Lee, K. J . Org. Chem. 1996, 61, 6581-
6586.
(30) Evans, D. A.; Weber, A. E. J . Am. Chem. Soc. 1986, 108, 6757-
6761.
(31) Vergne, C.; Bois-Choussy, M.; Ouazzani, J .; Beugelmans, R.;
Zhu, J . Tetrahedron Asymmetry 1997, 8, 391-398.
(32) Sala, T.; Sargent, M. V. J . Chem. Soc., Perkin Trans. 1 1979,
2593-2598.
(22) McDermott, J . R.; Benoiton, N. L. Can. J . Chem. 1973, 51,
2555-2561.
(23) (a) Henning, R.; Lehr, F.; Seebach, D. Helv. Chim. Acta 1976,
59, 2213-2217. (b) Seebach, D.; Henning, R.; Lehr, F.; Gonnermann,
J . Tetrahedron Lett. 1977, 1161-1164. (c) Seebach, D.; Henning, R.;
Lehr, F. Angew. Chem., Int. Ed. Engl. 1978, 17, 458-459. (d) Yamada,
K.; Tanaka, S.; Kohmoto, S.; Yamamoto, M. J . Chem. Soc., Chem.
Commun. 1989, 110-111. (e) Bergman, J .; Sand, P.; Tilstam, U.
Tetrahedron Lett. 1983, 24, 3665-3668.
(24) During cyclization, a phenolate anion is formed on the residue
at C-9, which further reduces the kinetic acidity of 9-H. We thank one
of reviewers for this insightful consideration.

6286 J . Org. Chem., Vol. 64, No. 17, 1999
Bigot et al.
Sch em e 3a
Sch em e 4a
The transformation of cyclophane 20a and 20b into the
cycloisodityrosine 6 was straightforward (Scheme 4).
Hydrogenation of 20a in MeOH in the presence of
catalytic amount of Pd/C afforded the amino derivative,
which was submitted, without further purification, to in
situ diazotization and reduction35 to afford compound
(9S,12S)-21 ([RD] ) +56, c 0.9, CHCl3; lit.16b [RD] ) +57,
c 0.6, CHCl3) in 75% overall yield. The same synthetic
sequence applied to compound 20b afforded a product
identical in all respects with that obtained from 20a ,
establishing thus firmly the atropisomerism of these two
compounds. We have not observed reactivity differences
between 20a and 20b in the above two-step sequence,
and in practical synthesis, we used the mixture of 20a
and 20b for the preparation of 21 without the erosion of
overall yield. Other reductive deamination procedures
(tBuONO, DMF;36 tBuONO, BF3‚Et2O, then FeSO4,
DMF37,19) were examined, but none of them was found
to be suitable in this specific case. The N-bis-methylation
of 21 was carried out by adding sodium hydride (NaH)
in a mixture of solvents (THF-DMF, 1/1) in the presence
of an excess of methyl iodide to provide compound 22 in
85% yield. Under classic conditions, i.e., formation of
amide anion of 21 followed by addition of MeI, a poor
yield of the desired product 22 was obtained. Removal of
the N-Boc moiety from 22 under mild acidic conditions
gave then L,L-N,N-dimethylcycloisodityrosine methyl es-
ter 6, whose physical data were identical in all respects
with the literature values.16b,20b While compounds 20 and
21 have a single solution conformation in CDCl3 and CD3-
OD, the N,N-dimethylated cycloisodityrosine derivatives
(22 and 6) exist in two rigid solution conformations (cis,
trans of internal amide bond). In the case of 6, the two
conformers were even detectable by TLC.9,20b
to give an atropdiastereomeric mixture of cycloisodity-
rosine 20a and 20b. The atropisomerism of 20a and 20b
was determined by NOE studies. As observed in the
vancomycin series,33 a NOE cross-peak between protons
H12 and H18 was observed in the NOESY spectrum of
M atropdiastereomer 20a , while that of H12 and H15 was
found for the P diasteromer 20b.34 This stereochemistry
assignment was of no consequence in the present syn-
thesis since the planar chirality will be destroyed in
subsequent synthetic operations. However, it did provide
useful information regarding the stereochemical integrity
of these two cyclophanes and supported the notion that
compounds 20a and 20b did not result from the partial
epimerization of the chiral carbon centers (vide infra).
In line with the configurational stability of 20a and 20b,
no epimerization occurred when they were treated with
DBU in THF, conditions known to epimerize 7 (degrada-
tion was, however, observed).
In the case of cyclophane 24 (Scheme 5) where the
terminal amino function was protected by benzyloxycar-
bonyl group, methylation (NaH, MeI, THF-DMF) fur-
nished a bicyclic compound 25 (85% yield) instead of the
desired N,N-bismethylated derivative of type 22. The
(33) (a) Vergne, C.; Bois-Choussy, M.; Beugelmans, R.; Zhu, J .
Tetrahedron Lett. 1997, 38, 1403-1406. (b) Bois-Choussy, M.; Vergne,
C.; Neuville, L.; Beugelmans, R.; Zhu, J . Tetrahedron Lett. 1997, 38,
5795-5798.
(34) The configuration (P or M) of the atropisomer was determined
by viewing the atropisomer as helix. “For this designation, only the
ligands of highest priority in front and in the back of the framework
are considered. If the turn from the priority front ligand to the priority
rear ligand is clockwise, the configuration is P, if counterclockwise it
is M”. See: Eliel, E. L.; Willen, S. H. Stereochemistry of Organic
Compounds; J ohn Wiley & Sons Inc.: New York, 1994; Chapter 14.
(35) Rhee, E. S.; Shine, H. J . J . Am. Chem. Soc. 1986, 108, 1000-
1006.
(36) (a) Doyle, M. P.; Dellaria, J . F.; Siegfried, J r. B.; Bishop, S. W.
J . Org. Chem. 1977, 42, 3494-3498. (b) Islas-Gonzalez, G.; Zhu, J . J .
Org. Chem. 1997, 62, 7544-7545.
(37) (a) Doyle, M. P.; Bryker, W. J . J . Org. Chem. 1979, 44, 1572-
1574. (b) Wassmundt, F. W.; Kiesman, W. F. J . Org. Chem. 1995, 60,
1713-1719.

Total Synthesis of an Antitumor Agent RA-VII
J . Org. Chem., Vol. 64, No. 17, 1999 6287
Sch em e 5a
Sch em e 7
Sch em e 8
Sch em e 6
Size-Selective Rin g-F or m in g P r ocess. Encouraged
by these results, we became interested in investigating
type 29 substrates (Scheme 7) in order to study the ring-
size selectivity during the cyclization (path a vs b) and
the possible thermoequilibrium of products 30 and 31 via
Smiles rearrangement.40 If the cyclization could be
driven, either kinetically or thermodynamically toward
the formation of type 30 m,p-cyclophane, a desirable
feature would be evident since this route would allow the
use of commercially available L-Dopa instead of side-
chain selectively protected L-Dopa derivatives.25 Linear
compounds 35 and 11 (Scheme 8) were prepared follow-
ing standard procedures. Thus, temporary protection of
two hydroxyl groups of L-Dopa methyl ester (32) as TMS
ethers (33), followed by EDC-mediated coupling with
4-fluoro-3-nitrophenylpropionic acid (34)41 or L-N-Boc-4-
fluoro-3-nitrophenylalanine (18)31 gave, after acidic aque-
ous workup, the cyclization precursors (9S)-35 or (9S,-
12S)-11 in higher than 90% yield.
structure of compound 25 was determined by spectro-
scopic studies. While the formation of imide from peptide
is amply precedented and readily explained by intramo-
lecular N-acylation,38,39 the high stereoselectivity ob-
served for the C-methylation was nevertheless intriguing.
There were in fact three bond-forming process, i.e.,
N-acylation, N- and C-methylation, occurred in this
transformation, the high stereoselectivity observed led
us to draw a reaction cascade as shown in Scheme 6.
After formation of dianion, N-methylation occurred first
at the terminal amide function leading to 26. Instead of
the second N-methylation, intramolecular N-acylation
was favored in this case for both steric and geometric
reasons leading to 27.39 Finally, formation of enolate
followed by C-methylation afforded compound 25. Due
to the rigidity of the bicyclic ring system, only one face
of the enolate was accessible to the electrophile leading
to the observed high diastereoselectivity (Scheme 6). That
C-methylation occurred at C-12 rather than at C-9 was
determined by a strong NOE effect observed between two
methyl groups. Diminished steric hindrance of the N-Cbz
in compound 24 vs N-Boc in 21 may account for their
different reactivity.
The initial cyclization study was carried out with model
compound 35 (Scheme 9). When a solution of 35 in THF
(0.01 M) was treated with NaH at room temperature, a
smooth reaction occurred to give a mixture of two
atropdiastereomers 36a and 36b in reasonable yields
(55-65%, entry 1, Table 1). Neither the formation of 15-
membered p,p-cyclophane 37 nor that of the dimer 38
was observed under these conditions. When K2CO3 was
used as a base in DMF (0.01 M), cyclophanes 36a and
36b were produced in 42% yield together with a signifi-
(38) (a) Andrus, M. B.; Li, W. K.; Keyes, R. F. Tetrahedron Lett.
1998, 39, 5465-5468. (b) Hargreaves, M. K.; Pritchard, J . G.; Dave,
H. R. Chem. Rev. 1970, 70, 439-469.
(39) A very similar product was obtained in Boger’s synthesis of
piperazinomycin; see: Boger, D. L.; Zhou, J . J . Am. Chem. Soc. 1993,
115, 11426-11433 and ref 9b.
(40) (a) Truce, W. E.; Kreider, E. M.; Brand, W. W. The Smiles and
related rearrangements of aromatic systems. Organic Reactions; J ohn
Wiley & Sons Inc.: New York, 1970; Vol. 18, pp 99-215. (b) Borchardt,
A.; Still, W. C. Synlett 1995, 539-540 and references therein.
(41) Beugelmans, R.; Singh, G. P.; Bois-Choussy, M.; Chastanet, J .;
Zhu, J . J . Org. Chem. 1994, 59, 5535-5542.

6288 J . Org. Chem., Vol. 64, No. 17, 1999
Bigot et al.
Sch em e 9a
Ta ble 2. Su r vey of Rea ction Con d ition s for th e
Cycliza tion of 11
yield of
concn
(M)
T
(°C)
time 41a + 41b
entry
base
NaH
solvent
(h)
(%)
1
2
3
4
5
6
7
8
9
THF
DMF
DMF
DMF
10-2
0-25
0-25
5
4
5
0a
21
NaH
10-2
10-2
10-2
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
63
7
<5
45
25
25
25
25
25
25
DMSO 10-2
2
43
b
THF
10-2
21
24
7
0c
HMPT 10-2
NDd
44
DMF
2 × 10-3
DMSO 2 × 10-3
2
56
Starting material was recovered. b In the presence of 18-crown-
a
6. c A significant amount of acyclic dimer was isolated. Not
d
determined, the conversion was too low to be meaningful.
intramolecular process. In a control experiment, we have
shown that the reaction of L-N-Boc dopamine methyl
ester with methyl N-trifluoroacetyl-L-4-fluoro-3-nitrophe-
nylalaninate (K2CO3, DMF) gave equal amount of the two
possible monoarylated compounds.
A variable amount of cyclic dimer was obtained when
the substrate concentration was higher than 0.005 M.
That the intermolecular SNAr reaction becoming more
competitive in the cyclization of 35 than in previously
studied substrates such as 10 could partly be explained
on statistical grounds as both hydroxyl groups of 35 can
participate to an intermolecular process. The atropisom-
erism between compounds 36a and 36b was confirmed
by the independent conversion of the individual macro-
cycles into a common 14-membered cyclophane 4013 via
a two-step sequence described earlier (vide supra).
With these results in hand, we then turned our
attention to the fully functionalized dipeptide 11. In
contrast to (9S)-35, treatment of (9S,12S)-11 in THF (0.01
M) with NaH gave no cyclic product and only starting
material was recovered (Table 2). Using DMF under
otherwise identical conditions, cyclic compound 41a and
41b were isolated in 20% yield. After a survey of reaction
parameters varying a base, solvent, and temperature, it
was found that no cyclic monomer was produced in THF
(dielectric constant ꢀ ) 7.6) and HMPT (ꢀ ) 30) with
either NaH or K2CO3 as a base. The cyclization proceeded
smoothly in more polar aprotic solvents such as DMF (ꢀ
) 37) and DMSO (ꢀ ) 47), the latter being the best in
accord with its higher dielectric constant. A reasonable
reaction rate was observed only at room temperature. At
5 °C, the reaction time was substantially prolonged
leading to a diminished yield due to partial decomposition
of cyclized product. Finally, under optimal conditions we
found (K2CO3, DMSO, 0.002 M, room temperature), a
mixture of cyclic products 41a and 41b was isolated in
55-65% yield. It was interesting to note that when the
cyclization was carried out in THF (0.01 M) in the
presence of potassium carbonate and crown ether 18-C-
6, only acyclic dimer was produced. An observation that
partial degradation of cyclic products 41a and 41b
occurred during flash chromatography purification and
the fact that both cyclization and methylation steps could,
a priori, be carried out under identical conditions prompted
us to examine the possibility of combining these two
operations in a one-pot fashion. Indeed, treatment of a
DMSO solution (0.002 M) of dipeptide (9S,12S)-11 with
K2CO3 at room temperature followed, after 2 h, by
addition of MeI (excess) gave compounds 20a and 20b
in greater than 75% isolated yield (Scheme 10).
Ta ble 1. Su r vey of Rea ction Con d ition s for th e
Cycliza tion of 35
yield of
concn
(M)
T (°C time 36a + 36b yield of
entry base solvent
(h)
(%)
38 (%)
1
2
3
4
5
6
7
NaH
THF
10-2
0-25
25
5
2
3
48
6
1
58
42
0a
60
70
68
0
0
20
0a
10
1
K2CO3 DMF
K2CO3 DMF
K2CO3 DMF
10-2
10-2
2 × 10-3 25
K2CO3 DMSO 2 × 10-3 25
K2CO3 DMSO 4 × 10-3 25
1.3
23
5
30
CsF
DMF
10-2
25
a
Degradation or oligomerization of starting materials.
cant amount of a cyclic dimer 38 (20%).42 The yields of
36a and 36b were increased to 60% when the concentra-
tion of 35 was decreased to 0.002 M. The best result was
obtained when the cyclization was performed in DMSO
at 0.002 M with K2CO3 as a base. Under these conditions,
compounds 36a and 36b were isolated in higher than
70% combined yield and the formation of the dimer 38
was minimized (<2%). Cesium fluoride (CsF) failed to
give the desired compounds and only dimer 38 was
isolated in less than 30% yield together with the recov-
ered starting materials.
The formation of the 15-membered p,p-cyclophane 37
was not observed. Furthermore, no Smiles rearrange-
ment was observed when pure cyclophanes 36a and 36b
were submitted to the cyclization conditions. This result
was understandable if one considers the high ring
constraints43 associated with the formation of the p,p-
cyclophane (37). A pleasant consequence is that the two
otherwise equally reactive hydroxyl functions26 were
successfully differentiated, a phenomenon inherent to the
(42) While it was a symmetric dimer, the regiochemistry was not
determined rigorously.
(43) Wiberg, K. B. Angew. Chem., Int. Ed. Engl. 1986, 25, 312-
322.

Total Synthesis of an Antitumor Agent RA-VII
J . Org. Chem., Vol. 64, No. 17, 1999 6289
Sch em e 10
Sch em e 12
Sch em e 11
reasonable yields. These results were in accord with the
previous observation that the 9S,12R diastereoisomer
was more prone to cyclization than the corresponding 9S,-
12S diastereoisomer.16,20b
Tota l Syn th esis of RA-VII. With a quantity of
cycloisodityrosine methyl ester 6 in hands, the total
synthesis of RA-VII was pursued. Following literature
precedents, we first tried to prepare the hexapeptide (50)
by assemblage of cycloisodityrosine (6) and tetrapeptide
49, which was in turn synthesized according to the
standard peptide coupling procedures (Scheme 12). How-
ever, under conditions prescribed for such transforma-
tion9,10 we were unable to isolate the desired hexapeptide
50, and degradations of two coupling partners were
instead observed. We thought that both the low reactivity
of the secondary amine present in 6 and the polypeptide
nature of the acid 49 contributed to the failure of this
coupling reaction.44 Reagents such as PyBrop and BOPCl
known to be especially successful for coupling of N-
methylamino acid were attempted without success. To
remedy this reactivity problem, we hypothesized that a
two-step sequence via coupling of 6 with N-Boc-L-alanine
51 followed by coupling of the resulting tripeptide 52 with
another linear tripeptide N-Boc-D-Ala-L-Ala-N,O-dim-
ethyl-L-Tyr 53 would be more efficient. The reason for
planning this alternative synthesis was that the activated
form of amino acid N-Boc-L-alanine 51 should be less
prone to side reactions and thus have a lifetime longer
enough to react with the secondary amine 6. The [3 + 3]
segment coupling between 52 and 53 should also be
facilitated by the fact that the nucleophile in this case
will be a primary amine, known to be more reactive than
the secondary amine. Indeed, coupling of 6 with 51
i
(PyBroP, Pr2EtN, DMF) gave the corresponding tripep-
tide 52 in 97% yield. Removal of N-Boc group from 52
followed by its coupling with tripeptide 53 (EDC, HOBt,
CH2Cl2) afforded hexapeptide 50 in 60% yield. Saponi-
fication followed by liberation of amino function gave the
seco-acid which was cyclized by treatment with DPPA
in DMF to provide the natural product RA-VII (1) in 20%
yield (Scheme 13). Attempts to increase the overall yield
of this three-step sequence by varying the deprotection
and macrolactamization conditions were unsuccessful.
The physical data of this synthetic RA-VII were shown
to be identical in all respects with an authentic sample
generously provided by Professor Itokawa.
F igu r e 2.
To verify if any epimerization had occurred during the
cyclization, we have synthesized compound (9S,12R)-42
by coupling L-Dopa (33) with D-4-fluoro-3-nitrophenyla-
lanine (43)31 (Scheme 11). When (9S,12R)-42 was sub-
mitted to the identical cycloetherification conditions as
described for (9S,12S)-11, a mixture of two atropodias-
tereomers 44a and 44b was obtained whose physical data
were completely different from those of 41a and 41b
(Scheme 10). This control experiment indicated that the
stereochemical integrity of (9S,12S)-11 was preserved in
both preparation and cyclization steps, in sharp contrast
to the easy epimerization encountered with compound
(9S,12S)-716,20b (Scheme 2).
Discu ssion
We have also examined the cyclization of dipeptide
(9S,12S)-45 and (9S,12R)-46 wherein a L- or D-N-Boc-N-
methyl-4-fluoro-3-nitrophenylalanine (48) was incorpo-
rated (Figure 2). Under various conditions examined,
compound (9S,12S)-45 did not give any cyclic product.
Conversely, treatment of (9S,12R)-46 with K2CO3 in
DMSO gave the desired cyclophane 47a and 47b in
A two step, i.e., addition-elimination sequence via
formation of a Meisenheimer-type intermediate is a
generally accepted mechanism for nucleophilic aromatic
(44) Humphrey, J . M.; Chamberlin, A. R. Chem. Rev. 1997, 97,
2243-2266.

6290 J . Org. Chem., Vol. 64, No. 17, 1999
Bigot et al.
Sch em e 13a
Sch em e 14
55 and two cyclophanes 41, 56 were generated by random
search Monte Carlo method46 and optimized by TNCG
Truncated Newton molecular mechanics minimization47
using the Macromodel (version 5.5) program48 with the
AMBER force field49 and GB/SA water solvation. The
search was carried out on blocks of 1000 Monte Carlo
steps until no additional conformation was found to be
of lower energy than the current minimum. Duplicated
conformations as well as those that had chirality changes
were discarded. From these conformational searches, all
the possible conformations within 3 kcal/mol from the
global minimum were analyzed.
substitution reaction (SNAr).45 Accordingly, the hybrid-
ization of the carbon atom bearing the leaving group
(fluoride in our case) changes from sp2 to sp3 when going
from the reactant to the intermediate and back to sp2
after expelling the fluoride. A consequence of this hy-
bridization change in the intramolecular version of this
reaction is that the ring constraint of the intermediate
may be lower than that of the macrolactamization
intermediate since deformation of a cyclohexadiene sys-
tem should in principle be energetically easier than that
of the planar aromatic ring. This is, in our opinion, one
of the reasons why intramolecular SNAr reaction is more
efficient in the construction of highly constrained mac-
rocycles than other methodologies such as macrolactam-
ization technique. This consideration raised an interest-
ing mechanistic question regarding the ring size selectivity
observed in the cycloetherification of substrate (9S,12S)-
11. Was the formation of the 15-membered Meisenheimer
intermediate 55 possible (Scheme 14) although the
formation of 15-membered cyclophane 56 was not ob-
served? To understand this point, a computational study
was carried out.
First of all, the lowest energy conformers of cyclization
precursor 11 were folded and the distance between the
two reactive sites O-CF was close enough to provide
entropy driving force for the cyclization and account for
the observed facile cyclization according to the proximity
theory.50
Since the entropy loss in the macrocycle-forming
process is considerable, a process that can lower the
rotation may be expected to lead to a substantial ac-
celeration of the overall rate of reaction. For this reason,
only the lowest energy conformations of 11 that have
similar torsional angles related to the intermediates 54,
55 and the cyclophane 41, 56 (Figure 3) were considered.
The calculated steric energies (AMBER) and the most
(46) Chang. G.; Guida, W. C.; Still, W. C. J . Am. Chem. Soc. 1989,
111, 4379-4386.
Five thousand conformations of each compounds, i.e.,
the dipeptide 11, the two zwitterionic intermediate 54,
(47) Ponder, J . W.; Richards, F. M. J . Comput. Chem. 1987, 8, 1016-
1024.
(48) Mohamadi, F.; Richards, N. J . G.; Guida, W. C.; Liskamp, R.;
Lipton, M. C.; Caufield, M.; Chang, G.; Hendrickson, T.; Still, W. C. J .
Comput. Chem. 1990, 11, 440-467.
(49) Allinger, N. L. J . Am. Chem. Soc. 1977, 99, 8127-8134.
(50) (a) Menger, F. M. Acc. Chem. Res. 1985, 18, 128-134. (b)
Mandolini, L. Bull. Soc. Chim. Fr. 1988, 173-176. (c) Bruice, T. C.;
Lightstone, F. C. Acc. Chem. Res. 1999, 32, 127-136.
(45) For recent books and reviews, see: (a) Terrier, F. Nucleophilic
Aromatic Displacement: The Role of the Nitro Group; VCH: New York,
1991; Chapter 1. (b) Paradisi, C. Arene Substitution via Nucleophilic
Addition to Electron Deficient Arenes. Comprehensive Organic Syn-
thesis; Pergamon Press: Oxford, 1991; Vol. 4, pp 423-450. (c) Vlasov,
V. M. J . Fluorine Chem. 1993, 61, 193-216.

Total Synthesis of an Antitumor Agent RA-VII
J . Org. Chem., Vol. 64, No. 17, 1999 6291
Ta ble 3. Ca lcu la ted Ster ic En er gies a n d Releva n t Geom etr ica l P a r a m eter s of Com p ou n d s 11, 41, a n d Rela ted
In ter m ed ia tes
11A
54
41
11B
55
56
E (kJ /mol)
-413.5
-347.0
-131.3
1.9
179.4
-104.7
59.2
-94.2
-179.2
177.1
80.9
-57.1
178.5
-177.9
-260.0
-156.8
-0.7
166.1
-103.5
58.7
-101.7
-176.5
179.0
-423.7
-347.0
-107.4
-6.6
174.9
-81.9
-68.9
160.7
-172.6
108.0
-50.1
99.4
-173.7
-214.9
-148.4
-0.3
O2-C1-C16-C15a
C1-C16-C15-C14
C16-C15-C14-C13
C15-C14-C13-C12
C14-C13-C12-C11
C13-C12-C11-N10
C12-C11-N10-C9
C11-N10-C9-C8
N10-C9-C8-C7
C9-C8-C7-C19
C8-C7-C19-C3
C7-C19-C3-O2
C7-C19-C3-C4
C19-C3-C4-O2
160.9
-81.3
-62.4
142.9
174.5
136.9
-54.9
107.2
-165.8
-106.15
78.46
-89.97
-177.17
170.41
60.51
-89.73
-66.66
143.97
-166.29
135.11
-48.97
89.87
82.2
-96.74
-58.0
171.1
-169.7
-0.6
174.7
1.0
152.3
a
The torsion angles are in degrees.
Energy analysis revealed that in view of their similar
steric energy both zwitterionic intermediates 54, 55 can
be produced. However, the energy difference between two
cyclophanes 41 and 56 was so enormous that only
formation of the former was observed.51 In fact, both
aromatic ring systems of the 15-membered p,p-cyclo-
phane 56 was perturbed in a great extent than that of
the m,p-cyclophane 41 (Table 3), and consequently, the
formation of 41 was largely favored. These considerations
suggested that the formation of both Meisenheimer
adducts 54 and 55 were energetically allowed. However,
in intermediate 55 the departure of fluoride was ham-
pered due to introduction of highly strained ring system.
Taking into account the reversibility of the addition step
in the SNAr mechanism, we concluded that it was the
elimination, but not the addition step that determined
the ring size selectivity observed in the cyclization of
substrate 11.
Con clu sion
We described efficient syntheses of cycloisodityrosine
(6) and subsequently, a total synthesis of bicyclic hexapep-
tide RA-VII (1). An intramolecular SNAr-based cycloet-
herification reaction was employed as the key ring-
closure step for the construction of the illusive 14-
membered m,p-cyclophane. The selective ring forming
process observed for the cyclization of linear dipeptide
11 is until now one of the shortest and the most efficient
synthesis of cycloisodityrosine. Computational studies
have revealed that the preferential formation of 14-
membered m,p-cyclophane over the alternative 15-
membered p,p-cyclophane is controlled by the elimination
step of SNAr mechanism. The difficult 2 + 4 peptide
coupling between cycloisodityrosine 6 and tetrapeptide
49 en route to RA-VII (1) was resolved by an alternative
3 + 3 assemblage strategy on a rational basis. The
synthetic scheme described in this paper should find
application in the synthesis of a range of natural product
analogues for detailed SAR studies.
Exp er im en ta l Section
F igu r e 3.
(4S)-3-[3-[3-Isop r op yloxy-4-m eth oxyp h en yl]-1-oxop r o-
p ion yl]-4-(p h en ylm eth yl)-2-oxa zolid in on e (14). To a pre-
cooled solution (-78 °C) of acid 12 (5.0 g, 21.0 mmol) in THF
relevant geometrical parameters of these conformers are
summarized in Table 3. It was noticed that the two
atropisomers have very similar steric energy, thus for
clarity only one atropisomer will be considered in the
following discussion.
(51) As pointed out by one of reviewers, we agree that the compari-
son of energies between 41 and 56 may not be relevant in the present
case since compound 56 has never been isolated.

6292 J . Org. Chem., Vol. 64, No. 17, 1999
Bigot et al.
(100 mL) under Ar were added, successively, Et3N (3.54 mL,
25.20 mmol) and pivaloyl chloride (2.7 mL, 22.1 mmol). The
resulting slurry was stirred at -78 °C for 1 h. In a separate
flask containing a solution of (4S)-4-benzyl-2-oxazolidinone 13
(4.1 g, 23.1 mmol) in THF (75 mL) was added n-BuLi (1.6 M
in hexane, 15.9 mL, 25.4 mmol) at -78 °C. After being stirred
at -78 °C for 30 min, this metalated oxazolidinone solution
was transferred to the flask containing the mixed anhydride
via cannula, and the resulting white slurry was stirred at -78
°C for 15 min and then overnight at room temperature. The
reaction was quenched with aqueous NH4Cl (60 mL) and
extracted five times with CH2Cl2. The combined organic layers
were washed with brine, dried over Na2SO4, and concentrated
in a vacuum to give an oily residue. Crystallization from
EtOAc/heptane gave 14 (7.0 g, 84%) as a white solid: mp 100-
101 °C (EtOAc-heptane); [R]D ) +42.0 (CHCl3, c 1.00); IR
Meth yl N-[N-(ter t-Bu tyloxycar bon yl)-L-(3-isopr opyloxy-
4-m eth oxyp h en yla la n yl]-L-4-flu or o-3-n itr op h en yla la n i-
n a te ((9S,12S)-19). A solution of 16 (2.0 g, 6.8 mmol) in MeOH
(20 mL) was hydrogenated at atmospheric pressure in the
presence of 10% Pd/C for 1 h. The mixture was filtered through
a short pad of Celite and washed with MeOH. The filtrate was
evaporated to dryness in vacuo to give 17 (1.82 g, 99%) as an
oil that was used without further purification. To a solution
of 17 (1.82 g, 6.83 mmol) in CH2Cl2 (40 mL) were added
sequentially l-N-Boc-4-fluoro-3-nitrophenylalanine 18 (2.24 g,
6.83 mmol), HOBt‚H2O (1.04 g, 6.83 mmol), and EDC (1.6 g,
8.3 mmol) at room temperature. After being stirred at room
temperature for 80 min, the reaction mixture was hydrolyzed
with aqueous HCl and extracted with CH2Cl2. The combined
organic layers were washed with brine, dried over Na2SO4, and
concentrated. Flash chromatography (SiO2, eluent: EtOAc/
heptane ) 1:3 then 1:1) gave 19 (3.54 g, 90%) as a yellow
solid: mp 44-45 °C (EtOAc-heptane); [R]D ) +20.9 (CHCl3,
(CHCl3) 1782, 1702, 1510, 1384 cm-1 1H NMR (300 MHz,
;
CDCl3) δ 1.36 (d, J ) 6.1 Hz, 6H), 2.75 (dd, J ) 9.5, 13.4 Hz,
1H), 2.92-2.98 (m, 2H), 3.15-3.35 (m, 3H), 3.82 (s, 3H), 4.14-
4.21 (m, 2H), 4.53 (septet, J ) 6.1 Hz, 1H), 4.66 (m, 1H), 6.81-
6.84 (m, 3H), 7.16-7.18 (m, 2H), 7.26-7.36 (m, 3H); 13C NMR
(62.5 MHz, CDCl3) δ 22.2, 29.9, 37.4, 37.8, 55.1, 56.1, 66.2,
71.4, 112.2, 116.6, 121.0, 127.4, 129.0, 129.4, 133.0, 135.3,
147.3, 149.0, 153.5, 172.5; MS m/z 397 (M+). Anal. Calcd for
c 0.75); IR (CHCl3) 3425, 1744, 1706, 1681, 1538, 1513 cm-1
;
1H NMR (300 MHz, CDCl3) δ 1.33 (d, J ) 6.1 Hz, 3H), 1.34 (d,
J ) 6.1 Hz, 3H), 1.41 (s, 9H), 2.95-3.02 (m, 3H), 3.15 (dd, J )
6.8, 14.0 Hz, 1H), 3.72 (s, 3H), 3.82 (s, 3H), 4.31 (m, 1H), 4.47
(septet, J ) 6.1 Hz, 1H), 4.78 (m, 1H), 5.07 (d, J ) 7.0 Hz,
NH), 6.20 (d, J ) 7.8 Hz, NH), 6.58 (dd, J ) 2.0, 8.1 Hz, 1H),
6.61 (d, J ) 2.0 Hz, 1H), 6.77 (d, J ) 8.1 Hz, 1H), 7.19 (dd, J
) 8.6, 10.6 Hz, 1H), 7.45 (ddd, J ) 2.3, 7.1, 8.6 Hz, 1H), 7.85
(dd, J ) 2.3, 7.1 Hz, 1H); 13C NMR (62.5 MHz, CDCl3) δ 22.2,
22.3, 28.5 (3 C), 37.4, 37.6, 52.5, 53.5, 55.3, 56.0, 71.7, 80.7,
112.2, 117.3, 118.5 (d, J ) 20.0 Hz), 122.0, 126.9, 127.7, 136.6
(d, J ) 9.0 Hz), 147.4, 150.0, 154.7 (d, J ) 261.0 Hz), 155.2,
C
23H27NO5: C, 69.50; H, 6.85; N, 3.52. Found: C, 69.59; H,
6.95; N, 3.54.
(4S,2S)-3-[2-Azido-3-[3-isopr opyloxy-4-m eth oxyph en yl]-
1-oxop r op ion yl]-4-(p h en ylm eth yl)-2-oxa zolid in on e (15).
To a stirred solution of the imide 14 (5.0 g, 12.6 mmol) in THF
(150 mL) at -78 °C was added KHMDS (0.5 M solution in
toluene, 37.8 mL, 18.9 mmol), and the resulting solution was
stirred at -78 °C for 30 min. To this solution was added, via
cannula, a precooled (-78 °C) solution of trisyl azide (5.1 g,
16.4 mmol) in THF (30 mL). The resulting solution was stirred
at -78 °C for 2 min, quenched by addition of glacial acetic
acid (3.3 mL, 57.9 mmol), and warmed to room temperature
with a water bath. After being stirred at room temperature
for 3 h, the reaction mixture was diluted with brine (100 mL)
and extracted four times with CH2Cl2. The combined organic
layers were washed with brine, dried over Na2SO4, and
concentrated. Flash chromatography (SiO2, eluent: EtOAc/
heptane ) 1/4) of the crude product gave 15 (4.6 g, 83%) as a
colorless oil: [R]D ) +76.4 (CHCl3, c 1.26); IR (CHCl3) 2113,
170.1, 171.6; MS m/z 577 (M+); HRMS m/z 577.2435 (C28H36
-
FN3O9 requires 577.2435).
Meth yl N-[N-(ter t-Bu tyloxyca r bon yl)-L-(3-h yd r oxy-4-
m et h oxyp h en yla la n yl]-L-4-flu or o-3-n it r op h en yla la n i-
n a te ((9S,12S)-10). To a cooled solution (-78 °C) of dipeptide
19 (100.0 mg, 0.17 mmol) in CH2Cl2 (6 mL) was added BCl3 (1
M solution in CH2Cl2 867 µL, 0.87 mmol), and the resulting
yellow solution was stirred at -78 °C for 5 min and at 0 °C
for 20 min. Five drops of MeOH were added to convert the
excess of BCl3 into B(OMe)3, and the volatile was evaporated
to dryness. To the solution of the so-obtained crude reaction
mixture in THF (4 mL) were added Et3N and Boc2O (42 mg,
0.19 mmol). After being stirred at room temperature for 2 h,
the reaction mixture was diluted with aqueous HCl and
extracted four times with EtOAc. The combined organic layers
were washed with brine, dried over Na2SO4, and concentrated.
Flash chromatography (SiO2, eluent: EtOAc/heptane ) 1/1.2)
gave 10 (92 mg, 99%) as a white solid: mp 159-160 °C
(EtOAc-heptane); [R]D ) +31.8 (CHCl3, c 0.66); IR (CHCl3)
3542, 3422, 1742, 1702, 1682, 1543, 1510 cm-1; 1H NMR (300
MHz, CDCl3) δ 1.41 (s, 9H), 2.98-3.04 (m, 3H), 3.14 (dd, J )
6.7, 14.0 Hz, 1H), 3.74 (s, 3H), 3.86 (s, 3H), 4.35 (m, 1H), 4.76
(m, 1H), 5.14 (d, J ) 7.1 Hz, NH), 5.75 (s, OH), 6.24 (d, J )
7.6 Hz, NH), 6.50 (dd, J ) 2.1, 8.1 Hz, 1H), 6.56 (d, J ) 2.1
Hz, 1H), 6.73 (d, J ) 8.1 Hz, 1H), 7.18 (dd, J ) 8.6, 10.6 Hz,
1H), 7.43 (ddd, J ) 2.2, 7.0, 8.6 Hz, 1H), 7.86 (dd, J ) 2.2, 7.0
Hz, 1H); 13C NMR (75 MHz, CDCl3) δ 28.5 (3 C), 37.3, 37.8,
52.9, 53.6, 55.3, 56.3, 80.7, 111.6, 116.3, 119.2 (d, J ) 21.0
Hz), 121.5, 127.7, 129.3, 134.7 (d, J ) 4.0 Hz), 137.5 (d, J )
7.0 Hz), 146.1, 154.6 (d, J ) 263.0 Hz), 154.8, 155.3, 171.1,
172.6; MS m/z 535 (M+). Anal. Calcd for C25H30FN3O9: C,
56.07; H, 5.65; N, 7.85. Found: C, 55.62; H, 5.71; N, 7.67.
(9S,12S)-12-[N-(ter t-Bu tyloxyca r bon yl)a m in o]-2,11-d i-
o x o -4-m e t h o x y -9-m e t h o x y c a r b o n y l-16-n it r o -10-a za -
t r icyclo[12.2.2.13,7]n on a d eca -3,5,7(19),14,16,17-h exa en e
(20). To a solution of linear dipeptide 10 (140.0 mg, 0.26 mmol)
in DMSO (26 mL, 0.01 M) containing 3 Å molecular sieves was
added K2CO3 (140 mg, 1.05 mmol) at room temperature. After
being stirred at room temperature for 2 h, the reaction mixture
was quenched by addition of water and extracted four times
with EtOAc. The combined organic extracts were washed with
brine, dried over Na2SO4, and concentrated. Purification by
preparative TLC (SiO2, eluent: EtOAc/heptane ) 1:1) afforded
atropisomer 20a (50 mg, 37%) as a colorless oil and atropiso-
mer 20b (51 mg, 38%) as a colorless oil. For 20a : [R]D ) +41.0
1
1781, 1706, 1513 cm-1; H NMR (250 MHz, CDCl3) δ 1.37 (d,
J ) 6.1 Hz, 6H), 2.82 (dd, J ) 9.5, 13.5 Hz, 1H), 2.97 (dd, J )
9.0, 13.6 Hz, 1H), 3.14 (dd, J ) 5.6, 13.6 Hz, 1H), 3.32 (dd, J
) 3.3, 13.5 Hz, 1H), 3.83 (s, 3H), 4.11 (t, J ) 9.1 Hz, 1H), 4.19
(dd, J ) 2.8, 9.1 Hz, 1H), 4.54 (septet, J ) 6.1 Hz, 1H), 4.59
(m, 1H), 5.24 (dd, J ) 5.6, 9.0 Hz, 1H), 6.83-6.88 (m, 3H),
7.19-7.23 (m, 2H), 7.29-7.39 (m, 3H); 13C NMR (62.5 MHz,
CDCl3) δ 22.1, 37.2, 37.6, 55.4, 56.0, 61.5, 66.6, 71.5, 112.1,
116.9, 121.8, 127.5, 128.0, 128.9, 129.1, 129.4, 134.7, 147.3,
149.7, 152.8, 170.6; MS m/z 438 (M+); HRMS m/z 438.1912
(C23H26N4O5 requires 438.1903).
(2S)-Meth yl 2-Aazido-3-(3-isopr opyloxy-4-m eth oxyph en -
yl)p r op ion a te (16). To methanol (20 mL) cooled at 0 °C was
added MeMgBr (3 M solution in ether, 6.7 mL, 20.1 mmol).
The white slurry was stirred at 0 °C for 2 min and transferred,
via cannula, to a precooled (0 °C) solution of compound 15 (4.0
g, 9.1 mmol) in MeOH (20 mL). After being stirred at 0 °C for
10 min, the reaction mixture was diluted with brine (50 mL).
The volatile was removed under reduced pressure and the
aqueous solution was extracted four times with CH2Cl2. The
organic layers were washed with brine, dried over Na2SO4, and
concentrated. Flash chromatography (SiO2, eluent: EtOAc/
heptane ) 1/3, then EtOAc) gave azido ester 16 (2.58 g, 96%)
as a colorless oil and chiral auxiliary 13 (1.4 g, 87%).
Compound 16: [R]D ) -22.8 (CHCl3, c 1.12); IR (CHCl3) 2107,
1
1742, 1516 cm-1; H NMR (250 MHz, CDCl3) δ 1.36 (d, J )
6.1 Hz, 6H), 2.94 (dd, J ) 8.5, 14.0 Hz, 1H), 3.10 (dd, J ) 5.6,
14.0 Hz, 1H), 3.77 (s, 3H), 3.83 (s, 3H), 4.03 (dd, J ) 5.6, 8.5
Hz, 1H), 4.52 (septet, J ) 6.1 Hz, 1H), 6.78-6.81 (m, 3H); 13
C
NMR (62.5 MHz, CDCl3) δ 22.1, 37.2, 52.6, 56.0, 63.5, 71.5,
112.1, 117.2, 121.9, 128.2, 147.2, 149.8, 170.5; MS m/z 293
(M+); HRMS m/z 293.1359 (C14H19N3O4 requires 293.1375).

Total Synthesis of an Antitumor Agent RA-VII
J . Org. Chem., Vol. 64, No. 17, 1999 6293
(CHCl3, c 0.31); IR (CHCl3) 1744, 1682, 1607, 1537, 1494 cm-1
;
J ) 8.3 Hz, 1H), 6.89 (dd, J ) 2.5, 8.2 Hz, 1H), 7.17 (dd, J )
2.5, 8.5 Hz, 1H), 7.33 (m, 1H), 7.46 (dd, J ) 1.8, 8.4 Hz, 1H);
Conformer B: δ 1.50 (s, 9H), 2.76 (s, 3H), 2.87 (s, 3H), 2.60-
3.35 (m, 4H), 3.65 (s, 3H), 3.93 (s, 3H), 4.38 (m, 1H), 4.81 (s,
1H), 5.53 (dd, J ) 4.8, 11.9 Hz, 1H), 6.63 (m, 1H), 6.75 (br. d,
J ) 8.1 Hz, 1H), 6.90 (m, 1H), 7.04 (m, 1H), 7.24 (m, 1H), 7.53
(d, J ) 8.3 Hz, 1H); MS m/z 499 (M + H).
1H NMR (300 MHz, CD3COCD3) δ 1.47 (s, 9H), 2.78-2.86 (m,
2H), 3.09 (dd, J ) 4.0, 13.0 Hz, 1H), 3.47 (dd, J ) 5.3, 13.0
Hz, 1H), 3.59 (s, 3H), 3.90 (s, 3H), 4.02 (m, 1H), 4.65 (m, 1H),
5.41 (d, J ) 2.0 Hz, 1H), 6.44 (m, NH), 6.73 (dd, J ) 2.0, 8.2
Hz, 1H), 6.91 (d, J ) 8.2 Hz, 1H), 7.20 (d, J ) 8.4 Hz, 1H),
7.28 (m, NH), 7.54 (dd, J ) 2.1, 8.4 Hz, 1H), 8.12 (br s, 1H);
13C NMR (75 MHz, CD3COCD3) δ 28.3 (3 C), 34.8, 38.5, 52.6,
54.1, 56.5, 56.8, 80.2, 112.7, 115.3, 123.2, 125.5, 128.5, 135.5,
137.6, 138.0, 147.6, 155.1, 156.3, 170.6, 171.1; MS (FAB)m/z
538 (M + Na). For 20b: [R]D ) -115.0 (CHCl3, c 0.10); IR
(9S,12S)-12-[N-(Ben zyloxyca r bon yl)a m in o]-2,11-d ioxo-
4-m et h oxy-9-m et h oxyca r b on yl-16-n it r o-10-a za t r icyclo-
[12.2.2.13,7]n on a d eca -3,5,7(19),14,16,17-h exa en e (23). A
solution of an equimolar mixture of 20a and 20b (43.0 mg,
0.083 mmol) in TFA (2 mL) was stirred a room temperature
for 20 min. The volatile was then removed, and the residue
was redissolved in THF (1 mL). To this solution were added
Et3N (35 µL, 0.25 mmol) and CbzOSu (62.0 mg, 0.25 mmol).
After being stirred at room temperature for 1 h, the reaction
mixture was hydrolyzed by addition of aqueous HCl and
extracted three times with EtOAc. The combined organic
layers were washed with brine, dried over Na2SO4, and
concentrated. Preparative TLC (SiO2, eluent: EtOAc/heptane
) 1.2/1) gave an equimolar mixture of 23a and 23b (44 mg,
95%) as a yellow oil: 1H NMR (250 MHz, CD3COCD3) δ 2.77-
2.84 (m, 4H), 3.06 (dd, J ) 6.3, 13.4 Hz, 1H), 3.14 (dd, J )
3.9, 13.1 Hz, 1H), 3.44-3.52 (m, 2H), 3.54 (s, 3H), 3.58 (s, 3H),
3.88 (s, 3H), 3.90 (s, 3H), 4.05 (m, 2H), 4.63 (m, 1H), 4.74 (m,
1H), 5.12 (m, 2H), 5.14 (m, 2H), 5.43 (d, J ) 2.0 Hz, 1H), 5.46
(br s, 1H), 6.63 (m, 2H), 6.67 (dd, J ) 2.2, 8.3 Hz, 1H), 6.72
(dd, J ) 2.0, 8.3 Hz, 1H), 6.87 (d, J ) 8.3 Hz, 1H), 6.90 (d, J
) 8.3 Hz, 1H), 7.19 (d, J ) 8.5 Hz, 1H), 7.26 (d, J ) 8.3 Hz,
1H), 7.33-7.43 (m, 12H), 7.54 (dd, J ) 2.1, 8.4 Hz, 1H), 7.76
(dd, J ) 1.9, 8.2 Hz, 1H), 7.97 (d, J ) 1.9 Hz, 1H), 8.15 (br s,
1H); MS m/z 549 (M); HRMS m/z 549.1759 (M) (C28H27N3O9
requires 549.1747).
(9S,12S)-12-[N-(Ben zyloxyca r bon yl)a m in o]-2,11-d ioxo-
4-m eth oxy-9-m eth oxyca r bon yl-10-a za tr icyclo[12.2.2.13,7]-
n on a d eca -3,5,7(19),14,16,17-h exa en e (24). To a stirred
solution of a mixture of 23a and 23b (15.0 mg, 0.027 mmo) in
DMF (1 mL) was added SnCl2‚2H2O (49 mg, 0.22 mmol), and
the resulting slurry was stirred at 50 C for 2 h. The reaction
mixture was then cooled to room temperature, hydrolyzed, and
extracted three times with EtOAc. The combined organic
extracts were washed with brine, dried over Na2SO4, and
concentrated to give aniline (13.0 mg, quantitative) as a brown
oil that was immediately used for the next step. To a solution
of above-obtained amino derivative in THF (1 mL) and water
(2 mL) cooled at 0 °C were added sequentially H3PO2 (50%
solution in water, 23 µL, 0.175 mmol), a catalytic amount of
Cu2O, and NaNO2 (2 mg, 0.03 mmol) in water (1 mL). After
being stirred at 0 °C for 5 min and at room temperature for
30 min, the reaction mixture was diluted with water (10 mL)
and extracted four times with EtOAc. The combined organic
extracts were washed with brine, dried over Na2SO4, and
concentrated. Preparative TLC (TLC (SiO2, eluent: EtOAc/
heptane ) 1:1) afforded 24 (10.3 mg, 75%) as a colorless oil:
1H NMR (300 MHz, CD3COCD3) δ 2.78-2.81 (m, 2H), 2.98 (dd,
J ) 4.2, 13.2 Hz, 1H), 3.37 (dd, J ) 5.0, 13.2 Hz, 1H), 3.59 (s,
3H), 3.87 (s, 3H), 3.98 (m, 1H), 4.65 (m, 1H), 5.14 (s, 2H), 5.21
(d, J ) 2.2 Hz, 1H), 6.47 (br s, 1H), 6.61 (dd, J ) 2.1, 8.2 Hz,
1H), 6.83 (d, J ) 8.2 Hz, 1H), 6.95 (dd, J ) 2.5, 8.2 Hz, 1H),
7.05 (dd, J ) 2.5, 8.2 Hz, 1H), 7.22 (dd, J ) 2.2, 8.4 Hz, 1H),
7.26-7.46 (m, 7H); MS m/z 504 (M); HRMS m/z 504.1891 (M)
(C28H28N2O7 requires 504.1897).
(CHCl3) 1736, 1708, 1687, 1602, 1532, 1518, 1497 cm-1 1H
;
NMR (300 MHz, CD3COCD3) δ 1.45 (s, 9H), 2.79 (m, 1H), 2.87
(m, 1H), 3.01 (dd, J ) 6.2, 13.1 Hz, 1H), 3.45 (dd, J ) 5.1,
13.1 Hz, 1H), 3.55 (s, 3H), 3.89 (s, 3H), 4.08 (m, 1H), 4.54 (m,
1H), 5.45 (d, J ) 2.0 Hz, 1H), 6.22 (m, NH), 6.68 (dd, J ) 2.0,
8.3 Hz, 1H), 6.88 (d, J ) 8.3 Hz, 1H), 7.27 (d, J ) 8.3 Hz, 1H),
7.32 (m, NH), 7.72 (br d, J ) 7.9 Hz, 1H), 7.96 (d, J ) 2.2 Hz,
1H); 13C NMR (50.05 MHz, CD3COCD3) δ 28.6 (3 C), 34.9, 39.3,
52.2, 55.5, 56.6, 58.0, 80.1, 113.6, 117.3, 123.5, 123.8, 128.4,
128.7, 129.4, 132.7, 132.9, 136.9, 137.4, 138.9, 145.9, 152.1,
171.1; MS m/z 516 (M+H), 460, 416; HRMS m/z 516.1975 (M
+ H) (C25H29N3O9 + H requires 516.1982).
(9S,12S)-12-[N-(ter t-Bu tyloxyca r bon yl)a m in o]-2,11-d i-
o x o -4-m e t h o x y -9-m e t h o x y c a r b o n y l-10-a za t r ic y c lo -
[12.2.2.13,7]n on a d eca -3,5,7(19),14,16,17-h exa en e (21). A
solution of a mixture of 20a and 20b (240 mg, 0.47 mmol) in
MeOH (10 mL) was hydrogenated in the presence of 10% Pd/C
at atmospheric pressure for 50 min. The reaction mixture was
then filtered through a pad of Celite and washed thoroughly
with MeOH. The filtrate was evaporated to dryness to give
the aniline (228.0 mg, quantitative) as a brown oil that was
immediately used for the next step. To the solution of the so-
obtained aniline in THF (2 mL), cooled at 0 °C, were added,
successively, water (5 mL), H3PO2 (50% solution in water,
0.434 mL, 3.29 mmol), a small amount of Cu2O, and a solution
of NaNO2 (39.0 mg, 0.56 mmol) in water (1 mL). After the
mixture was stirred at 0 °C for 5 min and then at room
temperature for 30 min, water (10 mL) was added, and the
aqueous phase was extracted four times with EtOAc. The
combined organic extracts were washed with brine, dried over
Na2SO4, and concentrated. Flash chromatography (SiO2, elu-
ent: EtOAc/heptane ) 1:2) afforded 21 (165.2 mg, 75%) as a
white solid: mp 114-115 °C (EtOAc-heptane); [R]D ) +56
(CHCl3, c 0.90) (li.t16b [R]D ) +57° (CHCl3, c 0.6)); IR (CHCl3)
3442, 1743, 1695, 1689, 1620, 1532 cm-1; 1H NMR (300 MHz,
CDCl3) δ 1.52 (s, 9H), 2.80-2.93 (m, 3H), 3.52 (dd, J ) 4.9,
13.5 Hz, 1H), 3.68 (s, 3H), 3.96 (s, 3H), 4.22 (m, 1H), 4.60 (m,
1H), 4.98 (d, J ) 8.9 Hz, NH), 5.04 (br s, 1H), 5.88 (br s, NH),
6.62 (dd, J ) 2.1, 8.3 Hz, 1H), 6.80 (d, J ) 8.3 Hz, 1H), 7.07
(dd, J ) 2.4, 8.3 Hz, 1H), 7.15 (dd, J ) 2.2, 8.3 Hz, 1H), 7.30
(m, 2H); 13C NMR (50.05 MHz, CDCl3) δ 28.4 (3 C), 34.8, 38.6,
52.4, 53.9, 56.2, 56.8, 81.1, 112.0, 115.2, 116.8, 121.7, 124.0,
125.7, 129.6, 132.9, 133.7, 147.0, 152.5, 154.8, 158.1, 170.8,
171.2; MS m/z 471 (M + H), 415, 371.
(9S,12S)-12-[N-(ter t-Bu tyloxycar bon yl)-N-m eth ylam in o]-
2,11-d ioxo-4-m eth oxy-9-m eth oxyca r bon yl-10-m eth yl-10-
a z a t r ic y c lo [12.2.2.13 ,7 ]n o n a d e c a -3,5,7(19),14,16,17-
h exa en e (22). To a precooled (0 °C) solution of 21 (13.0 mg,
0.028 mmol) in THF (1 mL) were added four drops of DMF
and excess MeI. NaH (80% dispersion, 1.8 mg, 0.06 mmol, 2.2
equiv) was then added in one portion, and the resulting slurry
was stirred at 0 °C for 10 min and at room temperature for 50
min. The reaction was quenched with aqueous HCl. The
aqueous solution was extracted three times with EtOAc, and
the combined organic extracts were washed with brine, dried
over Na2SO4, and concentrated. Purification by preparative
TLC (SiO2, eluent: toluene/EtOAc ) 4:1) afforded 22 (11.7 mg,
85%) as a 4:1 mixture of conformers: [R]D ) -160 (CHCl3, c
0.4) (lit.16b [R]D ) -161 (CHCl3, c 0.2)); IR (CHCl3) 1744, 1673,
1648, 1519, 1448 cm-1; 1H NMR (300 MHz, CDCl3, mixture of
two conformers A and B (4/1)). Conformer: δ 1.47 (s, 9H), 2.56
(s, 3H), 2.93 (s, 3H), 2.60-3.35 (m, 3H), 3.65 (m, 1H), 3.67 (s,
3H), 3.94 (s, 3H), 4.42 (br. s, 1H), 4.70 (dd, J ) 3.6, 12 Hz,
1H), 4.90 (dd, J ) 2.8, 11.3 Hz, 1H), 6.60 (m, 1H), 6.81 (br. d,
Bicyclic Hyd a n toin 25. To a precooled (0 °C) solution of
24 (12.0 mg, 0.024 mmol) in THF (1 mL) and DMF (1 mL)
was added an excess of MeI followed by NaH (75% dispersion,
1.7 mg, 0.052 mmol). After being stirred at 0 °C for 5 min and
at room temperature for 70 min, the reaction mixture was
quenched with aqueous HCl and extracted four times with
EtOAc. The combined organic extracts was washed with brine,
dried over Na2SO4, and concentrated. Purification by prepara-
tive TLC (TLC (SiO2, eluent: EtOAc/heptane ) 1:1) afforded
25 (9.0 mg, 87%) as a white solid: mp 198-199 °C (EtOAc-
heptane); [R]D ) +305.0 (CHCl3, c 0.20); IR (CHCl3) 1769, 1744,
1
1713, 1519 cm-1; H NMR (250 MHz, CDCl3) δ 1.53 (s, 3H),
3.02 (dd, J ) 1.9, 16.1 Hz, 1H), 3.07 (s, 3H), 3.00-3.09 (m,

6294 J . Org. Chem., Vol. 64, No. 17, 1999
Bigot et al.
2H), 3.72 (s, 3H), 3.93 (s, 3H), 4.07 (dd, J ) 12.1, 16.1 Hz,
1H), 4.46 (dd, J ) 1.9, 12.1 Hz, 1H), 4.91 (d, J ) 2.0 Hz, 1H),
6.66 (dd, J ) 2.0, 8.2 Hz, 1H), 6.77 (d, J ) 8.2 Hz, 1H), 6.92
(dd, J ) 2.4, 8.4 Hz, 1H), 7.03 (dd, J ) 2.2, 8.3 Hz, 1H), 7.16
(dd, J ) 2.4, 8.3 Hz, 1H), 7.22 (dd, J ) 2.2, 8.4 Hz, 1H); 13C
NMR (62.5 MHz, CDCl3) δ 22.0, 30.5, 39.7, 53.3, 55.7, 56.3,
67.4, 111.8, 116.3, 122.0, 124.4, 124.9, 129.5, 130.8, 132.0,
133.6, 152.4, 156.2, 158.8, 170.0; MS m/z 424 (M); HRMS m/z
424.1653 (M) (C23H24N2O6 requires 424.1634).
a la n in a te ((9S,12S)-45). Under the conditions described for
the preparation of compound 35, coupling between amino ester
33 and l-N-BOC-N-methyl-4-fluoro-3-nitrophenylalanine gave
dipeptide 45 as a yellow oil in 90% yield after flash chroma-
tography (SiO2, eluent: EtOAc/heptane ) 1.2/1): [R]D ) -16.4
(CHCl3, c 0.59); IR (CHCl3) 1743, 1680, 1616, 1539, 1518, 1476
1
cm-1; H NMR (300 MHz, CD3COCD3, mixture of two rotam-
ers) δ 1.30 (br s, 9H), 2.62 (br s, 3H), 2.88 (dd, J ) 8.2, 14.2
Hz, 1H), 3.02 (dd, J ) 5.4, 13.9 Hz, 1H), 3.04 (m, 1H), 3.34
(dd, J ) 5.4, 13.9 Hz, 1H), 3.68 (s, 3H), 4.64 (m, 1H), 5.03 (m,
1H), 6.53 (m, 1H), 6.71 (m, 1H), 6.73 (d, J ) 8.0 Hz, 1H), 7.19
(m, NH), 7.42 (m, 1H), 7.76 (m, 1H+2 OH), 8.03 (m, 1H); 13C
NMR (50.05 MHz, CD3COCD3, mixture of two rotamers) δ 28.3
(3 C), 31.1, 33.9, 37.4, 52.4, 54.5 and 54.6, 59.6, 80.5, 116.1,
117.1, 118.9 (d, J ) 19.0 Hz), 121.5, 127.2, 129.1, 136.9, 137.8
(d, J ) 8.0 Hz), 144.9, 145.9, 154.8 (d, J ) 259.0 Hz), 170.5,
172.6; MS m/z 536 (M + H); HRMS m/z 536.2024 (M + H)
(C25H30FN3O9 + H requires 36.2044).
(2S)-Meth yl 3-(3,4-Dih yd r oxyp h en yl)-2-[3-(4-flu or o-3-
n itr op h en yl)p r op ion yla m in o]p r op ion a te (35). To a solu-
tion of amino ester 33 (500 mg, 1.41 mmol) in 10 mL of CH2Cl2
were added sequentially acid 34 (350 mg, 1.64 mmol), HOBt
(250.9 mg, 1.64 mmol), and EDC (313.2 mg, 1.64 mmol) at
room temperature. After being stirred at room temperature
for 30 min, the reaction mixture was diluted with aqueous HCl
and extracted four times with CH2Cl2. The combined organic
layers were washed with brine, dried over Na2SO4, and
concentrated. Flash chromatography (SiO2, eluent: EtOAc)
gave 35 (561.0 mg, 98%) as a yellow oil: [R]D ) -5.8 (CH3OH,
c 2.10); IR (CHCl3) 3423, 1742, 1676, 1616, 1603, 1536, 1510,
1450 cm-1; 1H NMR (300 MHz, CD3OD) δ 2.50 (t, J ) 7.3 Hz,
2H), 2.74 (dd, J ) 8.8, 13.9 Hz, 1H), 2.89 (t, J ) 7.3 Hz, 2H),
2.93 (dd, J ) 5.5, 13.9 Hz, 1H), 3.64 (s, 3H), 4.56 (dd, J ) 5.5,
8.8 Hz, 1H), 6.43 (dd, J ) 2.0, 8.0 Hz, 1H), 6.58 (d, J ) 2.0 Hz,
1H), 6.64 (d, J ) 8.0 Hz, 1H), 7.24 (dd, J ) 8.6, 11.0 Hz, 1H),
7.42 (ddd, J ) 2.2, 7.2, 8.6 Hz, 1H), 7.87 (dd, J ) 2.2, 7.2 Hz,
1H); 13C NMR (75 MHz, CDCl3) δ 31.3, 37.6, 37.8, 52.6, 55.3,
116.2, 117.1, 119.1 (d, J ) 21.0 Hz), 121.5, 126.7, 129.4, 136.9
(d, J ) 9.0 Hz), 139.5, 145.2, 146.2, 155.1 (d, J ) 258.0 Hz),
173.6, 174.2; MS m/z 407 (M + H); HRMS m/z 407.1279 (M +
1) (C19H20FN2O7 requires 407.1255).
Meth yl N-[N-(ter t-Bu tyloxyca r bon yl-N-m eth yla m in o)-
L-(3,4-d ih yd r oxyp h en yla la n yl]-D-4-flu or o-3-n itr op h en yl-
a la n in a te ((9S,12R)-46). Under the conditions described for
the preparation of compound 35, coupling between amino ester
33 and d-N-BOC-N-methyl-4-fluoro-3-nitrophenylalanine gave
dipeptide 46 as a yellow oil in 90% yield after flash chroma-
tography (eluent: EtOAc/heptane ) 1/1): [R]D ) +41.3 (CHCl3,
c 1.95); IR (CHCl3) 1736, 1682, 1616, 1543, 1519, 1450 cm-1
;
1H NMR (300 MHz, CD3COCD3, mixture of two rotamers) δ
1.26 and 1.30 (2 br s, 9H), 2.76 (br s, 3H), 2.84-3.00 (m, 2H),
3.02 (dd, J ) 10,6, 14.5 Hz, 1H), 3.32 (m, 1H), 3.69 (s, 3H),
4.67 (m, 1H), 4.93 and 5.03 (2 m, 1H), 6.51 (m, 1H), 6.68 (m,
1H), 6.72 (d, J ) 8.0 Hz, 1H), 7.24 (m, 1H), 7.42 (m, 1H), 7.69
(m, 1H), 7.78 (m, 2H), 8.05 (m, 1H); 13C NMR (75 MHz, CD3-
COCD3, mixture of two rotamers) δ 28.3 (3 C), 30.7 and 31.1,
33.9 and 34.0, 37.4, 52.4, 54.6, 59.6 and 61.3, 80.6, 116.1, 117.1,
118.9 (d, J ) 19.0 Hz), 121.5, 127.3, 129.1 (d, J ) 11.0 Hz),
137.1, 137.8 (d, J ) 9.0 Hz), 144.9, 145.9, 154.8 (d, J ) 259.0
Hz), 170.3 and 170.5, 172.7; MS m/z 536 (M + H).
Meth yl N-[N-(ter t-Bu tyloxyca r bon yl)-L-(3,4-d ih yd r oxy-
p h en yla la n yl]-L-4-flu or o-3-n it r op h en yla la n in a t e ((9S,-
12S)-11). Under the conditions described for the preparation
of compound 35, coupling between amino ester 33 and L-N-
BOC-4-fluoro-3-nitrophenylalanine (18) gave dipeptide 11 as
a yellow oil in 90% yield after flash chromatography (SiO2,
eluent: EtOAc/heptane ) 2/1): [R]D ) +41.0 (CHCl3, c 0.33);
IR (CHCl3) 3419, 1738, 1686, 1615, 1538, 1506, 1448 cm-1; 1H
NMR (250 MHz, CDCl3) δ 1.40 (s, 9H), 2.90-2.99 (m, 3H), 3.11
(dd, J ) 6.2, 14.0 Hz, 1H), 3.75 (s, 3H), 4.48 (m, 1H), 4.80 (m,
(9S)-2,11-Dioxo-4-h ydr oxy-9-m eth oxycar bon yl-16-n itr o-
10-a za t r icyclo[12.2.2.13,7]n on a d e ca -3,5,7(19),14,16,17-
h exa en e (36). To a solution of 35 (10 mg, 0.025 mmol) in
DMSO (12.5 mL, 0.002 M) containing 3 Å molecular sieves
was added K2CO3 (10 mg, 0.074 mmol) at room temperature.
After being stirred at room temperature for 3 h, the reaction
mixture was diluted with water and extracted four times with
EtOAc. The combined organic extracts were washed with
brine, dried over Na2SO4, and concentrated. Purification by
preparative TLC (EtOAc) afforded atropisomer 36a (4 mg,
35%) as a white solid and its atropisomer 36b (4 mg, 35%) as
a yellow oil. Atropisomer 36a : mp 222-223 °C (EtOAc-
heptane); [R]D ) +121.8 (CHCl3, c 0.62); IR (CHCl3) 3436, 3309,
1749, 1676, 1536, 1516, 1497, 1437, 1350 cm-1; 1H NMR (250
MHz, CD3COCD3) δ 2.43 (dt, J ) 4.8, 13.1 Hz, 1H), 2.54 (ddd,
J ) 3.2, 4.7, 13.1 Hz, 1H), 2.73 (m, 1H), 2.88 (br s, 1H), 3.01
(dd, J ) 4.8, 12.4 Hz, 1H), 3.17 (dd, J ) 4.1, 12.4 Hz, 1H),
3.64 (s, 3H), 4.01 (m, 1H), 5.38 (d, J ) 2.0 Hz, 1H), 6.64 (dd,
J ) 2.0, 8.1 Hz, 1H), 6.79 (d, J ) 8.1 Hz, 1H), 7.16 (d, J ) 8.3
Hz, 1H), 7.45 (dd, J ) 2.1, 8.3 Hz, 1H), 7.57 (d, J ) 7.2 Hz,
NH), 8.10 (d, J ) 2.1 Hz, 1H), 8.28 (s, OH); 13C NMR (62.5
MHz, CD3COCD3) δ 32.1, 35.0, 40.3, 52.4, 55.2, 116.1, 117.3,
123.9, 126.6, 128.2, 131.3, 138.2, 141.5, 145.7, 151.3, 151.7,
155.7, 172.0; MS m/z 387 (M+H); HRMS m/z 387.1170 (M +
1H), 5.41 (d, J ) 8.9 Hz, NH), 6.42 (dd, J 1.9, 8.1 Hz, 1H),
)
6.48 (d, J ) 1.9 Hz, 1H), 6.63 (d, J ) 8.0 Hz, NH), 6.71 (d, J
) 8.1 Hz, 1H), 7.17 (dd, J ) 8.5, 10.5 Hz, 1H), 7.43 (ddd, J )
2.0, 7.0, 8.5 Hz, 1H), 7.86 (dd, J ) 2.0, 7.0 Hz, 1H); 13C NMR
(75 MHz, CD3OD) δ 28.5 (3 C), 37.8, 38.2, 52.6, 55.3, 56.5,
80.8, 116.3, 117.2, 119.0 (d, J ) 21.0 Hz), 121.7, 127.8, 129.0,
136.1, 137.9 (d, J ) 9.0 Hz), 145.3, 146.2, 155.5 (d, J ) 259.0
Hz), 156.8, 172.8, 173.3; MS m/z 522 (M + H). Anal. Calcd.
for C24H28FN3O9: C, 55.27; H, 5.41; N, 8.06. Found: C, 55.46;
H, 5.87; N, 7.87.
Meth yl N-[N-(ter t-Bu tyloxyca r bon yl)-L-(3,4-d ih yd r oxy-
p h en yla la n yl]-D-4-flu or o-3-n itr op h en yla la n in a te ((9S,-
12R)-42). Under the conditions described for the preparation
of compound 35, coupling between amino ester 33 and D-N-
BOC-4-fluoro-3-nitrophenylalanine gave dipeptide 42 as a
yellow oil in 90% yield after flash chromatography (SiO2,
eluent: EtOAc/heptane ) 2/1): [R]D ) +12.2 (CHCl3, c 0.49);
IR (CHCl3) 3420, 1738, 1680, 1622, 1538, 1519, 1499, 1448,
1370 cm-1; 1H NMR (250 MHz, CD3COCD3) δ 1.31 (s, 9H), 2.84
(dd, J ) 3.9, 8.0 Hz, 1H), 2.88 (dd, J ) 5.1, 8.0 Hz, 1H), 3.00
(dd, J ) 5.4, 13.9 Hz, 1H), 3.21 (dd, J ) 4.5, 13.9 Hz, 1H),
3.68 (s, 3H), 4.47 (m, 1H), 4.68 (dd, J ) 7.8, 13.9 Hz, 1H), 6.11
(d, J ) 8.4 Hz, NH), 6.54 (dd, J ) 2.0, 8.3 Hz, 1H), 6.71 (d, J
) 2.0 Hz, 1H), 6.73 (d, J ) 8.3 Hz, 1H), 7.35 (dd, J ) 8.7, 11.0
Hz, 1H), 7.49 (m, 1H), 7.60 (d, J ) 8.1 Hz, NH), 7.77 (s, OH),
7.81 (s, OH), 7.99 (br d, J ) 6.4, 1H); 13C NMR (75 MHz, CD3-
COCD3) δ 28.5 (3 C), 38.0, 38.2, 52.5, 54.7, 55.9, 79.7, 116.2,
117.3, 118.8 (d, J ) 21.0 Hz), 121.7, 127.7, 128.2, 136.5, 138.1
(d, J ) 10.0 Hz), 145.1, 146.0, 155.1 (d, J ) 269.0 Hz), 156.8,
172.1, 173.3; MS m/z 522 (M + H); HRMS m/z 522.1896 (M +
H) (C24H28FN3O9 + H requires 522.1888).
1) (C19H19N2O7 requires 387.1192). Atropisomer 36b: [R]D
)
+19.3 (CHCl3, c 1.00); IR (CHCl3) 3550, 3423, 1743, 1673, 1532,
1504, 1441, 1356 cm-1; 1H NMR (250 MHz, CD3COCD3) δ 2.32
(dt, J ) 5.2, 12.1 Hz, 1H), 2.53 (ddd, J ) 3.6, 4.9, 13.5 Hz,
1H), 2.75 (m, 1H), 2.89 (br s, 1H), 3.03 (dd, J ) 4.8, 12.3 Hz,
1H), 3.14 (ddd, J ) 3.4, 5.2, 12.7 Hz, 1H), 3.63 (s, 3H), 4.03
(m, 1H), 5.31 (d, J ) 2.1 Hz, 1H), 6.62 (dd, J ) 2.1, 8.1 Hz,
1H), 6.77 (d, J ) 8.1 Hz, 1H), 7.38 (d, J ) 8.3 Hz, 1H), 7.47 (d,
J ) 6.8 Hz, NH), 7.78 (dd, J ) 2.1, 8.3 Hz, 1H), 7.82 (d, J )
2.1 Hz, 1H), 8.20 (s, OH); 13C NMR (62.5 MHz, CD3COCD3) δ
32.2, 34.7, 40.0, 52.4, 54.9, 115.0, 117.3, 123.9, 128.4, 128.6,
131.2, 136.3, 141.5, 150.9, 151.3, 171.2, 173.1; MS m/z 387 (M
+ H).
Meth yl N-[N-(ter t-Bu tyloxyca r bon yl-N-m eth yla m in o)-
L-(3,4-d ih yd r oxyp h en yla la n yl]-L-4-flu or o-3-n itr op h en yl-

Total Synthesis of an Antitumor Agent RA-VII
J . Org. Chem., Vol. 64, No. 17, 1999 6295
A variable amount of cyclic dimer 38 was also isolated under
(9S,12S)-12-[N-(ter t-Bu tyloxyca r bon yl)a m in o]-2,11-d i-
oxo-4-h ydr oxy-9-m eth oxycar bon yl-16-n itr o-10-azatr icyclo-
[12.2.2.13,7]n on a d eca -3,5,7(19),14,16,17-h exa en e (41). To a
solution of 11 (200.0 mg, 0.38 mmol) in DMSO (200 mL, 0.002
M) containing 3 Å molecular sieves was added K2CO3 (212.0
mg, 1.54 mmol) at room temperature, and the resulting
reaction mixture was stirred at room temperature for 2 h. The
reaction was quenched by dropwise addition of water and
extracted four times with EtOAc. The combined organic
extracts were washed with brine, dried over Na2SO4, and
concentrated. Flash chromatography (SiO2, eluent: EtOAc/
heptane ) 1/1.5) afforded an inseparable mixture of atropiso-
mer 41a and atropisomer 41b (110 mg, 57%) as a white solid:
1H NMR (300 MHz, CD3COCD3) for 41a δ 1.47 (s, 9H), 2.79-
2.83 (m, 2H), 3.08 (dd, J ) 4.1, 13.3 Hz, 1H), 3.46 (dd, J )
5.3, 13.3 Hz, 1H), 3.58 (s, 3H), 4.05 (m, 1H), 4.65 (m, 1H), 5.41
(d, J ) 2.0 Hz, 1H), 6.44 (m, NH), 6.63 (dd, J ) 2.0, 8.1 Hz,
1H), 6.78 (d, J ) 8.1 Hz, 1H), 7.22 (d, J ) 8.4 Hz, 1H), 7.28
(m, NH), 7.53 (dd, J ) 2.1, 8.4 Hz, 1H), 8.11 (br s, 1H); 8.27
(s, OH); for 41b δ 1.45 (s, 9H), 2.79-2.83 (m, 2H), 3.00 (dd, J
) 6.2, 13.1 Hz, 1H), 3.46 (dd, J ) 5.3, 13.3 Hz, 1H), 3.55 (s,
3H), 4.05 (m, 1H), 4.55 (m, 1H), 5.47 (d, J ) 2.0 Hz, 1H), 6.25
(m, NH), 6.58 (dd, J ) 2.0, 8.2 Hz, 1H), 6.75 (d, J ) 8.2 Hz,
1H), 7.28 (m, 1H+NH), 7.72 (br d, J ) 7.7 Hz, 1H), 7.96 (d, J
) 2.1 Hz, 1H); 8.24 (s, OH); MS m/z 502 (M + H).
(9S,12R)-12-[N-(ter t-Bu tyloxyca r bon yl)a m in o]-2,11-d i-
oxo-4-h ydr oxy-9-m eth oxycar bon yl-16-n itr o-10-azatr icyclo-
[12.2.2.13,7]n on a d eca -3,5,7(19),14,16,17-h exa en e (44). To a
solution of 42 (15.0 mg, 0.029 mmol) in DMSO (6.0 mL, 0.002
M) containing 3 Å molecular sieves was added K2CO3 (16.0
mg, 1.2 mmol) at room temperature, and the resulting reaction
mixture was stirred at room temperature for 2 h. The reaction
was quenched by dropwise addition of water and extracted four
times with EtOAc. The combined organic extracts were washed
with brine, dried over Na2SO4, and concentrated. Preparative
TLC (SiO2, eluent: EtOAc/heptane ) 2/1) afforded an insepa-
rable mixture of atropisomer 44a and atropisomer 44b (8 mg,
55%) as a white solid: 1H NMR (300 MHz, CDCl3) for 44a δ
1.45 (s, 9H), 2.59-3.06 (m, 3H), 3.28-3.44 (m, 1H), 3.68 (s,
3H), 4.16 (m, 2H), 5.15 (d, J ) 2.1 Hz, 1H), 5.20 (d, J ) 6.7
Hz, NH), 5.77 (s, OH), 6.11 (m, NH), 6.62 (br d, J ) 8.0 Hz,
1H), 6.84 (d, J ) 8.1 Hz, 1H), 7.22 (d, J ) 8.3 Hz, 1H), 7.50
(dd, J ) 2.2, 8.4 Hz, 1H), 8.12 (d, J ) 2.1 Hz, 1H); for 44b δ
1.45 (s, 9H), 2.59-3.06 (m, 3H), 3.28-3.44 (m, 1H), 3.64 (s,
3H), 4.16 (m, 2H), 5.22 (br s, 1H), 5.24 (d, J ) 9.1 Hz, NH),
5.77 (s, OH), 6.11 (m, NH), 6.62 (br d, J ) 8.0 Hz, 1H), 6.84
(d, J ) 8.1 Hz, 1H), 7.35 (d, J ) 8.4 Hz, 1H), 7.67 (dd, J ) 2.1,
8.5 Hz, 1H), 7.94 (d, J ) 2.2 Hz, 1H); MS m/z 502 (M + H).
(9S,12S)-12-[N-(ter t-Bu tyloxyca r bon yl)a m in o]-2,11-d i-
o x o -4-m e t h o x y -9-m e t h o x y c a r b o n y l-16-n it r o -10-a za -
t r icyclo[12.2.2.13,7]n on a d eca -3,5,7(19),14,16,17-h exa en e
(20). Meth od A. To a solution of 41a and 41b (14.0 mg, 0.028
mmol) in acetone (5 mL) were added an excess of MeI and K2-
CO3 (13.0 mg, 0.09 mmol), and the resulting reaction mixture
was refluxed for 3 h. The volatile was removed, and the residue
was taken up in water and extracted five times with EtOAc.
The combined organic extracts were washed with brine, dried
over Na2SO4, and concentrated. Preparative TLC (SiO2, elu-
ent: EtOAc/heptane ) 1:1) afforded 20a (6 mg, 42%) and 20b
(6 mg, 42%) identical in all respects with those prepared
previously. Meth od B (one pot, cyclization-methylation): To
a solution of 11 (1.0 g, 2.0 mmol) in DMSO (900 mL, 0.002 M)
containing 3 Å molecular sieves was added K2CO3 (1.0 g, 7.3
mmol) at room temperature, and the resulting reaction
mixture was stirred at room temperature for 2 h. After the
total consumption of the starting material, an excess of MeI
was then added, and the resulting pale yellow solution was
stirred at room temperature for 2 h. The reaction was
quenched by addition of water and extracted four times with
EtOAc. The combined organic extracts were washed with
brine, dried over Na2SO4, and concentrated. Flash chroma-
tography (SiO2, eluent: EtOAc/heptane ) 1:1) afforded 20a
and 20b (783.0 mg, 76%) identical in all respects with those
prepared previously.
other cyclization conditions (see text) as
a white solid:
mp 238-239 °C (EtOAc-heptane); 1H NMR (300 MHz,
CD3COCD3) δ 2.51 (m, 2H), 2.77-3.05 (m, 8H), 3.09 (dd, J )
4.2, 13.6 Hz, 2H), 3.72 (s, 6H), 4.66 (m, 2H), 6.16 (dd, J ) 2.0,
8.0 Hz, 2H), 6.72 (d, J ) 8.6 Hz, 2H), 6.78 (d, J ) 2.0 Hz, 2H),
6.79 (d, J ) 8.0 Hz, 2H), 7.25 (d, J ) 8.0 Hz, 2 NH), 7.40 (dd,
J ) 2.0, 8.6 Hz, 2H), 7.86 (d, J ) 2.0 Hz, 2H), 8.52 (s, 2 OH);
MS (FAB + NaCl) m/z 795 (M + Na).
(M) (9S)-2,11-Dioxo-4-m eth oxy-9-m eth oxyca r bon yl-16-
n itr o-10-azatr icyclo[12.2.2.13,7]n on adeca-3,5,7(19),14,16,17-
h exa en e (39a ). To a solution of atropisomer 36a (22 mg, 0.057
mmol) in acetone (5 mL) were added K2CO3 (24 mg, 0.17 mmol)
and an excess of MeI. After being refluxed for 15 h, the reaction
mixture was filtered through a short pad of Celite, and the
filtrate was evaporated to dryness. Purification by preparative
TLC (SiO2, eluent: EtOAc) gave compound 39a (20 mg, 90%)
as a yellow oil: [R]D ) -173 (CHCl3, c 0.15); IR (CHCl3) 3438,
3013, 2931, 1744, 1681, 1538, 1494, 1438, 1350 cm-1; 1H NMR
(300 MHz, CD3COCD3) δ 2.38 (dt, J ) 4.8, 12.5 Hz, 1H), 2.53
(ddd, J ) 3.3, 4.7, 13.3 Hz, 1H), 2.79 (m, 2H), 3.04 (dt, J )
4.7, 12.4 Hz, 1H), 3.14 (ddd, J ) 3.2, 4.9, 12.6 Hz, 1H), 3.64
(s, 3H), 3.88 (s, 3H), 4.03 (m, 1H), 5.31 (d, J ) 2.0 Hz, 1H),
6.72 (dd, J ) 2.0, 8.3 Hz, 1H), 6.91 (d, J ) 8.1 Hz, 1H), 7.36
(d, J ) 8.4 Hz, 1H), 7.46 (d, J ) 7.0 Hz, 1H), 7.78 (dd, J ) 2.1,
8.4 Hz, 1H, NH), 7.82 (d, J ) 2.1 Hz, 1H); 13C NMR (75 MHz,
CD3COCD3) δ 31.5, 34.5, 40.2, 52.6, 53.7, 56.6, 112.8, 113.8,
122.9, 127.9, 130.3, 134.7, 139.8, 147.4, 150.6, 151.3, 171.5,
172.4; MS (CI) m/z 401 (M + H).
(P ) (9S)-2,11-Dioxo-4-m eth oxy-9-m eth oxyca r bon yl-16-
n itr o-10-a za tr icyclo[12.2.2.13,7]n on a d eca -3,5,7(19),14,16,-
17-h exa en e (39b). Methylation of atropisomer 36b under the
above-described conditions gave 39b as a yellow oil: [R]D
)
-90 (CHCl3, c 1.5); IR (CHCl3) 3433, 3020, 2962, 2937, 1744,
1
1680, 1531, 1493, 1441, 1351 cm-1; H NMR (300 MHz, CD3-
COCD3) δ 2.43 (dt, J ) 4.8, 12.6 Hz, 1H), 2.54 (ddd, J ) 3.2,
4.8, 13.1 Hz, 1H), 2.74-2.77 (m, 2H), 3.01 (dt, J ) 4.8, 12.5
Hz, 1H), 3.18 (dt, J ) 3.9, 12.6 Hz, 1H), 3.64 (s, 3H), 3.90 (s,
3H), 4.00 (dt, J ) 4.7, 7.8 Hz, 1H), 5.39 (d, J ) 2.2 Hz, 1H),
6.73 (dd, J ) 2.2, 8.2 Hz, 1H), 6.92 (d, J ) 8.2 Hz, 1H), 7.14
(d, J ) 8.3 Hz, 1H), 7.45 (dd, J ) 2.2, 8.3 Hz, 1H), 7.59 (dd, J
) 7.2 Hz, 1H, NH), 8.11 (d, J ) 2.2 Hz, 1H); 13C NMR (75
MHz, CD3COCD3) δ 31.7, 34.6, 39.8, 52.0, 54.7, 56.3, 113.4,
115.5, 123.0, 126.1, 127.6, 132.2, 137.7, 141.0, 148.0, 151.1,
152.4, 171.5, 173.0; MS (CI) m/z 401 (M + H); HRMS m/z
401.1335 (M + H) (C20H20N2O7 + H requires 401.1349).
(9S )-2,11-Dioxo-4-m e t h oxy-9-m e t h oxyca r b on yl-10-
a za tr icyclo[12.2.2.13,7]n on a d eca -3,5,7-(19),14,16, 17-h exa -
en e (40). To a stirred solution of 39a or 39b (10 mg, 0.025
mmol) in 5 mL of MeOH were added 2 drops of concentrated
HCl and a catalytic amount of 10% Pd/C. The resulting slurry
was hydrogenated at atmospheric pressure for 30 min. The
reaction mixture was then filtered through a short pad of
Celite and washed with MeOH. The filtrate was evaporated
to dryness under reduced pressure to give the hydrochloride
salt of aniline (10 mg, quantitative) as a white solid that was
immediately used for the next step. To the solution of aniline
in THF (1 mL) and water (2 mL), cooled to 0 °C, were added
sequentially H3PO2 (50% solution in water, 23 µL, 0.17 mmol),
a catalytic amount of Cu2O, and NaNO2 (2.0 mg, 0.027 mmol)
in water (1 mL). After being stirred at 0 °C for 5 min and at
room temperature for 30 min, the reaction mixture was diluted
with water (10 mL) and extracted five times with EtOAc. The
combined organic extracts were washed with brine, dried over
Na2SO4, and concentrated. Preparative TLC (SiO2, EtOAc)
afforded 40 (6.5 mg, 73%) as a colorless oil: [R]D ) -10.0 (CH3-
1
OH, c 0.50); H NMR (300 MHz, CDCl3) δ 2.10 (m, 1H), 2.68
(m, 2H), 2.88 (dd, J ) 1.3, 16.9 Hz, 1H), 3.06 (m, 2H), 3.72 (s,
3H), 3.96 (s, 3H), 4.22 (ddd, J ) 1.0, 7.4, 10.4 Hz, 1H), 5.10 (d,
J ) 2.0 Hz, 1H), 5.30 (d, J ) 7.1 Hz, NH), 6.60 (dd, J ) 2.0,
8.2 Hz, 1H), 6.79 (d, J ) 8.2 Hz, 1H), 7.02 (dd, J ) 2.4, 8.2 Hz,
1H), 7.10 (dd, J ) 2.4, 8.3 Hz, 1H), 7.26 (dd, J ) 2.4, 8.3 Hz,
1H), 7.32 (dd, J ) 2.2, 8.4 Hz, 1H); MS m/z 356 (M+H); HRMS
m/z 356.1515 (M+1) (C20H22NO5 requires 356.1498).

6296 J . Org. Chem., Vol. 64, No. 17, 1999
Bigot et al.
(9S,12R)-12-[N-(ter t-Bu tyloxyca r bon yl)-N-m eth yla m i-
n o]-2,11-d ioxo-4-m et h oxy-9-m et h oxyca r b on yl-16-n it r o-
10-a za t r icyclo[12.2.2.13,7]n on a d e ca -3,5,7(19),14,16,17-
h exa en e (47). The cyclization procedure described for 35 was
applied to 46. Preparative TLC (SiO2, eluent: EtOAc/heptane
) 1:1) afforded atropisomer 47a (28%) as a white solid and
atropisomer 47b (28%) as yellow oil. For 47a : mp 252-254
°C (EtOAc-heptane); [R]D ) +54.5 (CHCl3, c 0.55); IR (CHCl3)
3556, 3419, 1744, 1688, 1675, 1600, 1538, 1519 cm-1; 1H NMR
(250 MHz, CDCl3) δ 1.52 (s, 9H), 2.64 (dd, J ) 11.3, 16.5 Hz,
1H), 2.89 (d, J ) 15.6 Hz, 1H), 2.98 (s, 3H), 3.01 (dd, J ) 4.2,
12.0 Hz, 1H), 3.38 (t, J ) 12.0 Hz, 1H), 3.67 (s, 3H), 4.23 (t, J
) 9.8 Hz, 1H), 4.61 (dd, J ) 4.2, 12.1 Hz, 1H), 5.26 (br s, 1H),
5.89 (s, OH), 6.04 (d, J ) 9.1 Hz, NH), 6.63 (dd, J ) 2.0, 8.2
Hz, 1H), 6.83 (d, J ) 8.2 Hz, 1H), 7.33 (d, J ) 8.4 Hz, 1H),
7.70 (br d, J ) 8.2 Hz, 1H), 8.03 (d, J ) 2.2 Hz, 1H); 13C NMR
(62.5 MHz, CDCl3) δ 28.5 (3 C), 30.2, 34.6, 34.9, 52.6, 53.2,
61.0, 81.2, 113.8, 116.3, 124.2, 127.7, 130.0, 135.8, 136.8, 144.3,
149.0, 152.0, 156.3, 168.6, 172.0; MS m/z 516 (M + H). For
47b: [R]D ) +204.8 (CHCl3, c 0.84); IR (CHCl3) 3555, 3420,
3059, 2962, 2859, 1744, 1680, 1602, 1538, 1441 cm-1; 1H NMR
(250 MHz, CDCl3) δ 1.50 (s, 9H), 2.69 (dd, J ) 11.3, 16.7 Hz,
1H), 2.96 (d, J ) 14.0 Hz, 1H), 2.99 (s, 3H), 3.04 (dd, J ) 4.4,
12.0 Hz, 1H), 3.36 (t, J ) 12.0 Hz, 1H), 3.68 (s, 3H), 4.30 (t, J
) 9.8 Hz, 1H), 4.64 (m, 1H), 5.17 (br s, 1H), 5.93 (s, OH), 6.16
(d, J ) 7.8 Hz, NH), 6.62 (dd, J ) 1.9, 8.2 Hz, 1H), 6.82 (d, J
) 8.2 Hz, 1H), 7.19 (d, J ) 8.3 Hz, 1H), 7.57 (dd, J ) 2.2, 8.3
Hz, 1H), 8.13 (d, J ) 2.2 Hz, 1H); 13C NMR (62.5 MHz, CD3-
COCD3) δ 28.5 (3 C), 30.2, 34.4, 35.0, 52.7, 52.8, 61.1, 81.2,
113.7, 116.4, 123.9, 127.2, 127.9, 129.9, 136.8, 138.5, 144.0,
149.0, 150.9, 155.8, 169.0, 171.5; MS m/z 516 (M + H), 416,
386.
8.4 Hz, 1H), 7.20 (dd, J ) 2.4, 8.4 Hz, 1H), 7.28 (dd, J ) 2.3,
8.4 Hz, 1H), 7.42 (dd, J ) 2.3, 8.4 Hz, 1H); MS m/z 570 (M +
H); HRMS m/z 570.2807 (M + H) (C30H39N3O8 + H requires
570.2815).
Hexa p ep tid e (50). A solution of 52 (15 mg, 0.026 mmol)
in TFA (1 mL) was stirred at room temperature for 20 min.
The volatile was then evaporated, and the residue was
i
redissolved in CH2Cl2 (1 mL). To this solution was added Pr2-
NEt (excess), HOBt (12.2 mg, 0.08 mmol), EDC (15.3 mg, 0.08
mmol), and the tripeptide 53 (36.0 mg, 0.080 mmol). After
being stirred at room temperature for 24 h, the reaction
mixture was diluted with aqueous NaHCO3 and extracted
three times with EtOAc. The combined organic layers were
washed with brine, dried over Na2SO4, and concentrated.
Preparative TLC (SiO2, EtOAc) gave 50 (15.0 mg, 63%) as a
colorless oil: 1H NMR (300 MHz, CDCl3, mixture of conform-
ers) major conformer δ 0.85-0.98 and 1.22-1.48 (m, 18H), 2.48
(s, 3H), 2.94 (s, 3H), 3.20 (s, 3H), 2.70-3.65 (m, 6H), 3.62 (s,
3H), 3.75 (s, 3H), 3.92 (s, 3H), 4.12 (m, 1H), 4.39 (br s, 1H),
4.61-5.00 (m, 6H), 5.29 (dd, J ) 2.1, 7.8 Hz, 1H), 6.62 (br d,
J ) 8.3 Hz, 1H), 6.82 (d, J ) 8.5 Hz, 3H), 6.91 (dd, J ) 1.8,
8.3 Hz, 1H), 7.10 (d, J ) 8.5 Hz, 2H), 7.19 (dd, J ) 1.8, 8.3 Hz,
1H), 7.27 (dd, J ) 1.6, 8.4 Hz, 1H), 7.42 (dd, J ) 1.6, 8.4 Hz,
1H); MS (FAB Thioglycerol + NaCl) m/z 946 (M + H + Na).
RA VII (1). To a stirred solution of 50 (15.0 mg, 0.016 mmol)
in a mixture of solvents (THF/MeOH/H2O ) 4/1/1, 2 mL) was
added LiOH‚H2O (2 mg, 0.05 mmol), and the reaction mixture
was stirred at room temperature for 1 h. The volatile was then
removed in vacuo, and the resulting residue was taken up in
diluted HCl solution and extracted five times with EtOAc. The
combined organic layers were washed with brine, dried over
Na2SO4, and concentrated to give acid (12 mg, 82%) as a
colorless oil that was used whithout further purification for
the following reaction. The so-obtained product was dissolved
in 2 mL of a 3 M HCl-EtOAc solution. After 1 h, the solvent
was evaporated to give the seco acid as a white solid, MS (FAB
Thioglycerol) m/z 789 (M + H), which was used without further
purification for the cyclization reaction. To a precooled solution
(5 °C) of seco acid in DMF (1 mL) was added solid NaHCO3
(3.6 mg, 0.04 mmol), DPPA (4 µL, 0.024 mmol), and the
resulting slurry was stirred at the same temperature for 72
h. The reaction mixture was then filtrated and washedwith
EtOAc, the filtrate was evaporated to dryness, and the
resulting residue was submitted directly to preparative TLC
(SiO2, eluent: CH2Cl2/MeOH ) 10/1) to give 2.5 mg (20%) of
RA-VII 1 identical in all respects with natural sample: [R]D
) -222.0 (CHCl3, c 0.09; CHCl3) (lit.1a [R]D ) -229.0 (CHCl3,
c 0.1); li.t10b [R]D ) -209.0 (CHCl3, c 0.39)); IR (CHCl3) 3410-
3300, 3006, 2932, 1667, 1644, 1510 cm-1; 1H NMR (400 MHz,
CDCl3, mixture of conformers) major conformer δ 1.11 (d, J )
6.7 Hz, 3H), 1.31 (d, J ) 6.9 Hz, 3H), 1.37 (d, J ) 6.9 Hz, 3H),
2.64 (m, 1H), 2.70 (s, 3H), 2.87 (s, 3H), 2.95-3.10 (m, 2H), 3.14
(s, 3H), 3.32 (dd, J ) 10.6, 14.0 Hz, 1H), 3.38 (dd, J ) 5.0,
14.0 Hz, 1H), 3.48 (brd, J ) 3.2 Hz, 1H), 3.60 (dd, J ) 5.0,
10.6 Hz, 1H), 3.69 (t, J ) 11.5 Hz, 1H), 3.81 (s, 3H), 3.95 (s,
3H), 4.35 (d, J ) 1.9 Hz, 1H), 4.37 (m, 1H), 4.56 (dd, J ) 3.6,
12.0 Hz, 1H), 4.75-4.88 (m, 2H), 5.43 (dd, J ) 2.9, 11.5 Hz,
1H), 6.42 (d, J ) 6.5 Hz, 1H), 6.59 (dd, J ) 1.9, 8.1 Hz, 1H),
6.71 (d, J ) 7.6 Hz, 1H), 6.79-6.87 (m, 4H), 6.89 (dd, J ) 2.0,
8.2 Hz, 1H), 7.06 (d, J ) 8.2 Hz, 2H), 7.22 (dd, J ) 1.9, 8.3 Hz,
1H), 7.27 (dd, J ) 1.9, 8.4 Hz, 1H), 7.43 (dd, J ) 1.9, 8.4 Hz,
1H); MS (FAB thioglycerol + NaCl) m/z 793 (M + Na).
Cycloisod ityr osin e 6. A solution of compound 22 (380 mg,
0.76 mmol) in CH2Cl2 (15 mL) and CF3COOH (1.50 mL) was
stirred at room temperature for 1 h. The reaction mixture was
diluted with H2O and extracted with Et2O to remove the
neutral species. The aqueous solution was then carefully
basified and extracted with EtOAc. The combined organic
extracts were washed with brine, dried, and concentrated
under reduced pressure to give pure compound 6 (290 mg, 96%)
as a colorless oil. Compound 6 was found to exist as a mixture
of two distinct conformers that were detectable by TLC (SiO2,
Rf ) 0.41 and 0.48 in CH2Cl2/MeOH ) 10/1): IR (CHCl3) 2985,
1748, 1642, 1522, 1501 cm-1 1H NMR (300 MHz, CDCl3,
;
mixture of two conformers A and B (1/1) not assignable) δ 2.59
(s, 3H), 2.62 (s, 3H), 2.66 (s, 3H), 2.75 (s, 3H), 2.79-3.25 (m,
6H), 3.56 (dd, J ) 4.2, 10.1 Hz, 1H), 3.69 (s, 3H), 3.75 (s, 3H),
3.86 (m, 1H), 3.94 (s, 3H), 3.95 (s, 3H), 4.27 (d, J ) 2 Hz, 1H),
4.41 (dd, J ) 3.7, 12.1 Hz, 1H), 4.67 (d, J ) 2 Hz, 1H), 6.62
(br. d, J ) 8.1 Hz, 1H), 6.76 (d, J ) 8.2 Hz, 1H), 6.82 (d, J )
8.3 Hz, 1H), 6.93 (dd, J ) 2.5, 8.4 Hz, 1H), 7.07 (dd, J ) 2.3,
8.3 Hz, 1H), 7.22-7.29 (m, 1H), 7.3 (m, 1H), 7.4 (dd, J ) 2.1,
8.3 Hz, 1H), 7.48 (dd, J ) 2.1, 8.3 Hz, 1H); MS m/z 399 (M +
H); HRMS m/z 399.1911 (M + H) (C22H26N2O5 + H requires
399.1920).
NHBoc-(S)-Ala -NMe-cycloisod ityr osin e (52). To a pre-
cooled (0 °C) solution of 6 (52.0 mg, 0.13 mmol) in DMF (2
mL) were added 51 (49 mg, 0.26 mmol), PyBrOP (126.0 mg,
i
0.26 mmol), and Pr2NEt (excess), and the resulting solution
was stirred at 0 °C for 5 min and at room temperature for 2 h.
The reaction mixture was then diluted with aqueous NaHCO3.
The aqueous solution was extracted three times with EtOAc,
and the combined organic extracts were washed with brine,
dried over Na2SO4, and concentrated. Purification by prepara-
tive TLC (1:1 EtOAc/heptane) afforded 52 (72 mg, 97%, oil) as
a mixture of two separable conformers: [R]D ) -152.0 (CHCl3,
Ack n ow led gm en t. We thank Professor Itokawa for
generously providing us a sample and spectral data of
natural RA-VII. A doctoral fellowship from the MRES
to A.B. is gratefully acknowledged.
c 0.40); IR (CHCl3) 3438, 1744, 1706, 1638, 1519, 1500 cm-1
;
1H NMR (300 MHz, CDCl3, mixture of two conformers 8/1)
Major conformer δ 1.29 (d, J ) 6.8 Hz, 1H), 1.47 (s, 9H), 2.57
(s, 3H), 2.74 (dd, J ) 2.8, 11.4 Hz, 1H), 2.93 (dd, J ) 12.0,
18.0 Hz, 1H), 3.22 (s, 3H), 3.35 (dd, J ) 3.6, 18.0 Hz, 1H),
3.66 (m, 1H), 3.68 (s, 3H), 3.95 (s, 3H), 4.41 (d, J ) 2.0 Hz,
1H), 4.60 (m, 1H), 4.65 (dd, J ) 3.7, 12.2 Hz, 1H), 5.33 (dd, J
) 3.0, 11.4 Hz, 1H), 5.38 (d, J ) 7.7 Hz, NH), 6.61 (dd, J )
2.0, 8.3 Hz, 1H), 6.83 (d, J ) 8.3 Hz, 1H), 6.92 (dd, J ) 2.4,
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectra.
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