First total synthesis of the antitumor compound (-)-kazusamycin A and absolute structure determination

Article abstract of DOI:10.1021/ol049219z

(Equation Presented) The first total synthesis of kazusamycin A, a potent antitumor compound from an actinomycete, has been achieved, and its absolute structure was determined. Paterson's stereoselective aldol reaction was successfully applied to construct the contiguous chiral centers by using an originally designed optically active 2-acyl-1,3-propanediol derivative.

Full text of DOI:10.1021/ol049219z

ORGANIC
LETTERS
2004
Vol. 6, No. 17
2845-2848
First Total Synthesis of the Antitumor
Compound (−)-Kazusamycin A and
Absolute Structure Determination
,†,‡
Noriyoshi Arai,† Noriko Chikaraishi,† Satoshi Omura,‡ and Isao Kuwajima*
Creation and Function of New Molecules and Molecular Assemblies, Core Research
for EVolutional Science and Technology (CREST), Japan Science and Technology
Agency (JST), 1-15-1 Kitasato, Sagamihara, Kanagawa 228-8555, Japan, and
Kitasato Institute for Life Science, Kitasato UniVersity, 1-15-1 Kitasato, Sagamihara,
Kanagawa 228-8555, Japan
kuwajima@lisci.kitasato-u.ac.jp
Received April 28, 2004
ABSTRACT
The first total synthesis of kazusamycin A, a potent antitumor compound from an actinomycete, has been achieved, and its absolute structure
was determined. Paterson’s stereoselective aldol reaction was successfully applied to construct the contiguous chiral centers by using an
originally designed optically active 2-acyl-1,3-propanediol derivative.
Kazusamycin A, isolated from the culture broth of an
actinomycete strain, 81-484, has been found to exhibit potent
antitumor activity on P388 leukemia and sarcoma 180, as
well as anitimicrobial activity.1 It was also effective in
completely preventing growth of HeLa cells at a concentra-
tion of 3.3 ng/mL.2 In addition, it was found that kazusa-
mycin A shows potent inhibitory activity against Rev protein
translocation from the nucleus to the cytoplasm, which could
be a useful target for HIV therapy.3 These important bio-
logical activities, as well as an interesting structural feature,
attracted our attention toward its total synthesis. Although a
unique planar structure, including two types of dienes (E,E
and E,Z), R,â-unsaturated δ-lactone, and a hydroxymethyl
side chain, has been proposed,3-5 neither its absolute nor
relative configuration was determined. Several cytotoxic
natural products with similar structures, e.g., callystatin A,6
leptomycin B,4,7 and delactonmycin,3 have also been isolated,
and their absolute configurations were recently elucidated
by their total syntheses.8-10 At the beginning of our synthetic
studies together with elucidation of absolute configuration
(4) Schaumberg, J. P.; Hokanson, G. C.; French, J. C. J. Chem. Soc.,
Chem. Commun. 1984, 1450-1452.
(5) Komiyama, K.; Okada, K.; Oka, H.; Tomisaka, S.; Miyano, T.;
Funayama, S.; Umezawa, I. J. Antibiot. 1985, 38, 220-223.
(6) (a) Kobayashi, M.; Higuchi, K.; Murakami, N.; Tajima, H.; Aoki, S.
Tetrahedron Lett. 1997, 38, 2859-2862. (b) Murakami, N.; Wang, W.;
Aoki, M.; Tsutsui, Y.; Higuchi, K.; Aoki, S.; Kobayashi, M. Tetrahedron
Lett. 1997, 38, 5533-5536.
(7) (a) Hamamoto, T.; Gunji, S.; Tsuji, H.; Beppu, T. J. Antibiot. 1983,
36, 639-645. (b) Hamamoto, T.; Seto, H.; Beppu, T. J. Antibiot. 1983, 36,
646-650.
† JST.
‡ Kitasato University.
(1) Umezawa, I.; Komiyama, K.; Oka, H.; Okada, K.; Tomisaka, S.;
Miyano, T.; Takano, S. J. Antibiot. 1984, 37, 706-711.
(2) Komiyama, K.; Okada, K.; Hirokawa, Y.; Masuda, K.; Tomisaka,
S.; Umezawa, I. J. Antibiot. 1985, 38, 224-229.
(3) Wang, Y.; Ponelle, M.; Sanglier, J.-J.; Wolff, B. HelV. Chim. Acta
1997, 80, 2157-2167.
10.1021/ol049219z CCC: $27.50 © 2004 American Chemical Society
Published on Web 07/17/2004

Figure 2. Expected transition state in the aldol reaction.
(SiR3). As shown in Figure 2, when the aldol reaction is
carried out with an aldehyde, transition state 8 is expected
to be more favorable than 9 due to the difference in steric
and electronic character between OR and OSiR3,12 leading
to the aldol adduct with an absolute configuration suitable
for stereocontrolled preparation of fragment 2.
To test the stereoselectivity of the aldol reaction first, the
aldehyde 5a (R3 ) Bn) was prepared by a coupling reaction13
between vinyl bromide 1314 and optically pure zinc homo-
enolate 11,12 which was prepared in situ from cyclopropane
10 (Scheme 1).15 No loss of optical purity was observed
during the reaction.
Figure 1. Retrosynthetic analysis of (-)-kazusamycin A.
of kazusamycin A, we proposed structure 1, shown in Figure
1, by analogy to leptomycin B. Eventually, we confirmed
its relative and absolute configuration through the total
synthesis. Herein, we disclose our approach toward the first
total synthesis and structural elucidation of kazusamycin A.
Our synthetic plan for kazusamycin A is shown in Figure
1. The molecule was disconnected at the C(12)-C(13)
double bond into fragments 2 and 3 of almost the same size.
Fragment 3 was expected to be accessible using slight
modifications of known methods.8a,8e,9 The most critical
aspect for the synthesis is in construction of hydoxyketone
4, which was the intermediate for 2, in a stereocontrolled
manner.
Scheme 1. Preparation of Aldehyde 5aa
a Reagents and conditions: (a) ZnCl2, Et2O. (b) 2 mol %
PdCl2[P(o-Tol)3]2, 13, THF, 68%. (c) DIBAL, CH2Cl2, -78 f 45
°C, 96%. (d) Dess-Martin periodinane, CH2Cl2, quantitative.
For this purpose, we envisioned that Paterson’s stereose-
lective aldol reaction mediated by divalent tin11 would work
well by using an optically pure ethyl ketone 7. The
environment around two hydroxy moieties in the ketone 7
was differentiated by an alkyl group (R) and a silyl group
On the other hand, optically pure ketone 6a was prepared
by an enzymatic method according to the procedure recently
developed by us. 16
Thus, the stage was set for the aldol reaction. Treatment
of 6a with Sn(OTf)2 and Et3N at -78 °C followed by the
addition of the aldehyde 5a gave the aldol adduct 14 with
(8) Callystatin A: (a) Murakami, N.; Wang, W.; Aoki, M.; Tsutsui, Y.;
Sugimoto, M.; Kobayashi, M. Tetrahedron Lett. 1998, 39, 2349-2352. (b)
Crimmins, M. T.; King, B. W. J. Am. Chem. Soc. 1998, 120, 9084-9085.
(c) Smith, A. B., III; Brandt, B. M. Org. Lett. 2001, 3, 1685-1688. (d)
Kalesse, M.; Quitschalle, M.; Khandavalli, C. P.; Saeed, A. Org. Lett. 2001,
3, 3107-3109. (e) Vicario, J. L.; Job, A.; Wolberg, M.; Mu¨ller, M.; Enders,
D. Org. Lett. 2002, 4, 1023-1026. (f) Marshall, J. A.; Bourbeau, M. P. J.
Org. Chem. 2002, 67, 2751-2754.
(9) Leptomycin B: Kobayashi, M.; Wang, W.; Tsutsui, Y.; Sugimoto,
M.; Murakami, N. Tetrahedron Lett. 1998, 39, 8291-8294.
(10) Delactonmycin: Correa, I. R.; Pilli, R. A. Angew. Chem., Int. Ed.
2003, 42, 3017-3020.
(11) (a) Paterson, I.; Tillyer, R. D. Tetrahedron Lett. 1992, 33, 4233-
4236. (b) Paterson, I.; Norcross, R. D.; Ward, R. A.; Romea, P.; Lister, M.
A. J. Am. Chem. Soc. 1994, 116, 11287-11314.
(12) Comparison of basicity between alkyl ethers and siloxanes: Armit-
age, D. A. In ComprehensiVe Organometallic Chemistry; Wilkinson, G.,
Ed.; Pergamon Press: Oxford, 1982; Vol. 2, pp 160-162.
(13) (a) Nakamura, E.; Sekiya, K.; Kuwajima, I. Tetrahedron Lett. 1987,
28, 337-340. (b) Nakamura, E.; Aoki, S.; Sekiya, K.; Oshino, H.;
Kuwajima, I. J. Am. Chem. Soc. 1987, 109, 8056.
(14) Corey, E. J.; Bock, M. G.; Kozikowski, A. P.; Rama Rao, A. V.;
Floyd, D.; Lipshutz, B. Tetrahedron Lett. 1978, 1051-1054.
(15) Very recently, a similar approach was reported by Pilli et al. See
ref 10.
2846
Org. Lett., Vol. 6, No. 17, 2004

high diastereoselectivity (93%). Although small amounts of
other stereoisomers were also formed, silica gel column
chromatography allowed their complete removal, affording
stereochemically pure 14 in 77% yield. The configuration
of a newly generated stereocenter in 14 was determined by
a conventional method comprised of reduction to diol, trans-
formation to acetonides (inner and outer direction, respec-
tively), and NOE experiment.
Scheme 3. Preparation of Aldehyde 26a
Next, transformation to the left-half segment 19 was then
carried out as depicted in Scheme 2. Reduction of 14 with
Scheme 2. Preparation of the Left-Half Fragment 19a
a Reagents and conditions: (a) Bu2BOTf, Et3N, BnOCH2CHO,
CH2Cl2, -78 f 0 °C, 96% (>99% ds). (b) H2, Pd/C, PPTS,
Me2C(OMe)2, acetone, 90%. (c) LiBH4, MeOH, 0 °C, 95%. (d)
Dess-Martin periodinane, CH2Cl2. (e) Ph3P, CBr4, Zn, CH2Cl2,
60% (two steps). (f) BuLi, ClCO2Me, THF, -78 °C f rt, 93%.
(g) H2, Lindlar catalyst, MeOH, 96%. (h) Dowex 50WX8, MeOH,
then Amberlyst 15, CH2Cl2. (i) TBDPSCl, imidazole, DMF, 57%
(two steps). (j) DIBAL, CH2Cl2, -78 °C, 82%. (k) PPTS, i-PrOH,
benzene, 85%. (l) TBAF, THF, 85%. (m) (COCl)2, DMSO, CH2Cl2,
-78 °C, then Et3N, -78 °C f rt, 98%.
SelectiveWittig olefination of 17 by using (carbethoxyethyli-
dene)triphenylphosphorane proceeded well, giving unsatur-
ated ester 18 in good selectivity.20 DIBAL reduction of 18,
followed by protecting group manipulation and bromination,
gave allylic bromide 19 corresponding to the fragment 2.
Replacement of the Bn protecting group with Alloc was
carried out at this stage, since deprotection of Bn after the
construction of the sensitive diene moiety seemed to be
troublesome.
The right-half fragment corresponding to 3 was prepared,
starting from commercially available oxazolidin-2-one de-
rivative 20. An aldol adduct obtained by Evans aldol reac-
tion21 between 20 and benzyloxyacetaldehyde was sub-
jected to hydrogenolysis conditions in PPTS-(MeO)2CMe2-
acetone, to afford an acetonide directly, which was trans-
formed to alcohol 2122 via reductive removal of the chiral
auxiliary. Oxidation of 21 followed by the treatment with
PPh3-CBr4-Zn reagent23 produced the dibromoalkene 22,
which was converted to 23 by a successive treatment with
a Reagents and conditions: (a) Sn(OTf)2, Et2N, CH2Cl2, -78 °C,
then 5a, 77%. (b) Et2BOMe, NaBH4, THF-MeOH, -78 °C, 78%.
(c) TBAF, THF, 92%. (d) Me2C(OMe)2, PPTS, acetone, 86%.
(e) TBSOTf, 2,6-lutidine, CH2Cl2, 0 °C, 94%. (f) DDQ, CH2Cl2,
0 °C, 68%. (g) Dess-Martin periodinane, CH2Cl2. (h) Ph3Pd
CMeCO2Et; 69% (two steps). (i) DIBAL, CH2Cl2, -78 °C, 89%.
(j) TIPSCl, imidazole, DMF, 96%. (k) Na, liq NH3-THF, -78
°C, quantitative. (l) AllocCl, pyridine, THF, 96%. (m) TBAF, THF,
98%. (n) Ph3P, CBr4, CH2Cl2, 94%.
NaBH4-Et2BOMe gave the syn-diol 15 in almost complete
stereoselectivity.17 Deprotection of the TBDPS group fol-
lowed by selective protection of the triol moiety as aceto-
nide (C(15)-C(17)) and silylation of the remaining hydroxy
group afforded 16, which was converted to aldehyde 17 via
removal of PMB protecting group18 and oxidation.19 (E)-
Scheme 4. Preparation of Right-Half Fragment 29a
(16) Arai, N.; Chikaraishi, N.; Ikawa, M.; Omura, S.; Kuwajima, I.
Tetrahedron: Asymmetry 2004, 15, 733-741.
(17) Chen, K.-M.; Hardtmann, G. E.; Prasad, K.; Repic, O.; Shapiro,
M. J. Tetrahedron Lett. 1987, 28, 155-158.
(18) Horita, K.; Yoshioka, T.; Tanaka, T.; Oikawa, Y.; Yonamitsu, O.
Tetrahedron 1986, 42, 3021-3028.
(19) (a) Dess, D. B.; Martin, J. C. J. Am. Chem. Soc. 1991, 113, 7277-
7287. (b) Ireland, R. E.; Liu, L. J. Org. Chem. 1993, 58, 2899. (c) Frigerio,
M.; Santagostino, M.; Sputore, S. J. Org. Chem. 1999, 64, 4537-4538.
a Reagents and conditions: (a) (i) Bu3P, CH3CN; (ii) 26, t-BuOK,
toluene-THF, 0 °C, 91%. (b) TBAF, THF, 99%. (c) (COCl)2,
DMSO, CH2Cl2, -78 °C, then Et3N, -78 °C f rt, 92%.
Org. Lett., Vol. 6, No. 17, 2004
2847

of lactone moiety as a lactol followed by oxidation of alcohol
gave the aldehyde 269 (Scheme 3).
Coupling of 26 with bromide 278b,8e via Wittig reaction
gave 1,3-diene 28 in good yield and selectivity (E:Z ) ca.
7:1). 28 was then converted to the aldehyde 29 corresponding
to fragment 3 (Scheme 4).
Scheme 5. Completion of the Total Synthesis of Kazusamycin
Aa
The final stage of the total synthesis is shown in Scheme
5. Wittig reaction of tributylphosphonium salt derived from
19 with 298b,8e proceeded well in the presence of t-BuOK to
afford the product 30 having the basic skeleton of kazusa-
mycin A. Finally, appropriate functional group manipulation,8
including chemodifferentiation of prim-, sec-, and allylic
alcohol completed the total synthesis of kazusamycin A,
whose spectroscopic data (1H NMR, 13CNMR, IR, HRMS)
were in complete agreement with that of the natural kazusa-
mycin A. The synthetic sample showed negative optical
rotation ([R]27D -87.7°, c 0.358, MeOH) in accordance with
the natural compound ([R]20 -83.5°, c 0.1, MeOH).1 This
D
fact indicates that the natural kazusamycin A has the absolute
configuration shown in Figure 1.
Thus, we have achieved the first total synthesis and
structural elucidation of kazusamycin A. Among several
characteristic features of the synthesis, the remarkable aspect
for the present total synthesis exists in an exploration of
stereocontrolled aldol reaction by using an originally de-
signed optically active synthetic unit 6a, which led to suc-
cessful total synthesis of this highly biologically active
natural product. On the basis of this route, synthesis of arti-
ficial congeners of kazusamycin A and biological assay of
them are now underway.
Supporting Information Available: Experimental pro-
cedures and characterization. This material is available free
of charge via the Internet at http://pubs.acs.org.
a Reagents and conditions: (a) (i) Bu3P, CH3CN; (ii) 29, t-BuOK,
83%. (b) PPTS, MeOH, 84% (three cycles). (c) TIPSCl, imidazole,
DMF, 95%. (d) Dess-Martin periodinane, CH2Cl2, 95%. (e) PPTS,
aq acetone, 91% (three cycles). (f) Pd(PPh3)4, dimedone, THF, 96%.
(g) MnO2, CH2Cl2, 49%. (h) NaClO2, 2-methyl-2-butene, aq
t-BuOH, 80%. (i) HF-Py, Py, THF, 74%.
OL049219Z
(20) Morimoto, Y.; Matsuda, F.; Shirahama, H. Tetrahedron 1996, 52,
10609-10630.
(21) Gage, J. A.; Evans, D. A. Org. Synth., Coll. Vol. VIII 1993, 339-
343.
(22) (a) 1H NMR: Nakata, M.; Ishiyama, T.; Akamatsu, S.; Hirose, Y.;
Maruoka, H.; Suzuki, R.; Tatsuta, K. Bull. Chem, Soc. Jpn. 1995, 68, 967.
(b) [R]D of the enantiomer: Wittman, M. D.; Kallmerten, J. J. Org. Chem.
1988, 53, 4631.
BuLi and then with methyl chloroformate. Lindlar reduction
afforded the unsaturated ester 24, which underwent cycliza-
tion to unsaturated lactone after removal of the acetonide
protecting group by treatment with acidic resins. Protection
(23) Corey, E. J.; Fuchs, P. L. Tetrahedron Lett. 1972, 3769-3772.
2848
Org. Lett., Vol. 6, No. 17, 2004