Total Synthesis and Cytotoxicity of Haterumalides NA and B and Their Artificial Analogues Mitsuru Ueda, Masashi Yamaura, Yoichi Ikeda, Yuta Suzuki, Kensaku Yoshizato, Ichiro Hayakawa, and Hideo Kigoshi* Department of Chemistry, Graduate School of Pure and Applied Sciences, and Center for Tsukuba AdVanced Research Alliance, UniVersity of Tsukuba, Ibaraki 305-8571, Japan
[email protected] ReceiVed December 25, 2008
The total synthesis of haterumalides NA and B, potent cytotoxic marine macrolides, was achieved by using B-alkyl Suzuki-Miyaura coupling and Nozaki-Hiyama-Kishi coupling as key steps. Compared to our first-generation approach for ent-haterumalide NA methyl ester, this second-generation synthesis yielded much more of the key intermediate. This synthesis established the relative stereochemistry of haterumalide B. Furthermore, the structure-cytotoxicity relationships of haterumalides were investigated. The combination of macrolide and side chain parts proved to be important to the cytotoxicity.
Introduction In 1999, haterumalide B (1) was isolated from the Okinawan ascidian Lissoclinum sp. by Ueda and Hu.1 At the same time, haterumalides NA (2)-NE (6) were isolated from the Okinawan sponge Iricinia sp. by Uemura and co-workers.2 Haterumalide NA (2) exhibited cytotoxicity against P388 cells with an IC50 of 0.32 µg/mL, and moderate acute toxicity against mice with an LD99 of 0.24 g/kg. Also, haterumalide B (1) completely inhibited the first cleavage of fertilized sea urchin eggs at a concentration of 0.01 µg/mL.1 Oocydin A3a and haterumalide A3b were also isolated from the South American epiphyte Serratia marcescens and the soil bacterium Serratia plymuthica, respectively, and they were found to have the same gross * To whom correspondence should be addressed. Fax: +81-29-853-4313. (1) Ueda, K.; Hu, Y. Tetrahedron Lett. 1999, 40, 6305. (2) Takada, N.; Sato, H.; Suenaga, K.; Arimoto, H.; Yamada, K.; Ueda, K.; Uemura, D. Tetrahedron Lett. 1999, 40, 6309. (3) (a) Strobel, G.; Li, J.-Y.; Sugawara, F.; Koshino, H.; Harper, J.; Hess, W. M. Microbiology 1999, 145, 3557. (b) Thaning, C.; Welch, C. J.; Borowiez, J. J.; Hedman, R.; Gerhardson, B. Soil Biol. Biochem. 2001, 33, 1817. (4) (a) Teruya, T.; Shimogawa, H.; Suenaga, K.; Kigoshi, H. Chem. Lett. 2004, 33, 1184. (b) Teruya, T.; Suenaga, K.; Maruyama, S.; Kurotaki, M.; Kigoshi, H. Tetrahedron 2005, 61, 6561. (5) (a) Sato, B.; Nakajima, H.; Fujita, T.; Takase, S.; Yoshimura, S.; Kinoshita, T.; Terano, H. J. Antibiot. 2005, 58, 634. (b) Inai, M.; Kawamura, I.; Tsujimoto, S.; Yasuno, T.; Lacey, E.; Hirosumi, J.; Takakura, S.; Nishigaki, F.; Naoe, Y.; Manda, T.; Mutoh, S. J. Antibiot. 2005, 58, 640. (c) Kobayashi, M.; Sato, K.; Yoshimura, S.; Yamaoka, M.; Takase, S.; Ohkubo, M.; Fujii, T.; Nakajima, H. J. Antibiot. 2005, 58, 648. (d) Yamaoka, M.; Sato, K.; Kobayashi, M.; Nishio, N.; Ohkubo, M.; Fujii, T.; Nakajima, H. J. Antibiot. 2005, 58, 654.
3370 J. Org. Chem. 2009, 74, 3370–3377
structure as haterumalide NA (2). In 2004, we isolated biselides A (8) and B (9) from the Okinawan ascidian Didemnidae sp. and determined their structures to be oxygenated analogues of haterumalides (Figure 1).4a The next year, we reported the isolation of three analogues, biselides C (10)-E (12), and compared the cytotoxicity of haterumalide NA (2), haterumalide NA methyl ester (7), and biselides A (8), B (9), and C (10).4b Among the tested cell lines, haterumalide NA (2), haterumalide NA methyl ester (7), and biselides A (8) and B (9) showed stronger cytotoxicity than did anticancer drug cisplatin against human breast cancer MDA-MB-231 and human nonsmall cell lung cancer NCI-H460.4b Interestingly, haterumalide NA (2) showed strong toxicity against brine shrimp, with an LD50 of 0.6 µg/mL, while biselides A (8) and C (10) and haterumalide NA methyl ester (7) exhibited no toxicity against this animal, even at 50 µg/mL. In 2005, researchers at Fujisawa Pharmaceutical Company isolated an antimicrobial component FR177391, the enantiomer of haterumalide NA (2), from the soil bacterium Serratia liquefaciens.5a In addition, they identified its molecular target as protein phosphatase 2A (PP2A).5b-d The unique structures of haterumalides and biselides, in conjunction with their potent biological activities, have made them attractive synthetic targets.6 Several groups have reported approaches to synthesize the haterumalide NA (2). In 2003, Snider and Gu synthesized ent-haterumalide NA methyl ester (7).7a Their strategy involved a key fragment coupling at 10.1021/jo802806z CCC: $40.75 2009 American Chemical Society Published on Web 04/03/2009
Total Synthesis of Haterumalides NA and B SCHEME 1. Retrosynthetic Analyses of Haterumalides B (1) and NA (2)
SCHEME 2.
Synthesis of r,β-Unsaturated Ester 24
FIGURE 1. Structures of haterumalides and biselides.
C-5-C-6 using a Stille reaction. Hoye and Wang achieved the first total synthesis of haterumalide NA (2) itself.7b Their synthetic route involved a key intramolecular cyclization at C-6-C-7, based on the Kaneda reaction. Recently, Schomaker and Borhan synthesized haterumalides NA (2) and NC (4) by using chromium-mediated macrocyclization.7c Prior to those reports, we reported the first synthesis of ent-haterumalide NA methyl ester (7).8 This synthesis revised the stereochemistry of haterumalide NA (2) and determined its absolute configuration. However, because our previous synthetic route included lowyield steps, we planned to develop an efficient second-generation method for synthesizing haterumalides, biselides, and their derivatives, which will provide a practical supply for further biological studies. The second-generation synthesis of haterumalide NA was preliminarily reported.9 We describe in detail the synthesis of haterumalides NA (2) and B (1) by using a convergent synthetic methodology with a B-alkyl Suzuki-Miyaura coupling.10 Very recently, Roulland reported the total synthesis of haterumalide NA (2) using a similar cross-coupling strategy.7d (6) Kigoshi, H.; Hayakawa, I. Chem. Rec. 2007, 7, 254. (7) (a) Gu, Y.; Snider, B. B. Org. Lett. 2003, 5, 4385. (b) Hoye, T. R.; Wang, J. J. Am. Chem. Soc. 2005, 127, 6950. (c) Schomaker, J. M.; Borhan, B. J. Am. Chem. Soc. 2008, 130, 12228. (d) Roulland, E. Angew. Chem., Int. Ed. 2008, 47, 3762. (8) Kigoshi, H.; Kita, M.; Ogawa, S.; Itoh, M.; Uemura, D. Org. Lett. 2003, 5, 957. (9) Hayakawa, I.; Ueda, M.; Yamaura, M.; Ikeda, Y.; Suzuki, Y.; Yoshizato, K.; Kigoshi, H. Org. Lett. 2008, 10, 1859. (10) Miyaura, N.; Suzuki, A. Chem. ReV. 1995, 95, 2457.
Results and Discussion Our retrosynthetic analyses of haterumalides NA (2) and B (1) are shown in Scheme 1. Our strategy involved a key fragment coupling between macrolactone 13 and the appropriately protected side chain unit 14 or 15 using NozakiHiyama-Kishi coupling. We expected that macrolactonization of seco acid 16 provided macrolactone 13. Seco acid 16 might be obtained from a common intermediate 17 for haterumalides and biselides. The synthetic route to a common intermediate 17 for haterumalides and biselides involved the B-alkyl Suzuki-Miyaura coupling10 between the alkenylsilane segment 1911 and alkylborane 20, with subsequent stereoselective construction of a chloroolefin part from alkenylsilane 18. The starting point for this work was the construction of the common intermediate 17 (Scheme 2). The known glycal 21 was (11) Miura, K.; Hondo, T.; Okajima, S.; Nakagawa, T.; Takahashi, T.; Hosomi, A. J. Org. Chem. 2002, 67, 6082.
J. Org. Chem. Vol. 74, No. 9, 2009 3371
Ueda et al. TABLE 1.
Study of Intramolecular Oxy-Michael Cyclization of r,β-Unsaturated Ester 24
entry 1 2 a
conditions
SCHEME 4. Synthesis of the Precursors of B-Alkyl Suzuki-Miyaura Coupling
yielda (%)
NaOMe, MeOH, 0 °C f rt, 30 min 80% (trans:cis ) 9:1) Triton B, MeOH, 0 °C f rt, 15 min 87% (single diastereomer) Isolated yields calculated from dihydrofuran 22 (in 3 steps).
SCHEME 3. Intramolecular Oxy-Michael Cyclization in the Previous Work8 TABLE 2.
synthesized from commercially available D-mannose.12 The hydroxy group of glycal 21 was protected to give the 3,4dimethoxybenzyl (DMPM) ether 22. The DMPM ether 22 was transformed into the hemiacetal 23 by the oxymercurationreduction sequence.13 The hemiacetal 23 was converted into R,β-unsaturated ester 24 by the Wittig reaction. Table 1 summarizes our attempts toward the intramolecular oxy-Michael cyclization of R,β-unsaturated ester 24. In our previous report,8 similar intramolecular oxy-Michael cyclization was carried out by using NaOMe in MeOH, but the yield and stereoselectivity were not so high (56%, trans/cis ) 5.3:1) (Scheme 3). Treatment of R,β-unsaturated ester 24 under the same conditions gave the desired tetrahydrofuran 25 (80% in 3 steps, trans/cis ) 9:1) (entry 1). Next, oxy-Michael cyclization was performed with Triton B in MeOH (entry 2).14 This cyclization improved the stereoselectivity and enhanced the reaction rate. The success of oxy-Michael cyclization of the R,β-unsaturated ester 24 might be due to two factors: (1) steric hindrance of the acetonide group in 24 directed the addition and (2) Triton B was more effective in promoting oxy-Michael cyclization and the reaction was completed at lower temperature. The LiAlH4 reduction of 25 gave alcohol 26 (Scheme 4). Alcohol 26 was converted to iodide 27, a precursor of the requisite boranate. On the other hand, the primary alcohol of 26 was converted to the corresponding selenoether. Upon treatment with H2O2 and pyridine, the selenoether was oxidized and then eliminated to form the terminal olefin 28.15 With iodide 27 and terminal olefin 28 in hand, we attempted B-alkyl Suzuki-Miyaura coupling, as depicted in Table 2. The alkylboranate 29 generated in situ from iodide 2716 participated in the cross-coupling reaction with alkenylsilane 1911 to provide the desired coupling compound 18 in 32% yield (entry 1). We next tried B-alkyl Suzuki-Miyaura coupling with terminal olefin 28. Hydroboration of the terminal olefin 28 with 9-BBN-H/ (12) Ireland, R.; Thaisrivongs, S.; Vanier, N.; Wilcox, C. J. Org. Chem. 1979, 45, 48. (13) Oishi, T.; Ando, K.; Inomiya, K.; Sato, H.; Iida, M.; Chida, N. Bull. Chem. Soc. Jpn. 2002, 75, 1927. (14) (a) Ko, S.; Klein, L.; Pfaff, K.; Kishi, Y. Tetrahedron Lett. 1982, 23, 4415. (b) The stereochemistry was determined by NOESY correlations. (15) Grieco, P. A.; Gilman, S.; Nishizawa, M. J. Org. Chem. 1976, 41, 1485. (16) Marshall, J. A.; Johns, B. A. J. Org. Chem. 1998, 63, 7885.
3372 J. Org. Chem. Vol. 74, No. 9, 2009
Study of B-Alkyl Suzuki-Miyaura Coupling
entry
precursor
reagent
yield (%)
1 2 3
27 28 28
t-BuLi, 9-BBN-OMe 9-BBN-H/THF 9-BBN-H dimer
32 0 quant
THF, followed by the addition of PdCl2(dppf) and alkenylsilane 19, did not give the coupling compound 18 (entry 2). In this reaction, the hydroboration step was slow, and the intermediate borane decomposed gradually. The use of 9-BBN-H dimer instead of 9-BBN-H/THF gave the best result, maybe because of the concentrated conditions (entry 3). We next tried to construct a chloroolefin part stereoselectively from the alkenylsilane 18. In our previous report,8 a chloroolefin part was stereoselectively constructed from an alkenylsilane 18 by a modification of Tamao’s procedure.17 We reported that the addition of a small amount of water was important for the reaction to be reproducible. In this study, we attempted the same conditions with the alkenylsilane 18 but obtained a low and irreproducible yield. Thus, preparation of the chloroolefin 31 required optimization (Table 3). Chlorination of the alkenylsilane 18 without water gave the desired chloroolefin 31 and recovery of the alkenylsilane 18, but the yield was low (35%) (entry 1). We expected that a small amount of base would be neutralized in this reaction system. So we attempted the chlorination of the alkenylsilane 18 by NCS with a base. The reaction with CaCO3 did not give chloroolefin 31 (entry 2). An attempt at chlorination with KF afforded the desired chloroolefin 31 in 25% yield (entry 3). However, the reaction at higher temperature did not afford the desired chloroolefin 31 (entry 4). Treatment of alkenylsilane 18 with NCS-K2CO3 (1.0 equiv) did not further the reaction (entry 5). However, the chlorination was most efficiently effected by NCS (2.0 equiv) in DMF at 50 °C in the presence of K2CO3 (0.5 equiv) as a base (entry 6). This modification increased the yield of the desired chloroolefin to 58%, reproducibly. (17) Tamao, K.; Akita, M.; Maeda, K.; Kumada, M. J. Org. Chem. 1987, 52, 1100.
Total Synthesis of Haterumalides NA and B TABLE 3.
Study of Stereoselective Construction of Chloroolefin
entry
additive
temp, °C
yield, %
recovery of 18, %
1 2 3 4 5 6
none CaCO3 (2.0 equiv) KF (1.0 equiv) KF (1.0 equiv) K2CO3 (1.0 equiv) K2CO3 (0.5 equiv)
50 50 50 100 50 50
35
