生物活性を有するポリケチド型天然有機化合物の全合成研究

13) 上田実, 源治尚久. 化学と生物, 2013, 51, 90-97.

14) Y. Igarashi et al., Org. Lett. 2017, 19, 1406-1409.

15) 2020 年度祷雄太卒業論文

16) K. C. Nicolau, et al., Angew. Chem. Int. Ed. 2005, 44, 1378 –1382.

17) Y. Yoshida, Y. Sakakura, N. Aso, S. Okada, Y. Tanabe, Tetrahedron, 1999, 55, 21832192.

18) Xiaozhao Wang et al., Org. Lett., 2012, 14, 3998-4001.

19) Ravi V. J. Chari, John W. Kozarich, J. Org. Chem. 1982, 47, 2355-2358.

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2.7 Experimental

General information

IR spectra were recorded by Jasco FT/IR-4100 spectrometer using an ATR (ZnSe)

attachment. NMR spectra were recorded with TMS as internal standard in CDCl 3 by Varian

MR-400 spectrometer (400 MHz for 1H and 100 MHz for 13C). Optical rotation values were

measured with a Horiba Septa-300 polarimeter, and the mass spectra were obtained with a

Jeol JMS-700 spectrometer operated in the EI or FAB mode. Column chromatography was

conducted with Merck silica gel 60 (7-230 mesh). The solvents for the reactions were

distilled prior use: THF and Et2O from Na/benzophenone, and CH2Cl2 and MeCN from

CaH2. All reaction under heating condition were performed in an oil bath.

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Methyl 5-(1,3-dioxolan-2-yl)pent-2-ynoate (36).

Under N2 atmosphere, to a solution of TMS acetylene (758.3 mg, 7.72 mmol) in THF (15

ml) was added n-BuLi (2.64 M in hexane, 2.92 ml) at -78 ℃ and stirred for 30 min. The

resulting mixture was added compound 33 (1.0 g, 5.52 mmol) and HMPA (1.38 g, 7.72

mmol), slowly warmed to 0 ℃ and stirred for 4 hr. The reaction mixture was cooled to 78 ℃, added MeLi (1.5 M in THF, 10.3 ml) and stirred for 12 hr at -20 ℃. The reaction

mixture was re-cooled to -78 ℃, added chloromethylformate (2.6 g, 27.6 mmol) and

warmed to 0 ℃. After 6 hr, the resulting mixture was quenched with saturated aq. NH4Cl

and extracted with ethyl. The organic layer was washed with water and brine, dried over

Na2SO4. After filtration, the filtrate was concentrated under reduce pressure. The residue

was purified by silica gel column chromatography (hexane/EtOAc = 7 : 1 to 4 : 1) to give

compound 35 (535.6 mg, 53%).

Methyl (Z)-5-(1,3-dioxolan-2-yl)-3-ethylpent-2-enoate (32).

Under N2 atmosphere, to a stirring suspension of CuI (4.11 g, 21.6 mmol) in THF (130 ml)

was added EtMgBr (0.9 M in THF 24.0 ml), TMEDA (5.02 g, 43.2 mmol) at −25 ℃ and

then warmed to −15 ℃. After 1hr, the mixture was cooled to -85 ℃, added compound 36

(2.14 g, 10.80 mmol), in THF (20 ml) via syringe pump over 2 hr and stirred for 3hr. The

reaction mixture was quenched by adding MeOH/THF (1 : 5) via syringe pump over 2 hr.

The resulting mixture was added saturated aq. NH4Cl and stirred for additional 1hr,

extracted with ethyl. The organic layer was washed with sat. NH4Cl aq., water and brine,

dried over Na2SO4. After filtration, the filtrate was concentrated under reduce pressure. The

residue was purified by silica gel column chromatography (Hexane/EtOAc = 4 : 1) to give

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compound 32 (2.42 g, 98%, (E)- isomer was not detected).

(Z)-5-(1,3-dioxolan-2-yl)-3-ethylpent-2-en-1-ol (37).

Under N2 atmosphere, to a stirring solution of compound 36 (2.42 g, 10.60 mmol) in THF

(20 ml) was added DIBAL (1.0 M in hexane 23.3 ml) at – 78 ℃ and then warmed to 0 ℃.

After 1h, the resulting mixture was quenched with 30% Rochell salt aq. and stirred for

additional 1h. The mixture was extracted with ethyl and the organic layer was washed with

water and brine, dried over Na2SO4. After filtration, the filtrate was concentrated under

reduce pressure. The crude compound 37 was used for next reaction without further

purification.

(Z)-2-(5-bromo-3-ethylpent-3-en-1-yl)-1,3-dioxolane. (38)

Under N2 atmosphere, to a stirring solution of crude compound 37 (1.90 g) in THF (15 ml)

was added Et3N 2.48g, 24.48 mmol) and MsCl (1.64 g, 14.28 mmol) at -78 ℃ and then

warmed to 0 ℃. After 3h, the mixture was added LiBr (1.77 g, 20.40 mmol) and stirred for

1 h at room temperature. The resulting mixture was cooled to 0 ℃ and quenched with

saturated aq. NaHCO3. The mixture was extracted with ether and the organic layer was

washed with water and brine, dried over Na2SO4. After filtration, the filtrate was

concentrated under reduce pressure. The crude compound 38 was used for next reaction

without further purification.

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(R)-2-((tert-butyldimethylsilyl)oxy)-N-methoxy-N-methylpropanamide (39).

Under N2 atmosphere, to a solution of compound 15 (3.00 g, 13.73 mmol) in THF (20 ml)

was added NHMe(OMe)•HCl (2.68 g, 27.47 mmol) and i-PrMgCl (2.0 M in THF, 27.4 ml)

at 0 °C and stirred for 4 hr. The resulting mixture was quenched with saturated aq. NH4Cl

and extracted with EtOAc. The organic layer was washed with water and brine and dried

over Na2SO4. After filtration, the filtrate was concentrated under reduce pressure. The crude

compound 39 was used for next reaction without further purification.

(R)-3-((tert-butyldimethylsilyl)oxy)butan-2-one (40).

Under N2 atmosphere, to a stirring solution of crude compound 39 (3.36 g, 13.58 mmol) in

THF (30 ml) was added MeLi (1.5 M in THF 10.8 ml) at −78 °C 0 °C and then warmed to

0 °C. After1 hr, the resulting mixture was quenched with saturated aq. NH4Cl and extracted

with EtOAc. The organic layer was washed with water and brine and dried over Na2SO4.

After filtration, the filtrate was concentrated under reduce pressure. The residue was

purified by silica gel column chromatography (Hexane/EtOAc = 15 : 1) to give compound

40 (2.70 g, 97% yield over 2 steps). 1H NMR δ: 4.12(1H, q, J = 6.8 Hz), 2.19(3H, s),

1.28(3H, d, J = 6.8 Hz), 0.92(9H, s), 0.08(6H, s).

(R)-2,2,5,7,7,8,8-heptamethyl-4-methylene-3,6-dioxa-2,7-disilanonane (41).

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Under N2 atmosphere, to a stirring solution of compound 40 (100.0 mg, 494.1 μmol) in

MeCN (2 ml) was added Et3N (129.5, 1.28 mmol), TMSCl (129.3g, 1.19 mmol) and NaI

(191.9 mg, 1.28 mmol) at −30 °C and then warmed to room temperature. After 18 hr, the

resulting mixture was quenched with cooled water and extracted with hexane. The organic

layer was washed with water and brine and dried over Na2SO4. After filtration, the filtrate

was concentrated under reduce pressure. The crude compound 41 was used for next reaction

without further purification.

Methyl (R)-4-((tert-butyldimethylsilyl)oxy)-3-oxopentanoate (42).

Under N2 atmosphere, to a stirring solution of MeOAc (299.5 mg, 4.04 mmol) in THF (10

ml) was added LiHMDS (1.3 M in THF, 3.11 ml) at −78 °C. After 30 min., the reaction

mixture was added crude compound 39 (c.a. 2.02 mmol) and then warmed to −40 °C. After

18 hr, the resulting mixture was quenched with saturated aq. NH4Cl and extracted with

EtOAc. The organic layer was washed with water and brine and dried over Na2SO4. After

filtration, the filtrate was concentrated under reduce pressure. The residue was purified by

column chromatography to give compound 42 (364.2 mg, 69% yield). 1H NMR δ: 4.23(1H,

q, J = 6.8 Hz), 3.73(3H, s), 3.64(2H, d, J = 2.0 Hz), 1.32(3H, d, J = 6.8 Hz), 0.91(9H, s),

0.096-0.074(6H, m).

Methyl (Z)-2-((R)-2-((tert-butyldimethylsilyl)oxy)propanoyl)-7-(1,3-dioxolan-2-yl)-5ethylhept-4-enoate (44).

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Under N2 atmosphere, to a stirring solution of compound 38 (30 mg, 120 μmol) in

acetone/DMF(1 : 1, 500 μl) was added compound 42 (30 mg, 115μmol) and K2CO3 (15.8

mg, 115μmol) and then warmed to room temperature. After 6h, the mixture was cooled to

0 ℃ and quenched with saturated aq. NH4Cl. The mixture was extracted with ethyl and the

organic layer was washed with water and brine, dried over Na2SO4. After filtration, the

filtrate was concentrated under reduce pressure and the residue was The residue was

purified by silica gel column chromatography (Hexane/EtOAc = 6 : 1) to give compound

( 38 mg, 73% yield).

H NMR δ: 5.05-5.00(1H, br), 4.84(1H, dt, J = 9.6, 1.6 Hz), 4.26(2H, q, J = 6.8 Hz), 3.99-

3.83(5H, m), 3.674(3H, s), 3.669(3H, s), 2.62-2.50(2H, m), 2.18-2.14(2H, m), 1,99(2H, q, J

= 7.6 Hz), 1.72-1.66(2H, m), 1.35(3H, d, J = 6.8 Hz), 1.27(3H, d, J = 6.8 Hz), 0.95(3H, t, J

= 7.6 Hz), 0.91(9H, s), 0.09(6H, s), 0.08(6H, s).

(R,Z)-2-((tert-butyldimethylsilyl)oxy)-9-(1,3-dioxolan-2-yl)-7-ethylnon-6-en-3-one (43).

Under N2 atmosphere, to a stirring solution of compound 44 (505.8 mg, 1.18 mmol) in

THF (3 ml) was added PhSeNa (420.1 mg, 2.33 mmol) and HMPA (500 μl), warmed to

65 °C. After 6 hr, the reaction mixture was cooled to room temperature and quenched with

water. The organic layer was washed with water and brine, dried over Na2SO4. After

filtration, the filtrate was concentrated under reduce pressure. The residue was purified by

silica gel column chromatography(hexane/EtOAc = 7 : 1) to give compound 45 (402.1 mg,

92%). 1H NMR δ: 5.05(1H, t, J = 6.8 Hz), 4.82(1H, t, J = 4.8 Hz), 4.12(1H, q, J = 6.4 Hz),

3.97-3.81(4H, m), 2.63(1H, dt, J = 18.0, 7.6 Hz), 2.54(1H, dt, J = 18.0, 7.2 Hz), 2.26(2H, q,

J = 7.6 Hz), 2.16-2.12(2H, m), 1.96(2H, dq, J = 7.2, 1.2 Hz), 1.71-1.66(2H, m), 1.25(3H, d,

J = 6.8 Hz), 0.95(3H, t, J = 7.6 Hz), 0.89(9H, s), 0.51(6H, s).

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(R,Z)-9-(1,3-dioxolan-2-yl)-7-ethyl-2-hydroxynon-6-en-3-one (45).

To a solution of compound 43 (214.6 mg, 579.0 μmol) in THF (1 ml) was added TBAF

(1.0 M in THF, 869 μl) at 0 ℃ and stirred for 18 hr. the reaction mixture was quenched with

saturated aq. NH4Cl and extracted with ethyl. The organic layer was washed with water and

brine, dried over Na2SO4. After filtration, the filtrate was concentrated under reduce

pressure. The crude compound 47 was used for next reaction without further purification.

(R,Z)-9-(1,3-dioxolan-2-yl)-7-ethyl-3-oxonon-6-en-2-yl 4-methylbenzenesulfonate (47).

Under N2 atmosphere, to a solution of compound 45 (c.a. 1.08 mmol) in CH2Cl2 was

added TsCl (308.8 mg, 1.62 mmol), Et3N (78.9 mg, 2.16mmol) and Me3N•HCl (50 mg) at

0 ℃. After 3hr, the reaction mixture was quenched with saturated aq. NH4Cl and extracted

with ethyl. The organic layer was washed with water and brine, dried over Na2SO4. After

filtration, the filtrate was concentrated under reduce pressure. The residue was purified by

silica gel column chromatography (Hexan/EtOAc = 5 : 1) to give compound 47 (357.4 mg,

81% yield over 2 steps) 1H NMR δ: 7.80(2H, d, J = 8.4 Hz), 7.36(2H, d, J = 8.4 Hz),

5.01(1H, t, J = 7.2 Hz), 4.83(1H, t, J = 4.8 Hz), 4.78(1H, q, J = 7.2 Hz), 4.01-3.82(4H, m),

2.67-2.51(2H, m), 2.46(3H, s), 2.25(2H, q, J = 7.2 Hz), 2.156-2.115(2H, m), 1.99(2H, q, J =

7.2 Hz), 1.72-1.67(2H, m), 1.34(3H, d, J = 7.2 Hz), 0.968(3H, t, J = 7.2 Hz).

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West segment

Methyl 3-chloro-2,2-dimethoxypropanoate (53).

The mixture of pyruvic acid (32) (5.0 g, 56.78 mmol) and SO2Cl2 (23.0g, 170.34 mmol)

was stirred for 3 days. The reaction mixture was concentrated under reduce pressure, the

residue was diluted with MeOH. The solution was added Trimethyl orthoformate (33 ml)

and conc. H2SO4 (3 ml) and stirred for 2 days at reflux. The resulting mixture was cooled to

room temperature and quenched with saturated aq. NaHCO3. The mixture was extracted

with CHCl3 and the organic layer was washed with water and brine, dried over Na2SO4.

After filtration, the filtrate was concentrated under reduce pressure. The residue was

purified by silica gel column chromatography (Hexane/EtOAc = 4 : 1) to give compound 53

(3.59 g, 35 % yield). 1H NMR δ: 3.86(3H, s), 3.77(2H, s), 3.33(6H, s).

3-chloro-N,2,2-trimethoxy-N-methylpropanamide (54).

Under N2 atmosphere, to a solution of compound 53 (3.59 g, 19.66 mmol) in THF (15 ml)

was added NHMe(OMe)• HCl (3.84g, 39.32 mmol) and i-PrMgCl (2.0 M in THF, 39.32 ml)

at 0 ℃ and stirred for 2h. The resulting mixture was quenched with saturated aq.

NH4Cl.The aqueous layer was extracted with ethyl and the extracts was combined with

separated organic layer. The organic layer was washed with water and brine and dried over

Na2SO4. After filtration, the filtrate was concentrated under reduce pressure. The crude

compound 54 was used for next reaction without further purification.

72

Methyl 5-chloro-4,4-dimethoxy-3-oxopentanoate (55).

Under N2 atmosphere, to a solution of MeOAc (3.22 g, 41.29 mmol) in THF (50 ml) was

added LiHMDS (1.3 M in THF, 31.8 ml) at -78 ℃ and stirred for 30 min. The mixture was

added a solution of crude compound 54 (c.a. 19.66 mmol) in THF (10 ml) at -78 ℃ via

syringe pump over 30 min and then warmed to -40 ℃. After 3h, the mixture was quenched

with saturated aq. NH4Cl and extracted with ethyl. The organic layer was washed with

water and brine, dried over Na2SO4. After filtration, the filtrate was concentrated under

reduce pressure. The residue was purified by silica gel column chromatography

(Hexan/EtOAc = 4 : 1) to give compound 55 (2.94 g, 67% over 2steps).

Methyl 5-chloro-3,4-dioxopentanoate (50).

The mixture of compound 55 (100.4 mg, 446.9 μmol) and 4N HCl aq. (1 ml) was stirred

for 3 days. The reaction mixture was diluted with water and saturated with NaCl. The

resulting mixture was extracted with ether and dried over Na2SO4. After filtration, the

filtrate was concentrated under reduce pressure. The crude compound 50 was used for next

reaction

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結言

以上、筆者は生物活性を有するポリケチド型天然物に着目し、農薬、医薬に有

用な天然物を発展的応用研究につなげるべく全合成研究を行った。

第一章では Trichoderma 属菌由来の新規農薬として期待される cremenolide の構

造改訂および全合成を行った。Cremenolide の構造推定には計算化学支援による配

座探索および 13C NMR スペクトルの算出によって 8 つの候補化合物のうち 1 つを

選び合成することで効率的な構造改訂を達成した。絶対立体配置の決定には至ら

なかったことから、今後は天然品のサンプルデータの再測定による最終的な構造

決定を行いたい。

第二章ではグラム陽性菌に対する抗菌作用、癌細胞浸潤阻害、抗パーキンソン

病、オートファジー亢進といった多様な薬理活性を有する nonthmicin の標的タン

パク質の同定を見据えた全合成研究を行った。Nonthmicin を 3 つのセグメントに

分割し、その内、南東部位、西部位の合成に取り組んだ。南東部位は合成経路序

盤における効率的合成経路の確立に成功し、エーテル環化前駆体となる Ts 化体の

合成に成功した。西部位はピルビン酸から 4 工程で西部位の前駆体を合成した。

南東部位、西部位は現在、残りの合成経路について検討中である。

本博士論文では農薬、医薬として有用な 2 つの天然物の合成に取り組んだ。

Cremenolide は現在東京農業大学分子設計学研究室で本研究を発展させた類縁体合

成が進められており、aspinolide 類縁体の網羅的合成へと展開されている。

Nonthmicin は、合成に至らなかったことは心残りであるが、研究の障壁となる各

種課題の解決に少なからず寄与できたと考えており、今後の nonthmicin 研究の発

展を切に期待している。

本研究を通して得られた成果が天然物合成化学の発展に寄与し、ひいては今後

の農薬、医薬開発の一助となれば幸いである。

74

謝辞

本研究を行うにあたり、終始丁寧で心のこもった御指導、御助言を賜りました

東北大学農学研究科生物有機化学分野の桑原重文教授、榎本賢准教授、目黒康洋

助教に厚く感謝申し上げます。

お忙しい中、本博士論文の査読を引き受けて下さいました東北大学大学院農学

研究科の山下まり教授、仲川清隆教授に深く感謝申し上げます。

研究が円滑に進むようデータ測定等便宜を図って下さいました田口優佳技官に

深く感謝申し上げます。

私に有機化学の基礎からご教授いただき、cremenolide の合成では的確な御指

導、ご助言を賜りました額田恭郎先生、東京農業大学生命科学部分子生命化学科

の石神健教授、矢島新教授、勝田亮准教授に改めて御礼申し上げます。

公私共にお世話になりました諸先輩方をはじめとした東北大学農学研究科生物

有機化学分野の諸氏に感謝申し上げます。

博士課程に進学した私を経済、精神的に支えて下さいました私の両親、辛い時

に心の支えとなってくれた良き友人達に感謝申し上げます。

75

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