Stereocontrolled and efficient total synthesis of (-)-stephanotic acid methyl ester and (-)-celogentin C

Article abstract of DOI:10.1021/ol902944f

(Figure Presented) A highly stereocontrolled and efficient total synthesis of (-)-stephanotlc acid methyl ester and (-)-celogentin C was accomplished In longest linear 14 steps (4.6% overall yield) and In 20 steps (1.6% overall yield) from L-tryptophan, respectively. Highlights of the synthesis include a tandem asymmetric Michael addition/bromination/azidation strategy for a ready access to the leucine-tryptophan moiety (Leu-Trp linkage) and an oxidative coupling reaction to form the indole-imidazole linkage.

Full text of DOI:10.1021/ol902944f

Supporting Information
Stereocontrolled and Efficient Total Synthesis of (-)-Stephanotic Acid
Methyl Ester and (-)-Celogentin C
Weimin Hu, Fengying Zhang, Zhengren Xu, Qiang Liu, Yuxin Cui, Yanxing Jia*
State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking
University, 38 Xueyuan Road, Beijing 100191, China, State Key Laboratory of Drug Research, Shanghai
Institute of Materia Media, Chinese Academy of Sciences, Shanghai 201203, China, and State Key
Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 73000, China
S2.
S3-S12.
General information
Experimental procedure and physical data
S13-S44. 1H and 13C spectra of compounds
S1

General information
All reagents were obtained from commercial suppliers unless otherwise stated.
Tetrahydro- furan (THF) was distilled from potassium sodium alloys; dichloromethane and
acetonitrile were distilled from calcium hydride; N, N-Dimethylformamide (DMF) was
distilled from magnesium sulfate under vacuum; Methanol was distilled from magnesium
methoxide. Flasks were flame-dried under vacuum and cooled under a stream of nitrogen or
argon.
Flash chromatography was performed using silica gel (200-300 mesh) with solvents
distilled prior to use. Visualization was achieved under a UV lamp (254 nm and 365 nm), and
by developing the plates with phosphomolybdic acid or triketohydrindene hydrate in ethanol.
13
1H NMR were recorded at 300 MHz or 400 MHz NMR spectrometer, C NMR at 75
MHz or 100 MHz NMR spectrometer unless otherwise stated. The following abbreviations
are used for the multiplicities: s: singlet, d: doublet, t: triplet, m: multiplet, br s: broad singlet
for proton spectra. Coupling constants (J) are reported in Hertz (Hz). Infrared spectra were
recorded with a thin layer of the product on a KBr disk.
The following abbreviations are used: EtOAc; ethyl acetate; THF: Tetrahydrofuran;
DMF: N, N-Dimethylformamide; Boc2O: di-tert-butyldicarbonate; HOAc: acetic acid;
DMAP: 4-Dimethylaminopyridine; EDCI: 1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide
Hydrochloride;
HATU:
O-(7-Azabenzotriazol-1-yl)-N,N,N',N'-tetramethyluronium
HBTU: O-Benzotriazole-N,N,N',N'-tetramethyluronium
hexafluorophosphate;
hexafluorophosphate; HOBt: 1-Hydroxybenzotriazole; DIPEA: diisopropylethylamine; NBS:
N-Bromosuccinimide
S2

Experimental procedure and physical data
Compound 4.1,2,3 To the solution of (2E)-isohexenoic acid (2.67 g, 23.4 mmol)
Ph
O
N
and Et3N (2.5 equiv) in THF (volume corresponded to 0.2 M of the
O
O
oxazolidinone) was added trimethylacetyl chloride (2.62 g, 21.7 mmol) at -20
o
oC. A white solid was formed instantaneously. The mixture was stirred at -20 C for 2.0 h.
Lithium chloride (0.92 g, 21.6 mmol) was added, followed by the oxazolidinone (2.92 g, 17.9
mmol). The mixture was allowed to warm to room temperature slowly and stirred for 4.0 h.
The reaction was quenched by addition of saturated NH4Cl and the solution was extracted
with EtOAc; The organic layer was washed subsequently with saturated NaHCO3, brine and
water, dried over anhydrous Na2SO4 and filtered. EtOAc was removed in vacuo, and the
residue was purified by flash column chromatography(silica gel, 12% EtOAc in petroleum
ether) provided the desired product 4 (4.33 g, 93%). 1H NMR (300 MHz, CDCl3) δ 7.40-7.30
(m, 5H), 7.22 (dd, J = 15.6, 1.2 Hz, 1H), 7.05 (dd, J = 15.6, 6.6 Hz, 1H), 5.48 (dd, J = 8.7, 3.9
Hz, 1H), 4.68 (t, J = 9.0 Hz, 1H), 4.26 (dd, J = 9.0, 3.9 Hz, 1H), 2.52 (m, 1H), 1.07 (d, J = 6.6
13
Hz, 6H); C NMR (75 MHz, CDCl3) δ 165.0, 158.2, 153.8, 139.2, 129.1 (2C), 128.6, 126.0
(2C), 117.6, 69.8, 57.6, 31.3, 21.1, 21.0.
5
O
Compound 10.
To a stirred suspension of nitration of
OMe
N(Boc)2
6-nitro-L-tryptophan 8 4 (6.39 g, 25.7 mmol) in dry MeOH (90 mL) was
N
O2N
added slowly Me3SiCl (25.0 mL, 196 mmol) in an ice-cold bath. After
Boc
the addition was completed, The ice-cold bath was removed and the reaction was stirred at
room temperature for 18.0 h. Then, Et3N (50 mL, 361 mmol) and (Boc)2O (8.9 g, 40.8 mmol)
were sequentially added. The reaction mixture was stirred until TLC showed complete
protection. The solvent was removed under reduced pressure and the residue was extracted
between water and EtOAc (3 × 60 mL).The combined organic layers were dried over Na2SO4,
and then evaporated in vacuo.
To a solution of above crude product in dry CH3CN (90 mL) was added DMAP (650 mg,
1. Ho, G. J.; Mathre, D. J. J. Org. Chem. 1995, 60, 2271-2273.
2. Lin, J.; Liao, S.; Han, Y.; Qiu, W.; Hruby, V. J. Tetrahedron: Asymmetry 1997, 8, 3213-
3221.
3. Liao, S.; Shenderovich, M. D.; Lin, J.; Hruby, V. J. Tetrahedron 1997, 53, 16645-16662.
4. Moriya, T.; Hagio, K.; Yoneda, N. Bull. Chem. Soc. Jpn. 1975, 48, 2217-2218.
5. Jia, Y.; Bois-Choussy, M.; Zhu, J. Org. Lett. 2007, 9, 2401-2404.
S3

5.3 mmol) and (Boc)2O (12.4 g, 56.9 mmol) at room temperature. The mixture was stirred for
1 h,after which time TLC showed that some starting material still remained. More (Boc)2O
(4.4 g, 20.2 mmol) was added and the mixture was additionally stirred overnight. The solvent
was evaporated, and the crud purified by silica gel column chromatography to afford 10 (8.59
1
g, 77%). H NMR (300 MHz, CDCl3) δ 9.06 (s, 1H), 8.14 (dd, J = 8.7, 2.1 Hz, 1H), 7.68 (s,
1H), 7.64 (d, J = 8.7 Hz, 1H), 5.19 (dd, J = 9.9, 5.3 Hz, 1H), 3.77 (s, 3H), 3.55 (dd, J = 15.0,
5.3 Hz, 1H), 3.39 (dd, J = 15.0, 9.9 Hz, 1H), 1.69 (s, 9H), 1.39 (s, 18H); 13C NMR (75 MHz,
CDCl3) δ 170.4, 151.9 (2C), 148.6, 144.9, 135.3, 134.1, 129.3, 119.0, 117.7, 116.6, 111.5,
84.9, 83.1 (2C), 57.8, 52.3, 27.8 (3C), 27.5 (6C), 25.2.
Compound 6.5 To a solution of nitro-tryptophane 10 (8.59 g, 15.3 mmol)
O
OMe
and Zn dust (50.0 g) in CH2Cl2 (180 mL) was slowly added HOAc (14.0
N(Boc)2
mL) at 0 oC. The solution was stirred at room temperature for 20 min and
N
I
Boc
then the solution was filtered. The filtrate was washed with sat. aqueous NaHCO3, H2O and
brine, dried over Na2SO4. The solvent was evaporated under reduced pressure and the residue
was dissolved in THF (112 mL), H2O (79 mL) and 5% HCl (43 mL). NaNO2 was slowly
o
o
added to the solution at 0 C. After being stirred at 0 C for 5 min, the mixture was added to
the solution of KI (15.8 g 95.2 mmol) and I2 (4.06 g 16.0 mmol) in H2O (150 mL), then the
resulting reaction mixture was continued to stir at room temperature for 1.0 h. The reaction
mixture was basified to pH 7-8 with sat. aqueous NaHCO3, extracted with EtOAc, and the
combined organic phases were washed with sat. aqueous NaHSO3, H2O and brine, dried over
Na2SO4. The solvent was evaporated under reduced pressure and the residue was purified by
flash column chromatography (silica gel, 10-15% EtOAc in petroleum ether, then CH2Cl2
1
again) to provide the desired product 6 (7.08 g, 72%) and deiodo product (0.80 g 10%). H
NMR (300 MHz, CDCl3) δ 8.50 (s, 1H), 7.48 (d, J = 7.8 Hz, 1H), 7.27 (s, 1H), 7.23 (d, J =
7.8 Hz, 1H), 5.12 (dd, J = 9.9, 5.1 Hz, 1H), 3.72 (s, 3H), 3.44 (dd, J = 15.0, 5.1 Hz, 1H), 3.29
13
(dd, J = 15.0, 9.9 Hz, 1H), 1.60 (s, 9H), 1.30 (s, 18H); C NMR (75 MHz, CDCl3) δ 170.6,
151.7 (2C), 149.0, 136.3, 131.3, 129.8, 124.4, 124.1, 120.4, 116.3, 88.7, 83.9, 83.0 (2C), 58.0,
52.3, 28.0 (3C), 27.6 (6C), 25.3.
Compound 12. To a solution of iodo-tryptophane 6 (1.29 g, 2.0
O
OMe
N(Boc)2
Ph
mmol) in dry THF (4.0 mL) was added i-PrMgCl (2.0 M, 1.0 mL,
O
N
O
o
2.0 mmol) dropwise at -30 C and the reaction mixture was stirred
O
N
Br
Boc
at the same temperature for 30 min. CuBr·Me2S (83 mg, 0.4 mmol)
o
o
was added to the reaction at -30 C and the mixture was warmed to -20 C over 20 min. The
unsaturated amide 4 (519 mg, 2.0 mmol) in dry THF (2.0 mL) was added slowly at -15 to -10
S4

oC. After being stirred at the same temperature for 4.0 h, the reaction mixture was cooled to
-78 oC, and NBS (357 mg, 2.0 mmol) in dry THF (5.0 mL) was added. After an additional 2.0
h, the mixture was slowly warmed to 0 oC and then was stirred at 0 oC for 2.0 h. the reaction
mixture was quenched with saturated NaHSO3 and extracted with EtOAc (3 × 30 mL). The
combined organic phase was washed with water (30 mL), brine (30 mL), dried over Na2SO4,
and concentrated in vacuo. The residue was purified by flash column chromatography (silica
gel, 12% - 17% EtOAc in petroleum ether) to afford the desired product 12 (1.11 g, 65%).
30
[α]D –64.5 (c 1.00, MeOH); IR (neat): 2979, 1784, 1735, 1481, 1442, 1370, 1326, 1257,
1
1139, 1087, 851, 765, 699 cm-1; H NMR (400 MHz, CDCl3) δ 7.91 (s, 1H), 7.46 (d, J = 8.2
Hz, 1H), 7.40 (s, 1H), 7.37-7.32 (m, 5H), 7.05 (d, J = 8.2 Hz, 1H), 6.36 (d, J = 10.4 Hz, 1H),
5.46 (dd, J = 8.8, 4.4 Hz, 1H), 5.21 (dd, J = 10.0, 4.6 Hz, 1H), 4.82 (t, J = 8.8 Hz, 1H), 4.30
(dd, J = 8.8, 4.4 Hz, 1H), 3.76 (s, 3H), 3.50 (dd, J = 15.2, 4.6 Hz, 1H), 3.45 (dd, J = 10.4, 5.2
Hz, 1H), 3.34 (dd, J = 15.2, 10.0 Hz, 1H), 2.09 (m, 1H), 1.65 (s, 9H), 1.32 (s, 18H), 0.90 (d, J
13
= 6.8 Hz, 3H), 0.80 (d, J = 6.8 Hz, 3H); C NMR (100 MHz, CDCl3) δ 170.7, 167.9, 152.9,
151.6, 149.6, 137.7, 135.1, 134.1, 129.7, 129.1, 128.8, 125.8, 124.5, 118.1, 116.3, 83.5, 82.9,
70.0, 58.1, 53.8, 52.2, 30.8, 28.1, 27.7, 25.6, 21.9, 17.9; HRMS (ESI) m/z calcd for
C42H58BrN4O11 (M + NH4)+ 873.3280; found 873.3279.
Compound 13. To a solution of compound 12 (5.74 g, 6.7 mmol)
O
OMe
N(Boc)2
Ph
in DMF (21 mL) was added NaN3 (1.14 g, 17.5 mmol) in one
O
N
O
portion at room temperature. After being stirred for one day, DMF
was removed under vacuum. the residue was diluted with EtOAc
O
N
N3
Boc
(50 mL) and water (50 mL), and the aqueous phase was extracted with EtOAc (2 × 50 mL).
The combined organic extracts were washed with water (2 × 50 mL), brine (2 × 50 mL), dried
over Na2SO4, and concentrated in vacuo. The residue was purified by flash column
chromatography (silica gel, 10%-12% EtOAc in petroleum ether) to afford the desired
34
product 13 (4.52 g, 82%). [α]D –29.9 (c 1.00, MeOH); IR (neat): 2978, 2104, 1785, 1736,
1
1698, 1482, 1443, 1370, 1329, 1267, 1255, 1158, 1141, 1089, 851, 762, 701 cm-1; H NMR
(400 MHz, CDCl3) δ 7.77 (s, 1H), 7.47 (s, 1H), 7.31 (d, J = 8.0 Hz, 1H), 6.97 (t, J = 7.6 Hz,
1H), 6.93 (d, J = 8.0 Hz, 1H), 6.69 (t, J = 7.6 Hz, 2H), 6.35 (d, J = 7.6 Hz, 2H), 5.78 (d, J =
11.6 Hz, 1H), 5.26 (dd, J = 8.8, 4.4 Hz, 1H), 5.23 (dd, J = 10.0, 5.0 Hz, 1H), 4.57 (t, J = 8.8
Hz, 1H), 4.02 (dd, J = 8.8, 4.4 Hz, 1H), 3.78 (s, 3H), 3.55 (dd, J = 14.8, 5.0 Hz, 1H), 3.38 (dd,
J = 14.8, 10.0 Hz, 1H), 3.22 (dd, J = 11.6, 4.0 Hz, 1H), 2.34 (m, 1H), 1.66 (s, 9H), 1.35 (s,
18H), 0.94 (d, J = 6.8 Hz, 3H), 0.80 (d, J = 6.8 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ 170.7,
169.4, 152.8, 151.7, 149.3, 137.0, 134.9, 132.1, 129.7, 128.2, 127.7, 125.0, 124.6, 124.5,
118.3, 116.1, 115.9, 83.8, 82.9, 69.5, 58.9, 57.7, 57.3, 52.4, 52.2, 28.5, 28.0, 27.7, 25.4, 21.0,
S5

17.1; HRMS (ESI) m/z calcd for C42H54N6NaO11 (M + Na)+ 841.3743; found 841.3738.
L-isoleucyl-L-valine tert-butyl ester 14. A solution of valine tert-butyl
O
ester (113 mg, 0.65 mmol) and N-Cbz-L-isoleucine (193 mg, 0.73 mmol)
Ot-Bu
N
H
NH2
O
in dry THF (3.0 mL) at 0 ºC was treated with HOBt (97 mg, 0.72 mmol),
EDCI (193 mg, 1.01 mmol), and DIPEA (0.25 mL, 186 mg, 1.44 mmol). The reaction
mixture was stirred at 0 oC for 1 h and at room temperature overnight. Water was added to the
mixture, and the layers were separated. The aqueous layer was extracted with EtOAc (3 × 15
mL), and the combined organic layers were washed with water (20 mL), brine (20 mL), dried
over Na2SO4, and concentrated in vacuo. The residue was purified by flash column
chromatography(silica gel, 12% EtOAc in petroleum ether) to give the crude product
N-Cbz-L-isoleucyl-L-valine tert-butyl ester.
To a solution of above crude product in MeOH (1.5 mL) was added HCO2NH4 (214 mg,
3.40 mmol) and 10% Pd/C (47 mg). The resulting mixture was stirred under H2 (1 atm) at
room temperature for 16 h, then filtered through filter paper and concentrated in vacuo. the
residue was purified by flash column chromatography (silica gel, 1% Et3N in CH2Cl2) to
20
afford 14 (136 mg) in a total yield of 60% for two steps. [α]D –37.6 (c 1.00, MeOH); IR
(neat): 3330, 2966, 2934, 2877, 1733, 1665, 1509, 1370, 1150, 848 cm-1; 1H NMR (300 MHz,
CDCl3) δ 7.82 (d, J = 8.4 Hz, 1H), 4.39 (dd, J = 9.0, 4.2 Hz, 1H), 3.29 (d, J = 3.6 Hz, 1H),
2.15 (m, 1H), 1.96 (m, 1H), 1.51 (br s, 2H), 1.44 (s, 9H), 1.35 (m, 1H), 1.09 (m, 1H),
13
0.96-0.85 (m, 12H); C NMR (75 MHz, CDCl3) δ 174.3, 171.3, 81.6, 59.9, 56.9, 37.8, 31.1,
27.8 (3C), 23.6, 18.9, 17.4, 15.9, 11.7; HRMS (ESI) m/z calcd for C15H31N2O3 (M + H)+
287.2329; found 287.2334.
Compound 15. To a solution of azido compound 13 (409 mg, 0.50
O
O
mmol) in THF (6.0 mL) was added water (2.0 mL). The solution
Ot-Bu
N
OMe
N
H
o
O
was stirred at 0 C for 15 min, and then 30% H2O2 (0.45 mL, 8
HN
N3
N(Boc)2
O
equiv.) was added dropwise followed by dropwise addition of
Boc
lithium hydroxide monohydrate (81 mg, 1.93 mmol) in water (1.0
o
mL). The resulting mixture was stirred at 0 C for 6 h. The reaction was quenched with
saturated Na2SO3 and stirred at room temperature for 30 min. The mixture was acidified with
6 N HCI to pH = 2 and extracted with EtOAc (3 × 20 mL). The combined organic phase was
washed with water (30 mL), brine (30 mL), dried over Na2SO4, and concentrated in vacuo to
give crud product, which was used directly in the next step.
o
A solution of above acid and amine 14 in dry THF (3.0 mL) at 0 C was treated with
HATU (263 mg, 0.69 mmol) and DIPEA (0.30 mL, 223 mg, 1.73 mmol). The resulting
S6

mixture was stirred at room temperature for 1 d. The reaction mixture was diluted with EtOAc.
The organic phase was washed with 1% HCl (20 mL), saturated NaHCO3 (20 mL), water (20
mL), brine (20 mL), dried (Na2SO4), and concentrated in vacuo. The residue was purified by
flash column chromatography (silica gel, 12% - 17% EtOAc in petroleum ether) to afford the
22
desired product 15 (367 mg) in a total yield of 78% for two steps. [α]D –35.0 (c 1.00,
MeOH); IR (neat): 3401, 2975, 2108, 1736, 1699, 1655, 1516, 1443, 1370, 1257, 1155, 1088,
1
851, 768 cm-1; H NMR (300 MHz, CDCl3) δ 7.99 (s, 1H), 7.42 (d, J = 8.0 Hz, 1H), 7.36 (s,
1H), 7.06 (d, J = 8.0 Hz, 1H), 6.71 (d, J = 8.1 Hz, 1H), 6.14 (d, J = 8.4 Hz, 1H), 5.18 (dd, J =
10.2, 5.0 Hz, 1H), 4.34 (d, J = 5.4 Hz, 1H), 4.28 (dd, J = 8.7, 4.8 Hz, 1H), 4.08 (t, J = 7.8 Hz,
1H), 3.75 (s, 3H), 3.48 (dd, J = 15.0, 5.0 Hz, 1H), 3.29 (dd, J = 15.0, 10.2 Hz, 1H), 3.02 (dd, J
= 8.4, 5.4 Hz, 1H), 2.52 (m, 1H), 2.08-2.01 (m, 2H), 1.64 (s, 9H), 1.43 (s, 9H), 1.31 (s, 18H),
1.31-1.15 (m, 1H), 1.04 (d, J = 6.3 Hz, 3H), 0.85-0.66 (m, 16H); 13C NMR (75 MHz, CDCl3)
δ 170.8, 170.5, 170.2, 168.2, 151.6, 149.4, 135.5, 129.6, 124.4, 123.9, 118.6, 116.2, 115.5,
83.4, 82.9, 82.0, 67.0, 58.0, 57.7, 57.6, 55.0, 52.3, 36.9, 31.2, 28.8, 28.1, 27.9, 27.7, 25.5, 24.9,
21.4, 20.4, 18.7, 17.6, 14.9, 11.1; HRMS (ESI) m/z calcd for C48H75N7NaO12 (M + Na)+
964.5366; found 964.6365.
Compound 16. Trifluoroacetic acid (5.0 mL) was added slowly to a
O
H
CO2Me
N
solution of compound 15 (283 mg, 0.30 mmol) in CH2Cl2 (5.0 mL) at
oC. After 2.0 h the reaction mixture was concentrated ensuring all
excess trifluoroacetic had been removed. The residue was dissolved in
N
H
O
HN
N3
O
N
H
o
anhydrous DMF (150 mL), cooled to 0 C, DIPEA (0.75 mL, 4.31
mmol) and HATU (1.14 g, 3.0 mmol) were added sequentially. The reaction mixture was
allowed to warm to room temperature, was stirred for 9 days, and then was concentrated. The
residue was dissolved in EtOAc (50 mL) and was washed with 1% HCl (20 mL), saturated
NaHCO3 (2 × 30 mL) and brine (30 mL). The organic layer was dried over Na2SO4 and
concentrated in vacuo. The residue was purified by column chromatography (silica gel, 60% -
27
90% EtOAc in petroleum ether) to give the product 16 (82 mg, 48%). [α]D –18.5 (c 1.00,
1
MeOH); IR (neat): 3328, 2965, 2101, 1745, 1661, 1513, 1460, 1384, 1211 cm-1; H NMR
(400 MHz, CD3OD) δ 7.48 (d, J = 8.4 Hz, 1H), 7.01 (s, 1H), 6.98 (s, 1H), 6.87 (d, J = 8.4 Hz,
1H), 5.48 (m, 1H), 4.03 (d, J = 8.4 Hz, 1H), 3.92 (d, J = 11.6 Hz, 1H), 3.83 (d, J = 6.0 Hz,
1H), 3.78 (s, 3H), 3.48 (dd, J = 14.8, 5.6 Hz, 1H), 3.20-3.11 (m, 2H), 2.32 (m, 1H), 2.02 (m,
1H), 1.64 (m, 1H), 1.45 (m, 1H), 1.11 (m, 1H), 1.03 (d, J = 6.4 Hz, 3H), 0.96 (d, J = 6.4 Hz,
13
3H), 0.92-0.89 (m, 12H); C NMR (100 MHz, CD3OD) δ 173.7, 172.2, 171.7, 171.1, 138.4,
131.2, 127.1, 125.6, 120.2, 118.7, 115.8, 110.0, 66.6, 60.0, 59.4, 53.4, 52.8, 51.9, 38.9, 32.4,
30.1, 28.7, 26.0, 22.0, 19.0, 18.9, 15.9, 11.0; HRMS (ESI) m/z calcd for C29H42N7O5 (M + H)+
S7

568.3242; found 568.3247.
Stephanotic acid methyl ester 2. A solution of compound 16
(80 mg, 0.14 mmol) in MeOH (3.0 mL) was degassed for 20
min, then HCO2NH4 (115 mg) and 10% Pd/C (190 mg) was
added sequentially. The reaction mixture was stirred under
argon at room temperature for 10 h and filtered through filter
O
H
CO2Me
N
N
H
O
HN
O
O
H
N
N
N
O
H
H
paper. The filter pad was washed with MeOH, and the filtrate was concentrated. The residue
was dissolved in EtOAc (30 mL) and was washed with saturated NaHCO3 (10 mL), H2O (10
mL) and brine (10 mL). The organic layer was dried over Na2SO4 and concentrated in vacuo
to give crud product, which was used directly in the next step.
o
A solution of above crud product in dry DMF (2.0 mL) at 0 C was treated with
(S)-Pyroglutamic acid (32 mg, 0.25 mmol), DIPEA (0.1 mL, 0.58 mmol) and HATU (107 mg,
0.28 mmol). The reaction mixture was allowed to warm to room temperature overnight and
the solvent was removed under vacuum. The residue was dissolved in EtOAc (30 mL) and
was washed with HCl (1M; 10 mL), saturated NaHCO3 (10 mL) and brine (10 mL). The
organic layer was dried (Na2SO4) and concentrated in vacuo. The residue was purified by
column chromatography (silica gel, 3% - 4% MeOH in CH2Cl2) to give stephanotic acid
methyl ester 2 (64 mg, 70%). [α]D22 –112.4 (c 0.50, MeOH); 1H NMR (400 MHz, DMSO-d6)
δ 10.69 (s, 1H), 8.52 (d, J = 9.2 Hz, 1H), 8.30 (d, J = 10.0 Hz, 1H), 7.87 (s, 1H), 7.43 (d, J =
8.4 Hz, 1H), 7.36 (d, J = 8.4 Hz, 1H), 6.99-6.97 (m, 3H), 6.88 (s, 1H), 5.23 (m, 1H), 4.86 (t, J
= 10.4 Hz, 1H), 4.11 (dd, J = 8.8, 3.6 Hz, 1H), 3.88 (dd, J = 7.6, 6.0 Hz, 1H), 3.76 (dd, J =
10.4, 8.4 Hz, 1H), 3.65 (s, 3H), 3.27 (m, 1H), 3.13 (dd, J = 15.2, 8.8 Hz, 1H), 2.99 (dd, J =
11.6, 3.6 Hz, 1H), 2.24 (m, 1H), 2.13 (m, 1H), 2.08 (m, 2H), 2.01 (m, 1H), 1.71 (m, 1H), 1.62
(m, 1H), 1.22 (m, 2H), 0.92 (d, J = 6.8 Hz, 3H), 0.89 (d, J = 6.8 Hz, 3H), 0.85 (d, J = 6.8 Hz,
13
3H), 0.77 (d, J = 8.6 Hz, 3H), 0.68-0.63 (m, 6H); C NMR (100 MHz, DMSO-d6) δ 177.5,
172.2, 171.8, 170.7, 170.0, 169.7, 136.1, 129.8, 125.5, 123.5, 119.0, 117.8, 114.4, 108.4, 58.0,
57.7, 55.2, 55.1, 52.0, 51.9, 51.1, 37.2, 30.5, 29.0, 27.1, 26.8, 25.6, 24.1, 21.8, 18.7, 17.9, 17.3,
15.4, 10.4; HRMS (ESI) m/z calcd for C34H49N6O7 (M + H)+ 653.3657; found 653.3664.
L-leucyl-L-valine tert-butyl ester 17. A solution of valine tert-butyl ester
O
(5.19 g, 30.0 mmol) and N-Cbz-L-leucine (8.05 g, 30.4 mmol) in dry
Ot-Bu
N
H
o
NH2
O
CH2Cl2 (100 mL) at 0 C was treated with HOBt (4.72 g, 35.0 mmol),
EDCI (7.72 g, 40.3 mmol), and DIPEA (13.0 mL, 9.65 g, 74.8 mmol). The resulting mixture
was stirred at 0 oC for 1 h and at room temperature for 1 d. The reaction mixture was washed
with saturated NaHCO3 (50 mL), water (50 mL), brine (50 mL), dried (Na2SO4), and
S8

concentrated in vacuo. The residue was purified by flash column chromatography (silica gel,
12% EtOAc in petroleum ether) to give the product N-Cbz-L-leucyl-L-valine tert-butyl ester.
31
[α]D –46.5 (c 1.00, MeOH); IR (neat): 3313, 2963, 1733, 1701, 1658, 1548, 1458, 1369,
1270, 1239, 1148 cm-1; 1H NMR (400 MHz, CDCl3) δ 7.37-7.29 (m, 5H), 6.41 (d, J = 8.4 Hz,
1H), 5.22 (d, J = 7.2 Hz, 1H), 5.11 (s, 2H), 4.40 (dd, J = 8.8, 4.4 Hz, 1H), 4.21 (m, 1H), 2.13
13
(m, 1H), 1.70-1.62 (m, 2H), 1.53 (m, 1H), 1.46 (s, 9H), 0.94-0.87 (m, 12H); C NMR (100
MHz, CDCl3) δ 171.9, 170.7, 156.1, 136.2, 128.5 (2C), 128.1, 128.0 (2C), 81.9, 67.0, 57.4,
53.6, 41.3, 31.4, 28.0 (3C), 24.6, 22.9, 22.0, 18.8, 17.5; HRMS (ESI) m/z calcd for
C23H37N2O5 (M + H)+ 421.2697; found 421.2691.
To a solution of above product (5.66 g, 13.5 mmol) in MeOH (40.0 mL) was added 10%
Pd/C (319 mg). The resulting mixture was stirred under H2 (4 atm) at room temperature for 12
h, then filtered through filter paper and concentrated in vacuo to afford the desired product 17
(3.79 g, 98%), which was directly used for next reaction.
Compound 18 was prepared from compound 3 according to the same procedure as that
described for stephanotic acid methyl ester 2; Compound S3 and Celogentin C was prepared
according to the literature procedure 6 (Scheme 1).
O
O
O
H
OMe
O
CO2Me
1. 10% pd/C, HCO2NH4
Ot-Bu
N
1. TFA, CH2Cl2
2. HATU, DIPEA
DMF
OMe
N
H
N
H
17, HATU
O
MeOH
O
N(Boc)2
DIPEA, THF
HO
N3
O
HN
N3
N(Boc)2
HN
N3
O
O
2. (S)-pyroGlu-OH
HATU, DIPEA, DMF
70% (2 steps)
82%
48% (2 steps)
N
N
N
Boc
Boc
H
3
S1
S2
CO2Bn
O
H
N
N
O
CO2Me
H
1. LiOH, THF/H2O (3:1)
2. Pro-OBn, EDCI
HOBt, THF
1. Pro-OBn, NCS, CH2Cl2
1, 4-dimethylpiperazine
then 20
N
H
N
O
N
O
H
O
HN
O
O
HN
O
O
72% (2 steps)
2. 10% Pd/C, HCO2H4
MeOH/H2O (5:1)
3. HBTU, HOBt, DMF
H
N
H
N
H
N
H
N
O
N
H
N
H
O
18
19
NHPbf
NH2
O
HN
O
O
HN
O
N
N
H
H
H
H
NH
TFA/H2O (9:1)
N
N
NH
N
N
H
HN
HN
H
O
O
O
O
HN
O
HN
O
O
O
N
O
O
H
N
H
N
NH
CO2H
NH
CO2t-Bu
N
N
N
N
N
N
N
O
O
H
H
H
H
Celogentin C (1)
21
Scheme 1
6. Ma, B.; Litvinov, D. N.; He, L.; Banerjee, B.; Castle, S. L. Angew. Chem. Int. Ed. 2009, 48,
6104-6107.
S9

Compound S1. [α]D31 –40.0 (c 1.00, MeOH); IR (neat): 3336, 2976,
O
O
Ot-Bu
OMe
N
H
2109, 1736, 1698, 1661, 1520, 1442, 1370, 1257, 1142, 1087, 851,
O
HN
N3
1
768 cm-1; H NMR (400 MHz, CDCl3) δ 7.98 (s, 1H), 7.40 (d, J =
N(Boc)2
O
N
Boc
8.0 Hz, 1H), 7.34 (s, 1H), 7.03 (dd, J = 8.0, 1.2 Hz, 1H), 6.42 (d, J
= 8.0 Hz, 1H), 6.38 (d, J = 8.8 Hz, 1H), 5.16 (dd, J = 10.0, 4.8 Hz,
1H), 4.33 (d, J = 5.2 Hz, 1H), 4.29-4.21 (m, 2H), 3.72 (s, 3H), 3.46 (dd, J = 14.8, 4.8 Hz, 1H),
3.28 (dd, J = 14.8, 10.0 Hz, 1H), 2.99 (dd, J = 8.8, 5.2 Hz, 1H), 2.49 (m, 1H), 2.04 (m, 1H),
1.62(s, 9H), 1.41 (s, 9H), 1.45-1.38 (m, 1H), 1.29 (s, 18H), 1.29-1.13 (m, 2H), 1.02 (d, J = 6.8
Hz, 3H), 0.81 (d, J = 6.8 Hz, 6H), 0.75 (d, J = 6.8 Hz, 3H), 0.72 (d, J = 6.4 Hz, 3H), 0.68 (d, J
= 6.4 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ 170.9, 170.4, 170.2, 168.1, 151.4, 149.1, 135.2,
129.4, 124.2, 123.3, 118.3, 115.9, 115.5, 83.1, 82.5, 81.4, 66.7, 57.8, 57.3, 54.8, 52.0, 51.5,
40.3, 30.9, 28.6, 27.8, 27.7, 27.4, 25.2, 24.0, 22.4, 21.5, 21.2, 20.1, 18.5, 17.4; HRMS (ESI)
m/z calcd for C48H79N8O12 (M + NH4)+ 959.5812; found 959.5816.
24
Compound S2. [α]D –23.5 (c 1.00, MeOH); IR (neat): 3318, 2960,
O
H
2101, 1743, 1659, 1630, 1519, 1457, 1387, 1370, 1218 cm-1; 1H NMR
(400 MHz, CD3OD) δ 7.48 (d, J = 8.4 Hz, 1H), 7.03 (s, 1H), 6.98 (s,
1H), 6.86 (d, J = 8.4 Hz, 1H), 5.47 (dd, J = 10.4, 6.0 Hz, 1H), 4.30 (dd,
J = 9.2, 6.4 Hz, 1H), 3.91 (d, J = 11.2 Hz, 1H), 3.83 (d, J = 7.6 Hz,
CO2Me
N
N
H
O
HN
N3
O
N
H
1H), 3.77 (s, 3H), 3.49 (dd, J = 15.2, 6.0 Hz, 1H), 3.16 (dd, J = 15.2, 10.4 Hz, 1H), 3.12 (dd, J
= 11.2, 5.2 Hz, 1H), 2.31 (m, 1H), 2.04 (m, 1H), 1.56 (m, 1H), 1.48-1.36 (m, 2H), 1.01 (d, J =
13
7.2 Hz, 3H), 0.95 (d, J = 6.8 Hz, 3H), 0.91-0.86 (m, 12H); C NMR (100 MHz, CD3OD) δ
173.61, 173.58, 172.0, 170.8, 138.4, 131.1, 127.2, 125.6, 120.1, 118.7, 115.9, 110.0, 66.5,
59.5, 53.8, 53.4, 52.9, 52.0, 44.0, 32.5, 30.1, 28.6, 25.9, 23.3, 22.0, 21.7, 19.0, 18.82, 18.78;
HRMS (ESI) m/z calcd for C29H42N7O5 (M + H)+ 568.3242; found 568.3241.
34
Compound 18. [α]D –200.5 (c 1.00, MeOH); IR (neat): 3310,
2960, 1741, 1649, 1521, 1456, 1368, 1264, 1214 cm-1; 1H NMR
O
H
CO2Me
N
N
H
O
(400 MHz, DMSO-d6) δ 10.69 (s, 1H), 8.53 (d, J = 8.8 Hz, 1H),
8.39 (d, J = 10.0 Hz, 1H), 7.86 (s, 1H), 7.37 (d, J = 8.4 Hz, 1H),
7.31 (d, J = 8.4 Hz, 1H), 6.98 (s, 1H), 6.97 (d, J = 8.0 Hz, 1H),
HN
O
O
H
N
N
N
O
H
H
6.90 (s, 1H), 6.80 (d, J = 8.0 Hz, 1H), 5.22 (m, 1H), 4.86 (t, J = 10.4 Hz, 1H), 4.11 (dd, J =
8.4, 2.8 Hz, 1H), 4.03 (t, J = 9.2 Hz, 1H), 3.88 (t, J = 7.0 Hz, 1H), 3.65 (s, 3H), 3.28 (m, 1H),
3.15 (dd, J = 15.2, 8.4 Hz, 1H), 2.99 (dd, J = 11.8, 3.0 Hz, 1H), 2.24 (m, 1H), 2.12-2.04 (m,
4H), 1.70 (m, 1H), 1.40-1.35 (m, 2H), 1.23 (m, 1H), 0.91 (d, J = 6.8 Hz, 3H), 0.87 (d, J = 6.4
Hz, 3H), 0.85 (d, J = 6.0 Hz, 3H), 0.79-0.75 (m, 6H), 0.69 (d, J = 6.4 Hz, 3H); 13C NMR (100
S10

MHz, DMSO-d6) δ 177.4, 172.3, 172.1, 171.7, 169.9, 169.8, 136.0, 129.9, 125.6, 123.4, 119.0,
117.7, 114.5, 108.4, 58.2, 55.14, 55.05, 52.0, 51.9, 51.7, 51.3, 42.9, 30.5, 29.0, 27.0, 26.8,
25.5, 23.7, 23.1, 21.8, 20.9, 18.6, 17.6, 17.3; HRMS (ESI) m/z calcd for C34H49N6O7 (M + H)+
653.3657; found 653.3651.
Compound 19.7 To a solution of compound 18 (33 mg, 0.05
CO2Bn
N
O
H
mmol) in THF/H2O (3:1, 2.0 mL) was added lithium
N
O
N
H
o
O
hydroxide monohydrate (21 mg, 0.50 mmol) at 0 C. The
HN
O
O
o
H
resulting mixture was stirred at 0 C for 3 h. The reaction
N
N
N
O
H
H
mixture was acidified with 6 N HCI to pH = 2 and was
diluted with EtOAc (30 mL). The mixture was dried over Na2SO4, and concentrated in vacuo
to give crud product, which was used directly in the next step.
A solution of above crud product and L-proline benzyl ester (20 mg, 0.10 mmol) in
anhydrous THF (3.0 mL) was treated with HOBt (13 mg, 0.10 mmol), EDCI (21 mg, 0.11
mmol) and DIPEA (25 μL, 0.14 mmol). The resulting mixture was allowed to warm to room
temperature and stirred for 2 days. The reaction was treated with saturated NaHCO3 (5 mL)
and extracted with CH2Cl2 (6×5 mL). The combined organic layers were dried (Na2SO4) and
concentrated in vacuo. Preparative TLC (silica gel, 1:10 MeOH/CH2Cl2 elution) afforded 19
(30 mg, 72%). [α]D34 –128.0 (c 1.00, MeOH); 1H NMR (400 MHz, DMSO-d6) δ 10.63 (s, 1H),
8.51 (d, J = 9.2 Hz, 1H), 8.33 (d, J = 9.2 Hz, 1H), 7.86 (s, 1H), 7.39-7.38 (m, 5H), 7.35-7.34
(m, 2H), 6.98 (s, 1H), 6.93 (d, J = 8.4 Hz, 1H), 6.87 (s, 1H), 6.73 (d, J = 8.0 Hz, 1H), 5.31 (m,
1H), 5.18 (d, J = 12.4 Hz, 1H), 5.12 (d, J = 12.4 Hz, 1H), 4.85 (t, J = 10.2 Hz, 1H), 4.41 (dd,
J = 8.4, 5.6 Hz, 1H), 4.11 (dd, J = 8.4, 2.8 Hz, 1H), 4.02 (m, 1H), 3.90-3.82 (m, 2H), 3.76 (m,
1H), 3.23 (dd, J = 15.2, 4.6 Hz, 1H), 3.04 (dd, J = 15.2, 7.6 Hz, 1H), 2.98 (dd, J = 11.6, 3.2
Hz, 1H), 2.28-2.20 (m, 2H), 2.13-2.06 (m, 4H), 2.03-1.95 (m, 2H), 1.85 (m, 1H), 1.69 (m,
1H), 1.39-1.34 (m, 2H), 1.24 (m, 1H), 0.85 (d, J = 6.8 Hz, 6H), 0.80-0.75 (m, 9H), 0.69 (d, J
13
= 6.4 Hz, 3H); C NMR (100 MHz, DMSO-d6) δ 177.5, 172.2, 171.9, 171.8, 170.0, 169.5,
169.2, 135.9, 129.5, 128.5, 128.1, 128.0, 126.0, 124.2, 118.7, 117.9, 114.3, 108.0, 66.0, 58.7,
57.6, 55.2, 55.0, 52.0, 51.7, 50.0, 46.7, 42.8, 30.3, 29.0, 28.6, 26.8, 26.2, 25.6, 24.9, 23.8, 23.2,
21.8, 20.9, 18.8, 17.7, 17.3; HRMS (ESI) m/z calcd for C45H60N7O8 (M + H)+ 826.4498;
found 826.4496.
25
7
25
1
Compound S3. [α]D –24.0 (c 0.50, CH2Cl2), lit [α]D –28.0 (c 0.067, CH2Cl2); H
NMR (400 MHz, DMSO-d6) δ 11.42 (s, 1H), 8.75 (d, J = 9.6 Hz, 1H), 8.51 (d, J = 8.8 Hz,
1H), 8.38 (d, J = 9.2 Hz, 1H), 8.31 (d, J = 10.0 Hz, 1H), 7.87 (s, 1H), 7.85 (s, 1H), 7.52 (d, J
= 8.4 Hz, 1H), 7.33 (s, 1H), 7.02 (br s, 1H), 6.99 (d, J = 8.0 Hz, 1H), 6.94 (d, J = 8.4 Hz, 1H),
S11

NHPbf
NH
O
O
N
HN
H
H
6.85 (s, 1H), 6.66 (br s, 1H), 6.59 (d, J = 5.2 Hz,
1H), 6.38 (br s, 1H), 5.69 (m, 1H), 4.88-4.79 (m,
2H), 4.14-4.07 (m, 3H), 4.03-3.92 (m, 2H),
3.90-3.84 (m, 1H), 3.56 (t, J = 7.8 Hz, 1H),
N
N
H
HN
O
O
HN
O
O
N
O
H
NH
CO2t-Bu
N
N
N
N
O
H
H
3.19-3.13 (m, 2H), 3.06 (d, J = 2.8 Hz, 1H), 3.03-2.98 (m, 2H), 2.95 (s, 2H), 2.78 (dd, J =
16.4, 12.4 Hz, 1H), 2.59 (t, J = 14.0 Hz, 1H), 2.47 (s, 3H), 2.42 (s, 3H), 2.26-2.19 (m, 2H),
2.15-2.12 (m, 1H), 2.10-2.02 (m, 4H), 1.99 (s, 3H), 1.88-1.82 (m, 1H), 1.77-1.69 (m, 3H),
1.62 (m, 1H), 1.50-1.37 (m, 3H), 1.41 (s, 9H), 1.39 (s, 3H), 1.38 (s, 3H), 1.25 (m, 1H),
1.18-1.12 (m, 1H), 0.82 (d, J = 6.4 Hz, 3H), 0.77 (d, J = 6.4 Hz, 3H), 0.72 (d, J = 6.8 Hz, 3H),
13
0.69-0.65 (m, 9H); C NMR (100 MHz, DMSO-d6) δ 177.4, 172.1, 171.5, 171.3, 171.1,
170.8, 170.0, 169.3, 169.1, 157.4, 156.0, 138.2, 137.4, 137.2, 134.2, 132.7, 131.4, 130.6,
129.4, 125.0, 124.3, 119.4, 116.6, 116.2, 113.8, 99.9, 86.2, 81.5, 61.6, 57.2, 55.1, 54.7, 52.2,
51.2, 50.4, 47.2, 46.8, 42.5, 41.4, 31.5, 31.2, 29.9, 29.0, 28.3, 27.6, 27.5, 26.5, 26.1, 25.5, 25.1,
24.4, 23.9, 23.1, 21.8, 20.9, 18.9, 18.7, 18.1, 17.6, 17.0, 12.2; HRMS (ESI) m/z calcd for
C67H95N14O13S (M + H)+ 1335.6918; found 1335.6820.
1
Celogentin C. H NMR (400 MHz, DMSO-d6) δ
NH2
O
O
N
HN
H
H
11.83 (s, 1H), 9.33 (s, 1H), 8.81 (d, J = 8.8 Hz,
1H), 8.54 (d, J = 8.8 Hz, 1H), 8.34 (d, J = 9.6 Hz,
1H), 8.14 (d, J = 8.8 Hz, 1H), 7.88 (s, 1H), 7.76 (s,
1H), 7.62 (br s, 1H), 7.56 (d, J = 8.4 Hz, 1H), 7.01
N
NH
N
H
HN
O
O
HN
O
O
N
O
H
NH
CO2H
N
N
N
N
O
H
H
(d, J = 8.4 Hz, 1H), 6.95 (d, J = 10.4 Hz, 1H), 6.94 (s, 1H), 6.81 (d, J = 6.4 Hz, 1H), 5.62 (dd,
J = 15.8, 9.0 Hz, 1H), 4.90 (t, J = 10.6 Hz, 1H), 4.83 (t, J = 10.4 Hz, 1H), 4.20 (dd, J = 15.8,
9.0 Hz, 1H), 4.15-4.09 (m, 2H), 3.99-3.94 (m, 2H), 3.82-3.74 (m, 1H), 3.56 (t, J = 7.6 Hz,
1H), 3.42 (d, J = 16.0 Hz, 1H), 3.32 (dd, J = 15.4, 5.8 Hz, 1H), 3.12-3.06 (m, 3H), 2.93 (dd, J
= 15.2, 12.8 Hz, 1H), 2.59 (dd, J = 15.2, 11.6 Hz, 1H), 2.27-2.20 (m, 2H), 2.16-2.12 (m, 1H),
2.12-2.06 (m, 2H), 2.03-1.96 (m, 2H), 1.87-1.74 (m, 3H), 1.72-1.65 (m, 1H), 1.63-1.58 (m,
1H), 1.48-1.37 (m, 4H), 1.23-1.15 (m, 1H), 0.83 (d, J = 6.4 Hz, 3H), 0.77 (d, J = 6.0 Hz, 1H),
13
0.73-0.70 (m, 9H), 0.67 (d, J = 6.0Hz, 3H); C NMR (100 MHz, DMSO-d6) δ 177.4, 172.1,
171.3, 171.2, 170.9, 169.3, 169.1, 156.8, 136.5, 132.8, 131.5, 131.1, 128.6, 124.9, 119.5,
114.0, 100.9, 61.6, 57.2, 55.1, 54.7, 52.1, 51.3, 49.9, 47.2, 46.9, 41.5, 40.5, 31.1, 29.7, 29.0,
26.6, 25.5, 25.0, 23.9, 23.0, 21.7, 20.9, 18.6, 18.2, 17.0; HRMS (ESI) m/z calcd for
C45H60N7O8 (M + H)+ 1027.5472; found 1027.5455.
S12

1H-NMR of compound 4
Ph
O
O
N
O
CDCl3, 300MHz
S13

13C-NMR of compound 4
Ph
O
O
N
O
CDCl3, 75MHz
S14

1H-NMR of compound 10
O
OMe
N(Boc)2
N
O2N
Boc
CDCl3, 300MHz
S15

13C-NMR of compound 10
O
OMe
N(Boc)2
N
O2N
Boc
CDCl3, 75MHz
S16

1H-NMR of compound 6
O
OMe
N(Boc)2
N
I
Boc
CDCl3, 300MHz
S17

13C-NMR of compound 6
O
OMe
N(Boc)2
N
I
Boc
CDCl3, 75MHz
S18

1H-NMR of compound 12
O
OMe
Ph
O
N(Boc)2
N
O
O
N
Br
Boc
CDCl3, 400MHz
S19

13C-NMR of compound 12
O
OMe
Ph
O
N(Boc)2
N
O
O
N
Br
Boc
CDCl3, 100MHz
S20

1H-NMR of compound 13
O
OMe
Ph
O
N(Boc)2
N
O
O
N
N3
Boc
CDCl3, 400MHz
S21

13C-NMR of compound 13
O
OMe
Ph
O
N
N(Boc)2
O
O
N
N3
Boc
CDCl3, 100MHz
S22

1H-NMR of compound 14
O
Ot-Bu
N
H
NH2
O
CDCl3, 300MHz
S23

13C-NMR of compound 14
O
Ot-Bu
N
H
NH2
O
CDCl3, 75MHz
S24

1H-NMR of compound 15
O
O
Ot-Bu
N
OMe
N
H
O
HN
N3
N(Boc)2
O
Boc
CDCl3, 300MHz
S25

13C-NMR of compound 15
O
O
Ot-Bu
N
OMe
N(Boc)2
N
H
O
HN
N3
O
Boc
CDCl3, 75MHz
S26

1H-NMR of compound 16
O
H
CO2Me
N
N
H
O
HN
N3
O
N
H
CD3OD, 400MHz
S27

13C-NMR of compound 16
O
H
CO2Me
N
N
H
O
HN
N3
O
N
H
CD3OD, 100MHz
S28

1H-NMR of stephanotic acid methyl ester 2
O
H
CO2Me
N
N
H
O
HN
O
O
H
N
N
N
O
H
H
DMSO-d6, 400MHz
S29

13C-NMR of stephanotic acid methyl ester 2
O
H
CO2Me
N
N
H
O
HN
O
O
H
N
N
N
O
H
H
DMSO-d6, 100MHz
S30