A convergent total synthesis of the potent cephalostatin/ritterazine hybrid-25-epi ritterostatin GN1N

Article abstract of DOI:10.1021/jo401171q

The convergent synthesis of 25-epi ritterostatin G_N1_N is described for the first time, starting from hecogenin acetate (HA). Stereoselective dihydroxylation employing the chiral ligand (DHQ) ₂PHAL was used as the key step

Full text of DOI:10.1021/jo401171q

Subscriber access provided by - Access paid by the | UCSB Libraries
Article
A Convergent Total Synthesis of the Potent Cephalostatin/
Ritterazine hybrid - 25-epi Ritterostatin GN1N
Ananda Kumar Kanduluru, Prabal Banergee, John Albert Beutler, and Philip L. Fuchs
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/jo401171q • Publication Date (Web): 30 Jul 2013
Downloaded from http://pubs.acs.org on August 1, 2013
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
The Journal of Organic Chemistry is published by the American Chemical Society.
1155 Sixteenth Street N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 31
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
10
1
12
13
14
15
16
17
18
19
20
21
2
23
24
25
26
27
28
29
30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
46
47
48
49
50
51
52
53
54
5
56
57
58
59
60
A Convergent Total Synthesis of the Potent Cephalostatin/ Ritterazine hybrid
- 25-epi Ritterostatin GN1N
Ananda Kumar Kanduluru*,† Prabal Banerjee,† John A Beutler,‡ and Philip L Fuchs*,†
†Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States and ‡Molecular Targets
Laboratory, Center for Cancer Research, National Cancer Institute, Frederick, Maryland 21702, United States
kanduluruak@yahoo.com; pfuchs@purdue.edu
ABSTRACT: The convergent synthesis of 25-epi ritterostatin GN1N is described for the first
time, starting from hecogenin acetate (HA). Stereoselective dihydroxylation employing the chiral
ligand (DHQ)2PHAL was used as the key step to introduce the C25 epi- stereocenter on the north
1 segment. The title compound was obtained through a coupling reaction between the C3-keto-
azide (cstat North 1) and North G.
INTRODUCTION
1
Cephalostatin 1 (Cstat 1) was isolated by the Petitt group from the marine tubeworm
Cephalodiscus gilchristi, collected from the Indian Ocean. It is one of the most potent anticancer
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 2 of 31
1
2
3
4
5
6
7
8
9
10
1
12
13
14
15
16
17
18
19
20
21
2
23
24
25
26
27
28
29
30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
46
47
48
49
50
51
52
53
54
5
56
57
58
59
60
molecules reported in the NCI 60 cell line testing (Figure 1).2 Much effort has been devoted to
the cephalostatins3 and very recently a new enantioselective synthesis of this complex molecule
has been published4. A number of congeners have been isolated from marine sources, including
cephalostatins 2-195 and ritterazines A-Z.5 The antineoplastic mechanism of the trisdecacyclic
pyrazines is only partly known and the functionality present in these trisdecacyclic steroidal
pyrazine bisspiroketals is quite different from that of other anticancer agents, likely indicating a
new mechanism of action.6 Beyond in vitro testing, cephalostatin 1 has been shown to be
effective in several xenografts including melanoma, sarcoma, leukemia and in a human
mammary carcinoma model.7-8
Among the series of analogs tested at the NCI (Table 1), 25-epi ritterostatin GN1N 5 exhibited
sub-nanomolar activity (mean GI50 0.48 nM, Table 1 & Figure 1),8 which is 30 fold more potent
than ‘natural’ epimer 4. These compounds showed selectivity for CNS, leukemia, and renal
cancer cell lines, with ovarian cancer lines relatively resistant.7-8 As noted previously, this pattern
of selectivity is shared with several less potent natural products, including OSW-1,
schweinfurthins, and stelletins.7 Several empirical calculations and docking/modeling studies
also supported this higher activity. 6 In order to move agents of the trisdecacyclic pyrazine class
to the clinic, a more efficient route to the north 1 hemisphere was required. This issue is
addressed herein via a complete synthesis of 25-epi ritterostatin GN1N in a convergent manner
from the readily available hecogenin for both segments, leading to 245 mg of the hybrid
molecule.9 In this synthesis, the north G segment could be readily obtained from hecogenin
acetate (HA).3
ACS Paragon Plus Environment

Page 3 of 31
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
10
1
12
13
14
15
16
17
18
19
20
21
2
23
24
25
26
27
28
29
30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
46
47
48
49
50
51
52
53
54
5
56
57
58
59
60
Figure 1. IC50 values of Cstat analogs
Table 1. Selected results from NCI-60 cell line testing (IC50 values in nM).
Compd
NSC#
363979
699013
720780
Leukemia
HL-60
0.4
Lung
A-549
0.5
Colon
HT-29
1.4
CNS
SF-295
<0.1
Breast
MCF-7
0.4
Ovary
IGROV1
4.0
Melanoma
M-14
Renal
A-498
1.4
Prostate
PC-3
0.3
Cephalostatin 1 (2)
n = 9
1.0
Ritterostatin GN1N (4)
n = 3
2.4
9.8
79
1.3
28
141
11
>1000
7.2
25-epi Ritterostatin
GN1N (5)
<0.1
<0.1
0.3
<0.1
<0.1
<0.1
0.7
0.2
<0.1
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 4 of 31
1
2
3
4
5
6
7
8
9
10
1
12
13
14
15
16
17
18
19
20
21
2
23
24
25
26
27
28
29
30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
46
47
48
49
50
51
52
53
54
5
56
57
58
59
60
n = 4
‘n’ is the number of separate full tests- each test was conducted in triplicate at each point (full
details in Supporting Information).
Results and Discussion
Synthesis of North 1 Segment. The synthesis began from dihydroxyhecogenin acetate 6
derived from crude hecogenin.10 The ∆14 olefin was formed by SOCl2 mediated dehydration of 6
providing the cyclic vinyl ether 7 in 85% yield. The C23 hydroxyl group (8) was introduced via
dimethyldioxirane oxidation, followed by reduction of the C16 hydroxyl group using
phenylselenol at -45˚C to obtain 9 (Scheme 1).11 Borohydride reduction of 9 at -78˚C gave the
C12 alcohol 10 favoring β (β:α, 8:1) and subsequent bis benzoylation, providing 11 in 86% yield
over two steps. Regio- and stereoselective [5,6] spiroketal F-ring reductive opening using
triethylsilane12 to primary alcohol 12 was followed by sequential iodination to 13, DBU-assisted
E2 elimination ultimately provided the terminal olefin 14 (Scheme 1). These reactions were
routinely conducted on >10 g scale with highly reproducible yields (72-88%).
Scheme 1. Synthesis of olefin 14
ACS Paragon Plus Environment

Page 5 of 31
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
10
1
12
13
14
15
16
17
18
19
20
21
2
23
24
25
26
27
28
29
30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
46
47
48
49
50
51
52
53
54
5
56
57
58
59
60
Treatment of terminal olefin 14 with trifluoroacetyl triflate (TFAT) at -40˚C effected
spiroketal ring opening,13,12 smoothly providing the expected cyclopentadiene as the C22-OTFA
ester 15. Selective deprotection of 15 gave alcohol 16 and its subsequent TBS ether 17 without
disturbing the C3-OAc. The C3-keto intermediate 19 was easily obtained in quantitative yield by
saponification to 18 followed by oxidation with NMO and catalytic TPAP.13 Reaction of 19 with
singlet oxygen led to the stereospecific α-1,4-adduct 20.13 Cleavage of the TBS group at C22 to
alcohol 21, followed by Swern oxidation afforded ketone 22 which was confirmed by X-ray
crystallographic analysis (Figure 2).14 Reductive cleavage of the peroxide bond using Zn/AcOH
to diol 2312 followed by acid catalyzed cyclization provided olefin 24 (Scheme 2) along with
some C3-dimethylacetal 24a which exhibited two additional methoxy acetal singlets at  3.08 &
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 6 of 31
1
2
3
4
5
6
7
8
9
10
1
12
13
14
15
16
17
18
19
20
21
2
23
24
25
26
27
28
29
30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
46
47
48
49
50
51
52
53
54
5
56
57
58
59
60
3.15 in addition to the C22-OMe singlet at  3.32. This was easily hydrolyzed to 24 by addition
of few drops of water (see experimental section).
Scheme 2. Preparation of Cstat north 1 azide, 29
ACS Paragon Plus Environment

Page 7 of 31
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
10
1
12
13
14
15
16
17
18
19
20
21
2
23
24
25
26
27
28
29
30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
46
47
48
49
50
51
52
53
54
5
56
57
58
59
60
Figure 2. X-Ray structure of peroxide 22
Asymmetric Dihydroxylation. Several ligands were screened for oxy-functionalization of
terminal olefin 24 at C25,26 using Sharpless asymmetric dihydroxylation15 (Table 2). As
expected, a reasonable enantiomeric excess (ee) of C25- epi, R-25 (9.5:1 ratio, epi:natural) was
obtained when (DHQ)2PHAL AD-mix-α was used, whereas with other ligands the selectivity
was poor (Table 2). The C26 primary alcohol of diol 25 was protected as benzoyl ester 26 in
88% yield, followed by acid catalyzed cyclization to spiroketal 2714 in 85% yield (Scheme 2,
Figure 3) along with some C3 dimethylacetal [27a, X=(OMe)2]. This material was easily
hydrolyzed to the C3 ketone (27) by addition of a few drops of H2O to the reaction flask prior to
workup (see Supporting Information).
Table 2. Asymmetric dihydroxylation of olefin 24
Ligands
Compound 25,
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 8 of 31
1
2
3
4
5
6
7
8
9
10
1
12
13
14
15
16
17
18
19
20
21
2
23
24
25
26
27
28
29
30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
46
47
48
49
50
51
52
53
54
5
56
57
58
59
60
screened*
None
C25 ratio, epi:natural (R:S)
2.2:1
1:1
(DHQD)2PHAL
(DHQ)2PHAL
(DHQD)2PYR
(DHQ)2PYR
DHQD
9.5:1 (82%)
1:3.8
2:1
1.8:1
DHQ
2.5:1
a Conditions: K2OsO4 (2 mol%), ligand (10 mol%), t-BuOH/H2O (1:1), 0˚C, 40 h.
Figure 3. X-Ray structure of 27
The North 1 coupling partner C3-keto-azide 2916 was prepared by bromination of 27 in THF
using phenyltrimethylammonium tribromide (PTAB) in 84% yield (28) followed by azide
formation with tetramethylguanidinium azide (TMGA) (29) in 81% yield (Scheme 2). C3-keto-
azide 29 of 25-epi Cstat North 1 was thus prepared in 23 steps and 1.6% overall yield from
C14,16-dihydroxy hecogenin acetate 6. The North G (30) segment was synthesized according to
the literature protocol from HA.3,6
ACS Paragon Plus Environment

Page 9 of 31
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
10
1
12
13
14
15
16
17
18
19
20
21
2
23
24
25
26
27
28
29
30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
46
47
48
49
50
51
52
53
54
5
56
57
58
59
60
End game. Coupling of aminomethoxime North G 30 with C3-keto-azide of North 1 29 using
PVP, Bu2SnCl2 in refluxing benzene provided trisdecacyclic pyrazine 31 in 58% yield (Scheme
3).17 Completion of 25-epi ritterostatin GN1N (5) in nearly quantitative yield simply involved
global deprotection with NaOH.
Scheme 3. Formation of trisdecacyclic pyrazine 5
In conclusion, the first synthesis of 25-epi ritterostatin GN1N 5 is reported with excellent
stereocontrol. The highly functionalized North 1 hemisphere featured introduction of the C25-epi
stereocenter via asymmetric dihydroxylation as the key step. Reactions were performed at multi-
gram scale with reproducible yields.
EXPERIMENTAL SECTION
General Methods. All reagents purchased were used as received. Tetrahydrofuran (THF) and
diethyl ether were distilled from benzophenone ketyl. Benzene, toluene, and methylene chloride
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 10 of 31
1
2
3
4
5
6
7
8
9
10
1
12
13
14
15
16
17
18
19
20
21
2
23
24
25
26
27
28
29
30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
46
47
48
49
50
51
52
53
54
5
56
57
58
59
60
(CH2Cl2) were distilled from calcium hydride. Acetonitrile (CH3CN) and methanol were
purchased spectral grade and used without further purification. Sodium sulfate (Na2SO4) was
anhydrous. All recrystallization, chromatographic, and workup solvents were distilled. Unless
otherwise indicated, all reactions were carried out under in a positive pressure of nitrogen in
anhydrous solvents and the reaction flasks were fitted with rubber septa for the introduction of
substrates and reagents via syringe. Progress of reactions was monitored by thin layer
chromatography (TLC) using silica gel plates. The TLC plates were visualized with a UV lamp
(254 nm) and/or with TLC visualizing solutions activated with heat. The two commonly
employed TLC visualizing solutions were: (i) p-anisaldehyde solution (1350mL absolute
ethanol, 50mL concentrated H2SO4, 37mL p-anisaldehyde), and (ii) Iodine.
1H NMR and 13C NMR spectra were recorded on 400-500 MHz spectrometers in CDCl3
solution. Chemical shifts were reported in parts per million (ppm) on the δ scale from an internal
standard (NMR descriptions: s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet; br, broad;
dd, doublet of doublet; td, triplet of doublet and/or quint, quintet). Coupling constants, J, are
reported in Hertz. Melting points were obtained on a capillary melting point apparatus or
automated melting point system and are uncorrected. The high resolution mass measurements
were obtained on a LTQ Orbitrap XL mass spectrometer utilizing electrospray ionization (ESI)
C12 Reduction (10) followed by benzoyl protection, 11. C23 alcohol (9, 3.1 g, 6.37 mmol)
was dissolved in CH2Cl2 and MeOH (1:1, 50 mL). The solution was cooled to -78C (dry
ice/acetone) under a nitrogen atmosphere. NaBH4 was added into the mixture in 3 portions in
five-minute intervals (200 mg, 5.3 mmol each portion). The solution was maintained at -78C for
ACS Paragon Plus Environment

Page 11 of 31
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
10
1
12
13
14
15
16
17
18
19
20
21
2
23
24
25
26
27
28
29
30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
46
47
48
49
50
51
52
53
54
5
56
57
58
59
60
8 hours with vigorous stirring. The temperature was then slowly raised to -20C. TLC showed
the complete absence of starting material (7:3 EtOAc/Hexane, Rf = 0.3). The reaction was
quenched with HCl (2 N, 40 mL). CH2Cl2 was used to extract the reaction mixture (50 mL x 3).
The combined organic phase was washed with brine, dried over Na2SO4 and concentrated
1
followed by application of vacuum for 2 h before proceeding to next step with crude 10. H
NMR (400 MHz, CDCl3) δ 0.83 (d, J = 6.5, 3H), 0.88 (s, 3H), 1.01 (s, 4H), 1.21 (d, J = 6.7, 3H),
1.28-1.39 (m, 6H), 1.43-1.49 (m, 2H), 1.63-1.75 (m, 6H), 1.80-1.88 (m, 2H), 2.02 (s, 6H), 2.13-
2.18 (t, 1H), 2.43 (t, 1H), 3.17 (dd, J = 4.6, 4.6, 1H), 3.48-3.57 (m, 2H), 3.64 (t, 1H), 4.63-4.70
(m, 1H), 4.89 (d, J = 9.5, 1H), 5.37 (s, 1H); LRMS (ESI) m/z calc for C29H45O6 (M+H) 489.32,
found 489.27.
To crude 10 in CH2Cl2 (30 mL) were added DMAP (80 mg 0.1 eq.), pyridine (8 mL) under N2
and the flask was cooled in an ice water bath. To this solution benzoyl chloride (2.2 mL, 19
mmol) was added and the reaction was stirred for 16 hours, until TLC showed starting material
disappeared (3:7 EtOAc/Hexane, Rf = 0.5). The solvent was removed under reduced pressure and
the reaction mixture was purified by silica gel column chromatograph by using EtOAc-Hexane
to provide the desired product 11 (3:7 EtOAc/Hexane, Rf = 0.5), 3.8 to 3.9 g, yield 86% for two
1
steps. H NMR (400 MHz, CDCl3) δ 0.79 (d, J = 6.6, 3H), 0.89 (s, 3H), 0.94 (d, J = 6.7, 3H),
1.01-1.09 (m, 1H), 1.01-1.09 (m, 1H), 1.21 (s, 3H), 1.33-1.43 (m, 3H), 1.46-1.52 (m, 1H), 1.61–
1.69 (m, 2H), 1.74-1.84 (m, 3H), 1.88-1.99 (m, 4H), 2.02 (s, 3H), 2.05 (s, 2H), 2.07-2.14 (m,
2H), 2.43 (t, 1H), 3.53 (t, 1H), 3.58-3.62 (m, 1H), 4.63-4.71 (m, 2H), 4.98 (dd, J = 2.1, 2.2, 1H),
5.13 (s, 1H), 5.47 (s, 1H), 7.37-7.56 (m, 6H), 7.99 (d, J = 8.2, 2H), 8.08 (d, J = 8.2, 2H); HRMS
(ESI) calcd for C43H53O8 [M+H]+ 697.3740, found 697.3734.
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 12 of 31
1
2
3
4
5
6
7
8
9
10
1
12
13
14
15
16
17
18
19
20
21
2
23
24
25
26
27
28
29
30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
46
47
48
49
50
51
52
53
54
5
56
57
58
59
60
F-ring cleavage compound 12. The C12, 23-dibenzoate (11, 10.0 g, 14.35 mmol) and
triethylsilane (13.35 g, 114.8 mmol, 8 eq.) were dissolved in CH2Cl2 (100 mL) under N2.
BF3•OEt2 (14.5 mL, 114.8 mmol, 8 eq.) was added to the reaction mixture at <5°C. The reaction
was stirred at room temperature for 40 hours and then quenched with NaHCO3 (200 mL, ice
water bath). The reaction mixture was extracted with CH2Cl2 (50 mL x 3) and combined organic
layer was washed with brine, dried over Na2SO4 and concentrated. The crude mass was subjected
to chromatography on silica gel to provide the C26 alcohol (12) 7.21 g, yield 72% (3:7
1
EtOAc/Hexane, Rf = 0.25). H NMR (400 MHz, CDCl3) δ 0.89 (s, 3H), 0.90-0.92 (m, 4H), 0.95
(d, J = 6.5, 3H), 1.24-1.27 (m, 4H), 1.35 (t, 2H), 1.56 (t, 1H), 1.64-1.76 (m, 3H), 1.90-1.97 (m,
8H), 2.02 (s, 3H), 2.04 (s, 2H), 2.08-2.12 (m, 1H), 2.25 (t, 1H), 3.47 (t, 1H), 3.55-3.59 (m, 1H),
4.65-4.70 (m, 4H), 4.84 (dd, J = 1.5, 1.3, 1H), 5.35-5.39 (m, 1H), 5.45 (t, 1H), 7.43 (t, J = 15.0,
4H), 7.55 (t, J = 14.6, 2H), 7.98-8.15 (m, 4H); HRMS (ESI) calcd for C43H55O8 [M+H]+
699.3897, found 699.3887.
Iodo compound 13. To the C26 alcohol (12, 5.0 g, 7.15 mmol) in diethyl ether (150 mL) and
CH3CN (15 mL) were added triphenylphosphine (4.7 g, 17.9 mmol, 2.5 eq.), imidazole (2.47 g,
35.8 mmol, 5 eq.) followed by iodine (5.45 g, 21.5 mmol, 3 eq.) at <5C. The reaction was
stirred at this temperature for 30 minutes and then at room temperature for an additional 3 hours.
Aq. NaHSO3 was added to the reaction and stirred for 30 minutes. The organic solution was
separated and the aqueous phase was extracted with ethyl acetate (25 mL x 3). The combined
organic layer dried over Na2SO4 and removal of the solvent under reduced pressure followed by
1
chromatography on silica gel provided 13 (3:7 EtOAc/Hexane, Rf = 0.65), 5.11 g, yield 88%. H
NMR (400 MHz, CDCl3) δ 0.84-0.97 (m, 2H), 0.89 (s, 6H), 0.91 (s, 2H), 0.93-0.99 (m, 1H), 1.03
ACS Paragon Plus Environment

Page 13 of 31
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
10
1
12
13
14
15
16
17
18
19
20
21
2
23
24
25
26
27
28
29
30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
46
47
48
49
50
51
52
53
54
5
56
57
58
59
60
(d, J = 6.5, 3H), 1.26 (s, 3H), 1.36 (t, 2H), 1.56-1.63 (m, 6H), 1.64-1.71 (m, 2H), 1.76-1.86 (m,
1H), 1.88-1.99 (m, 1H), 2.01 (s, 3H), 2.04 (s, 1H), 2.07-2.12 (m, 1H), 2.25 (t, 1H), 3.17 (t, 2H),
3.55 (dd, J = 5.0, 5.1, 1H), 4.67-4.70 (q, 2H), 4.83 (dd, J = 2.2, 2.4, 1H), 5.31-5.35 (m, 1H), 5.46
(t, 1H), 7.41-7.45 (m, 4H), 7.51-7.57 (m, 2H), 8.00-8.06 (m, 4H); 13CNMR (CDCl3, 100 MHz) δ
11.9, 14.1, 16.3, 17.8, 18.3, 19.9, 21.3, 22.5, 25.2, 26.6, 27.2, 28.0, 29.4, 31.2, 31.4, 33.6, 34.0,
34.5, 35.8, 36.4, 37.7, 37.9, 44.0, 51.7, 52.0, 60.0, 73.0, 81.4, 86.5, 87.9, 120.0, 128.3, 129.3,
129.6, 129.8, 130.2, 131.9, 132.0, 132.9, 157.0, 165.6, 165.8, 170.2; LRMS (ESI) calcd for
C43H54IO7 [M+H]+ 809.29, found 809.25.
Olefin 14. Iodide (13, 901 mg, 1.13 mmol) was dissolved in CH3CN (25 mL) under argon
atmosphere and freshly distilled DBU over CaH2 (255 µL, 1.7 mmol, 1.5 eq.) was added to the
reaction mixture. The reaction was stirred at 55C for 4 hours and then at room temperature for
10 hours. The solvent was removed under reduced pressure and the crude mass was purified via
silica gel column chromatography using EtOAc-Hexane (3:7 Rf = 0.45) to provide 14, 591 mg,
yield 80%. 1H NMR (400 MHz, CDCl3) δ 0.77-0.81 (m, 2H), 0.82 (s, 3H), 0.89 (d, J = 6.4, 3H),
0.94-1.04 (m, 2H), 1.10-1.20 (m, 2H) 1.23 (s, 3H), 1.26-1.34 (m, 4H), 1.37-1.45 (m, 1H), 1.57-
1.65 (m, 2H), 1.70 (s, 3H), 1.73-1.86 (m, 2H), 1.88-1.91 (m, 1H), 1.92 (s, 3H), 2.02-2.13 (m,
2H), 2.23 (t, 1H), 2.46 (d, J = 6.4, 2H), 3.53 (dd, J = 5.4, 5.2, 1H), 4.60-4.64 (m, 1H) 4.68 (br,
1H), 4.80 (dd, J = 2.3, 2.3, 1H), 5.37-5.41 (m, 1H), 5.42 (t, 1H), 7.30-7.36 (m, 4H), 7.41-7.47
13
(m, 2H), 7.95-7.99 (m,4H); CNMR (CDCl3, 100 MHz) δ 11.8, 14.1, 16.2, 18.3, 20.6, 21.2,
22.4, 25.2, 26.6, 27.1, 28.0, 29.4, 31.4, 33.6, 34.0, 34.3, 34.5, 35.8, 36.4, 38.1, 39.4, 44.0, 51.7,
52.0, 60.1, 73.0, 73.1, 81.4, 86.4, 87.6, 113.1, 120.1, 128.2, 128.3, 129.3, 129.5, 130.2, 130.3,
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 14 of 31
1
2
3
4
5
6
7
8
9
10
1
12
13
14
15
16
17
18
19
20
21
2
23
24
25
26
27
28
29
30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
46
47
48
49
50
51
52
53
54
5
56
57
58
59
60
132.7, 141.2, 157.0, 165.6, 165.7, 170.2; HRMS (ESI) calcd for C43H53O7 [M+H]+ 681.3792,
found 681.3778.
Synthesis of D-ring diene 15. The olefin (14, 2.8 g, 4.11 mmol) and 2,6-di-t-butyl-4-methyl
pyridine (3.28 g, 16 mmol, 4 eq.) were dissolved in CH2Cl2 (200 mL) and cooled to -40C.
Freshly prepared trifluoroacetyl trifluoromethanesulfonate (TFAT, 1.5 mL, 8 mmol, 2 eq.) was
added slowly and stirred for 1 h. A second portion of TFAT (1.5 mL, 2 eq.) was added and
stirred another 2.5 h and finally, a 3rd portion of TFAT (0.7 mL, 1 eq.) was added and stirring
continued for another 1 h. After disappearance of starting material shown by TLC (3:7
EtOAc/Hexane, Rf = 0.55), the reaction was quenched with aq. NaHCO3 (100 mL). The organic
layer was separated and aqueous phase was extracted with CH2Cl2 (15 x 3). The combined
organic phase was washed with brine, dried over Na2SO4 and concentrated under reduced
pressure. The crude product was loaded on a silica gel column and eluted with hexane followed
by EtOAc-Hexanes. The 2,6-di-t-butyl-4-methyl pyridine was recovered first by flushing 1:10 to
1:8 and then desired product 15 was isolated with 1:4 EtOAc-Hexanes respectively. The yield
was 70%, 2.23 g. 1H NMR (400 MHz, CDCl3) δ 0.80-0.88 (m, 3H), 0.93 (s, 3H), 0.96 (d, J = 6.5,
3H), 1.10-1.15 (m, 1H), 1.21 (s, 3H), 1.26 (t, 1H), 1.34-1.47 (m, 3H), 1.52 (s, 3H), 1.64-1.75 (m,
2H), 1.78-1.86 (m, 1H), 1.96-2.00 (m, 2H), 2.02 (s, 3H), 2.03-2.09 (m, 1H), 2.14-2.24 (m, 2H),
2.49 (q, 1H), 2.96 (dd, J = 6.6, 6.7, 1H), 4.46 (dd, J = 4.4, 4.4, 1H), 4.63 (br, 1H), 4.67-4.72 (m,
2H), 5.42 (d, J = 10.6, 1H), 5.51 (dd, J = 2.4, 2.4, 1H), 5.88 (s, 1H), 6.15 (s, 1H), 7.38-7.62 (m,
13
6H), 7.89 (d, J = 8.1, 2H), 8.10 (d, J = 8.2, 2H). 19F NMR (376 MHz) δ -76.43; CNMR
(CDCl3, 100 MHz) δ 11.9, 13.7, 13.8, 19.2, 20.7, 21.0, 21.8, 27.1, 27.9, 28.9, 32.9, 33.6, 34.5,
35.2, 35.6, 36.8, 44.0, 53.1, 56.6, 60.0, 70.8, 73.0, 76.9, 77.2, 77.5, 79.0, 81.5, 113.1, 114.0,
ACS Paragon Plus Environment

Page 15 of 31
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
10
1
12
13
14
15
16
17
18
19
20
21
2
23
24
25
26
27
28
29
30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
46
47
48
49
50
51
52
53
54
5
56
57
58
59
60
115.9, 120.6, 125.4, 128.2, 129.2, 130.3, 132.9, 133.1, 140.0, 155.9, 156.2, 156.6, 165.1, 165.2,
170.1, 170.6; LRMS (ESI) calcd for C45H52F3O8 [M+H]+ 777.36, found 777.31.
Synthesis of C22 alcohol 16. The C22-OTFA (15) was dissolved in THF/MeOH (70 mL, 6:1)
and Cs2CO3 (1.3 g, 1 eq.) was added to the reaction and stirred at room temperature. After
ensuring the consumption of starting material by TLC (3:7 EtOAc/Hexane, Rf = 0.3), the reaction
was diluted by EtOAc (80 mL), followed by water (60 mL). The organic phase was separated
and the aqueous phase was extracted with EtOAc (30 mL x 3). The combined organic phase was
washed once with brine (20 mL), dried (Na2SO4) and concentrated. After evaporation of the
solvent under reduced pressure, the crude product was purified on a silica gel column using
1
EtOAc-Hexane (1:4) to provide C23 alcohol, 16, 2.38 g in 85% yield. H NMR (400 MHz,
CDCl3) δ 0.84-0.88 (m, 2H), 0.91 (d, J = 6.4, 3H), 0.93 (s, 3H), 1.05-1.15 (m, 1H), 1.20-1.25 (m,
2H), 1.27 (s, 3H), 1.34-1.50 (m, 3H), 1.65-1.73 (m, 1H), 1.75-1.85 (m, 2H), 2.0-2.07 (m, 9H),
2.13-2.25 (m, 3H), 2.61-2.74 (m, 2H), 3.90 (dd, J = 2.5, 2.4, 1H), 4.46 (dd, J = 4.5, 4.4, 1H),
4.68 (br, 3H), 5.30-5.33 (m, 1H), 5.96 (s, 1H), 6.21 (s, 1H), 7.39-7.47 (m, 4H), 7.52-7.59 (m,
2H), 8.01 (d, J = 8.1, 2H), 8.09 (d, J = 8.2, 2H); LRMS (ESI) calcd for C43H52NaO7 [M+Na]+
703.36, found 703.33.
Formation of C-22 OTBS ether 17. To the C22 alcohol (16, 2.36 g, 3.47 mmol) in CH2Cl2
(35 mL) were added 2,6-Lutidine (2.1 mL, 18 mmol, 5.0 eq.) followed by TBSOTf (4 eq.) in
three portions under N2 at room temperature and the reaction was stirred for 3 h. The reaction
mixture was quenched by adding aq. NaHCO3 solution (20 mL), the aqueous phase was
extracted with CH2Cl2 (15 mL x 3) and the combined organic phases were dried over Na2SO4
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 16 of 31
1
2
3
4
5
6
7
8
9
10
1
12
13
14
15
16
17
18
19
20
21
2
23
24
25
26
27
28
29
30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
46
47
48
49
50
51
52
53
54
5
56
57
58
59
60
and concentrated under reduced pressure. The crude product was subjected to chromatography
1
on silica gel to provide 17 (3:7 EtOAc/Hexane, Rf = 0.65), 2.21 g in 81% yield. H NMR (400
MHz, CDCl3) δ 0.85 (s, 6H), 0.88 (br, 12H), 0.90-0.95 (m, 5H), 1.04-1.12 (m, 1H), 1.19-1.24 (m,
1H), 1.28 (s, 3H), 1.33-1.42 (m, 3H), 1.44-1.50 (m, 2H), 1.62-1.71 (m, 2H), 1.74-1.80 (m, 1H),
1.97-2.00 (m, 4H), 2.16-2.23 (m, 2H), 2.49 (s, 4H), 2.61-2.70 (m, 1H), 2.72-2.80 (m, 1H), 3.99
(dd, J = 1.4, 1.5, 1H), 4.40 (dd, J = 4.4, 4.2, 1H), 4.66 (br, 2H), 5.29 (d, J = 10.1, 1H), 5.93 (s,
1H), 6.21 (s, 1H), 6.91 (d, J = 7.6, 1H), 7.35-7.56 (m, 6H), 7.98 (d, J = 7.8, 2H), 8.08 (d, J = 8.1,
2H; 13CNMR (CDCl3, 100 MHz) δ -4.6, -3.8, -3.6, 12.1, 12.8, 17.9, 18.3, 20.3, 21.3, 22.0, 24.1,
25.6, 26.0, 27.1, 27.3, 28.1, 29.1, 33.7, 34.6, 35.7, 36.2, 36.4, 36.9, 44.2, 53.2, 56.8, 73.3, 75.1,
78.3, 80.0, 113.0, 120.2, 121.1, 125.6, 128.2, 128.4, 129.3, 129.6, 130.5, 132.7, 132.9, 136.7,
141.7, 154.6, 157.3, 158.5, 165.6, 166.4, 170.5; LRMS (ESI) calcd for C49H67O7Si [M+H]+
795.46, found 795.41.
Synthesis of C-3 alcohol 18. C3-acetyl compound (17, 2.21 g, 2.78 mmol) was dissolved in
THF: MeOH: H2O (1:1:1, 30 mL), K2CO3 (4.28 g, 30 mmol) was added in one portion and the
reaction mixture was stirred for 70 h at room temperature. After ensuring the absence of starting
material from TLC (3:7 EtOAc/Hexane, Rf = 0.2), the mixture was diluted with EtOAc (60 mL)
followed by H2O (30 ml). The organic phase was separated and aqueous phase was extracted
with EtOAc (20 x 3). The combined organic phase was dried over Na2SO4, the solvent was
evaporated under reduced pressure and the resulting crude product was subjected to
chromatography on silica gel using EtOAc-Hexane to provide the C3-OH, 18 (3:7
1
EtOAc/Hexane, Rf = 0.2), 1.99 g and yield 95%. H NMR (400 MHz, CDCl3) δ -0.23 (s, 3H), -
0.07 (s, 3H), 0.79-0.81(m, 1H), 0.86 (s, 9H), 0.91 (s, 3H), 0.92-0.95 (m, 3H), 1.02-1.17 (m, 3H),
ACS Paragon Plus Environment

Page 17 of 31
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
10
1
12
13
14
15
16
17
18
19
20
21
2
23
24
25
26
27
28
29
30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
46
47
48
49
50
51
52
53
54
5
56
57
58
59
60
1.21-1.25 (m, 2H), 1.28 (s, 3H), 1.31-1.36 (m, 1H), 1.41-1.44 (m, 3H), 1.57-1.71 (m, 3H), 1.75-
1.82 (m, 1H), 1.97-2.04 (m, 4H), 2.17-2.27 (m, 2H), 2.64-2.70 (m, 1H), 2.75-2.80 (m, 1H), 3.56-
3.65 (m, 1H), 4.01(dd, J = 1.5, 1.5, 1H), 4.40 (dd, J = 4.4, 4.2, 1H), 4.67 (br, 2H), 5.30 (d, J =
10.7, 1H), 5.94 (t, J = 4.1, 1H), 6.22 (d, J = 2.2, 1H), 7.38-7.59 (m, 6H), 7.99 (d, J = 8.1, 2H),
8.10 (d, J = 7.9, 2H); 13CNMR (CDCl3, 100 MHz) δ -4.5, -3.8, -0.03, 12.3, 12.8, 14.2, 18.9, 20.4,
21.0, 22.2, 26.1, 27.4, 28.3, 29.2, 31.2, 34.7, 35.8, 36.2, 36.5, 37.2, 37.8, 44.5, 53.4, 56.9, 60.4,
71.0, 75.2, 78.4, 80.2, 113.0, 121.1, 125.6, 128.2, 128.5, 129.4, 129.6, 130.5, 130.6, 132.8, 133.0,
141.9, 154.6, 158.6, 165.7, 166.5; LRMS (ESI) calcd for C47H65O6Si [M+H]+ 753.45, found
753.41.
Synthesis of C3 ketone 19. The C3 alcohol (18, 781 mg, 1.04 mmol) was dissolved in CH2Cl2
(10 mL) under N2 and NMO (240 mg, 2 mmol, 2.0 eq.) followed by tetrapropylammonium
perruthenate (TPAP, 17.5 mg, 0.05 mmol) was added at room temperature and the mixture was
stirred for 3 h. After ensuring the disappearance of starting material by TLC (3:7 EtOAc/Hexane,
Rf = 0.55), the solvent was removed and the crude product was subjected to flash
1
chromatography on a short silica gel column to provide C3 ketone 19, 744 mg in 99% yield. H
NMR (400 MHz, CDCl3) δ -0.24 (s, 3H), -0.07 (s, 3H), 0.85 (s, 12H), 0.93 (d, J = 6.5, 2H), 1.05
(s, 3H), 1.31 (s, 3H), 1.36-1.45 (m, 6H), 1.87-1.95 (m, 2H), 1.98-2.11 (m, 4H), 2.19-2.31 (m,
5H), 2.64-2.71 (m, 1H), 2.79 (t, 1H), 4.01 (d, J = 7.4, 1H), 4.40 (dd, J = 4.5, 4.2, 1H), 4.66 (d, J
= 5.3, 2H), 5.31 (dd, J = 2.7, 2.8, 1H), 5.94 (s, 1H), 6.21 (s, 1H), 7.33-7.53 (m, 6H), 7.98 (d, J =
13
8.2, 2H), 8.09 (d, J = 8.1, 2H); CNMR (CDCl3, 100 MHz) δ -4.5, -3.8, 11.3, 12.7, 18.3, 20.3,
22.1, 26.1, 27.5, 28.4, 28.8, 34.5, 35.8, 36.2, 36.4, 37.7, 38.4, 44.3, 46.0, 52.8, 56.9, 75.0, 78.3,
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 18 of 31
1
2
3
4
5
6
7
8
9
10
1
12
13
14
15
16
17
18
19
20
21
2
23
24
25
26
27
28
29
30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
46
47
48
49
50
51
52
53
54
5
56
57
58
59
60
79.7, 113.0, 121.5, 125.5, 128.2, 128.4, 129.3, 129.5, 130.4, 132.7, 133.0, 141.7, 154.0, 158.8,
165.4, 166.2, 210.4; LRMS (ESI) calcd for C47H63O6Si [M+H]+ 751.43, found 751.40.
Peroxide formation (20) followed by deprotection of C22-OTBS (21). The diene (19, 500
mg, 0.64 mmol) in CH2Cl2 (40 mL) was cooled to -78C. 5,10,15,20-Tetraphenyl-21H,23H-
porphine (TPP) (0.1 mol %) was added and oxygen was bubbled into the solution via a balloon
with photoactivation (GE Sunlamp 300 W) at a distance of approximately 8 to 9 inches from the
reaction flask. The reaction was stirred with irradiation at -78C for 2 hours. After ensuring the
disappearance of starting material by TLC (3:7 EtOAc/Hexane, Rf = 0.4), solvent was removed
and the crude peroxide (20) was directly used in the next step after drying for 1 h under high
vacuum.
In the second step, crude product 20 was dissolved in THF (7 mL) under N2 and TBAF
(tetrabutylammonium fluoride, 1.0 M in THF, 1.5 mL) was added at room temperature and the
reaction was stirred for 3 h. The reaction was quenched with brine and extracted with ethyl
acetate (10 mL x 3). The combined organics were dried over Na2SO4, the solvent evaporated
under reduced pressure and crude product was subjected to column chromatography on neutral
alumina using EtOAc-Hexane (3:7 EtOAc/Hexane, Rf = 0.22) to provide C22 alcohol (21), 263
mg, 74% for two steps. 1H NMR (400 MHz, CDCl3) δ 0.85 (s, 4H), 0.90-0.96 (m, 3H) 1.04-1.08
(t, 3H), 1.13 (s, 3H), 1.20-1.29 (m, 3H), 1.62-1.69 (m, 1H), 1.74-1.80 (m, 3H), 1.83 (s, 3H),
1.88-1.96 (m, 3H), 2.02-2.11 (m, 4H), 2.24-2.33 (m, 1H), 2.35-2.42 (m, 1H), 3.37 (s, 1H), 4.47
(d, J = 5.2, 2H), 5.22 (d, J = 8.9, 1H), 5.48 (dd, J = 4.4, 5.9, 1H), 6.25 (d, J = 5.6, 1H), 6.44 (d, J
= 5.4, 1H), 7.18-7.27 (m, 4H), 7.33-7.43 (m, 2H), 7.80 (d, J = 8.1, 2H), 7.87 (d, J = 8.3, 2H);
13CNMR (CDCl3, 100 MHz) δ 10.6, 10.7, 11.6, 13.4, 14.0, 20.8, 22.2, 22.3, 26.4, 26.8, 28.5,
ACS Paragon Plus Environment

Page 19 of 31
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
10
1
12
13
14
15
16
17
18
19
20
21
2
23
24
25
26
27
28
29
30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
46
47
48
49
50
51
52
53
54
5
56
57
58
59
60
33.3, 35.0, 35.4, 35.6, 37.5, 37.9, 44.0, 44.9, 45.4, 60.1, 63.3, 72.0, 73.4, 73.6, 97.5, 98.2, 113.1,
128.1, 128.2, 129.2, 129.5, 129.9, 130.0, 132.0, 132.8, 135.9, 141.1, 165.3, 165.5, 170.8, 210.8;
LRMS (ESI) calcd for C41H49O8 [M+H]+ 669.34, found 669.29.
Synthesis of C-22 ketone 22.14 A flame dried flask was charged with DMSO (118 L, 1.65
mmol) in CH2Cl2 (8 mL) and cooled to -78C under argon atmosphere. TFAA (175 L, 1.24
mmol) was added to the solution dropwise and stirred for 45 minutes. To the reaction was added
C22-alcohol (21, 263 mg, 0.413 mmol) in CH2Cl2 (6 mL) via syringe over 4 minutes and the
reaction stirred another 50 minutes at -78C. Diisopropylethyl amine (456 L) was added to the
reaction and the temperature was allowed to warm to -30C over 1.5 h. TLC (3:7 EtOAc/Hexane,
Rf = 0.5) showed no starting material remaining and the reaction was quenched by adding brine.
The organic layer was separated and aqueous phase was extracted with CH2Cl2 (10 mL x 3). The
combined organics were dried over Na2SO4, concentrated and crude product was subjected to
flash column chromatography on neutral Al2O3 by using EtOAc-Hexane to provide C3, 22-
diketone (22), 187 mg, yield 68%. An X-ray structure was obtained which confirmed the singlet
oxygen Diels-Alder reaction proceeded with the desired stereochemistry.14 However, due to the
1
potential instability of the peroxide, this material was normally used immediately. H NMR (400
MHz, CDCl3) δ 1.01-1.23 (m, 10H), 1.28-1.34 (m, 1H), 1.50-1.56 (m, 1H), 1.64-1.73 (m, 2H),
1.78-1.87 (m, 3H), 1.94-2.09 (m, 5H), 2.35 (s, 7H), 3.05-3.14 (m, 1H), 4.32 (s, 1H), 4.38 (s, 1H),
5.04 (dd, J = 3.6, 3.3, 1H), 5.40 (dd, J = 4.7, 4.6, 1H), 6.15 (d, J = 5.8, 1H), 6.41 (d, J = 6.0, 1H),
7.12-7.19 (m, 4H), 7.28-7.34 (m, 2H), 7.63 (d, J = 8.2, 2H), 7.68 (d, J = 7.9, 2H); LRMS (ESI)
calcd for C41H47O8 [M+H]+ 667.32, found 667.28.
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 20 of 31
1
2
3
4
5
6
7
8
9
10
1
12
13
14
15
16
17
18
19
20
21
2
23
24
25
26
27
28
29
30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
46
47
48
49
50
51
52
53
54
5
56
57
58
59
60
Synthesis of diol 23. To the C3,22-diketone (22) in CH2Cl2 (6 mL) were added activated Zn
powder18 (260 mg, 4 mmol) followed by AcOH (50 L). The mixture was stirred at roon
temperature for 2 h. After disappearance of starting material from TLC (1:1 EtOAc/Hexane, Rf =
0.3), NaHCO3 (aq. 10 mL) was added to quench the reaction. The organic layer was separated
and aqueous phase was extracted with CH2Cl2 (10 mL x 3). Combined organics were dried over
anhydrous Na2SO4, concentrated under reduced pressure and purified by chromatography on
1
silica gel to provide 23, 196 mg, yield 71%. H NMR (400 MHz, CDCl3) δ 1.00 (s, 3H), 1.04 (s,
2H), 1.17 (t, 3H), 1.22 (d, J = 6.5, 3H), 1.34-1.41 (m, 1H), 1.62-1.68 (m, 1H), 1.72 (s, 3H), 1.80-
1.86 (m, 3H), 1.95 (s, 3H), 1.98-2.07 (m, 2H), 2.12-2.27 (m, 3H), 2.45-2.57 (m, 2H), 3.02 (q,
1H), 3.78 (s, 1H), 4.75 (s, 1H), 4.81 (d, J = 10.7, 2H), 5.42 (dd, J = 3.8, 3.6, 1H), 5.73 (d, J = 5.8,
1H), 6.03-6.07 (m, 1H), 6.28 (d, J = 6.0, 1H), 7.34-7.38 (m, 4H), 7.46-7.52 (m, 2H), 7.92 (d, J =
8.2, 2H), 7.98 (d, J = 8.1, 2H); 13CNMR (CDCl3, 100 MHz) δ 10.8, 12.2, 14.2, 14.8, 21.0, 22.1,
26.0, 26.9, 28.7, 34.6, 35.9, 37.8, 37.9, 38.7, 44.4, 45.2, 46.1, 54.5, 60.3, 71.1, 75.7, 87.3, 88.6,
114.8, 128.4, 128.5, 128.9, 129.6, 129.7, 130.6, 132.9, 135.5, 137.7, 138.4, 139.6, 165.4, 165.6,
170.9, 211.2, 213.0; LRMS (ESI) calcd for C41H49O8 [M+H]+ 669.34, found 669.30.
Synthesis of methoxy ketal 24. To the C14, 16 diol (23, 196 mg, 0.29 mmol) dissolved in dry
MeOH (5 mL) was added camphor sulfonic acid (CSA, 6.8 mg, 0.03 mmol) and the reaction was
stirred for 4 to 5 hours at room temperature. After ensuring the disappearance of starting material
from TLC (3:7 EtOAc/Hexane, Rf = 0.45), the solvent was evaporated under reduced pressure
and CH2Cl2 (30 mL) was added to the reaction and the mixture was washed with aq. NaHCO3 (5
mL), brine (10 ml) and dried over Na2SO4 and concentrated. The crude product was subjected to
chromatography (EtOAc-Hexane) on silica gel to provide 24, 181 mg in 75% yield. Data for
ACS Paragon Plus Environment

Page 21 of 31
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
10
1
12
13
14
15
16
17
18
19
20
21
2
23
24
25
26
27
28
29
30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
46
47
48
49
50
51
52
53
54
5
56
57
58
59
60
1
C3-ketone, 24: H NMR (400 MHz, CDCl3) δ 0.82-0.86 (m, 1H), 0.88-0.94 (m, 3H), 1.01 (s,
3H), 1.13 (d, J = 6.8, 3H), 1.20-1.30 (m, 3H), 1.37 (s, 3H), 1.40-1.47 (m, 1H), 1.52-1.63 (m, 1H),
1.76 (s, 3H), 1.85-1.92 (m, 1H), 1.95-2.01 (m, 2H), 2.04-2.10 (m, 1H), 2.17-2.22 (m, 3H), 2.24-
2.30 (m, 2H), 2.39-2.43 (m, 1H), 2.63-2.68 (q, 1H), 3.32 (s, 3H), 4.70 (d, J = 8.0, 2H), 5.10 (t, J
= 3.6, 1H), 5.23 (dd, J = 4.4, 4.0, 1H), 5.68 (dd, J = 4.6, 4.8, 1H), 7.38-7.44 (m, 4H), 7.49-7.54
13
(m, 2H), 7.97 (d, J = 8.2, 2H), 8.02 (d, J = 8.0, 2H); CNMR (CDCl3, 100 MHz) δ 8.5, 11.1,
15.0, 22.0, 27.4, 28.1, 33.6, 35.9, 37.7, 38.3, 42.7, 44.2, 45.8, 48.8, 51.8, 53.9, 69.8, 74.9, 91.4,
93.7, 109.8, 113.4, 119.9, 128.1, 128.2, 129.4, 129.6, 130.3, 131.0, 132.6, 141.2, 152.9, 165.5,
165.7, 210.9; LRMS (ESI) calcd for C42H51O8 [M+H]+ 683.35, found 683.31.
Data for C3-dimethylketal (24a)§: 1H NMR (400 MHz, CDCl3) δ 0.81 (s, 3H), 0.85-0.89 (m,
1H), 1.04-1.08 (m, 1H), 1.14 (d, J = 6.8, 3H), 1.19-1.28 (m, 6H), 1.35 (s, 3H), 1.43-1.48 (m, 1H),
1.60-1.63 (m, 1H), 1.77 (s, 3H), 1.80-1.85 (m, 1H), 1.92-1.97 (m, 2H), 2.02 (s, 2H), 2.40-2.45
(m, 2H), 2.55 (s, 1H), 2.63-2.68 (q, 1H), 3.08 (s, 3H), 3.15 (s, 3H), 3.32 (s, 3H), 4.70 (t, J = 3.5,
1H), 4.73 (d, J = 7.1, 2H), 5.10 (t, 1H), 5.24 (dd, J = 5.1, 5.0, 1H), 5.69 (dd, J = 5.0, 4.8, 1H),
13
7.38-7.44 (m, 4H), 7.50-7.54 (m, 2H), 7.98 (d, J = 8.2, 2H), 8.03 (d, J = 7.9, 2H); CNMR
(CDCl3, 100 MHz) δ 8.5, 11.3, 14.1, 14.9, 20.9, 22.0, 27.2, 27.6, 28.1, 28.3, 33.8, 34.6, 35.2,
36.1, 38.3, 41.8, 42.7, 47.3, 47.4, 48.8, 52.1, 53.9, 60.3, 69.8, 75.2, 91.4, 93.8, 99.9, 109.8, 113.4,
119.4, 128.1, 128.2, 129.4, 129.5, 130.3, 131.0, 132.5, 132.6, 141.2, 153.5, 165.5, 165.7; LRMS
(ESI) calcd for C44H57O9 [M+H]+ 729.40, found 729.37.
§ The C3-dimethylketal, 24a was easily converted to C3 ketone 24 by stirring (1-2 h) with a few
drops of water in CH2Cl2:MeOH and then subjected to the work-up procedure above.
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 22 of 31
1
2
3
4
5
6
7
8
9
10
1
12
13
14
15
16
17
18
19
20
21
2
23
24
25
26
27
28
29
30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
46
47
48
49
50
51
52
53
54
5
56
57
58
59
60
Asymmetric dihydroxylation 25. The olefin 24 (190 mg 0.278 mmol) was mixed with
K2OsO4 (2 mg, 0.0056 mmol 2 mol %), (DHQ)2PHAL (20 mg, 0.026 mmol, 5 eq. relative to
Osmium) and AD mix-α (390 mg). The reaction flask was placed in a 0C cooling bath and tert-
butyl alcohol-water (16 mL, 1:1) was added to the flask while stirring was continued for 40 h at
this temperature. The reaction was monitored by TLC (1:1 EtOAc/Hexane, Rf = 0.2) by
quenching (aq. NaHSO3) reaction mixture aliquots. After ensuring disappearance of starting
material, the reaction was quenched using aq. NaHSO3 (10 mL) and stirred at room temperature
for 1 h. The reaction mixture was extracted with EtOAc (15 mL) and CH2Cl2 (20 mL x 3), the
combined organic layer was washed with brine, dried over anhydrous Na2SO4 and concentrated.
The crude product was chromatographed on silica gel using EtOAc-Hexane followed by 2%
MeOH in CHCl3 to provide product 25§, 164 mg and yield 82%. The selectivity is 9.5:1, C25
1
epi-natural favor to ‘R’ configuration at C25. Data for C3-keto compound, 25: H NMR (400
MHz, CDCl3) δ 0.82-0.88 (m, 1H), 1.01 (s, 3H), 1.13 (d, J = 6.9, 3H), 1.15 (s, 2H), 1.17-1.20 (m,
1H), 1.22-1.24 (m, 2H), 1.24 (s, 3H), 1.25-1.26 (m, 1H), 1.27-1.31 (m, 1H), 1.36 (s, 3H), 1.42-
1.49 (m, 1H), 1.79-1.90 (m, 1H), 1.92-1.99 (m, 1H), 2.03 (s, 2H), 2.06-2.21 (m, 2H), 2.25-2.32
(m, 2H), 2.52 (s, 1H), 2.63 (q, 1H), 3.32 (s, 3H), 3.15 (s, 3H), 3.39 (s, 2H), 4.72 (t, J = 1.8, 1H),
5.03 (s, 1H), 5.21 (dd, J = 5.2, 4.9, 1H), 5.78 (d, J = 9.7, 1H), 7.40-7.44 (m, 4H), 7.52-7.56 (m,
2H), 7.98 (d, J = 8.2, 2H), 8.02 (d, J = 8.4, 2H); LRMS (ESI) calcd for C42H53O10 [M+H]+
717.36, found 717.33.
Data for C3-dimethylacetal (OMe)2 compound, 25a: 1H NMR (400 MHz, CDCl3) δ 0.81 (s,
3H), 0.85-0.91 (m, 1H), 1.04-1.10 (m, 1H), 1.12 (d, J = 6.9, 3H), 1.16 (s, 2H), 1.20-1.23 (m, 2H),
1.24-1.28 (m, 7H), 1.34 (s, 3H), 1.54-1.63 (m, 1H), 1.76-1.86 (m, 2H), 1.89-1.97 (m, 2H), 2.04
(s, 1H), 2.10-2.18 (m, 1H), 2.38 (br, 1H), 2.53 (s, 1H), 2.64 (q, 1H), 2.73 (br, 1H), 3.08 (s, 3H),
ACS Paragon Plus Environment

Page 23 of 31
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
10
1
12
13
14
15
16
17
18
19
20
21
2
23
24
25
26
27
28
29
30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
46
47
48
49
50
51
52
53
54
5
56
57
58
59
60
3.16 (s, 3H), 3.32 (s, 3H), 3.40 (s, 2H), 4.73 (t, 1H), 5.03 (s, 1H), 5.21 (dd, J = 5.1, 5.0, 1H), 5.78
(d, J = 10.8, 1H), 7.40-7.44 (m, 4H), 7.51-7.55 (m, 2H), 7.98 (d, J = 7.6, 2H), 8.03 (d, J = 7.9,
2H); 13CNMR (CDCl3, 100 MHz) δ 8.6, 11.3, 14.1, 14.7, 23.4, 27.2, 27.6, 28.1, 28.3, 29.6, 33.7,
34.6, 35.1, 36.1, 37.5, 41.8, 42.9, 47.3, 47.4, 48.8, 52.1, 53.8, 68.9, 70.1, 71.7, 75.3, 91.5, 93.8,
100.0, 109.9, 119.3, 128.1, 128.2, 129.4, 129.6, 130.1, 131.0, 132.5, 132.9, 153.5, 165.7, 166.2;
LRMS (ESI) calcd for C44H59O11 [M+H]+ 763.40, found 763.37.
§The selectivity is 9.5:1, C25 epi-natural favoring the ‘R’ configuration at C25, whereas, in
another case the selectivity is 3.8:1, C25 natural-epi when the ligand was (DHQD)2PYR and
Na2CO3, K3FeCN6, (see Table 1 in the manuscript).
Synthesis of benzoate 26. To the diol (25, 164 mg, 0.25 mmol) in CH2Cl2 (10 mL) were added
pyridine (2.5 mL), DMAP (5 mg, 0.025 mmol, 0.1 eq.) followed by benzoyl chloride (50 µL, 0.4
mmol, 1.5 eq.) under N2 at room temperature and stirred for 16 h. After ensuring the
disappearance of starting material via TLC (3:7 EtOAc/Hexane, Rf = 0.45), the solvent was
removed under reduced pressure, and the crude product was purified by column chromatography
1
on silica gel using EtOAc-Hexane to provide 26, 0.123 g in 88% yield. H NMR (400 MHz,
CDCl3) δ 0.77-0.84 (m, 3H), 0.98 (s, 3H), 1.12 (d, J = 6.5, 3H), 1.21 (t, 5H), 1.26 (s, 4H), 1.32
(s, 3H), 1.37-1.45 (m, 1H), 1.83-1.88 (m, 1H), 1.91-1.97 (m, 3H), 2.02-2.07 (m, 1H), 2.14-2.28
(m, 4H), 2.53 (br, 1H), 2.62 (q, 1H), 3.30 (s, 3H), 4.19 (d, J = 4.2, 1H), 4.70 (t, J = 2.8, 1H), 5.00
(t, J = 3.9, 1H), 5.18 (dd, J = 5.5, 5.0, 1H), 5.87 (d, J = 8.6, 1H), 7.34-7.42 (m, 6H), 7.46-7.54
(m, 3H), 7.94-8.02 (m, 6H); 13CNMR (CDCl3, 100 MHz) δ 8.5, 11.1, 14.1, 20.9, 23.8, 27.3, 28.0,
33.5, 35.9, 37.7, 37.8, 38.0, 44.2, 45.8, 48.8, 51.8, 53.4, 53.8, 60.3, 68.4, 70.7, 71.6, 74.9, 91.4,
93.7, 109.9, 119.8, 128.1, 128.2, 128.3, 129.4, 129.5, 129.6, 129.7, 129.8, 130.1, 130.9, 132.6,
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 24 of 31
1
2
3
4
5
6
7
8
9
10
1
12
13
14
15
16
17
18
19
20
21
2
23
24
25
26
27
28
29
30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
46
47
48
49
50
51
52
53
54
5
56
57
58
59
60
132.8, 133.0, 152.8, 165.7, 165.8, 166.2, 171.1, 211.0; LRMS (ESI) calcd for C49H57O11
[M+H]+ 821.39, found 821.35.
Synthesis of spiroketal 27.14 To 26 in CH2Cl2: MeOH (1:1, 10 mL) was added camphor
sulfonic acid (CSA, 6 mg) at room temperature and the reaction was stirred for 4 h. H2O (0.5
mL) was added and the reaction was stirred for another 1 h (to hydrolyze the C3-dimethylketal,
27a to C3-ketone 27). After removal of the solvent, the reaction was diluted by adding CH2Cl2
(10 mL) and H2O (5 mL) and extracted with CH2Cl2 (10 mL x 3). The combined organic layers
were dried over Na2SO4 and concentrated under reduced pressure. The crude product was
purified on silica gel column chromatography to provide 2714 (3:7 EtOAc/Hexane, Rf = 0.55),
0.101 g and yield 85%. 1H NMR (400 MHz, CDCl3) δ 0.87-0.94 (m, 1H), 1.02 (s, 3H), 1.11 (d, J
= 6.4, 3H), 1.23 (t, 3H), 1.30-1.36 (m, 3H), 1.38 (s, 3H), 1.42 (s, 3H), 1.46-1.51 (m, 1H), 1.81-
1.83 (m, 1H), 1.89-1.95 (m, 2H), 2.04-2.13 (m, 3H), 2.19-2.23 (m, 1H), 2.25-2.30 (m, 2H), 2.33-
2.37 (m, 1H), 2.60-2.65 (q, 1H), 4.33 (d, J = 11.0, 1H), 4.50 (d, J = 11.2, 1H), 4.82 (d, J = 2.2,
1H), 5.19 (dd, J = 4.9, 4.8, 1H), 5.38 (d, J = 7.7, 1H), 5.41 (t, J = 3.8, 1H), 7.37-7.45 (m, 7H),
7.50-7.56 (m, 2H), 7.95-8.0 (m, 3H), 8.06-8.10 (m, 3H); 13CNMR (CDCl3, 100 MHz) δ 8.3, 11.1,
14.1, 14.8, 21.0, 25.1, 27.3, 28.2, 28.4, 33.8, 35.9, 37.8, 37.9, 38.2, 44.3, 45.5, 45.9, 51.7, 54.7,
60.3, 70.1, 72.9, 75.5, 79.6, 89.3, 93.3, 116.4, 121.2, 128.2, 128.3, 128.4, 128.5, 129.3, 129.4,
129.7, 130.0, 130.6, 132.8, 132.9, 133.3, 152.6, 165.7, 166.3, 211.1; LRMS (ESI) calcd for
C48H53O10 [M+H]+ 789.36, found 789.32.
Synthesis of α-bromoketone 28. C3-ketone (27, 148 mg, 0.188 mmol) was dissolved in dry
THF (3 mL) under N2 and was cooled to -5C. Phenyltrimethylammonium tribromide (PTAB,
ACS Paragon Plus Environment

Page 25 of 31
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
10
1
12
13
14
15
16
17
18
19
20
21
2
23
24
25
26
27
28
29
30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
46
47
48
49
50
51
52
53
54
5
56
57
58
59
60
70.5 mg, 0.188 mmol, 1 eq.) was added to the reaction in one portion while stirring. In about 5
minutes, the orange solution turned cloudy, and then turned to a light red color. The reaction
mixture was stirred for an additional 15 minutes and then quenched with aq. NaHSO3. The
reaction was diluted and extracted with EtOAc (10 mL x 3). The combined organic layers were
washed with brine, dried over Na2SO4 and concentrated under reduced pressure. The crude
product was chromatographed on silica gel using EtOAc-Hexane to provide C2-bromide 28 (3:7
1
EtOAc/Hexane, Rf = 0.6), 142 mg in 84 yield %. H NMR (400 MHz, CDCl3) δ 0.93-1.00 (m,
1H), 1.11 (s, 8H), 1.24 (t, 1H), 1.30-1.36 (m, 1H), 1.38 (s, 3H), 1.42 (s, 3H), 1.44-1.50 (m, 1H),
1.57-1.66 (m, 1H), 1.74-1.87 (m, 2H), 2.04-2.11 (m, 1H), 2.29-2.38 (m, 2H), 2.39-2.44 (m, 2H),
2.54 (dd, J = 6.2, 6.4, 1H), 2.61 (q, 1H), 2.79 (br, 1H), 4.33 (d, J = 11.0, 1H), 4.59 (d, J = 10.9,
1H), 4.67 (dd, J = 6.0, 6.2, 1H), 4.80 (d, J = 2.3, 1H), 5.19 (dd, J = 5.1, 5.1, 1H), 5.38 (d, J = 7.3,
1H), 5.42 (t, 1H), 7.40-7.46 (m, 7H), 7.52-7.57 (m, 3H), 7.95-7.99 (m, 3H), 8.07-8.09 (m, 2H);
13CNMR (CDCl3, 100 MHz) δ 8.3, 11.8, 14.1, 14.8, 21.0, 25.1, 27.3, 27.6, 28.2, 33.4, 38.2, 39.0,
43.5, 45.6, 45.7, 50.8, 51.3, 53.7, 54.7, 60.3, 70.0, 73.0, 75.2, 79.6, 89.3, 93.2, 116.4, 121.5,
128.2, 128.3, 128.5, 129.3, 129.4, 129.7, 130.0, 130.5, 132.9, 133.3, 133.4, 152.0, 165.7, 166.1,
163.3, 200.4; LRMS (ESI) calcd for C48H52BrO10 [M+H]+ 867.27, found 867.23.
Synthesis of α-azidoketone 29. C2-bromide (28, 142 mg, 0.164 mmol) was dissolved in dry
nitromethane (12 mL, freshly distilled) under N2 and cooled in an ice-water bath. A clear
solution of tetramethyl guanidinium azide (TMGA, 103 mg, 0.66 mmol, 4.0 eq.) in nitromethane
(3 mL) was added to the reaction mixture dropwise. After five minutes, the cooling bath was
removed and the reaction was stirred at room temperature for 14 h. The reaction was quenched
by adding brine, diluted and extracted with EtOAc (15 mL x 3). The combined organics were
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 26 of 31
1
2
3
4
5
6
7
8
9
10
1
12
13
14
15
16
17
18
19
20
21
2
23
24
25
26
27
28
29
30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
46
47
48
49
50
51
52
53
54
5
56
57
58
59
60
dried (Na2SO4), and concentrated under reduced pressure at room temperature. The crude
product was subjected to chromatography on silica gel using EtOAc-Hexane to provide azide 29
(3:7 EtOAc/Hexane, Rf = 0.5) (C25 epi: natural, >9.5:1) favoring C25-epi, 110 mg and a yield of
1
81%. H NMR (400 MHz, CDCl3) δ 0.85-0.93 (m, 1H), 0.94-1.11 (s, 2H), 1.12 (s, 6H), 1.26 (t,
1H), 1.31-1.36 (m, 2H), 1.38 (s, 4H), 1.43 (s, 3H), 1.46-1.60 (m, 2H), 1.84-1.91 (m, 1H), 2.04-
2.13 (m, 1H), 2.19-2.27 (m, 1H), 2.30 (d, J = 4.2, 1H), 2.32-2.40 (m, 2H), 2.58-2.67 (q, 1H),
2.75 (br, 1H), 3.93 (dd, J = 6.3, 6.1, 1H), 4.33 (d, J = 10.9, 1H), 4.50 (d, J = 11.0, 1H), 4.80 (d, J
= 2.2, 1H), 5.19 (dd, J = 5.2, 5.0, 1H), 5.38 (t, 1H), 5.42 (s, 1H), 7.40-7.45 (m, 7H), 7.52-7.58
13
(m, 3H), 7.95-8.01 (m, 3H), 8.08-8.10 (m, 2H); CNMR (CDCl3, 100 MHz) δ 8.3, 12.1, 14.1,
14.8, 20.9, 25.1, 27.3, 27.6, 28.2, 33.3, 37.1, 38.2, 43.3, 44.8, 45.6, 46.8, 51.4, 54.7, 60.3, 63.5,
70.0, 73.0, 75.2, 79.6, 89.3, 93.2, 116.4, 121.5, 128.2, 128.3, 128.4, 128.6, 129.3, 129.4, 129.5,
129.7, 130.0, 130.5, 132.8, 132.9, 133.3, 152.0, 165.7, 166.1, 166.2, 171.0, 204.5; LRMS (ESI)
calcd for C48H52N3O10 [M+H]+ 830.36, found 830.33.
Pyrazine formation – C12, 12’, 23 & 26-tetra-O-Benzoyl protected 25-epi Ritterostatin
GN1N (31). To the mixture of North G aminomethoxime 30 (17 mg, 0.029 mmol, 1.2 eq.) and
North 1 azidoketone 29 ( 20 mg, 0.024 mmol, 1.0 eq.) in benzene (8 mL) were added polyvinyl
pyridine, PVP (37 mg) and dichlorodibutylstannane (catalytic) at room temperature. The reaction
flask was heated to 90C using a Dean-Stark trap and continued for 4 h at this temperature under
N2. TLC (3:7 EtOAc/Hexane, Rf = 0.4) showed the non-polar ketoazide was almost absent. The
reaction was filtered through a short plug of celite, the solvent was evaporated under reduced
pressure and the crude mass was purified by silica gel column chromatography using EtOAc-
Hexane to provide 31 (3:7 EtOAc/Hexane, Rf = 0.4), 18.3 mg in 58% yield. 1H NMR (400 MHz,
ACS Paragon Plus Environment

Page 27 of 31
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
10
1
12
13
14
15
16
17
18
19
20
21
2
23
24
25
26
27
28
29
30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
46
47
48
49
50
51
52
53
54
5
56
57
58
59
60
CDCl3): δ 0.83 (d, J = 6.7, 5H), 0.95 (d, J = 6.4, 2H), 1.11 (s, 9H), 1.25 (s, 1H), 1.26 (s, 3H),
1.34 (s, 3H), 1.39 (s, 3H), 1.42 (s, 7H), 1.65-1.74 (m, 8H), 1.92-2.01 (m, 6H), 2.02-2.07 (m, 1H),
2.10-2.20 (m, 3H), 2.32-2.40 (m, 2H), 2.46-2.64(m, 7H), 2.75-2.87 (m, 3H), 4.33 (d, J = 11.0,
1H), 4.49 (d, J = 11.0, 1H), 4.64 (dd, J = 4.4, 4.7, 1H), 4.82 (s, 1H), 4.96 (d, J = 8.2, 1H), 5.20
(dd, J = 5.2, 4.8, 1H), 5.39 (t, 1H), 5.44 (d, J = 2.1, 1H), 5.49 (d, J = 2.2, 1H), 7.40-7.46 (m, 8H),
7.52-7.56 (m, 4H), 7.95-8.05 (m, 6H), 8.09 (d, J = 8.1, 2H); 13C NMR (CDCl3, 100 MHz) δ 8.3,
11.6, 11.7, 14.0, 14.6, 14.8, 25.1, 26.4, 26.9, 27.1, 27.6, 27.8, 28.3, 29.1, 29.9, 33.1, 33.7, 34.9,
35.0, 35.8, 35.9, 37.1, 38.1, 41.1, 41.2, 41.3, 45.5, 51.4, 51.7, 54.6, 55.8, 70.1, 72.8, 75.7, 79.5,
81.3, 81.9, 84.1, 89.4, 93.3, 108.6, 116.3, 117.2, 121.0, 121.3, 128.2, 128.3, 128.5, 129.3, 129.4,
129.7, 130.1, 130.6, 130.7, 132.7, 132.8, 132.9, 133.2, 148.1, 148.2, 148.3, 148.4, 152.7, 155.7,
165.3, 166.1, 166.2; HRMS (ESI) calcd for C82H93N2O13 [M+H]+ 1313.6677, found 1313.6703.
Global deprotection of all OBz groups – Synthesis of 25-epi Ritterostatin GN1N, (5).9 C-12,
12’, 23, 26-tetra-O-benzoyl protected 25-epi ritterostatin GN1N (31, 15 mg, 0.0114 mmol) was
dissolved in 1.5 mL of THF/MeOH/H2O (2:2:1). NaOH (5.0 mg, 10 eq.) was added and the
reaction was stirred for 12 h at room temperature. The solvent was evaporated under reduced
pressure and the crude product was diluted, extracted with EtOAc (5 mL x 2) and CH2Cl2 (5 mL
x 4). Combined organics dried over Na2SO4, concentrated and crude product was purified by
flash chromatography on silica gel with 3% MeOH in CH2Cl2 to provide 5 as a colorless solid
(10.1 mg, 98%), m.p 222-225 C. Rf = 0.25 (2 % MeOH:EtOAc). 1H NMR (400 MHz, CDCl3): δ
0.83 (s, 3H), 0.85 (s, 3H), 0.87 (s, 1H), 0.95 (s, 1H), 0.97 (s, 1H), 0.99 (br, 2H), 1.06 (s, 6H),
1.09 (d, J = 6.8, 3H), 1.15 (s, 4H), 1.18 (s, 3H), 1.19 (s, 3H), 1.23-1.28 (t, 2H), 1.50-1.65 (m,
5H), 1.68-1.75 (m, 3H), 1.80-1.88 (m, 3H), 1.90-1.95 (m, 3H), 1.97-2.10 (m, 3H), 2.31-2.41 (m
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 28 of 31
1
2
3
4
5
6
7
8
9
10
1
12
13
14
15
16
17
18
19
20
21
2
23
24
25
26
27
28
29
30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
46
47
48
49
50
51
52
53
54
5
56
57
58
59
60
2H), 2.43-2.48 (m, 2H), 2.49-2.55 (m, 4H), 2.59 (d, J = 5.6, 1H), 2.60 (s, 1H), 2.63 (s, 1H), 2.78
(d, J = 4.8, 1H), 2.82 (d, J = 5.6, 1H), 2.85 (s, 1H), 2.90 (s, 1H), 3.24 (dd, J = 16.0, 7.8, 1H), 3.32
(m, 1H), 3.55 (d, J = 12.0, 1H), 3.62 (d, J = 12.0, 1H), 3.82-3.86 (m, 1H), 3.99 (br, 1H), 4.18 (m,
13
1H), 4.69 (s, 1H), 4.81 (s, 1H), 4.93 (d, J = 8.2, 1H), 5.35 (s, 1H), 5.39 (s, 1H); C NMR
(CDCl3, 100 MHz) δ 8.5, 11.6, 11.7, 11.9, 13.3, 13.9, 14.0, 20.6, 22.5, 24.4, 25.2, 27.7, 27.8,
27.9, 28.0, 28.2, 28.4, 28.7, 28.9, 29.1, 29.6, 29.8, 30.0, 31.5, 34.5, 35.9, 36.0, 37.1, 41.2, 45.3,
45.4, 52.0, 52.7, 54.7, 55.7, 67.9, 70.8, 75.0, 78.6, 81.9, 82.6, 84.2, 91.7, 92.7, 116.0, 117.4,
119.8, 120.6, 147.9, 148.3, 148.5, 148.6, 153.1, 156.9; HRMS (ESI) calcd for C54H77N2O9
[M+H]+ 897.5629, found 897.5615.
ASSOCIATED CONTENT
Supporting Information. Copies of all NMR (1H, 13C and 19F) spectra, x-ray data and NCI 60
cell line full data. This material is available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*Email: kanduluruak@yahoo.com, pfuchs@purdue.edu
Notes
The authors declare no competing financial interest.
ACKNOWLEDGEMENT
ACS Paragon Plus Environment

Page 29 of 31
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
10
1
12
13
14
15
16
17
18
19
20
21
2
23
24
25
26
27
28
29
30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
46
47
48
49
50
51
52
53
54
5
56
57
58
59
60
This research work was supported by the NIH (CA 60548) and in part by the Intramural
Research Program of NIH, National Cancer Institute, Center for Cancer Research. We sincerely
acknowledge Dr. Douglas Lantrip for technical support from the lab, Dr. Hui Cao for his initial
experiments on north 1 synthesis and thank Dr. Karl Wood and Arlene Rothwell of Purdue
University for mass spectral data.
REFERENCES
 (a) Pettit, G. R.; Inoue, M.; Kamano, Y.; Herald, D. L.; Arm, C.; Dufresne, C.; Christie, N. D.;
Schmidt, J. M.; Doubek, D. L.; Krupa, T. S. J. Am. Chem. Soc. 1988, 110, 2006–2007. (b)
Fukuzawa, S.; Matsunaga, S.; Fusetani, N. J. Org. Chem. 1995, 60, 608–614.
(2) NCI-60 data are available on the web at http://dtp.nci.nih.gov. Cephalostatin 1 is NSC-363979.
(3) (a) Jeong, J. U.; Sutton, S. C.; Kim, S.; Fuchs, P. L. J. Am. Chem. Soc. 1995, 117, 10157–10158.
(b) LaCour, T. G.; Guo, C.; Bhandaru, S.; Fuchs, P. L.; Boyd, M. R. J. Am. Chem. Soc. 1998,
120, 692–707. (c) Jeong, J. U.; Guo, C.; Fuchs, P. L. J. Am. Chem. Soc. 1999, 121, 2071–2084.
(d) Kim, S.; Sutton, S. C.; Guo, C.; LaCour, T. G.; Fuchs, P. L. J. Am. Chem. Soc. 1999, 121,
2056–2070.
(4) (a) Fortner, K. C.; Kato, D.; Tanaka, Y.; Shair, M. D. J. Am. Chem. Soc. 2010, 132, 275-280. (b)
Shi, Y.; Jia, L.; Xiao, Q.; Lan, Q.; Tang, X.; Wang, D.; Li, M.; Ji, Y.; Zhou, T.; Tian, W. Chem.
Asian. J. 2011, 6, 786-796.
(5) (a) Moser, R. J. Nat. Prod. 2008, 71, 487-491. (b) Flessner, T.; Jautelat, R.; Scholz, U.;
Winterfeldt, E. Fortschr. Chem. Org. Naturst. 2004, 87, 1-80. (c) Lee, S.; LaCour, T.G.; Fuchs,
P. L. Chem. Rev. 2009, 109, 2275-2314.
ACS Paragon Plus Environment