Studies Towards a Scalable Second-Generation Total
Synthesis of the Aplyronines as Novel Payloads for
Antibody-Drug Conjugates!
Nika Anžiček, Simon Williams, Michael P. Housden and Ian Paterson!
University Chemical Laboratory, Lensfield Road, Cambridge, CB2 1EW, UK!
E-mail: [email protected]!
1. Introduction
2. Retrosynthesis
O
•" The aplyronines (A-H) comprise a family of structurally complex and
extremely scarce marine macrolides isolated from the Japanese sea
hare Aplysia kurodai by Yamada.1"
Me2N
OH
O
7
O
OH
O
MeO
boron aldol, dehydration,
reduction
OMe
14
O
Yamaguchi
macrolactonisation
O
O
O
TESO
23
N
OH
C28−C34 side chain (B)
1
O
O
OMe
Ba(OH)2-mediated HWE
OMe
OAlloc
C15−C27 aldehyde (C)
C1−C14 phosphonate (A)
antibody
Cys
Aplyronine A-actin complex
tBu
BnO
O
O
Sn(OTf)2, Et3N
CH2Cl2, −78 °C
OTIPS
+
H
BnO
OH
21
88%, 9:1 dr
O
OTIPS
O
27
23
O
tBu
Si
O
OTIPS
H
Ba(OH)2-mediated HWE9
78% over 4 steps
tin(II)-mediated aldol7
(TS-I)
TBSO
PMP
O
CO2H
OH
O
O
OH
tBu
1
OTIPS
O
4. C15−C27 Aldehyde Synthesis
O
H
1. SmI2, EtCHO, −20 °C
2. TESOTf, 2,6-lutidine, −78 °C
3. DIBALH, −78 °C
3,4-syn
Ti(OiPr)Cl3, iPr2NEt
CH2Cl2, −78 °C
OBn
PMBO
21
82%, 12:1 dr
OH
O
OBn
27
23
titanium-mediated aldol reaction8
(TS-II)
improved dr and scalability
PMBO
OH
OTES
O
O
1. TCBC, Et3N, DMAP
(60% of 26m macrocycle)
2. Ti(OiPr)4, CH2Cl2
(1:3 26m : 24m)
3. HF (40% aq. sol.)
4. TESOTf, 2,6-lutidine
5. 4:1:1 THF:AcOH:H2O
42% over 5 steps
OBn
89%, >95:5 dr
1. DDQ
2. DIBALH, −78 °C
3. Dess−Martin
periodinane
52%
O
P(OMe)2
15
OMe
C15−C20 phosphonate (E)
O
PMBO
OTES
TESO
OMe
OBn
20
1. (S)-Me CBS catalyst,
BH3•SMe2, −20 °C
2. NaH, MeI
O
Ba(OH)2, 40:1 THF:H2O
27
15
88%, >95:5 E:Z
OTIPS
27
1
O
28
TES
O
15
OMe
•" lack of protecting group orthogonality
34
O
CHO
TES
TESO
O
27
Ba(OH)2-mediated HWE
Me
OAc
N
TES
TESO
1
O
O
27
3. Burgess reagent
4. [CuH⋅PPh3]6, wet PhH
56% over 4 steps
OMe
MeO
OTES
OBn
TESO
OMe
PMBO
H
OTES
stronger chelation of the electron-rich
OBn to the more Lewis-acidic titanium
leads to better selectivity of the aldol
H
PMBO
Me
Me
MeO
O
Me
TS-I
OBn
O
H
SnOTf
O
H
1. THF:AcOH:H2O (5:2:1)
2. DMP
90%
H
OTIPS
BnO
OAlloc
57%
O
TiLn
OMe
PMBO
OTES
27
H
O
15
OAlloc
OH
O
9
7
O
1
O
Me2N
R
O
O
OH
23
•" 29 steps LLS, 1.6% overall
(vs. Yamada 47 LLS, 0.39% yield)"
orthogonal protecting groups at C23, C25 and C27
MeO
Me
OAc
29
yield5
C15−C27 aldehyde (C)
Me
TS-II
O
Me2N
CHO
NMe2 , DCC,
HO
DMAP•HCl
R
3. HF•py, py
4. N,N,O-trimethylserine, TCBC
DMAP, Et3N
30% over 4 steps
H
34
1. Zn(BH4)2, 0 °C
2. O
OMe
C21−C27 aldehyde (D)
10 steps, 38% yield
1. LiDBB, −78 °C
2. allyl chloroformate,
CH2Cl2:pyr (1:1)
Me
OAc
N
23
OH
OBn
MeO
O
OTES
C28−C34 ketone (B)
23
PMB
OTES
21
91%, >95:5 dr
PMBO
O
1. (COCl)2, DMSO, Et3N
2. cHex2BCl, Et3N, −78 °C
O
27
H
O
+
P(OEt)2
H
O
20
TESO
14
tBu
Si
O
1,4-syn
TESO
O
45% over 6 steps
14
MeO
P(OMe)2
Ba(OH)2
40:1 THF:H2O
OTBS
O
27
23
O
20
PMP
1
O
15
78% over 5 steps
+
OTES
15
H
3. First-Generation Total Synthesis
S
•" An efficient and scalable total synthesis is required to access viable quantities of suitably
modified aplyronines incorporating a linker for conjugation to selected antibodies."
O
PMBO
27
P(OMe)2
14
O
CHO
34
OTBS
OTES
CHO
34
•" The aplyronine side chain intercalates into a hydrophobic cleft of actin with both amino acid
residues protruding into the bulk solvent region.4 This allows for attachment to antibodies
through amino acid modification without foreseeable loss of actin binding ability."
PMBO
Me
OAc
N
OTES
27
14
NMe2
28
1
O
O
DMGly =
NMe2
TES
TESO
N
n
O
DMAla =
NMe2
O
OMe
O
TMSer =
Me
OAc
29
23
MeO
H
C1−C27 macrocyclic alcohol
1
O
N
O
MeO
Me2N
O
Aplyronine A1 R1 = TMSer R2 = DMAla
Aplyronine C1 R1 = H
R2 = DMAla
Aplyronine D1 R1 = TMSer R2 = DMGly
Me
OAc
34
alkylation
MeO
O
R2O
OH
27
•" It forms an unprecedented heterotrimeric complex with its cellular
targets, cytoskeletal proteins actin and tubulin, disrupting cell
division. This novel dual mode of action makes it an exciting
payload candidate for a new class of antibody-drug conjugates for
targeted cancer chemotherapy.4"
MeO
O
23
•" Aplyronine A exhibits potent biological activity in vivo2 and picomolar
cancer cell growth inhibition against the NCI 60 cell line panel.3"
Aplysia kurodai
1
OR1
HO
N
34
CHO
R = Me Aplyronine A
R = H Aplyronine D
OMe
• first total synthesis of aplyronine D
esterification occurs exclusively on the C7 alcohol in the challenging final step
5. C1−C14 Phosphonate Synthesis
3,4-anti
PMBO
O
O
+
CO2Me
cHex
2BCl, Et3N
Et2O, 0 °C
PMBO
O
11
H
86% over 4 steps
6. Completion of the Macrocycle and Conclusions
1
OH
CO2Me
TESO
7
87%, >95:5 dr
OTES
1,4-syn
85%
1. SmI2, EtCHO, −20 °C
2. PPh3, PhOH
3. K2CO3, MeOH
14
O
OTES
1. TESOTf, 2,6-lutidine, −78 °C
2. DDQ, CH2Cl2−pH 9.2 buffer (4:1)
2. I2, PPh3, imid.
O
OH
H
O
OTBS
75%
OMe
OTES
PMB
OTBS
CO2H
OH
O
OTES
O
14
P(OEt)2
C1−C14 phosphonate (A)
Me
H
Me
H
1. NaH, MeI
2. DDQ, 1:1 DCM:pH 7 buffer
3. NaClO2, NaH2PO4⋅H2O,
2-methyl-2-butene, H2O, tBuOH
TES
TESO
O
OTBS
PMB
O
OTES
OAlloc
formyl
H-bond
O
1
O
(R)-Me CBS catalyst,
BH3•SMe2, −5 °C
OMe
TES
TESO
NaH, nBuLi, HMPA, 0 °C
85%
I
14
O
15
OAlloc
TESO
1
11
OAlloc
37% (99% BRSM)
O
P(OEt)2
OTES
Ba(OH)2,
40:1 THF:H2O
OMe
PMBO
TESO
OAlloc
O
67%
97%
+
O
OH
OMe
I
1. DIBALH, −78 °C
2. TBSOTf, 2,6-lutidine, −78 °C
OTES
27
P(OEt)2
O
27
PMBO
O
OTBS
PMB
1
O
OTES
TES
TESO
1
boron-mediated aldol reaction
(TS-III)
TESO
OTBS
c-Hex
O
MeO
OMe
HO
B
O
c-Hex
1. TCBC, Et3N, DMAP
2. Pd(PPh3)4, dimedone
H
TS-III
O
OMe
•" synthesised multi-gram quantities of the C21−C27
aldehyde (D) via the revised route, successfully
substituting the tin(II) for titanium(IV) aldol"
TES
TESO
1
O
O
OTES
27
7. References
1
2
3
4
5
6
7
8
9
(a) Yamada, K.; Makoto, O.; Ishigaki, T.; Yoshida, Y. J. Am. Chem. Soc. 1993, 115, 11020; (b) Yamada, K.; Ojika, M.; Kigoshi, H.; Suenaga, K. Nat. Prod. Rep. 2009, 26, 27; (c) Ojika. M.; Kigoshi, H.; Suenaga, K.; Imamura, Y.; Yoshikawa, K.; Ishigaki, T.; Sakakura A.; Mutou, T.; Yamada, K. Tetrahedron 2012, 68, 982"
(a) Ojika, M.; Kigoshi, H.; Yoshida, Y.; Ishigaki, T.; Nisiwaki, M.; Tsukada, I.; Arakawa, M.; Ekimoto, H.; Yamada, K. Tetrahedron 2007, 63, 3138 "
Dr David Newman, NCI, personal communication to Prof Ian Paterson"
(a) Saito, S.; Watabe, S.; Ozaki, H. J. Biochem. 1996, 120, 552; (b) Hirata, K.; Muraoka, S.; Suenaga, K.; Kuroda, T.; Kato, K.; Tanaka, H.; Yamamoto, M.; Takata, M.;
Yamada, K.; Kigoshi, H. J. Mol. Biol. 2006, 356, 945; (c) Kuroda, T.; Suenaga, K.; Sakakura, A.; Handa, T.; Okamoto, K.; Kigoshi, H. Bioconjug. Chem. 2006, 17, 524;
(d) Kita, M.;
Hirayama K.; Yoneda, K.; Yamagishi, K.; Chinen, T.; Usui, T.; Sumiya, E.; Uesugi; Kigoshi, H. J. Am. Chem. Soc. 2013, 135, 18089"
(a) Paterson, I.; Fink, S. J.; Lee, L. Y. W.; Atkinson, S. J; Blakey, S. B. Org. Lett. 2013, 15, 3118 (b) Williams S., Paterson, I., manuscript in preparation"
(a) Paterson, I.; Woodrow, M. D.; Cowden, C. J. Tetrahedron Lett. 1998, 39, 6041; (b) Paterson, I.; Cowden, C. J.; Woodrow, M. D. Tetrahedron Lett. 1998, 39, 6037"
Paterson, I.; Tillyer, R. D. Tetrahedron Lett. 1992, 33, 4233"
Solsona, J. G.; Nebot, J.; Romea, P.; Urpí, F. J. Org. Chem. 2005, 70, 6533"
Paterson, I.; Yeung, K.-S.; Smaill, J.B. Synlett. 1993, 774"
23
MeO
OH
•" altered the protecting group strategy to enable sitespecific macrolactonisation and convergence on to a
known intermediate"
OMe
known intermediate from the
first-generation route
O
Me
OAc
N
known endgame5
28
aplyronine A, C, D
•" prepared the C15−C20 phosphonate (E) using a highly
enantioselective pig liver esterase mediated
desymmetrisation on 15 g scale"
34
CHO
•" future work will involve completion of the secondgeneration total synthesis, synthesis of macrocycle
analogues and investigation of linker strategies to
produce ADCs
We thank Drs Cam Cowden, Michael Woodrow, Simon Blakey, Lydia Lee, Stephen Atkinson and Sarah Fink for their contributions to the first-generation total synthesis
of the aplyronines; the EPSRC for support and the National Mass Spectrometry Facility for providing mass spectroscopy data; the Slovene Human Resources
Development and Scholarship Fund (NA), the Todd–Raphael Scholarship (SW) and the Isaac Newton–Mays Wild Fellowship from Downing College (MPH)."