Robust asymmetric synthesis of unnatural alkenyl amino acids for conformationally constrained α-helix peptides

Article abstract of DOI:10.1039/c4ob01832j

The efficient asymmetric synthesis of unnatural alkenyl amino acids required for peptide 'stapling' has been achieved using alkylation of a fluorine-modified Ni^II Schiff base complex as the key step.

Full text of DOI:10.1039/c4ob01832j

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ARTICLE TYPE
Robust Asymmetric Synthesis of Unnatural Alkenyl Amino Acids for
Conformationally Constrained αꢀHelix Peptides
Boris Aillard,a Naomi S. Robertson,a Adam R. Baldwin,a Siobhan Robinsa and Andrew G. Jamieson*a
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
5
The majority of research in this area focuses on the regulation of
50 αꢀhelixꢀmediated proteinꢀprotein interactions (PPIs). A plethora
of synthetic approaches have therefore been developed to
promote αꢀhelical structure in peptides. Examples include:
triazole bridge,3 lactam bridge,4 hydrogen bond surrogates,5
disulphide bridges,6 electrostatic interaction between side chains,7
55 and incorporation of α,αꢀdisubstituted amino acids.8 Blackwell
and Grubbs developed an i, i+4 crossꢀlinked peptide via cross
metathesis of Oꢀallyl functionalised residues.9
Verdine and coꢀworkers expanded this method through the
develop of an all hydrocarbon peptide “staple”, determining the
60 optimal chain length of αꢀmethyl αꢀdisubstituted unnatural amino
acids bearing alkenes for i, i+3, i, i+4, and i, i+7 staples.10 These
hydrocarbon stapled peptides were found to exhibit increased αꢀ
helicity and resistance to proteolysis.11
Recent literature suggests that peptides stapled with monoꢀ
65 substituted alkenyl amino acids can demonstrate similar
improvements in αꢀhelicity and proteolytic stability as their αꢀ
methyl αꢀdisubstituted counterparts. 12,13
During our research into the design and synthesis of peptide
conformational constraints we required unnatural alkenyl αꢀ
70 methyl αꢀamino acids 1 & 2 (Figure 1). The synthesis of these
amino acids has previously been achieved by alkylation of
alanineꢀderived oxazinones.14 We disregarded this method due to
the potential for overꢀreduction of the olefin moiety during the
required metal reduction step. 15
The efficient asymmetric synthesis of unnatural alkenyl
amino acids required for peptide ‘stapling’ has been achieved
using alkylation of a fluorineꢀmodified NiII Schiff base
complex as the key step.
10 Introduction
The asymmetric synthesis of enantiomerically pure unnatural αꢀ
amino acids using chiral auxiliaries or catalysts is an important
field of bioꢀorganic chemistry. These amino acids provide the
starting materials required to generate peptidomimetic tools for
15 the investigation of protein form and function. Conformationally
constraining peptides to adopt the appropriate bioactive
conformation decreases the entropic penalty of folding and can
provide enhanced binding affinity to target receptors.1 Employing
synthetic, unnatural functionality as the constraining moiety has
20 also been demonstrated to provide a range of other favourable
physicochemical and pharmacological properties including
improved stability toward peptidase degradation, increased
bioavailability and membrane permeability.2 Conformationally
constrained peptides have thus come of age as tools for chemical
25 biology and drug discovery.
30
35
40
75 Belekon and coꢀworkers have developed a more convenient
method for the synthesis of αꢀmethyl αꢀdisubstituted amino acids
that involves αꢀCꢀalkylation of chiral NiII Schiff base complexes
derived from alanine. However, in our hands the key alkylation
step gave low yield (42%) and poor diastereoselectivity (72%
80 d.e.). The diastereoselectivity of this reaction originates from the
benzylproline moiety that sterically hinders one face of the
complex. Attempts to increase selectivity have thus focused on
modification of the benzylproline functionality within the NiII
Schiff base complex. Introduction of the sterically bulky
85 naphthylmethyl16 or 2,4,6ꢀtrimethylbenzyl17 functionality are
reported to result in either poor chemical yield or complexes with
limited solubility. Introduction of halogens onto the aromatic ring
of the Nꢀbenzylproline moiety have been more successful in
enhancing diastereoselectivity.18 The aim of this work was to
90 develop a robust asymmetric synthesis of enantiopure unnatural
alkenyl amino acids required for peptide stapling.
45
Figure 1. (S)ꢀAlkenyl αꢀmethyl αꢀamino acids required for i, i+4
and i, i+7 peptide conformational constraints.
Here we report the use of NiII Schiff base complexes, derived
from a 2ꢀfluorobenzyl ligand18 for the diastereoselective synthesis
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of four alkenyl amino acids required for i ꢀ i + 4 and i ꢀ i + 7
peptide hydrocarbon staples.
diastereoselectivity (>95:5 d.r.) (Scheme 2, entry 1). Under the
60 same reaction conditions, (S)ꢀNiꢀGlyꢀ2FBPB 5 also underwent
efficient, stereoselective alkylation with 8ꢀbromooctene (Scheme
2, entry 2). The αꢀproton of the amino acid of the glycine derived
Schiff base moiety has a pKa of around 11 and can be
deprotonated relatively easily under basic reaction conditions.
The method is notable for the high diastereoselectivities of the
alkylation reactions and the fluorinated substituent in the NiII
Schiff base complexes facilitate purity and d.e. analysis by 19F
NMR. Insights into the origin of the diastereoselectivity were
5
observed from the Xꢀray crystal structure of the alkylated NiII 65 The second αꢀproton has a pKa of around 15 and so is more
Schiff base complex 9.
difficult to deprotonate, however is labile using these reaction
conditions. Addition of alkyl halide at room temperature
prevented formation of α,α−dialkylation product.
10 Results and discussion
Thus, the diastereomeric ratio of products obtained from these
Our initial aim was the efficient synthesis of the chiral auxiliary 70 reactions reflects the position of the thermodynamic equilibrium.
(S)ꢀNꢀ(2ꢀbenzoylphenyl)ꢀ1ꢀ(2ꢀfluorobenzyl)ꢀpyrrolidineꢀ2ꢀ
carboxamide 4 (2ꢀFBPB) from ꢀproline (Scheme 1).
15 Nꢀalkylation of ꢀproline with 2ꢀfluorobenzyl bromide gave
tertiary amine 3 in very good yield. Condensation of 3 with 2ꢀ
The nickel Schiff base complexes produced from these alkylation
reactions were isolated in diastereomerically pure form, as red
crystalline solids after flash column chromatography.
L
L
A further advantage of the 2ꢀFBPB ligand 4 is that 19F NMR
aminobenzophenone using methanesulfonyl chloride and Nꢀ 75 spectroscopy can be used to monitor both reaction progression
methylimidazole gave 2ꢀFBPB 4 in respectable yield given the
sterically cumbersome nature of the aniline nucleophile.
20 However, the enantiopurity of 2ꢀFBPB 4 was a disappointing
97% e.e. as determined by chiral HPLC and has not previously
and also diastereoselectivity and constitutes an extremely useful
tool functionality.
Alkylation of (S)ꢀNiꢀAlaꢀ2FBPB 6 with 5ꢀbromopentꢀ1ꢀene or 8ꢀ
bromopentꢀ1ꢀene was also found to be successful when the
been reported. We therefore undertook a slow recrystallisation to 80 enolate was formed at 0 oC and then alkylation at 50 oC to
enrich the desired enantiomer to >99% e.e. (see SI).
produce complexes 9 and 10 with good diastereoselectivity and
yield (Scheme 2, entries 3 & 4). The αꢀmethylꢀαꢀsubstituted
amino acid functionality produced during these alkylation
reactions lacks an αꢀproton and so no epimerisation can occur,
85 resulting in the kinetic diastereomer as the major product. (S)ꢀNiꢀ
Glyꢀ2FBPB 5 gives better diastereoselectivity in comparison with
(S)ꢀNiꢀAlaꢀ2FBPB 6 in part, due to increased temperature of the
alkylation reaction required for the latter.
25
30
35
90
95
Scheme 1. Reagents and conditions: i. 2ꢀfluorobenzylbromide,
i
40 KOH, PrOH, 93%; ii. 2ꢀaminobenzophenone, 1ꢀMeꢀimidazole,
MsCl, CH2Cl2, 50 oC, 55%; iii. glycine (5) or
ꢀalanine (6),
L
Ni(NO3)2, KOH, MeOH, 70 oC.
Entry
Initial
complex
Alkyl
bromide
5ꢀBrꢀpentene
8ꢀBrꢀoctene
5ꢀBrꢀpentene
8ꢀBrꢀoctene
Product
Isolated
yield
83%
72%
62%
d.r
Complexation of 4 with nickel nitrate and either glycine or Lꢀ
1
2
3
4
5
5
6
6
7
8
9
>95:5
>95:5
88:12
89:11
45 alanine under basic conditions gave a thermodynamic mixture of
diastereomers of nickel Schiff base complexes (S)ꢀNiꢀGlyꢀ2FBPB
5 and (S)ꢀNiꢀAlaꢀ2FBPB 6, respectively, in excellent yield as red
crystals that could be stored in air without any significant
decomposition (Scheme 1).
10
42%
100
Scheme 2. Reagents and conditions: i. Br(CH2)nCH=CH2, NaOH,
DMF, 0 oC to RT (R = H) or 50 oC (R = Me). Alkylation of chiral
complexes 5 and 6 (d.r was determinated by 19F NMR on crude
materials).
50
With the nickel Schiff base complexes 5 and 6 in hand, we turned
our attention to asymmetric alkylation reactions with the
appropriate electrophiles to provide the desired alkenyl amino
acids required to synthesise stapled peptides.
105
The absolute stereochemistry of complexes 7, 8 and 9 were
determined from the xꢀray crystal structures (Figure 2 and SI).
The crystal structure also gives an insight into the origin of the
asymmetric induction. The 2ꢀFꢀbenzyl moiety is positioned
55 Stereoselective alkylation of (S)ꢀNiꢀGlyꢀ2FBPB
5 through
formation of the enolate using sodium hydroxide as base
followed by nucleophilic substitution reaction with 5ꢀ
bromopentene gave complex 7 in excellent isolated yield and
110 across the Reꢀface of the complex and sterically restricts access to
the electrophile, forcing reaction from the Siꢀface of the complex
2
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to give the 2S configuration at the amino acid αꢀcarbon. It has
been proposed that an interaction between the halide atom and the
central Niꢀatom constrains the complex,19 however the distance
between these two atoms in the crystal structure of complex 9
(3.1 Å) exactly matches the sum of the VanꢀderꢀWaals radii and
suggests that no such attractive interaction exists in the solid
state. Our preferred explanation for the increase in
diastereoselectivity using the 2ꢀFBPB ligand, over the BPB
ligand is a displaced πꢀ π stacking interaction between the Nꢀ
10 benzyl functionality and the proline amide bond that constrains
the complex. The fluorine atom creates a dipole with positive
charge situated on the aromatic that may interact with ionised
amide bond oxygen and so will facilitate this interaction.
50
5
Alkylated
complex
Amino
acid
11
12
13
Yield
Fmocꢀ
AA
15
16
1
Yield
7
8
9
60%
67%
65%
68%
65%
63%
82%
62%
10
14
2
55
Scheme 4. Reagents and conditions: i. 3 M HCl/MeOH; ii.
FmocꢀOSu, K2CO3, dioxane/H2O. Decomposition of alkylated
complexes 7ꢀ10 to amino acids 11ꢀ14 and Fmoc protection to
compounds 1ꢀ2, 15ꢀ16.
O
F
Ni
O
Me
R
N
N
N
O
RꢀBr
RꢀBr
O
O
F
F
O
O
H
NaOH
Ni
60 Conclusions
N
Ni
N
(S, S)
Me
N
N
Me
N
N
O
O
In summary, the outlined method enabled the diastereoselective
synthesis of a range of enantiopure unnatural alkenyl amino acids
required for peptide stapling in six steps from proline in up to
17% yield.
O
F
O
R
6
Ni
N
N
Me
N
O
65 Incorporation of a fluorine atom on the chiral ligand of the nickel
Schiff base complex increases diastereoselectivity of the key
alkylation reactions and also facilitates chiral analysis by 19F
NMR. Moreover, we observed that the directing effect of the key
alkylation step is the result of the electrophile approaching the
70 enolate complex from the opposite face of the proline Nꢀbenzyl
moiety. These features make this method applicable to the largeꢀ
scale synthesis of custom α,αꢀdisubstituted amino acids. Efforts
to establish inꢀdepth structural understanding of the role played
by the fluorine atom on diastereoselectivity are currently under
75 active investigation in our laboratories. We are also currently
using this method to synthesis other α,αꢀdisubstituted amino
acids to develop new peptide conformational constraints.
(S, R)
15 Scheme 3. Deprotonation and alkylation pathway of 6.
20
25
30
Experimental
80 (S)ꢀ1ꢀ(2ꢀFluorobenzyl)pyrrolidineꢀ2ꢀcarboxylic acid (3)
LꢀProline (100.0 g, 869.0 mmol) was added to a solution of
potassium hydroxide (146.0 g, 2607.0 mmol, 3.0 equiv.)
dissolved in isopropyl alcohol (1.0 L) at 40 °C. 2ꢀFluorobenzyl
bromide (15.6 mL, 130 mmol, 1.0 equiv.) was added to the
85 solution drop wise. The solution was allowed to stir at 40 °C for
18 hours and progress was monitored by TLC (MeOH:CH2Cl2,
1:4). Aqueous hydrochloric acid (37%) was added drop wise to
the mixture until the solution reached pH 6–5 (as determined
using a pH probe). The suspension was then cooled in an ice bath,
90 filtered and the filtrate concentrated in vacuo to give (S)ꢀ1ꢀ(2ꢀ
fluorobenzyl)pyrrolidineꢀ2ꢀcarboxylic acid as a yellow solid
Figure 2. Crystal structure of compound 9 (hydrogen atoms have
35 been omitted from diagrams).
Alkylated complexes 7ꢀ10 were readily decomposed under acidic
conditions to give amino acids 11ꢀ14 and the chiral auxiliary 4.
40 Chiral ligand 4 was easily extracted from the crude mixture
(enantiomerically pure as assessed by chiral HPLC) and can be
reused, thus providing added value to this synthetic method.
Purification via ion exchange chromatography gave amino acids
11ꢀ14, which were subsequently treated with Fmoc succinimide
45 under mildly basic conditions to afford Fmoc protected amino
acids 1ꢀ2, 15ꢀ16 (Scheme 4).
(209.0 g, 93%). m.p: 78ꢀ80 oC (EtOH); [α]20 –24.1 (c 0.1 in
D
MeOH); 1H NMR (300 MHz; CDCl3) δ 8.42 (1H, br s, OH), 7.52
(1H, td, J = 7.5, 1.3 Hz, ArꢀCH), 7.35 (1H, m, ArꢀCH), 7.12 (1H,
95 t, J= 7.5 Hz, ArꢀCH), 7.08 (1H, t, J = 8.8 Hz, ArꢀCH), 4.37 (1H,
d, J = 13.5 Hz, NꢀCH2), 4.20 (1H, d, J = 13.5 Hz, NꢀCH2), 3.74
(1H, dd, J = 9.2, 6.3 Hz, αꢀCH), 3.59 (1H, ddd, J = 10.6, 6.9, 3.8
Hz, δꢀCH2), 2.85 (1H, dt, J= 9.3, 8.5 Hz, δꢀCH2), 2.39ꢀ2.13 (2H,
m, βꢀCH2), 2.06ꢀ1.81 (2H, m, γꢀCH2); 13C NMR (75 MHz;
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CDCl3) δ 171.9 (s), 163.0 (s), 132.8 (d), 131.4 (d), 124.8 (d),
119.4 (s), 115.9 (d), 67.3 (d), 53.5 (t), 50.9 (t), 29.0 (t), 23.0 (t).
Additional peaks arise from rotamers at 131.2, 119.2 and 115.6;
19F NMR (282 MHz; CDCl3) –116.3 (s); IR (νmax/cm–1, neat):
7.37 (1H, m, ArꢀCH), 7.33ꢀ7.23 (2H, m, ArꢀCH), 7.21ꢀ7.10 (2H,
m, ArꢀCH), 7.03 (1H, m, ArꢀCH), 6.87 (1H, d, J = 8.2 Hz, Arꢀ
CH), 6.76 (1H, t, J = 7.8 Hz, ArꢀCH), 4.52 (1H, d, J = 12.9 Hz,
NꢀCH2), 3.98 (1H, d, J = 12.9 Hz, NꢀCH2), 3.82 (1H, d, J = 20.3
5
3458, 3013, 2970, 1736, 1618, 1443, 1369, 1229, 1109, 898, 758; 70 Hz, CH2), 3.72 (1H, m, δꢀCH2), 3.70 (1H, d, J = 20.3 Hz, CH2),
HRMSꢀESI (calcd for C12H15NO2F [M+H]+) 224.1087, found
224.1091 (ꢁ = 1.8 ppm).
3.5 (1H, dd, J = 10.6, 5.9 Hz, αꢀCH2), 3.41 (1H, m, γꢀCH2), 2.71
(1H, m, βꢀCH2), 2.51 (1H, m, βꢀCH2), 2.24ꢀ2.06 (2H, m, δꢀCH2);
13C NMR (100 MHz, CDCl3) δ 181.0 (s), 177.9 (s), 171.7 (s),
142.5 (s), 134.6 (s), 134.3 (s), 133.3 (d), 132.3 (d), 131.5 (d),
75 131.4 (d), 129.8 (d), 129.7 (d), 129.4 (d), 126.3 (d), 125.7 (s),
125.3 (d), 124.6 (d), 121.0 (d), 120.4 (s), 116.3 (d), 116.0 (d),
70.1 (d), 61.3 (t), 57.3 (t), 55.8 (t), 30.7 (t), 23.7 (t); 19F NMR
(376 MHz; CDCl3) –113.6 (s).; IR (νmax/cm–1, neat): 2935, 2354,
1672, 1634, 1588, 1490, 1471, 1440, 1362, 1334, 1256, 1165,
(S)ꢀNꢀ(2ꢀBenzoylphenyl)ꢀ1ꢀ(2ꢀfluorobenzyl)pyrrolidineꢀ2ꢀ
10 carboxamide ((2S)ꢀFBPB) (4)
Methanesulfonyl chloride (1.0 mL, 13.4 mmol, 1.0 equiv.) was
added to
a solution of (S)ꢀ1ꢀ(2ꢀfluorobenzyl)pyrrolidineꢀ2ꢀ
carboxylic acid 3 (3.0 g, 13.4 mmol) and N-methylimidazole (2.4
mL, 29.6 mmol, 2.2 equiv.) in CH2Cl2 (30.0 mL) at 0 °C. After 5
15 minutes 2ꢀaminobenzophenone (2.4 g, 12.1 mmol, 0.9 equiv.) 80 1111, 1063, 962, 754, 723, 704.; HRMSꢀESI (calcd for
was added. The reaction mixture was heated to 50 °C for 12
hours, cooled and then saturated aqueous sodium hydrogen
carbonate solution (30.0 mL) was added. The two layers were
separated and the aqueous layer extracted with CH2Cl2 (3 x 30.0
20 mL). The combined organic layers were dried (MgSO4) and
concentrated in vacuo. Purification by flash column
chromatography (15% ethyl acetate/hexane) followed by a
recrystallisation with hexane and few drops of EtOAc gave the
C27H24N3O3F58Ni [M+H]+) 516.1233, found 516.1224 (ꢁ = –1.7
ppm); HPLC (ODꢀH column, hexane (50%)/iPrOH isocratic):
18.76 min. Xꢀrays: see SI.
85 (S)ꢀ({2ꢀ[1ꢀ(2ꢀFluorobenzyl)pyrrolidineꢀ2ꢀ
carboxamide]phenyl}phenylmethylene)ꢀ(S)ꢀalaninatoꢀ
N,N′,N″,O}nickel(II) and (S)ꢀ({2ꢀ[1ꢀ(2ꢀ
Fluorobenzyl)pyrrolidineꢀ2ꢀ
title compound as a pale yellow crystals (2.7 g, 55%). m.p: 88ꢀ90
carboxamide]phenyl}phenylmethylene)ꢀ(R)ꢀalaninatoꢀ
90 N,N′,N″,O}nickel(II) (NiꢀAlaꢀ2ꢀFBPB) (6)
30
25 oC (hexane/EtOAc); [α]D
–125.1 (c 0.25, MeOH); 1H NMR
(300 MHz; CDCl3) δ 11.41 (1H, s, NH), 8.56 (1H, dd, J = 8.4,
1.0 Hz, ArꢀCH), 7.79ꢀ7.73 (2H, m, ArꢀCH), 7.61 (1H, td, J = 6.9,
1.1 Hz), 7.57ꢀ7.44 (5H, m, ArꢀCH), 7.15ꢀ7.04 (2H, m, ArꢀCH),
6.93 (1H, td, J = 7.4, 1.2 Hz, ArꢀCH), 6.80 (1H, td, J = 9.0, 1.2
Yield 98%, 99:1 d.r; m.p: 284ꢀ286 °C (hexane/EtOAc) (lit: 283ꢀ
285 oC)18; [α]D20 + 3664.5 (c 0.05 in CHCl3) (lit: + 3126.6 (c 0.05
in CHCl3)18; 1H NMR (400 MHz, CDCl3) δ 8.33 (1H, td, J = 7.3
Hz, ArꢀCH), 8.13 (1H, dd, J = 8.6 Hz, ArꢀCH), 7.53ꢀ7.49 (2H m,
30 Hz, ArꢀCH), 3.89 (1H, d, J = 13.3 Hz, NꢀCH2), 3.73 (1H, dd, J = 95 ArꢀCH), 7.46 (1H, m, ArꢀCH), 7.27ꢀ7.20 (2H, m, ArꢀCH), 7.20ꢀ
13.3, 1.2 Hz, NꢀCH2), 3.36 (1H, dd, J = 10.2, 4.7 Hz, αꢀCH), 3.24
(1H, m, βꢀCH2), 2.48 (1H, m, βꢀCH2), 2.25 (1H, m, δꢀCH2), 1.96
(1H, m, δꢀCH2), 1.89ꢀ1.73 (2H, m, γꢀCH2).; 13C NMR (75 MHz;
CDCl3) δ 197.8 (s), 174.3 (s), 139.0 (s), 138.6 (s), 133.2 (d),
7.13 (2H,m, ArꢀCH), 7.06 (1H, ddd, J = 9.8, 8.2 Hz, ArꢀCH),
6.96 (1H, m, ArꢀCH), 6.71ꢀ6.63 (2H, m, ArꢀCH), 4.41 (1H, dd, J
= 12.9, 1.2, NꢀCHH), 3.91 (1H, q, J = 7.0 Hz, αꢀC(Me)H), 3.83
(1H, dd, J = 12.9, 0.8, NꢀCHH), 3.70 (1H, m, β(Pro)ꢀCHH), 3.55ꢀ
35 132.4 (d), 131.6 (d), 130.0 (d), 128.9 (d), 128.8 (d), 128.2 (d), 100 3.46 (2H, m, α(Pro)ꢀCH, γ(Pro)ꢀCHH), 2.38 (1H, m, δ(Pro)ꢀ
125.6 (s), 124.9 (s), 124.8 (s), 123.9 (d), 123.8 (d), 122.2 (d),
121.4 (d), 115.2 (d), 114.9 (d), 67.9 (d), 53.7 (t), 52.0 (t), 31.0 (t),
24.2 (t); 19F NMR (376 MHz; CDCl3) –117.5 (s); IR (νmax/cm–1,
neat): 3276, 1682, 1647, 1577, 1512, 1444, 1286, 1266, 1102,
CHH), 2.57 (1H, m, δ(Pro)ꢀCHH), 2.22 (1H, m, γ(Pro)ꢀCHH),
2.07 (1H, m, β(Pro)ꢀCHH), 1.58 (3H, d, J = 7.0 Hz, CH3); 13C
NMR (100 MHz, CDCl3) δ 180.4 (s), 180.1 (s), 170.3 (s), 142.1
(s), 134.2 (d), 133.5 (s), 133.2 (d), 132.1 (d), 129.7 (d), 128.9 (d),
40 923, 768, 697; HRMSꢀESI (calcd for C25H24N2O2F [M+H]+) 105 127.5 (d), 127.2 (d), 126.6 (s), 124.5 (d), 123.9 (d), 120.8 (d),
403.1822, found 403.1825 (ꢁ = 0.7 ppm); HPLC (ODꢀH column,
120.5 (s), 119.8 (s), 117.9 (d), 116.2 (d), 116.0 (d), 70.3 (d), 66.6
(d), 57.1 (t), 55.6 (t), 30.7 (t), 24.1 (t), 21.8 (q); 19F NMR (376
MHz, CDCl3) δ –113.9 (s); IR (νmax/cmꢀ1, neat) 1680, 1626, 1593,
1440, 1359, 1330, 1302, 1266, 1231, 1168, 1064, 7621, 748, 710,
110 682; HRMSꢀASAP (calcd for C28H27N3O3F58Ni [M+H]+)
hexane (5%)/iPrOH isocratic): 15.2 min. Xꢀrays: see SI.
General method of formation of GlyꢀNi or AlaꢀNi complexes
45 (5)ꢀ(6).
(S)ꢀNꢀ(2ꢀBenzoylphenyl)ꢀ1ꢀ(2ꢀfluorobenzyl)pyrrolidineꢀ2ꢀ
carboxamide (2ꢀFBPB) 4 (9.0 g, 22.4 mmol, 1.0 equiv.),
Ni(NO3)2.6H2O (13.0 g, 44.7 mmol, 2.0 equiv.) and glycine (3.4
g, 44.7 mmol, 2.0 equiv.) were dissolved in methanol (225.0 mL,
50 0.1 M) at 50 °C. Potassium hydroxide (8.8 g, 156.5 mmol, 7.0
equiv.) was added and the mixture was heated to 70 °C for 1
hour. The reaction mixture was cooled and then concentrated.
The resulting residue was taken up in water (200.0 mL) and
extracted with EtOAc (3 x 200.0 mL). The combined organic
530.1390, found 530.1397 (ꢁ = 1.3 ppm), (calcd for
C28H27N3O3F60Ni [M+H]+) 532.1344, found 532.1381 (ꢁ = 7.0
ppm); HPLC: ODꢀH column, hexane (50%)/iPrOH isocratic):
14.71 min. Xꢀrays: see SI.
115
General method of alkylation of (5)ꢀ(6) with alkyl bromides.
Freshly ground sodium hydroxide (0.54 g, 13.4 mmol, 4.0 equiv.)
o
was taken up in DMF (20.0 mL) with stirring at 0 C under an
55 layers were washed with saturated brine solution (3 x 600.0 mL), 120 atmosphere of nitrogen. (S)ꢀ({2ꢀ[1ꢀ(2ꢀFluorobenzyl)pyrrolidineꢀ
dried (MgSO4) and concentrated in vacuo to give the title
2ꢀcarboxamide]phenyl}phenylmethylene)ꢀglycinatoꢀ
compound as a red crystalline solid.
N,N′,N″,O}nickel(II) 5 (1.73 g, 3.4 mmol, 1.0 equiv.) was added
and stirred for 2 minutes; the solution darkened in colour and the
ice bath was removed. A solution of 1ꢀbromoꢀ4ꢀpentene (1.2 mL,
125 10.1 mmol, 3.0 equiv.) was added to reaction mixture. The
solution was left to stir for 15 minutes at room temperature (for
(S)ꢀ({2ꢀ[1ꢀ(2ꢀFluorobenzyl)benzyl)pyrrolidineꢀ2ꢀ
60 carboxamide]phenyl}phenylmethylene)ꢀglycinatoꢀ
N,N’,N’’,O}nickel (II) (NiꢀGlyꢀ2ꢀFBPB) (5)
o
o
Yield 94%; m.p: 124ꢀ126 C (hexane/EtOAc) (lit: 125ꢀ127 oC)18;
GlyꢀNiꢀ2ꢀFBPB 5), or for 1 h at 50 C (for AlaꢀNiꢀ2ꢀFBPB 6)
then quenched with the addition of water. The mixture was
concentrated in vacuo, taken up in water (20.0 mL) and extracted
[α]D +1897.9 (c 0.05, CHCl3) (lit: +1300.0 (c 0.05, CHCl3)18;
20
1H NMR (400 MHz, CDCl3) δ 8.40 (1H, dd, J = 7.8, 1.6 Hz, Arꢀ
65 CH), 8.35 (1H, d, J = 9.0 Hz, ArꢀCH), 7.63ꢀ7.50 (3H, m, ArꢀCH), 130 with dichloromethane (3 x 25.0 mL). The combined organic
4
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DOI: 10.1039/C4OB01832J
extracts were washed with aqueous lithium chloride solution (5%
v/v) (3 x 50.0 mL), brine (3 x 50.0 mL), dried (MgSO4) and
concentrated in vacuo. Purification by flash column
chromatography (EtOAc/hexane 1:1) gave the title compound as
a deep redꢀorange solid.
pentenylalaninatoꢀN,N’,N’’,O}nickel (II) (Niꢀαꢀpentꢀ4ꢀenyl
Alaꢀ2ꢀFBPB) (9)
20
Yield 62%; m.p: 190ꢀ192 °C (hexane/EtOAc); [α]D +2271.2 (c
1
0.05, CHCl3); H NMR (500 MHz, CDCl3) δ 8.29 (1H, td, J =
5
70 7.4, 1.0 Hz, ArꢀCH), 8.03 (1H, d, J = 8.5 Hz, ArꢀCH), 7.51ꢀ7.44
(2H, m, ArꢀCH), 7.38 (1H, m, ArꢀCH), 7.33 (1H, m, ArꢀCH),
7.29 (1H, m ArꢀCH), 7.20 (1H, t, J = 7.4 Hz, ArꢀCH), 7.16 (1H,
ddd, J = 8.4, 6.2, 2.2 Hz, ArꢀCH), 7.06 (1H, t, J = 9.1 Hz, Arꢀ
CH), 6.97 (1H, d, J = 7.6 Hz, ArꢀCH), 6.68ꢀ6.61 (2H, m, ArꢀCH),
75 5.86 (1H, ddt, J = 17.0, 10.3, 6.5 Hz, CH=CH2), 5.08 (1H, dd, J =
(S)ꢀ({2ꢀ[1ꢀ(2ꢀFluorobenzyl)benzyl)pyrrolidineꢀ2ꢀ
carboxamide]phenyl}phenylmethylene)ꢀ(S)ꢀ
pentenylglycinatoꢀN,N’,N’’,O}nickel (II) (Niꢀαꢀpentꢀ4ꢀenyl
10 glyꢀ2ꢀFBPB) (7)
o
20
Yield 83%; m.p: 170ꢀ172 C (hexane/EtOAc).; [α]D +2813.2 (c
0.05 in CHCl3) (lit: +2172 (c 0.1, MeOH, 25 oC)20; 1H NMR (400
MHz, CDCl3) δ 8.31 (1H, t, J = 6.7 Hz, ArꢀCH), 8.18 (1H, d, J =
8.6 Hz, ArꢀCH), 7.57ꢀ7.41 (3H, m, ArꢀCH), 7.32ꢀ7.20 (2H, m,
17.0, 1.0 Hz, CH=CH2cis), 5.02 (1H, d, J = 10.3 Hz,
CH=CH2trans), 4.52 (1H, d, J = 13.1 Hz, NꢀCHH), 3.95 (1H, d, J
= 13.1 Hz, NꢀCHH), 3.60 (1H, dd, J = 9.9, 6.5 Hz, α(Pro)ꢀCH),
3.41 (1H, dd, J = 10.7, 6.4 Hz, δ(Pro)ꢀCHH), 3.26 (1H, m,
15 ArꢀCH), 7.16 (2H, t, J = 7.0 Hz, ArꢀCH), 7.05 (1H, t, J = 8.8 Hz, 80 β(Pro)ꢀCHH), 2.78 (1H, m, γ(Pro)ꢀCHH), 2.52 (1H, m, γ(Pro)ꢀ
ArꢀCH), 6.92 (1H, d, J = 7.0 Hz, ArꢀCH), 6.72ꢀ6.60 (2H, m, Arꢀ
CH), 5.72 (1H, tdd, J = 13.3, 5.9, 4.3 Hz, CH=CH2), 5.06ꢀ4.91
(2H, m, CH=CH2), 4.44 (1H, d, J = 12.9 Hz, NꢀCH2), 3.91 (1H,
dd, J = 7.6, 3.3 Hz), 3.85 (1H, d, J = 12.9 Hz, NꢀCH2), 3.61ꢀ3.40
CHH), 2.40 (1H, m, γꢀCHH), 2.17ꢀ1.98 (5H, m, δꢀCH2, γꢀCHH,
δ(Pro)ꢀCHH, β(Pro)ꢀCHH), 1.75ꢀ1.62 (2H, m, βꢀCH2), 1.23 (3H,
s, CH3); 13C NMR (126 MHz, CDCl3) δ 182.3 (s), 180.1 (s),
172.4 (s), 141.5 (s), 137.8 (d), 136.5 (s), 134.2 (d), 133.4 (d),
20 (3H, m), 2.84 (1H, m), 2.56 (1H, m), 2.31ꢀ1.84 (6H, m), 1.78ꢀ 85 131.6 (d), 131.3 (d), 130.3 (d), 129.4 (d), 128.7 (s), 127.9 (d),
1.55 (2H, m); 13C NMR (100 MHz, CDCl3) δ 180.0 (s), 179.2 (s),
170.4 (s), 160.3 (s), 142.2 (s), 137.7 (d), 134.2 (d), 133.8 (s),
133.3 (d), 132.1 (d), 131.2 (d), 129.7 (d), 128.9 (d), 128.8 (d),
127.6 (d), 127.1 (d), 126.6 (s), 124.5 (d), 123.6 (d), 120.7 (d),
127.3 (s), 126.9 (d), 124.5 (d), 124.0 (d), 120.8 (d), 120.3 (s),
116.2 (d), 116.0 (d), 115.4 (t), 78.1 (s), 70.1 (d), 56.7 (t), 55.9 (t),
39.8 (t), 33.7 (t), 30.5 (t), 29.6 (q), 25.2 (t), 23.2 (t); 19F NMR
(376 MHz, CDCl3) δ –113.7 (s); IR (νmax/cmꢀ1, neat) 2927, 2854,
25 120.4 (s), 116.2 (d), 115.9 (d), 115.2 (t), 70.4 (d), 56.7 (t), 55.6 90 1662, 1635, 1435, 1354, 1334, 1254, 1234, 1163, 1111, 1064,
(t), 34.7 (t), 33.3 (t), 30.6 (t), 24.5 (t), 23.6 (t); 19F NMR (376
MHz; CDCl3) –113.9 (s).; IR (νmax/cm–1, neat): 2920, 2854, 1645,
1333, 1256, 1168, 752; HRMSꢀESI (calcd for C32H33N3O3F58Ni
[M+H]+) 584.1895, found 584.1893 (ꢁ = 4.6 ppm), (calcd for
765, 745, 708, 698, 673; HRMSꢀASAP (calcd for
C33H35N3O3F58Ni [M+H]+) 598.2016, found 598.2004 (ꢁ = –2.0
ppm), (calcd for C33H35N3O3F60Ni [M+H]+) 600.1970, found
600.1999 (ꢁ = 4.8 ppm); HPLC (ODꢀH column, hexane
30 C32H33N3O3F60Ni [M+H]+) 586.1814, found 586.1841(ꢁ = –1.7 95 (60%)/iPrOH isocratic): 10.78 min. Xꢀrays: see SI.
ppm); HPLC (ODꢀH column, hexane (50%)/iPrOH isocratic):
14.23 min. Xꢀrays: see SI.
(S)ꢀ({2ꢀ[1ꢀ(2ꢀFluorobenzyl)benzyl)pyrrolidineꢀ2ꢀ
carboxamide]phenyl}phenylmethylene)ꢀ(S)ꢀoctenylalaninatoꢀ
N,N’,N’’,O}nickel (II) (Niꢀαꢀoctꢀ4ꢀenylꢀAlaꢀ 2ꢀFBPB) (10)
20
100 Yield 42%; m.p: 70ꢀ72 °C (hexane/EtOAc); [α]D +1978.1 (c
35 (S)ꢀ({2ꢀ[1ꢀ(2ꢀFluorobenzyl)benzyl)pyrrolidineꢀ2ꢀ
carboxamide]phenyl}phenylmethylene)ꢀ(S)ꢀoctenylglycinatoꢀ
N,N’,N’’,O}nickel (II) (Niꢀαꢀoctꢀ7ꢀenylglyꢀ2ꢀFBPB) (8)
1
0.05, CHCl3); H NMR (500 MHz, CDCl3) δ 8.29 (1H, td, J =
7.5, 1.2 Hz, ArꢀCH), 8.03 (1H, d, J = 9.1 Hz, ArꢀCH), 7.50ꢀ7.44
(2H, m, ArꢀCH), 7.38 (1H, m, ArꢀCH), 7.34 (1H, m, ArꢀCH),
7.29 (1H, m, ArꢀCH), 7.20 (1H, td, J = 7.6, 1.2 Hz, ArꢀCH), 7.15
o
20
Yield 72%; m.p: 144ꢀ146 C (hexane/EtOAc); [α]D +3013.3 (c
1
0.05 in CHCl3); H NMR (400 MHz, CDCl3) δ 8.31 (1H, td, J =
40 7.3, 1.8 Hz, ArꢀCH), 8.18 (1H, d, J = 8.6 Hz, ArꢀCH), 7.56ꢀ7.42 105 (1H, ddd, J = 8.5, 6.2, 2.4 Hz, ArꢀCH), 7.09 (1H, t, J = 9.1 Hz,
(3H, m, ArꢀCH), 7.26ꢀ7.14 (4H, m, ArꢀCH), 7.04 (1H, t, J = 9.4
Hz, ArꢀCH), 6.92 (1H, d, J = 6.7 Hz, ArꢀCH), 6.67 (2H, m, Arꢀ
CH), 5.79 (1H, tdd, J = 10.2, 7.0, 3.1 Hz, CH=CH2), 5.04ꢀ4.91
(2H, m), 4.45 (1H, d, J = 12.9 Hz), 3.92 (1H, dd, J = 7.8, 3.1 Hz),
ArꢀCH), 6.95 (1H, d, J = 7.9 Hz, ArꢀCH), 6.68ꢀ6.61 (2H, m, Arꢀ
CH), 5.81 (1H, ddt, J = 17.1, 10.3, 6.8 Hz, CH=CH2), 5.01 (1H,
dq, J = 17.1, 1.6 Hz, CH=CH2cis), 4.94 (1H, m, CH=CH2trans),
4.52 (1H, d, J = 13.1 Hz, NꢀCHH), 3.96 (1H, d, J = 13.1 Hz, Nꢀ
45 3.86 (1H, d, J = 12.9 Hz), 3.62ꢀ3.44 (3H, m), 2.86 (1H, m), 2.57 110 CHH), ), 3.59 (1H, dd, J = 10.1, 6.6 Hz, α(Pro)ꢀCH), 3.41 (1H,
(1H, m), 2.23ꢀ2.12 (2H, m), 2.11ꢀ1.99 (3H, m), 1.93 (1H, m),
1.73ꢀ1.57 (2H, m), 1.41ꢀ1.24 (4H, m), 1.23ꢀ1.07 (2H, m); 13C
NMR (100 MHz, CDCl3) δ 180.0 (s), 179.4 (s), 170.3 (s), 160.4
(s), 142.3 (s), 138.9 (d), 134.2 (d), 133.9 (s), 133.3 (d), 132.1 (d),
dd, J = 10.5, 6.6 Hz, δ(Pro)ꢀCHH), 3.27 (1H, m, β(Pro)ꢀCHH),
2.77 (1H, m, γ(Pro)ꢀCHH), 2.52 (1H, m, γ(Pro)ꢀCHH), 2.35 (1H,
m, γꢀCHH), ), 2.12ꢀ1.97 (5H, m, δꢀCH2, γꢀCHH, δ(Pro)ꢀCHH,
β(Pro)ꢀCHH), 1.69 (1H, td, J = 13.3 Hz, ηꢀCHH), 1.58 (1H, m, ηꢀ
50 131.2 (d), 139.7 (d), 129.7 (d), 128.8 (d), 127.6 (d), 127.2 (d), 115 CHH), 1.48ꢀ1.37 (4H, m, βꢀCH2, εꢀCH2),1.37ꢀ1.27 (2H, m, ζꢀ
126.7 (s), 124.5 (d), 123.7 (d), 120.7 (d), 120.4 (s), 116.2 (d),
116.0 (d), 114.3 (t), 70.5 (d), 56.8 (t), 55.6 (t), 35.3 (t), 33.7 (t),
30.7 (t), 29.2 (t), 28.9 (t), 28.8 (t), 25.3 (t), 23.6 (t). Additional
peaks arise from rotamers at 131.1 (d), 128.9 (d), 124.4 (d), 120.3
CH2), 1.23 (3H, s, CH3); 13C NMR (126 MHz, CDCl3) δ 182.5
(s), 180.1 (s), 172.4 (s), 141.5 (s), 138.9 (d), 136.5 (s), 134.2 (d),
133.4 (d), 131.6 (d), 131.3 (d), 130.4 (d), 129.4 (d), 128.5 (s),
128.0 (d), 127.3 (s), 126.9 (d), 124.6 (d), 124.0 (d), 120.8 (d),
55 (s), 70.4 (d); 19F NMR (376 MHz; CDCl3) 113.7 (s); IR (νmax/cm– 120 120.5 (s), 116.3 (d), 116.1 (d), 114.4 (t), 78.3 (s), 70.1 (d), 56.7
1
,
neat): 3020, 1741, 1365, 1222; HRMSꢀESI (calcd for
(t), 55.9 (t), 40.3 (t), 33.8 (t), 30.6 (t), 29.7 (q), 29.6 (t), 29.2 (t),
28.9 (t), 20.0 (t), 23.22 (t); 19F NMR (376 MHz, CDCl3) δ –113.7
(s); IR (νmax/cmꢀ1, neat) 2923, 2858, 1672, 1639, 1574, 1490,
1456, 1438, 1352, 1251, 1165, 1112, 1062, 903, 750, 711, 669;
125 HRMSꢀASAP: (calcd for C36H41N3O3F58Ni [M+H]+) 640.2485,
found 640.2485 (ꢁ = 0 ppm), (calcd for C36H41N3O3F60Ni
[M+H]+) 642.2440, found 642.2471 (ꢁ = 4.8 ppm); HPLC (ODꢀH
column, hexane (50%)/iPrOH isocratic): 8.34 min.
C35H39N3O3F58Ni [M+H]+) 626.2329, found 626.2321 (ꢁ = –1.3
ppm), (calcd for C35H38N3O3FNa58Ni [M+Na]+) 648.2148, found
648.2155 (ꢁ = 1.1 ppm); HPLC (ODꢀH column, hexane
60 (50%)/iPrOH isocratic): 13.62 min. Xꢀrays: see SI.
(S)ꢀ({2ꢀ[1ꢀ(2ꢀFluorobenzyl)benzyl)pyrrolidineꢀ2ꢀ
65 carboxamide]phenyl}phenylmethylene)ꢀ(S)ꢀ
General method of formation of amino acids (11)ꢀ(14).
This journal is © The Royal Society of Chemistry [year]
Journal Name, [year], [vol], 00–00 | 5

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DOI: 10.1039/C4OB01832J
20
(S)ꢀ({2ꢀ[1ꢀ(2ꢀFluorobenzyl)pyrrolidineꢀ2ꢀ
Yield 68%; m.p: 262ꢀ264 °C (Et2O); [α]D +3.59 (c 0.05,
1
carboxamide]phenyl}phenylmethylene)ꢀ(S)ꢀpentenylglycinatoꢀ
N,N’,N’’,O}nickel(II) 5 (0.49 g, 0.87 mmol, 1.0 equiv.) was
dissolved in methanol (52 mL) and added drop wise to 3 M
MeOH); H NMR (500 MHz, D2O) δ 5.89 (1 H, ddt, J = 17.1,
10.3, 6.8 Hz, CH=CH2), 5.02 (1 H, d, J = 17.1 Hz, CH=CH2cis),
4.95 (1 H, d, J = 10.3 Hz, CH=CH2trans), 2.30 (2 H, q, J = 6.8
5
hydrochloric acid (7.0 mL) at 70 oC, over 5 minutes. The solution 70 Hz, ηꢀCH2), 1.82 (1 H, m, βꢀCHH), 1.68 (1 H, m, βꢀCHH), 1.44
was stirred for 30 minutes, a colour change of red to a transparent
green/yellow was observed. The reaction was cooled to room
temperature and methanol removed in vacuo. The residue was
taken up in water (25.0 mL) and extracted with dichloromethane
(3 H, s, CH3), 1.39ꢀ1.26 (7 H, m, γꢀCHH, δꢀCH2, εꢀCH2, ζꢀCH2),
1.19 (1 H, m, γꢀCHH); 13C NMR (126 MHz, D2O) δ 177.2 (s,
C=O), 140.3 (d, CH=CH2), 114.0 (t, CH=CH2), 61.7 (s, αꢀqC),
37.2 (t, βꢀCH2), 33.0 (t, ηꢀCH2), 28.5 (t, δꢀCH2), 27.9 (t, ζꢀCH2),
10 (3 x 25.0 mL). The organic extracts were combined, dried 75 27.8 (t, εꢀCH2), 23.1 (t, γꢀCH2), 22.5 (t, αꢀCH3); IR (νmax/cmꢀ1,
(MgSO4) and concentrated in vacuo to reclaim compound 4 for
reꢀuse. The aqueous solution was added to a Dowex 50WX2 200
H+ column (prewashed with H2O to pH 7) and washed with
H2O:EtOH (1:1, v/v, 250.0 mL) to remove the nickel salts. The
15 amino acid product was eluted with 20% NH4OH:EtOH (1:1 v/v,
350.0 mL). Fractions containing product were identified by
staining with ninhydrin. The fractions where combined and
concentrated in vacuo, triturated with Et2O to give (S)ꢀ2ꢀ
aminoheptꢀ6ꢀenoic acid as a white powder.
neat) 3079, 2981, 2922, 2855, 1595, 1457, 1434, 1399, 1367,
1318, 1259, 993, 909, 791; HRMSꢀESI: (calcd for C11H22NO2
[M+H]+) 200.1651, found 200.1651 (ꢁ = 0.0 ppm).
80 General method of formation of Fmoc protected amino acids
(1)ꢀ(2), (15)ꢀ(16)
(S)ꢀamino heptꢀ6ꢀenoic acid 11 (90 mg, 0.63 mmol, 1.0 equiv.)
and potassium carbonate (174 mg, 1.26 mmol, 2.0 equiv) was
dissolved in water (2.0 mL) and cooled to
0
oC. 9ꢀ
85 Fluorenylmethyl Nꢀsuccinimidyl carbonate (320 mg, 0.95 mmol,
1.5 equiv.) was dissolved in dioxane (4.0 mL) and added drop
wise to aqueous solution over 20 minutes. The reaction was
warmed to room temperature and left for 24 hours. An excess
volume of water was added and the mixture extracted (2 x 20.0
20
(S)ꢀ2ꢀaminoheptꢀ6ꢀenoic acid (11)
30
Yield 60%; m.p: 225ꢀ226 oC (Et2O) (lit: 224ꢀ225 oC)12; [α]D
+1.5 (c 0.1, H2O) (lit: + 9.5 (c 0.5, H2O, 26 C)12; 1H NMR (300
MHz, D2O) δ 5.85 (1H, ddt, J = 17.5, 10.5, 6.7 Hz, CH=CH2),
o
25 5.06 (1H, d, J = 19.3 Hz, CH=CH2 trans), 4.99 (1H, d, J = 10.5 90 mL) with ethyl acetate. The combined organic fractions were
Hz, CH=CH2 cis), 3.67 (1H, t, J = 6.1 Hz, CHCH2CH2), 2.08
(2H, q, 7.0 Hz, CH2CH=CH2), 1.92ꢀ1.70 (2H, m,
back extracted with saturated bicarbonate solution and the
aqueous layers acidified to pH 1 with 3 M HCl. The aqueous
fractions were then extracted with EtOAc (3 x 20.0 mL). The
organic layers were dried (MgSO4) and concentrated in vacuo.
J
=
CHCH2CH2), 1.56ꢀ1.32 (2H, m, CH2CH2CH2). NH2 and OH
protons are missing from spectrum; 13C NMR (75 MHz, CDCl3) δ
30 175.5 (s, C=O), 138.6 (d, CH=CH2), 115.0 (t, CH=CH2), 54.8 (d, 95 Purification by column chromatography (SiO2 eluted
CHCH2CH2), 32.5 (t, CH2CH=CH2), 30.1 (t, CHCH2CH2), 23.6
(t, CH2CH2CH2); IR (νmax/cm–1, neat): 2929 (br), 1579, 1514,
1407, 1355, 1322, 989, 912, 839; HRMSꢀESI (calcd for
C7H14NO2 [M+H]+) 144.1025, found 144.1028 (ꢁ = 2.1 ppm).
MeOH/CH2Cl2/AcOH (2:97:1)) gave the title compound as a
white powder.
(S)ꢀ2((((9Hꢀfluorenꢀ9ꢀyl)methoxy)carbonyl)amino)heptꢀ6ꢀ
35
100 enoic acid (15)
o
30
(S)ꢀ2ꢀaminodecꢀ9ꢀenoicꢀacid (12)
Yield 65%; m.p: 125ꢀ127 C (Et2O); [α]D +0.1 (c 0.1, CHCl3)
Yield 67%; m.p: 255ꢀ257 oC (Et2O); [α]D30 +0.7 (c 0.03, MeOH);
1H NMR (300 MHz, D2O) δ 5.85 (1H, ddt, J = 17.1, 10.3, 6.7 Hz,
CH=CH2), 4.97 (1H, dq, J = 17.2, 2.3 Hz, CH=CH2 trans), 4.90
(lit: +3.1 (1.0, CHCl3, 22.4 C)12; 1H NMR (500 MHz, MeOD) δ
7.79 (2 H, d, J = 7.6 Hz, ArꢀCH), 7.68 (2 H, d, J = 7.7 Hz, Arꢀ
CH), 7.39 (2 H, t, J = 7.2 Hz, ArꢀCH), 7.31 (2 H, t, J = 7.5 Hz,
o
40 (1H, ddt, J = 10.3, 2.5, 1.2 Hz, CH=CH2 cis), 3.13 (1H, dd, J = 105 ArꢀCH), 5.81 (1 H, ddt, J = 17.0, 10.2, 6.7 Hz, CH=CH2), 5.03 (1
6.8, 6.1 Hz, CHCH2CH2), 1.97 (2H, qt, J = 7.0, 1.2 Hz,
CH2CH=CH2), 1.57ꢀ1.41 (2H, m, CHCH2CH2), 1.37ꢀ1.18 (8H,
m, CH2(CH2)4CH2). NH2 and OH protons are missing from
spectrum; 13C NMR (75 MHz, CDCl3) δ 184.0 (s, C=O), 140.5
H, d, J = 17.5 Hz, CH=CH2 trans), 4.96 (1 H, d, J = 9.5 Hz,
CH=CH2 cis), 4.35 (2 H, d, J = 7.2 Hz, CH2OCONH), 4.23 (1 H,
t, J = 6.8 Hz, CHCH2OCONH), 4.14 (1 H, dd, J = 9.1, 4.8 Hz,
CHCH2CH2), 2.14ꢀ2.05 (2 H, m, CH2CH=CH2), 1.85 (1 H, m,
45 (d, CH=CH2), 114.0 (t, CH=CH2), 56.1 (d, CHCH2CH2), 34.7 (t, 110 CHCH2CH2), 1.69 (1 H, m, CHCH2CH2), 1.56ꢀ1.44 (2 H, m,
CH2CH=CH2), 33.0 (t, CHCH2CH2), 28.5 (t, CH2), 28.1 (t, CH2),
28.0 (t, CH2), 24.9 (t, CH2); IR (νmax/cm–1, neat): 2929 (br), 2925,
2851, 1579, 1513, 1443, 1406, 1319, 1066, 911; HRMSꢀESI
(calcd for C10H20NO2 [M+H]+) 186.1494, found 186.1493 (ꢁ = –
50 0.5 ppm).
CH2CH2CH2). NH and OH protons are missing from spectrum;
13C NMR (125 MHz, MeOD) δ 176.1 (s), 158.8 (s), 145.6 (s),
142.6 (s), 139.4 (d), 128.8 (d), 128.2 (d), 126.3 (d), 120.9 (d),
115.4 (t), 68.0 (t), 55.2 (d), 48.3 (d, identified by HMQC), 34.3
115 (t), 32.2 (t), 26.3 (t); IR (νmax/cm–1, neat): 3336, 3017, 2971,
1739, 1681, 1532, 1446, 1366, 1229, 1217, 910, 758, 736;
HRMSꢀESI (calcd for C22H24NO4 [M+H]+) 366.1705, found
366.1705 (ꢁ = 0.0 ppm), (calcd for C22H23NO4Na [M+Na]+)
388.1525, found 388.1500 (ꢁ = –6.4 ppm); HPLC (ODꢀH
(S)ꢀ2ꢀaminoꢀ2ꢀmethylheptꢀ6ꢀenoic acid (13)
Yield 65%; m.p: 250ꢀ252 °C (Et2O) (lit: >200 oC decomp)21;
[α]D20 +3.22 (c 0.05, MeOH) (lit: +10.8 (c 0.83, MeOH, 25 oC)21;
55 1H NMR (300 MHz, D2O) δ 5.84 (1 H, ddt, J = 17.0, 10.2, 6.7 120 column, hexane/iPrOH isocratic + 0.1% AcOH): 9.56 min.
Hz, CH=CH2), 5.11ꢀ4.96 (2 H, m, CH=CH2), 2.07 (2 H, q, J = 7.0
Hz, δꢀCH2), 1.86 (1 H, m, βꢀCHH), 1.71 (1 H, m, , βꢀCHH), 1.54
ꢀ1.40 (4 H, m, CH3, γꢀCHH), 1.31 (1 H, m, γꢀCHH); 13C NMR
(100 MHz, D2O) δ 177.0 (s, C=O), 138.7 (d, CH=CH2), 115.1 (t,
(S)ꢀ2ꢀ((((9Hꢀfluorenꢀ9ꢀyl)methoxy)carbonyl)decꢀ9ꢀenoic acid
(16)
Yield 63%; m.p: 225ꢀ226 oC (Et2O); [α]D30 +0.2 (c 0.02, CHCl3);
60 CH=CH2), 61.6 (s, αꢀqC), 36.7 (t, βꢀCH2), 32.8 (t, δꢀCH2), 22.5 (t, 125 1H NMR (500 MHz, MeOD) δ 7.77 (2 H, d, J = 7.3 Hz, ArꢀCH),
γꢀCH2), 22.5 (q, CH3); IR (νmax/cmꢀ1, neat) 3124, 3033, 2982,
1738, 1595, 1456, 1397, 1367, 1316, 1232, 912; HRMSꢀESI
(calcd for C8H16NO2 [M+H]+) 158.1181, found 158.1175 (ꢁ = –
3.8 ppm).
7.60 (2 H, d, J = 6.7 Hz, ArꢀCH), 7.41 (2 H, t, J = 7.6 Hz, Arꢀ
CH), 7.32 (2 H, t, J = 7.0 Hz, ArꢀCH), 5.81 (1 H, ddt, J = 17.0,
10.2, 6.7 Hz, CH=CH2), 5.03 (1 H, d, J = 17.5 Hz, CH=CH2
trans), 4.96 (1 H, d, J = 9.5 Hz, CH=CH2 cis), 4.35 (2 H, d, J =
130 7.2 Hz, CH2OCONH), 4.23 (1 H, t, J = 6.8 Hz, CHCH2OCONH),
65 (S)ꢀ2ꢀaminoꢀ2ꢀmethyldecꢀ9ꢀenoic acid (14)
6
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Organic & Biomolecular Chemistry
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DOI: 10.1039/C4OB01832J
4.14 (1 H, dd, J = 9.1, 4.8 Hz, CHCH2CH2), 2.03 (2 H, q, J = 6.7
Notes and references
Hz, CH2CH=CH2), 1.89 (1 H, m, CHCH2CH2), 1.67 (1 H, m,
CHCH2CH2), 1.46ꢀ1.18 (8 H, m, CH2(CH2)4CH2). NH and OH
protons are missing from spectrum; 13C NMR (125 MHz, MeOD)
δ 176.4 (s), 158.9 (s), 145.4 (s), 142.8 (s), 140.2 (d), 128.9 (d),
128.3 (d), 126.4 (d), 121.1 (d), 114.9 (t), 68.1 (t), 55.5 (d), 47.4
(d), 35.0 (t), 32.9 (t), 30.1 (3 x t), 27.0 (t); IR (νmax/cm–1, neat):
3072, 2931, 2858, 2487, 1687, 1537, 1450, 1264, 1236, 1167,
1086, 1045, 992, 907, 738; HRMSꢀESI (calcd for C25H30NO4
a Department of Chemistry, University of Leicester, Leicester, LE1 7RH,
65 UK, Fax: +44 (0)116 252 3789; Tel: +44 (0)116 252 2105; E-mail:
andrew.jamieson@le.ac.uk
† Electronic Supplementary Information (ESI) available: [Full
experimental procedures and spectroscopic data for compounds 1ꢀ16. ].
See DOI: 10.1039/b000000x/
5
70
1
2
3
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10 [M+H]+) 408.2175, found 408.2170 (ꢁ = –1.2 ppm), (calcd for
C25H29NO4Na [M+Na]+) 430.1994, found 430.1989 (ꢁ = –1.2
ppm); HPLC (ODꢀH column, hexane/iPrOH isocratic + 0.1%
AcOH): 7.54 min.
75
80
4
5
6
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15 (S)ꢀ2ꢀ((((9Hꢀfluorenꢀ9yl)methoxy)carbonyl)amino)ꢀ2ꢀ
methylheptꢀ6ꢀenoic acid (1)
20
1
Yield 82%; [α]D +3.5 (c 1.0 in MeOH); H NMR (300 MHz;
CDCl3) δ 7.78 (2 H, d, J = 7.5 Hz, ArꢀCH), 7.60 (2 H, d, J = 7.2
Hz, ArꢀCH), 7.41 (2 H, t, J = 7.4 Hz, ArꢀCH), 7.33 (2 H, t, J =
20 7.5, ArꢀCH), 5.76 (1 H, m, CH2CH=CH2), 5.50 (1 H, s, NH),
5.09ꢀ4.89 (2 H, m, CH2CH=CH2), 4.53ꢀ4.33 (2 H, m,
C(O)OCH2CH), 4.23 (1 H, t, J = 6.6 Hz, C(O)OCH2CH), 2.22ꢀ
1.95 (2 H, m, CH2CH=CH2), 1.95ꢀ1.78 (1 H, m, C(Me)CH2CH2),
1.60 (3 H, s, C(CH3)CH2), 1.50ꢀ1.26 (2 H, t, J = 7.1 Hz,
25 C(Me)CH2); 13C NMR (75 MHz; CDCl3) δ 178.3 (s), 154.8 (s),
143.8 (s), 141.4 (s), 138.0 (d), 127.7 (d), 127.1 (d), 125.0 (d),
120.0 (d), 115.1 (t), 66.5 (t), 59.7 (s), 47.2 (d), 36.2 (t), 33.4 (t),
30.9 (t), 23.3 (q); IR (νmax/cmꢀ1, neat) 2932, 1701, 1507, 1450,
1334, 1253, 1074, 910, 758, 737; HRMSꢀESI (calcd for
30 C23H26NO4 [M+H]+) 380.1862, found 380.1860 (ꢁ = –0.5 ppm),
(calcd for C23H25NO4Na [M+Na]+) 402.1681, found 402.1692 (ꢁ
= 2.7 ppm). HPLC (ODꢀH column, hexane (50%)/iPrOH isocratic
+ 0.1% AcOH): 8.07 min.
7
8
9
85 10 C. E. Schafmeister, J. Po and G. L. Verdine, J. Am. Chem. Soc.,
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16 Y. N. Belekon, V. I. Maleev, M. B. Saporovskaya, V. I. Bakhmutov,
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35 (S)ꢀ2ꢀ((((9Hꢀfluorenꢀ9ꢀyl)methoxy)carbonyl)amino)ꢀ2ꢀ
methyldecꢀ9ꢀenoic acid (2)
20
1
Yield 62%; [α]D +5.89 (c 1.0, CHCl3); H NMR (500 MHz,
CDCl3) δ 7.77 (2 H, d, J = 7.5 Hz, ArꢀCH), 7.59 (2 H, d, J = 7.5
Hz, ArꢀCH), 7.40 (2 H, t, J = 7.4 Hz, ArꢀCH), 7.32 (2 H, t, J =
40 7.4 Hz, ArꢀCH), 5.79 (1 H, ddt, J = 17.1, 10.2, 6.8 Hz, CH=CH2),
5.46 (1 H, br s, NH), 4.98 ( 1 H, dd, J = 17.1, 1.5 Hz,
CH=CH2cis), 4.92 (1 H, d, J = 10.1 Hz, CH=CH2trans), 4.41 (2
H, s, C(O)OCH2CH), 4.22 (1 H, t, J = 6.8 Hz, C(O)OCH2CH),
2.02 (2 H, q, J = 6.9 Hz, CH2CH=CH2), 1.82 (1 H, m,
45 CHHCH2CH=CH2), 1.60 (3 H, s, CH3), 1.39ꢀ1.10 (9 H, m,
CHHCH2CH=CH2, CH3C(CH2)4); 13C NMR (100 MHz, CDCl3) δ
179.3 (s), 157.7 (s), 143.9 (s), 141.4 (s), 139.0 (d), 127.7 (d),
127.0 (d), 124.9 (d), 120.0 (d), 114.2 (t), 66.5 (d), 59.8 (t), 47.2
(s), 36.8 (t), 33.7 (t), 29.3 (t), 28.9 (t), 28.8 (t), 23.9 (t), 23.2 (q);
50 IR (νmax/cmꢀ1, neat) 2926, 1705, 1506, 1450, 1338, 1251, 1105,
1086, 1052, 995, 909, 776, 758, 737, 674; HRMSꢀESI (calcd for
C26H32NO4 [M+H]+) 422.2331, found 422.2331 (ꢁ = 0.0 ppm);
HPLC (ODꢀH column, hexane (50%)/iPrOH isocratic + 0.1%
AcOH): 7.28 min.
18 A. S. Saghyan, A. S. Dadayan, S. A. Dadayan, A. F. Mkrtchyan, A.
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55
Acknowledgments
We thank Prof. Paul M. Cullis for insightful discussions. This
work was funded by Engineering and Physical Sciences Research
Council (EPSRC) (EP/L018152/1), University of Leicester
60 Innovation Fellowship for A.G.J. The authors thank Mick Lee
(mass spectrometry), Dr. Gerry Griffith (NMR) and Kuldip Singh
(xꢀray crystallography) for technical assistance.
This journal is © The Royal Society of Chemistry [year]
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