Mapping the pathway toward thiophosphinic pseudopeptides. synthesis of suitably protected PG-Phe-Ψ[P(S)(OX)CH2]-Gly-OY analogues as thiophosphinyl dipeptide isosters (TDI), a comparative study for selective deprotection and further elongation

Article abstract of DOI:10.1021/jo401084v

In the present study, we describe in detail the first synthesis of a new class of phosphorus compounds, thiophosphinyl pseudopeptides. We prepared several fully protected thiophosphinate pseudodipeptides of the general formula PG-Phe-Ψ[P(S)(OX)CH₂]-Gly-OY starting from the corresponding phosphinate pseudodipeptide using Lawesson's reagent. Selective deprotection, further elongation, and stability of these compounds were studied, and the results are disclosed. These compounds can be used as transition-state-mimicking inhibitors for several zinc metalloproteases.

Full text of DOI:10.1021/jo401084v

Article
pubs.acs.org/joc
Mapping the Pathway toward Thiophosphinic Pseudopeptides.
Synthesis of Suitably Protected PG-Phe-Ψ[P(S)(OX)CH2]‑Gly-OY
Analogues as Thiophosphinyl Dipeptide Isosters (TDI), a
Comparative Study for Selective Deprotection and Further
Elongation
Stamatia Vassiliou* and Eirini Tzouma
Laboratory of Organic Chemistry, Department of Chemistry, University of Athens, Panepistimiopolis, Zografou, 15771, Athens,
Greece
S
* Supporting Information
ABSTRACT: In the present study, we describe in detail the first synthesis of a
new class of phosphorus compounds, thiophosphinyl pseudopeptides. We
prepared several fully protected thiophosphinate pseudodipeptides of the general
formula PG-Phe-Ψ[P(S)(OX)CH2]-Gly-OY starting from the corresponding
phosphinate pseudodipeptide using Lawesson’s reagent. Selective deprotection,
further elongation, and stability of these compounds were studied, and the results are disclosed. These compounds can be used as
transition-state-mimicking inhibitors for several zinc metalloproteases.
Scheme 2. Representation of the Subsites of a Zinc Protease
and a Phosphinic Peptide Sequence
INTRODUCTION
■
The backbone modification of bioactive peptides with
replacement of the scissile peptide bond in enzymatic
hydrolysis is a well-established strategy for developing protease
inhibitors.1,2 In particular, for zinc metalloproteases, which
contain a zinc atom in their active site, several successful
modifications have been reported over the past years.3,4
The presence of a zinc ion in the active site of these proteases
and the functional role of this atom in substrate hydrolysis led
to the suggestion that potent synthetic inhibitors could be
developed by grafting to short peptide sequences chemical
groups able to interact potently with the zinc ion. The choice of
a particular zinc-binding group may critically determine the
inhibitor selectivity profile. In fact, the contribution of the zinc-
binding group to overall inhibitor affinity depends on its
chemical structure and differs for each zinc-binding group
(Scheme 1).
inhibitor structures cannot be prepared when other zinc-
binding groups are used. Exploiting both the primed and
nonprimed subsites of the enzyme active site can be critical to
the control of both inhibitor potency and selectivity.
Phosphinic pseudopeptides are among the best candidates
when addressing the challenge to potent and selectively inhibit
zinc proteases.5−7 Phosphinyl dipeptide isosters (PDIs)
(Scheme 3) are the building blocks for the synthesis of
phosphinic pseudopeptides, and their chemistry is well
documented.8−10 PDIs, presented as NH2XaaΨ[P(O)(OH)-
CH2]XaaOH, mimic the transition state for tetrahedral
geometry of a scissile peptide bond during enzymatic
hydrolysis.
An important property of the zinc-binding group, depending
on its chemistry, is the ability to use both primed and
nonprimed subsites when developing inhibitors (Scheme 2).
With the exception of phosphinic and silanediol groups, such
Scheme 1. Six Zinc-Binding Groups Shown in Bold [(a)
Thiolate, (b) Carboxylate, (c) Phosphinate, (d)
Hydroxamate, (e) Hydroxythiopyrone, and (f) Diolsilane)]
in Complex with Zinc Ion
In contrast to phosphinyl dipeptide isosters, there is no
scientific report concerning thiophosphinyl dipeptide isosters
(TDIs). A thorough overview of the literature11 revealed the
absence of any synthetic method providing this class of
Received: May 17, 2013
Published: September 19, 2013
© 2013 American Chemical Society
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a
Scheme 3. Similarity between the Structure of a Peptidic
Sequence in the so-Called Tetrahedral Intermediate, a
Phosphinic Dipeptide Isoster (PDI), and a Thiophosphinic
Dipeptide Isoster (TDI)
Scheme 5. Synthesis of Protected Phosphinates
compounds. The only relevant approaches dealt with the
a
Reagents and conditions: (a) P(OCH3)3, 90 °C, 10 h, 93% for 6, 91%
for 10, 93% for 11; (b) 1-Ad-Br, Ag2O, CHCl3, reflux, 3 h, 82% for 7,
81% for 9; (c) EDC·HCl, MeOH, CH2Cl2, rt, 1 h, 91% for 8.
12
synthesis of Cbz-GlyΨ[P(S)(OH)]CH3 and Cbz-GlyΨ[P-
(S)(OH)]CH2OH13 as a potent inhibitors of bacterial ureases.
Herein, we present the first synthesis of fully protected
thiophosphinate pseudodipeptides of the general formula PG-
Phe-Ψ[P(S)(OX)CH2]-Gly-OY, a systematic deprotection
study, as well as further elongation and stability behavior.
Then, we focused on establishing a synthetic methodology to
obtain PG-Phe-Ψ[P(S)(OX)CH2]-Gly-OY. Starting point
seemed to be the corresponding phosphinate, and two
thionating agents, P4S10 and Lawesson’s reagent20 (LR),
19
RESULTS AND DISCUSSION
■
Phosphinic pseudodipeptides (Scheme 4) are typically defined
as dipeptide analogues that replace the amide bond with the
phosphinate moiety. The most traditional approach to obtain a
pseudodipeptide skeleton involves the phospha-Michael
addition of a suitably N-protected α-amino-H-phosphinic acid
to an acrylate. The H-phosphinic acid requires activation to the
more nucleophilic tervalent ester form that is typically achieved
in the presence of a silylation agent (Scheme 4).14
were the most promising to be tested. These two thionating
agents have been extensively used to transform mainly carbonyl
to thiocarbonyl compounds as well as for the synthesis of a
wide range of heterocyclic compounds having a sulfur atom.
Generally it is claimed that LR has advantages over P4S10 in
terms of requirements for excess P4S10 and longer reaction
time. This was confirmed in our case, since in initial
experiments using Cbz-Phe-Ψ[P(O)(OMe)CH2]-Gly-OEt
and P4S10 in warm toluene, no thionation product was
observed. By contrary, using LR in warm toluene the desired
product Cbz-Phe-Ψ[P(S)(OMe)CH2]-Gly-OEt appeared both
in mass spectrometry and phosphorus NMR.
Because Lawesson’s reagent is also the reagent of choice for
transformations of functional groups such as urethanes and
esters,21 we should carefully examine the reactivity of
Lawesson’s reagent toward the carbonyl group present in our
substrate. Indeed, by careful control of the temperature and by
adding 0.5 equiv of LR, we selectively thionated the phosphorus
atom without affecting the carbamate or the ester function.
Therefore, after detailed experimentation, we found that the
optimal reaction conditions were heating at 95 °C, for 2 h in
dry toluene using 0.5 equiv of Lawesson’s reagent.
Under these conditions, compound 12 was obtained in 89%
yield after column purification (Table 1). It can be noted the
less polar character of this compound allowed the use of
CH2Cl2/EtOAc as eluent compared to CH2Cl2/MeOH needed
for its oxygen counterpart. Of special interest, the increase of
the 31P NMR chemical shift, 54.44 and 55.44 ppm for the two
diasteroisomers of 6 compared to 104.87, 106.09 ppm for 12, is
very diagnostic. The absence of any overthionation product was
confirmed by means of mass spectrometry and 13C NMR (C
O appears around 155 ppm for CONH, whereas CS for
The phosphinic pseudodipeptide scaffold Phe-Ψ[P(O)-
(OH)CH2]-Gly was used as a template in this study. PG-
Phe-Ψ[P(O)(OH)CH2]-Gly-OY 1, 2, 3, and 4 were prepared
using the well-described procedures15,16 based on the Michael
addition of a disilyl phosphonite to a Michael acceptor. Special
citation is needed concerning the synthesis of Cbz-Phe-
Ψ[P(O)(OH)CH2]-Gly-OAllyl 5. This compound was pre-
pared using TMSCl as silylating agent, allyl acrylate as Michael
acceptor, and imidazole as base to avoid the corresponding
rearrangement product.17 Two protecting groups, methyl (for
6, 8, 10, 11) and adamantyl (for 7 and 9) covering the alkaline
and the acidic removal, respectively, were used for the
esterification of the hydroxyphosphinyl group. Introduction of
the methyl group was achieved by warming 1, 4, and 5 (Scheme
5) with trimethylphosphite P(OCH3)3 at 90 °C for 10 h,
providing the corresponding esters in excellent yield.18
Exceptionally, carbodiimide-mediated esterification of 2 with
methanol furnished 8. Introduction of the adamantyl group,
particularly useful in the phosphinopeptide chemistry, was
feasible by mixing 1 and 3 with 1-adamantyl bromide in
refluxing chloroform followed by portion-wise addition of
silver(I) oxide.16 Because of the two chiral centers, P and C
atoms, in all cases 6−11, mixtures of diastereomers were
obtained, the ratio being around 70/30, as judged by 31P NMR.
Scheme 4. General Structure of a Phosphinic Pseudodipeptide Analogue and a Common Synthetic Strategy Leading to It
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With these thiophosphinates in hand, their reactivity was
examined using common deprotection conditions. Therefore,
thiophosphinates 12, 13, 14, 15, 16, and 17 were subjected to
common acidic and basic deprotection conditions (Table 2).
The results of the reactions were analyzed by 31P NMR and
mass spectrometry. Phosphorus NMR was the most valuable
tool during this study since, during the deprotection course,
three main types of compounds (Scheme 7) appeared to a
smaller or a lesser extent. Compounds of the general formula I,
whose thiophosphinate is protected and the carboxy group is
still protected or not, appear in a range from 90 to 106 ppm. An
upfield shift toward 67−75 ppm occurs when the thiophos-
phinyl functionality is deprotected (II), with the carboxyl group
again protected or not. With TFA treatment, S→O exchange
was observed in substrates 13 and 16 (entries f, h, j, k, Table 2).
The presence of water did not seem to be the crucial factor.
This exchange has been again observed under TMSBr-mediated
deprotection of a methyl thiophosphinate in an analogue
substrate in one of our previous work.12 It was not observed
under alkaline hydrolysis conditions, which is again confirmed
in this work. A further upfield shift, reaching the area of 53−57
ppm, is indicative of this S→O exchange, characteristic of
phosphinates III. Since hydrogenolytic removal of the Na-Cbz
group is not possible due to the poisonous effect of sulfur to
Pd-catalyst, 12 was mixed with 33% HBr/AcOH for 1 h. To our
delight, the Cbz group was completely removed while no S→O
exchange was observed after workup (entry l, Table 2). Of
special interest, Fmoc-thiophosphinate 24 is a suitable block for
future Fmoc-solid phase thiophosphinic peptide synthesis
(entry g, Table 2).
Table 1. Synthesis of Thiophosphinates from the
Corresponding Phosphinates Using Lawesson’s Reagent
product
Pg
X
Y
yield (%)
12
13
14
15
16
17
Cbz
Cbz
Fmoc
Boc
Me
Ad
Et
89
84
82
80
89
92
Et
Me
Ad
t-Bu
Et
Cbz
Cbz
Me
Me
t-Bu
allyl
CSNH is usually observed around 195 ppm).22 The presence
of the bulky adamantyl hydroxyphosphinyl protecting group
did not affect the reaction progress, and thus thionation of 7
proceeded smoothly under the previously described conditions,
providing 13 in 84% yield. The Fmoc- and Boc-protected
thiophosphinic dipeptide analogues 14 and 15 were easily and
selectively prepared without affecting either the Nα-carbamate
carbonyl or the ester carbonyl. The presence of the allyl ester in
11 was equally well tolerated to give 17, adding an extra aspect
of orthogonality in this type of molecules.
Apart from the downfield shift of about 50 ppm observed in
1
31P NMR, a similar trend was recorded in H NMR with the
PCH2 and CH(Ph)P protons appearing in higher chemical
shift, about 0.15−0.20 ppm for the thiophosphinates compared
to their phosphinates counterparts. In 13C spectra, the two
carbons directly bonded to phosphorus, PCH2 and CH(Ph)P,
were 3−5 ppm downfield shifted. This increase in chemical
shift can be attributed to the electron density, which is located
more on the sulfur bound to phosphorus, compared to oxygen.
The mechanism of thionation can be rationalized as follows
(Scheme 6). LR is in equilibrium with the highly reactive
From the saponification experiment for 12 (entry a, Table 2),
it was concluded that the thiophosphinyl methyl ester is 85%
stable during the removal of the carboxyl ethyl ester, which is a
great difference from the corresponding phosphinyl methyl
ester, which was quantitatively removed under the same
conditions in 40 min.25
Removal of the thiophosphinyl protecting group, taking into
consideration the S→O exchange under acidic conditions, is
feasible under basic conditions. Therefore a volatile amine,
aqueous NH3 in methanol, was first checked using 12 and 16 as
substrates. Due to both its high basicity and nucleophilicity,
demethylation occurred smoothly, and at the same time the
carboxyl ethyl ester was transformed to the corresponding
amide 26, in the case of 12 (entry m, Table 2). In the case of
16, however, no product was detected during the same period
of time. This can be attributed to the insolubility of the starting
material in the reaction mixture. The use of n-butanol instead of
methanol increased the solubility of the starting materials but
also increased the reaction time. Reaction of 16 with aqueous
dimethylamine instead of aqueous NH3 in methanol gave a
demethylated 27 in 8 days (entry p, Table 2). In order to
obtain the demethylated thiophosphinyl derivative with free
carboxyl group instead of amide, we thought to use aqueous
NH3 in methanol for the saponified derivative 22. Surprisingly,
no reaction took place even after 10 days (entry q, Table 2).
Compounds 26 and 27 were loaded on silica gel column
chromatography but they were completely decomposed during
the elution with a mixture CH2Cl2/MeOH−acetic acid, most
probably due to the acidic nature of the eluent. The same was
observed when HPLC characterization was attempted. Due to
the presence of TFA in the solvent system, thiophosphinate 26
was transformed to its oxygen analogue. Therefore we decided
to isolate 26 and 27 in the form of their salt with the
Scheme 6. Possible Mechanism for the Thionation of a
Phosphinate
dithiophosphine ylide (18, 19). Both mesomeric structures 18
and 19 can react with a PO-containing compound to form
thiaoxaphosphetane 20, which decomposes in a Wittig-
analogous reaction to the corresponding thiophosphinate.
The whole process may be summarized as cis-syn addition−
ellimination. Thermodynamically, 21 is more stable than 18,
given the fact that the PO bond is much stronger than the
PS bond (bond energy is 120 kcal/mol for PO in POCl3
vs 76 kcal/mol for PS in PSCl3), and this must be the driving
force behind this mechanism.23,24
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Table 2. Reactivity of 12−17 under Acidic/Basic Conditions
a
b
entry
reactant
conditions
product(s) ratio
X = Na, Y = Na, Z = S, 15%
a
b
c
d
e
f
12
13
16
17
12
13
14
16
17
16
16
12
12
16
12
16
22
A
A
A
A
B
B
C
B
B
D
E
X = Me, Y = H, Z = S, 22, 85%
X = Ad, Y = H, Z = S, 23, 100%
X = Me, Y = t-Bu, Z = S, 10%
X = Na, Y = t-Bu, Z = S + X = Na, Y = Na, Z = S, 90%
X = Me, Y = allyl, Z = S, 30%
X = Na, Y = allyl, Z = S + X = Na, Y = Na, Z = S, 70%
X = Me, Y = Et, Z = S, 12, 100%
X = Ad, Y = Et, Z = S, 46%, X = H, Y = Et, Z = S, 48%
X = Me, Y = H, Z = S, 24, 100%
X = Me, Y = t-Bu, Z = S + X = Me, Y = H, Z = S, 90%
X = Me, Y = allyl, Z = S, 17, 100%
X = Me, Y = t-Bu, Z = S + X = Me, Y = H, Z = S, 95%
X = Me, Y = H, Z = S, 22, 80%
X = H, Y = Et, Z = O, 6%
g
h
i
X = Me, Y = H, Z = O + X = H, Y = H, Z = O, 10%
j
X = Me, Y = H, Z = O + X = H, Y = H, Z = O, 5%
X = Me, Y = H, Z = O + X = H, Y = H, Z = O, 20%
k
l
F
Pg = HBr, X = Me, Y = Et, Z = S, 25, 100%
Y = NH2, X = NH4, Z = S, 26, 100%
16, 100%
m
n
o
p
q
G
G
H
I
Y = NH2, X = NH4, Z = S, 26, 100%
Y = OtBu, X = dimethylamine, Z = S, 27, 100%
22, 100%
G
a
(A) 0.35 N NaOH/MeOH,1 h; (B) TFA/CH2Cl2/H2O, 50/49.5/0.5, 1 h; (C) TFA/CH2Cl2/TIPS, 50/49.5/0.5, 30 min; (D) TFA/CH2Cl2, 50/
50, 30 min; (E) TFA/CH2Cl2, 90/10, 30 min; (F) 33% HBr/AcOH, 1 h; (G) 25% NH4OH/MeOH, 50/50, 5 days; (H) 25% NH4OH/n-BuOH,
b
50/50, 19 days; (I) 40% aq dimethylamine/MeOH, 50/50, 8 days. Determined by 31P NMR.
Scheme 7. Products of the Deprotection Study and 31P NMR
Reading carefully the results of the deprotection study, we
Area in Which They Appear
were able to proceed in C-terminal and N-terminal elongation.
For the C-elongation, compound 22, derived either from entry
a or from entry k (Table 2), was coupled with H-(L)Leu-OMe·
HCl using standard EDC·HCl procedure, providing 28 in high
yield after column chromatography (Scheme 9).
Scheme 9. C-Elongation of Thiophosphinate 22
corresponding amine after trituration with CHCl3 and filtration.
In this form, these compounds are stable for months, as judged
by 31P NMR stability control.
Thiophosphinates that were selectively deprotected and
characterized are summarized in Scheme 8.
For the N-elongation hydrobromic salt 25, Table 2, entry l
was neutralized with DIPEA and coupled with Cbz-L-Phe-OH
to give pseudotripeptide 29 in good yield (Scheme 10).
Scheme 8. Thiophosphinates Selectively Deprotected
CONCLUSION
■
We have devised the first procedure that enables access to
orthogonally protected thiophosphinyl dipeptide isoster (TDI)
PG-Phe-Ψ[P(S)(OX)CH2]-Gly-OY. The synthetic strategy is
based on the logical selection of protecting groups as well as on
the careful reaction conditions between the corresponding
phosphinyl dipeptide isoster (PDI) and Lawesson’s reagent. In
addition, each functionality’s selective deprotection was
successfully studied, giving the possibility for further C-and
N-elongation. Derived thiophosphinyl pseudopeptides are
stable for months if isolated in the form of their salt.
Taking into consideration the increasing interest for zinc
binding groups with unusual structural features due to their
improved biological properties, the described synthesis is of
particular practical value.
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Scheme 10. N-Elongation of Thiophosphinate 25
= 7.0 Hz, 2H), 4.06−4.32 (m, 1H), 4.95 (s, 2H), 6.41 (d, J = 10.3 Hz,
1H), 7.09−7.36 (m, 10H); 13C NMR (50 MHz, CDCl3) δ 14.0, 23.3
EXPERIMENTAL SECTION
■
General. Dry methylene chloride (CH2Cl2) was obtained by
distillation of commercially available predried solvent from NaH.
Toluene was dried and kept over 4 Å molecular sieves. Reagents were
purchased at the highest commercial quality and were used without
further purification. Reactions were monitored by thin-layer
chromatography (TLC) carried out on 0.25 mm silica gel plates
(silica gel 60F254), and components were visualized by the following
methods: UV light absorbance, and/or charring after spraying with a
solution of NH4HSO4, and/or an aqueous solution of cerium
molybdate/H2SO4 (“Blue Stain”), and heating. Purification of
compounds by column chromatography was carried out on silica gel
1
1
(d, JPC = 90.0 Hz), 27.0, 31.0, 34.3, 35.5, 44.4, 50.8 (d, JPC = 108.3
Hz), 60.6, 66.3, 82.9, 126.3, 126.4, 127.3, 127.5, 127.7, 127.8, 128.1,
3
128.2, 129.0, 136.1, 136.4, 136.7, 137.0, 137.2, 156.2 (d, JPC = 6.0
3
Hz), 172.2 (d, JPC = 17.1 Hz). 31P NMR (81 MHz, CDCl3) δ 48.51,
48.76; ESMS m/z calcd for C31H41NO6P (M + H)+ 554.3, found
554.2.
(R,R,S,S)-3-((1′-(N-(9-Fluorenylmethoxycarbonyl)-amino)-2′-
phenylethyl)methyloxyphosphinyl) Propanoic Acid tert-Butyl
Ester (8). To a solution of 2 (470 mg, 0.88 mmol) and MeOH (0.5
mL) in CH2Cl2 (5 mL) at room temperature was added EDC·HCl
(203 mg, 1.06 mmol). After stirring for 1 h, the mixture was diluted
with CH2Cl2 and washed successively with 5% NaHCO3, H2O, dried
over Na2SO4, and evaporated to give the crude product, which was
further purified by column chromatography using CH2Cl2/MeOH
9.8−0.2 as eluent to give 0.44 g of 8 as white solid (91%). Rf = 0.75
(70−230 mesh) and the indicated solvents. H, 13C, and 31P NMR
1
spectra were recorded on a 200 MHz spectrometer. 1H and 13C
spectra are referenced according to the residual peak of the solvent
based on literature data. 31P NMR chemical shifts are reported in ppm
downfield from 85% H3PO4 (external standard). 13C and 31P NMR
spectra are fully proton decoupled. The presence of asymmetric
centers and rotamers in these compounds complicates the
interpretation of the spectra. Numbers I and II were used to describe
the 13C resonances corresponding to the different diastereoisomers.
ESI mass spectral analyses were performed on a mass spectrometer,
using direct sample injection. Negative or positive ion ESI spectra were
acquired by adjusting the needle and cone voltages accordingly.
HRMS spectra were registered using a Orbitrap mass spectrometer in
the m/z range of 100−700.
1
(CH2Cl2/MeOH 9.5−0.5). H NMR (200 MHz, CDCl3) mixture of
two diastereoisomers ∼70:30, only signals of the major isomer are
given: δ 1.42 (s, 9H), 2.00−2.22 (m, 2H), 2.40−2.67 (m, 2H), 2.80−
3.05 (m, 1H), 3.10−3.36 (m, 1H), 3.71 (s, 3H/2), 3.77 (s, 3H/2),
3.97−4.10 (m, 2H), 4.14−4.44 (m, 2H), 6.55 (d, J = 9.6 Hz, 1H),
1
7.10−7.73 (m, 13H); 13C NMR (50 MHz, CDCl3) δ 20.9 (d, JPC
=
88.6 Hz), 21.9 (d, 1JPC = 90.4 Hz), 25.5, 28.2, 34.0, 47.3, 50.5 (d, 1JPC
= 106.4 Hz), 52.3, 67.4, 81.3, 120.1, 125.2, 125.3, 125.4, 127.0, 127.2,
127.9, 128.7, 129.4, 129.5, 136.9, 137.1, 141.4, 143.9, 144.1, 156.5 (d,
3JPC = 5.7 Hz), 171.7 (d, 3JPC = 14.3 Hz). 31P NMR (81 MHz, CDCl3)
(R,R,S,S)-3-((1′-(N-Benzyloxycarbonyl)-amino)-2′-
phenylethyl)methyloxyphosphinyl) Propanoic Acid Ethyl Ester
(6).25 Trimethylphosphite (1 mL) was added to 1 (650 mg, 1.55
mmol), and the reaction mixture was warmed to 90 °C for 10 h. The
crude product was taken up by Et2O and extracted with NaOH 0.1 N
twice, with H2O, dried over Na2SO4, and purified by column
chromatography using CH2Cl2/MeOH 9.8−0.2 as eluent. Phosphinate
6 was obtained as a sticky gum. Yield 624 mg (93%). Rf = 0.58 (ethyl
acetate). 1H NMR (200 MHz, CDCl3) mixture of two diaster-
eoisomers ∼75:25, only signals of the major isomer are given: δ 1.24
(t, J = 7.2 Hz, 3H), 1.99−2.20 (m, 2H), 2.40−2.62 (m, 2H), 2.70−
3.00 (m, 1H), 3.09−3.34 (m, 1H), 3.61(s, 3H/2), 3.68 (s, 3H/2), 4.14
(q, J = 7.2 Hz, 2H), 4.28−4.48 (m, 1H), 5.00 (s, 2H), 6.87 (d, J = 10.1
Hz, 1H), 7.10−7.36 (m, 10H); 13C NMR (50 MHz, CDCl3) δ 13.8,
δ 54.32, 55.56; ESMS (m/z) calcd for C31H36NO6P (M + H)+ 550.2,
found 550.3. HRMS (ESI-orbitrap) m/z calcd for C31H36NO6PNa [M
+ Na]+ 572.2178, found 572.2163.
(R,R,S,S)-3-((1′-(N-tert-Butoxycarbonyl)-amino)-2′-
phenylethyl)adamantyloxyphosphinyl) Propanoic Acid Ethyl
Ester (9). Following the same procedure as described for compound
7, 0.59 g of compound 9 was obtained as gummy solid in 91% yield
starting from 3. Rf = 0.82 (ethyl acetate). 1H NMR (200 MHz,
CDCI3) mixture of two diastereoisomers ∼72:33, only signals of the
major isomer are given: δ 1.20−l.30 (s+t, J = 7.2 Hz, 12H), 1.46−1.75
(m, 6H), 2.00−2.22 (m, 11H), 2.40−2.90 (m, 3H), 3.10−3.35 (m,
1H), 4.01−4.24 (m+q, J = 7.2 Hz, 3H), 4.68 (d, J = 10.6 Hz, lH),
7.21−7.31 (m, 5H); 13C NMR (50 MHz, CDCI3) δ 14.1, 24.0 (d, 1JPC
1
1
20.6 (d, 1JPC = 90.9 Hz), 21.3 (d, JPC = 90.9 Hz), 26.3, 33.7, 50.6 (d,
= 89.0 Hz), 24.2 (d, JPC = 89.0 Hz), 28.3, 31.4, 34.2, 35.6, 44.6, 50.0
(d, 1JPC = 111.3 Hz), 60.7, 79.6, 83.9 (d, 2JPC= 10.1 Hz), 126.6, 126.7,
1JPC = 106.3 Hz), 51.4, 60.8, 66.4, 126.4, 126.5, 127.3, 127.5, 128.1,
3
3
3
128.5, 129.4, 136.9, 137.0, 155.4 (d, JPC = 7.1 Hz), 175.6 (d, JPC
=
128.2, 128.8, 136.1, 136.2, 136.4, 156.1 (d, JPC = 4.9 Hz), 171.8 (d,
17.4 Hz); 31P NMR (81 MHz, CDCI3) 49.65, 49.97; ESMS m/z calcd
for C28H42NO6P (M + H)+ 520.3, found 520.4. HRMS (ESI-orbitrap)
m/z calcd for C28H42NO6PNa [M + Na]+ 542.2647, found 542.2658.
(R,R,S,S)-3-((1′-(N-Benzyloxycarbonyl)-amino)-2′-
phenylethyl)methyloxyphosphinyl) Propanoic Acid tert-Butyl
Ester (10). Following the same procedure as described for compound
6, 1.12 g of compound 10 was obtained as gummy solid in 91% yield
3JPC = 15.1 Hz). 31P NMR (81 MHz, CDCl3) δ 54.44, 55.44; ESMS
m/z calcd for C22H29NO6P (M + H)+ 434.2, found 434.1.
(R,R,S,S)-3-((1′-(N-Benzyloxycarbonyl)-amino)-2′-
phenylethyl)adamantyloxyphosphinyl) Propanoic Acid Ethyl
Ester (7).25 To a refluxing solution of compound 1 (360 mg, 0.86
mmol) and 1-adamantyl bromide (0.22 g, 1.03 mmol) in CHCl3 (8
mL) was added silver(I) oxide (0.24 g, 1.03 mmol) portion wise over 1
h. After the solution was refluxed for 2 h, the solvent was removed in
vacuo, and the residue was treated with Et2O (10 mL). The resulting
mixture was filtered through Celite, and the filtrate was evaporated.
The residue was purified by column chromatography using CH2Cl2/
MeOH 9.8−0.2 as eluent to give 0.39 g of 7 as white solid (82%). Rf =
1
starting from 4. Rf = 0.70 (CH2Cl2/MeOH 9.5−0.5). H NMR (200
MHz, CDCl3) mixture of two diastereoisomers ∼68:32, only signals of
the major isomer are given: δ 1.38 (s, 9H), 1.90−2.18 (m, 2H), 2.37−
2.60 (m, 2H), 2.65−2.98 (m, 1H), 3.06−3.30 (m, 1H), 3.60(s, 3H/2),
3.65 (s, 3H/2), 4.18−4.40 (m, 1H), 4.94 (s, 2H), 6.61 (d, 3JHH = 10.0
Hz, 1H), 7.10−7.40 (m, 10H); 13C NMR (50 MHz, CDCl3) δ 20.5 (d,
1JPC = 91.5 Hz), 21.4 (d, 1JPC = 91.5 Hz), 28.2, 34.1, 34.7 (d, 2JPC = 4.0
1
0.79 (ethyl acetate). H NMR (200 MHz, CDCl3) mixture of two
diastereoisomers ∼65:45, only signals of the major isomer are given: δ
1.23 (t, J = 7.0 Hz, 3H), 1.52−1.66 (m, 6H), 2.00−2.19 (m, 11H),
2.20−2.42 (m, 2H), 2.77−3.00 (m, 1H), 3.13−3.36 (m, 1H), 4.11 (q, J
1
Hz), 50.6 (d, JPC = 105.5 Hz), 52.3, 67.0, 81.3, 126.9, 127.0, 127.8,
3
128.0, 128.1, 128.2, 128.6, 129.4, 136.6, 136.7, 137.2, 156.5 (d, JPC
=
10073
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3
5.3 Hz), 171.8 (d, JPC = 14.7 Hz). 31P NMR (81 MHz, CDCl3) δ
(d, 1JPC = 76.6 Hz), 28.2,, 28.7 (d, 2JPC = 17.0 Hz), 34.9 (d, 2JPC = 17.3
Hz), 47.2, 50.5 (d, JPC = 84.3 Hz), 52.8, 67.5, 81.3, 120.2, 125.2,
54.63, 55.87; ESMS m/z calcd for C24H32NO6P (M + H)+ 462.2,
found 462.2. HRMS (ESI-orbitrap) m/z calcd for C24H32NO6PNa [M
+ Na]+ 484.1865, found 484.1872.
(R,R,S,S)-3-((1′-(N-Benzyloxycarbonyl)-amino)-2′-
phenylethyl)methyloxyphosphinyl) Propanoic Acid Allyl Ester
(11). Following the same procedure as described for compound 6,
0.30 g of compound 11 were obtained as gummy solid in 93% yield
1
125.3, 127.1, 127.3, 127.9, 128.7, 129.4, 129.5, 136.5, 136.7, 141.4,
3
3
143.7, 144.0, 155.9 (d, JPC = 5.4 Hz,), 171.4 (d, JPC = 15.4 Hz). 31P
NMR (81 MHz, CDCl3) δ 106.52; ESMS m/z calcd for C31H36NO5PS
(M + Na)+ 588.2, found 588.3. HRMS (ESI-orbitrap) m/z calcd for
C31H36NO5PSNa [M + Na]+ 588.1950, found 588.1946
(R,R,S,S)-3-((1′-(N-tert-Butoxycarbonyl)-amino)-2′-
phenylethyl)adamantyloxythiophosphinyl) Propanoic Acid
Ethyl Ester (15). Following the general procedure (A), compound
15 was obtained from phosphinate 9 as solid in 80% yield. Rf = 0.77
1
starting from 5. Rf = 0.73 (CH2Cl2/MeOH 9.5−0.5). H NMR (200
MHz, CDCl3) mixture of two diastereoisomers ∼62:38, only signals of
the major isomer are given: δ 1.90−2.20 (m, 2H), 2.48−2.70 (m, 2H),
2.73−2.97 (m, 1H), 3.07−3.30 (m, 1H), 3.62(s, 3H/2), 3.68 (s, 3H/
2), 4.19−4.38 (m, 1H), 4.45−4.60 (m, 2H), 5.00 (s, 2H), 5.16−5.30
1
(CH2Cl2/EtOAc 9.5−0.5). H NMR (200 MHz, CDCI3) mixture of
two diastereoisomers ∼72:33, only signals of the major isomer are
given: δ 1.20-l.38 (s+t, J = 7.2 Hz, 12H), 1.61 (bs, 6H), 2.05−2.22 (m,
9H), 2.25−2.40 (m, 2H, PCH2), 2.50−2.98 (m, 3H), 3.13−3.30 (m,
1H), 4.01−4.24 (m+q, J = 7.2 Hz, 3H) 4.70 (d, J = 11.0 Hz, lH,),
7.21−7.31 (m, 5H); 13C NMR (50 MHz, CDCI3) δ 14.4, 28.3, 29.4
3
(m, 2H), 5.72−5.97 (m,1H), 6.37 (d, JHH = 9.7 Hz, 1H), 7.05−7.38
(m, 10H); 13C NMR (50 MHz, CDCl3) δ 20.7 (d, JPC = 90.7 Hz),
1
1
1
21.2 (d, JPC = 90.7 Hz), 26.7, 34.1, 50.5 (d, JPC = 116.8 Hz), 52.2,
65.9, 67.0, 118.7, 126.9, 127.1, 127.8, 128.1, 128.2, 128.8, 129.4, 136.4,
3
3
1
136.6, 136.8, 137.0, 132.0, 156.5 (d, JPC = 5.1 Hz), 172.3 (d, JPC
=
(d, JPC = 82.6 Hz), 31.5, 34.8 (d, J = 5.9 Hz), 36.0, 44.4 (d, J = 4.2
14.0 Hz). 31P NMR (81 MHz, CDCl3) δ 54.18, 55.13; ESMS m/z
calcd for C23H28NO6P (M + H)+ 446.2, found 446.1. HRMS (ESI-
orbitrap) m/z calcd for C23H28NO6PNa [M + Na]+ 468.1552, found
468.1547.
1
2
Hz), 52.0 (d, JPC = 92.1 Hz), 61.0, 80.2, 85.3 (d, JPC= 10.8 Hz),
126.7, 126.8, 128.5, 129.4, 137.1, 137.4, 155.1 (d, 3JPC = 6.0 Hz), 175.1
(d, 3JPC = 7.1 Hz); 31P NMR (81 MHz, CDCl3) δ 91.21, 92.47; ESMS
m/z calcd for C28H42NO5PS (M + H)+ 536.3, found 536.4. HRMS
(ESI-orbitrap) m/z calcd for C28H42NO5PSNa [M + Na]+ 558.2419,
found 588.2409.
General Procedure for the Synthesis of Thiophosphinates
(A). To a stirred solution of phosphinate (1 mmol) in dry toluene (5
mL) under argon atmosphere was added Lawesson’s reagent (0.5
mmol), and the reaction mixture was heated at 95 °C for 2 h. The
solvent was removed in vacuo, and the residue was purified with
column chromatography using CH2Cl2/EtOAc 9.5−0.5 as eluent.
(R,R,S,S)-3-((1′-(N-Benzyloxycarbonyl)-amino)-2′-
phenylethyl)methyloxythiophosphinyl) Propanoic Acid Ethyl
Ester (12). Following the general procedure (A), compound 12 was
obtained from phosphinate 6 as solid in 89% yield. Rf = 0.40 (CH2Cl2/
EtOAc 9.5−0.5). 1H NMR (200 MHz, CDCl3) mixture of two
diastereoisomers ∼75:25, only signals of the major isomer are given: δ
1.27 (t, J = 7.2 Hz, 3H), 2.17−2.36 (m, 2H), 2.57−2.70 (m, 2H),
2.76−3.00 (m, 1H), 3.09−3.31 (m, 1H), 3.62 (s, 3H/2), 3.69 (s, 3H/
2), 4.14 (q, J = 7.2 Hz, 2H), 4.40−4.61 (m, 1H), 4.98 (s, 2H), 5.05 (d,
J = 11.0 Hz, 1H), 7.18−7.30 (m, 10H); 13C NMR (50 MHz, CDCl3) δ
(R,R,S,S)-3-((1′-(N-Benzyloxycarbonyl)-amino)-2′-
phenylethyl)methyloxythiophosphinyl) Propanoic Acid tert-
Butyl Ester (16). Following the general procedure (A), compound 16
was obtained from phosphinate 10 as solid in 89% yield. Rf = 0.72
1
(CH2Cl2/EtOAc 9.5−0.5). H NMR (200 MHz, CDCl3) mixture of
two diastereoisomers ∼68:32, only signals of the major isomer are
given: δ 1.43 (s, 9H), 2.06−2.38 (m, 2H), 2.42−2.62 (m, 2H), 2.67−
2.97 (m, 1H), 3.08−3.29 (m, 1H), 3.63(s, 3H/2), 3.68 (s, 3H/2),
4.22−4.60 (m, 1H), 4.97 (s, 2H), 7.05−7.38 (m, 11H); 13C NMR (50
1
1
MHz, CDCl3) δ 27.4 (d, JPC = 69.5 Hz), 27.2 (d, JPC = 69.5 Hz),
2
2
1
28.3, 34.9 (d, JPC = 7.1 Hz), 35.4 (d, JPC = 5.0 Hz), 53.0 (d, JPC
=
83.9 Hz), 52.4, 67.3, 81.4, 127.0, 127.1, 128.0, 128.2, 128.3, 128.4,
3
3
129.4, 136.3, 136.4, 137.2, 155.8 (d, JPC = 5.6 Hz), 171.5 (d, JPC
=
13.8 Hz). 31P NMR (81 MHz, CDCl3) δ 105.1, 106.4; ESMS m/z
1
1
13.8, 27.0 (d, JPC = 70.0 Hz), 27.7, 36.0, 53.6 (d, JPC = 75.8 Hz),
51.5, 61.0, 66.7, 126.2, 126.4, 127.1, 127.4, 127.5, 128.2, 128.3, 128.8,
136.1, 136.3, 136.4, 156.0 (d, 3JPC = 5.0 Hz), 171.8 (d, 3JPC = 15.4 Hz).
31P NMR (81 MHz, CDCl3) δ 104.87, 106.09; ESMS m/z calcd for
calcd for C24H32NO5PS (M + H)+ 477.2, found 422.2 (M − Bu).
t
HRMS (ESI-orbitrap) m/z calcd for C24H32NO5PSNa [M + Na]+
500.1637, found 500.1633.
(R,R,S,S)-3-((1′-(N-Benzyloxycarbonyl)-amino)-2′-
phenylethyl)methyloxythiophosphinyl) Propanoic Acid Allyl
Ester (17). Following the general procedure (A), compound 17 was
obtained from phosphinate 11 as solid in 92% yield. Rf = 0.78
C22H28NO5PS (M + H)+ 450.1, found 450.0. HRMS (ESI-orbitrap)
m/z calcd for C22H28NO5PSNa [M + Na]+ 472.1323, found 472.1313.
(R,R,S,S)-3-((1′-(N-Benzyloxycarbonyl)-amino)-2′-
phenylethyl)adamantyloxythiophosphinyl) Propanoic Acid
Ethyl Ester (13). Following the general procedure (A), compound
13 was obtained from phosphinate 7 as solid in 84% yield. Rf = 0.65
1
(CH2Cl2/EtOAc 9.5−0.5). H NMR (200 MHz, CDCl3) mixture of
two diastereoisomers ∼62:38, only signals of the major isomer are
given: δ 2.10−2.40 (m, 2H), 2.47−2.68 (m, 2H), 2.71−2.98 (m, 1H),
3.05−3.27 (m, 1H), 3.61(s, 3H/2), 3.68 (s, 3H/2), 4.37−4.47 (m,
1H), 4.50−4.65 (m, 2H), 4.96 (s, 2H), 5.10−5.30 (m, 2H), 5.78−6.00
(m, 1H), 6.97 (d, 3JHH = 9.7 Hz, 1H), 7.10−7.40 (m, 10H); 13C NMR
(50 MHz, CDCl3) δ 27.0 (d, 1JPC = 70.2 Hz), 27.4 (d, 1JPC = 70.2 Hz),
1
(CH2Cl2/EtOAc 9.5−0.5). H NMR (200 MHz, CDCl3) mixture of
two diastereoisomers ∼65:45, only signals of the major isomer are
given: δ 1.25 (t, J = 7.0 Hz, 3H), 1.54−1.64 (m, 6H), 2.05−2.20 (m,
11H), 2.20−2.40 (m, 2H), 2.50−2.70 (m, 2H), 2.72−3.00 (m, 1H),
3.11−3.35 (m, 1H), 3.38−3.55 (m, 1H) 4.12 (q, J = 7.0 Hz, 2H),
4.06−4.40 (m, 1H), 4.95 (s+d, 3H), 7.10−7.40 (m, 10H); 13C NMR
1
27.6, 34.1 (2JPC = 5.8 Hz), 53.4 (d, JPC = 85.0 Hz), 52.8, 65.9, 67.3,
118.8, 127.0, 127.1, 127.8, 128.1, 128.2, 128.8, 129.4, 136.3, 136.6,
1
(50 MHz, CDCl3) δ 14.4, 28.4, 29.3 (d, JPC = 81.3 Hz), 31.0, 34.8,
36.3, 44.9, 52.8 (d, JPC = 90.2 Hz), 60.7, 67.0, 84.9, 126.9, 127.9,
3
3
1
136.8, 132.1, 156.0 (d, JPC = 6.0 Hz), 172.2 (d, JPC = 15.2 Hz). 31P
NMR (81 MHz, CDCl3) δ 104.8, 105.9; ESMS m/z calcd for
C23H28NO5PS (M + H)+ 462.1, found 462.2. HRMS (ESI-orbitrap)
m/z calcd for C23H28NO5PSNa [M + Na]+ 484.1323, found 484.1310.
General Procedure for the Saponification Experiments (B).
To a stirred solution of thiophosphinate (25 mg) in MeOH (1 mL)
was added a 4 N aqueous solution of NaOH (0.1 mL). After 1 h at
room temperature, the reaction mixture was concentrated in vacuo,
and the conversion ratios appearing in Table 2 were determined by 31P
NMR using D2O as solvent. The products were acidified and purified,
when possible, using appropriate eluent systems and characterized.
General Procedure for the Acid-Catalyzed Experiments (C).
Method (i). The thiophosphinate (25 mg) was dissolved in the
appropriate solution of TFA/CH2Cl2/H2O, and the resulting mixture
was stirred at room temperature. After the indicated reaction time, the
mixture was concentrated to dryness. The determination of the
3
127.8, 128.1, 129.2, 129.4, 136.3, 136.7, 137.0, 137.2, 156.6 (d, JPC
=
3
5.7 Hz), 172.4 (d, JPC = 15.2 Hz); 31P NMR (81 MHz, CDCl3) δ
91.90, 92.15; ESMS m/z calcd for C31H40NO5PS (M + H)+ 570.2
found 570.4. HRMS (ESI-orbitrap) m/z calcd for C31H40NO5PSNa
[M + Na]+ 592.2263, found 592.2249.
(R,R,S,S)-3-((1′-(N-(9-Fluorenylmethoxycarbonyl)-amino)-2′-
phenylethyl)methyloxythiophosphinyl) Propanoic Acid tert-
Butyl Ester (14). Following the general procedure (A), compound 14
was obtained from phosphinate 8 as solid in 82% yield. Rf = 0.40
(CH2Cl2).1H NMR (200 MHz, CDCl3) mixture of two diaster-
eoisomers ∼70:30, only signals of the major isomer are given: δ 1.42
(s, 9H), 2.18−2.38 (m, 2H), 2.43−2.68 (m, 2H), 2.79−3.00 (m, 1H),
3.11−3.30 (m, 1H), 3.64(s, 3H/2), 3.71 (s, 3H/2), 3.98−4.13 (m,
2H), 4.14−4.40 (m, 2H), 5.10 (d, J = 10.5 Hz, 1H), 7.10−7.78 (m,
13H); 13C NMR (50 MHz, CDCl3) δ 26.2 (d, JPC = 76.6 Hz), 27.3
1
10074
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The Journal of Organic Chemistry
Article
conversion percentages reported in Table 2 was based on 31P NMR
spectra of the crude reaction product in CDCl3.
Method (ii). Thiophosphinate 12 (30 mg) was stirred for 1 h in
33% HBr/AcOH (0.5 mL) in a flask fitted with a CaCl2 drying tube.
Toluene was added, and the volatiles were removed in vacuo. The
procedure was repeated twice, and the residue was analyzed by 31P
NMR and mass spectrometry.
104.54, 106.00; ESMS m/z calcd for C27H27NO5PS (M − H)+ 508.1,
found 508.1. HRMS (ESI-orbitrap) m/z calcd for C27H28NO5PSNa
[M + Na]+ 532,1323, found 532,1329.
(R,S)-3-((1′-(N-Benzyloxycarbonylamino)-2′-phenylethyl)-
hydroxythiophosphinyl) Propanamide Ammonium Salt (26).
Following the general procedure (D), compound 26 was obtained as
1
solid in 76% yield. Rf = 0.29 (CHCl3/MeOH/AcOH 7−0.5−0.5). H
NMR (DMSO-d6) δ 1.62−1.85 (bq, 2H), 2.00−2.25 (bq, 2H), 2.58−
2.80 (m, 1H), 3.00−3.20 (m, 1H), 3.70−3.85 (m, 1H), 4.86 (s, 2H),
6.41 (d, J = 6.4 Hz, 1H), 6.68 (bs, 1H), 7.13−7.23 (m, 11H); 13C
NMR (DMSO-d6) δ 29.7, 31.6 (d, 1JPC = 68.9 Hz), 34.7, 55.8 (d, 1JPC
= 77.1 Hz), 65.5, 126.3, 127.0, 127.8, 128.3, 128.5, 129.5, 129.8, 138.0,
Method (iii). Thiophosphinate 14 (50 mg, 0.09 mmol) was treated
with TFA/CH2Cl2/TIPS 50−49.5−0.5, at room temperature for 30
min followed by concentration to dryness. CH2Cl2 was added and
concentrated again. The crude reaction mixture was purified by
column chromatography using CHCl3/MeOH 9.5−0.5 as eluent to
give 24 as a glassy solid in 98% yield (44 mg).
General Procedure for the Base-Catalyzed Experiments (D).
The thiophosphinate (25 mg) was stirred for the time and the
conditions mentioned in Table 2 until total consumption of the
starting material as judged by TLC. Then the volatile materials were
removed in vacuo, and the residue was treated with CHCl3. The solid
was filtered and stored in the form of the salt.
General Procedure for the Coupling Experiments (E). EDC·
HCl (1.2 equiv) and N,N-diisopropylethylamine (3 equiv) were added
to a solution of amine (1 equiv), acid (1 equiv), and HOBt (1.2 equiv)
in CH2Cl2 (5 mL/1 mmol) and stirred for 18 h at room temperature.
The solvent was removed in vacuo, the residue was partitioned
between EtOAc/H2O, and the organic phase was washed with 5%
NaHCO3, 0. 5N HCl, and H2O, and dried over Na2SO4. The organic
solvent was removed, and the residue was purified by column
chromatography.
140.7, 156.2 (d, JPC = 5.3 Hz), 175.4 (d, JPC = 15.4 Hz); 31P NMR
(DMSO-d6) δ 71.21; ESMS m/z calcd for C19H23N2O4PS (M − H −
NH3)− 405.1, found 405.1. HRMS (ESI-orbitrap) m/z calcd for
C19H22N2O4PS [M − H − NH3]− 405.1038, found 405.1033.
(R,S)-3-((1′-(N-Benzyloxycarbonyl)-amino)-2′-phenylethyl)-
hydroxy thiophosphinyl) Propanoic Acid tert-Butyl Ester
Dimethylammonium Salt (27). Following the general procedure
(D), compound 27 was obtained as solid in 70% yield. Rf = 0.48
3
3
1
(CHCl3/MeOH/AcOH 7−0.5−0.5). H NMR (200 MHz, CDCl3) δ
1.41 (s, 9H), 1.90−2.10 (m, 2H), 2.51−2.70 (m, 8H), 2.75−3.10 (m,
2H), 4.00−4.20 (m, 1H), 4.91 (s, 2H), 5.28 (d, J = 5.3 Hz 1H), 7.05−
1
7.38 (m, 10H); 13C NMR (50 MHz, CDCl3) δ 30.0 (d, JPC = 64.3
Hz), 28.3, 29.7, 30.0 (d, 1JPC = 64.3 Hz), 35.2, 54.1 (d, 1JPC = 86.1 Hz),
67.8, 81.1, 126.6, 127.9, 128.7, 129.7, 136.8, 138.3, 156.2 (d, 3JPC = 4.6
3
Hz), 173.4 (d, JPC = 7.8 Hz);31P NMR (81 MHz, CDCl3) δ 77.45;
ESMS m/z calcd for C23H29NO5PS (M − H − dimethylamine)−
462.1, found 462.2. HRMS (ESI-orbitrap) m/z calcd for
C23H29NO5PS [M − H − dimethylamine]− 462.1510, found
462.1524.
(R,R,S,S)-3-((1′-(N-Benzyloxycarbonyl)-amino)-2′-
phenylethyl)methyloxyphosphinyl) Propanoic Acid (22). Fol-
lowing the general procedure (B), compound 22 was obtained as
foamy solid in 85% yield after column chromatography using CHCl3/
MeOH 9−1 as eluent. Rf = 0.39 (CHCl3/MeOH 9−1). 1H NMR (200
MHz, CDCl3) mixture of two diastereoisomers only signals of the
major isomer are given: δ 2.17−2.36 (m, 2H), 2.57−3.00 (m, 3H),
3.09−3.25 (m, 1H), 3.62 (s, 3H/2), 3.69 (s, 3H/2), 4.40−4.61 (m,
1H), 4.98 (s, 2H), 5.25 (d, J = 5.5 Hz, 1H), 7.00−7.40 (m, 10H), 9.25
Cbz-(R,S)Phe-ψ[P(S)(OMe)]Gly-(S)Leu-OMe (28). Following the
general procedure (E), using H-(L)Leu-OMe.HCl as amine and 22 as
acid, compound 28 was obtained as solid in 70% yield after column
chromatography using CHCl3/EtOAc 4−1 as eluent. Rf = 0.72
(CHCl3/ethyl acetate 1−1). 1H NMR (200 MHz, CDCl3): mixture of
four diastereoisomers, δ 0.92 (s, 3H), 1.11(s, 3H), 1.23 (s, 1H), 1.40−
1.70 (m, 4H), 2.20−2. 90 (m, 3H), 3.08−3.32 (m, 1H), 3.64 (s, 3H/
2), 3.70 (s, 3H/2), 4.40−4.58 (m, 2H), 4.98 (bs, 2H), 5.40 (bd, 1H),
6.35 (bd, 1H), 7.10−7.30 (m, 10H); 13C NMR (50 MHz, CDCl3) δ
21.1, 23.4, 25.0, 27.3 (set of 3d, 1JPC = 68.7 Hz), 29.4, 34.8, 41.6, 51.2,
1
(bs, 1H); 13C NMR (50 MHz, CDCl3) δ 27.0 (d, JPC = 71.0 Hz),
1
27.9, 34.9, 52.5, 53.7 (d, JPC = 73.8 Hz), 66.7, 126.3, 127.4, 128.4,
128.8, 128.9, 136.0, 136.4, 156.2, 177.4. 31P NMR (81 MHz, CDCl3) δ
104.87, 106.09; ESMS m/z calcd for C20H24NO5PS (M + H)+ 422.1,
found 422.1. HRMS (ESI-orbitrap) m/z calcd for C20H24NO5PSNa
[M + Na]+ for 444.1010, found 444.1006.
1
51.6, 52.3, 53.3 (d, JPC = 71.7 Hz), 67.3, 126.7, 127.7, 128.0, 128.4,
128.3, 129.5, 135.9, 136.7, 156.5, 171.1, 176.3. 31P NMR (81 MHz,
CDCl3) δ 106.3, 106.0, 105.7, 105.4; ESMS m/z calcd for
C27H37N2O6PS (M + H)+ 549.2, found 549.4. HRMS (ESI-orbitrap)
m/z calcd for C27H37N2O6PSNa [M + Na]+ 571.2008, found
571.2005.
(R,R,S,S)-3-((1′-(N-Benzyloxycarbonyl)-amino)-2′-
phenylethyl)adamantyloxythiophosphinyl) Propanoic Acid
(23). Following the general procedure (B), compound 23 was
obtained as foamy solid quantitatively after column chromatography
using CH2Cl2/isopropyl alcohol 9−1 as eluent. Rf = 0.62 (CH2Cl2/
Cbz-(S)Phe-(R,S)Phe-ψ[P(S)(OMe)]Gly-OEt (29). Following the
general procedure (E), using 25 as amine and Cbz-(L)Phe-OH as acid,
compound 29 was obtained as solid in 61% yield after column
chromatography using CHCl3/EtOAc 4−1 as eluent. Rf = 0.59
1
isopropyl alcohol 9−1). H NMR (200 MHz, CDCl3) mixture of two
diastereoisomers ∼65:45, only signals of the major isomer are given: δ
1.54−1.64 (m, 6H), 2.05−2.20 (m, 11H), 2.22−2.42 (m, 2H), 2.55−
3.00 (m, 3H), 3.11−3.35 (m, 1H), 3.40−3.52 (m, 1H), 4.40−4.55 (m,
1H), 4.91−5.17 (m, 3H), 7.15−7.30 (m, 10H), 8.05 (bs, 1H); 13C
1
(CHCl3/EtOAc 4−1). H NMR (200 MHz, CDCl3): mixture of four
diastereoisomers, δ 1.10−1.40 (m, 2H), 1.80−2.90 (m, 4H), 3.08−
3.32 (m, 1H), 3.30−3.50 (m, 1H), 3.64 (d, 3H/2), 3.70 (d, 3H/2),
4.00−4.20 (m, 2H), 4.20−4.40 (bd, 1H), 5.00 (bs, 2H), 5.30 (bd, 1H),
6.40 (bd, 1H), 7.10−7.40 (m, 15H); 13C NMR (50 MHz, CDCl3) δ
1
NMR (50 MHz, CDCl3) δ 25.4, 29.2 (d, JPC = 72.3 Hz), 28.5, 34.6,
1
35.9, 44.5, 53.2 (d, JPC = 85.2 Hz), 67.3, 85.7, 126.9, 128.0, 128.3,
128.4, 128.7, 129.5, 136.3, 136.3, 136.8, 137.2, 156.1, 177.4; 31P NMR
(81 MHz, CDCl3) δ 91.73, 91.51, 90.49, 89.24; ESMS m/z calcd for
C29H36NO5PS (M − H)− 540.2 found 540.1. HRMS (ESI-orbitrap)
m/z calcd for C29H36NO5PSNa [M + Na]+ 564.1950, found 564.1947.
(R,R,S,S)-3-((1′-(N-(9-Fluorenylmethoxycarbonyl)-amino)-2′-
phenylethyl)methyloxyphosphinyl) Propanoic Acid (24). Fol-
lowing the general procedure (C), method (iii), compound 24 was
1
1
14.4, 26.5 (d, JPC = 74.7 Hz), 27.7, 34.5, 37.7, 52.8, 52.9 (3d, JPC
=
72.0 Hz), 61.3, 67.5, 127.1, 128.0, 128.2, 128.4, 128.8, 129.5, 136.2,
136.6, 156.1, 171.0, 172.7. 31P NMR (81 MHz, CDCl3) δ 106.2, 106.1,
105.0, 104.7; ESMS m/z calcd for C31H37N2O6PS (M + H)+ 597.2,
found 597.2. HRMS (ESI-orbitrap) m/z calcd for C31H38N2O6PS [M
+ H]+ 597.2188, found 597.2192.
1
obtained. Rf = 0.30 (CHCl3/MeOH 9.5−0.5). H NMR (200 MHz,
CDCl3) mixture of two diastereoisomers only signals of the major
isomer are given: δ 2.15−2.45 (m, 2H), 2.55−2.85 (m, 3H), 3.10−
3.27 (m, 1H), 3.63 (s, 3H/2), 3.68 (s, 3H/2), 4.00−4.51 (m, 4H),
5.07 (d, J = 5.1 Hz, 1H), 7.00−7.91 (m, 14H); 13C NMR (50 MHz,
CDCl3) δ 26.4 (d, 1JPC = 78.5 Hz), 27.8, 34.8, 47.1, 52.6 (d, 1JPC = 79.8
Hz), 54.1, 66.6, 120.2, 125.2, 127.3, 128.0, 128.8, 129.4, 136.3, 141.5,
143.9, 156.0, 177.5 (d, 3JPC = 8.5 Hz). 31P NMR (81 MHz, CDCl3) δ
ASSOCIATED CONTENT
■
S
* Supporting Information
1
Copies of H, 13C, and 31P NMR spectra of 6, 8−12, 14−17,
22−24, and 26−29. This material is available free of charge via
the Internet at http://pubs.acs.org.
10075
dx.doi.org/10.1021/jo401084v | J. Org. Chem. 2013, 78, 10069−10076

The Journal of Organic Chemistry
Article
AUTHOR INFORMATION
Corresponding Author
*E-mail:svassiliou@chem.uoa.gr.
■
Notes
The authors declare no competing financial interest.
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