Synthesis of achiral α,α-bis(aminomethyl)-β-alanines and their use in the preparation of branched β-peptide conjugates of N-2-alkyl-1,2,3,4-tetrahydroisoquinolines on solid support

Article abstract of DOI:10.1002/1099-0690(200011)2000:21<3647::AID-EJOC3647>3.0.CO;2-F

Three achiral branching units 1-3 derived from α,α-bis(aminomethyl)-β-alanine were synthesized and evaluated in the construction of branched and sterically compact β-peptide conjugates on a solid support. Several peptide conjugates bearing an N-alkylated 1,2,3,4-tetrahydroisoquinoline moiety were prepared to demonstrate the applicability of the branching units in a solid phase peptide synthesis. The most useful building block 3 incorporated Boc-protected aminomethyl side chains at the α-carbon of N-phthaloyl-β-alanine.

Full text of DOI:10.1002/1099-0690(200011)2000:21<3647::AID-EJOC3647>3.0.CO;2-F

FULL PAPER
Synthesis of Achiral α,α-Bis(aminomethyl)-β-alanines and Their Use in the
Preparation of Branched β-Peptide Conjugates of N-2-Alkyl-1,2,3,4-
tetrahydroisoquinolines on Solid Support
Petri Heinonen,*[a] Jaana Rosenberg,[a] and Harri Lönnberg[a]
Keywords: Solid-phase synthesis / Peptides / Peptide conjugates / Amino acids
Three achiral branching units 1−3 derived from α,α-bis(ami-
ety were prepared to demonstrate the applicability of the
nomethyl)-β-alanine were synthesized and evaluated in the branching units in a solid phase peptide synthesis. The most
construction of branched and sterically compact β-peptide
conjugates on a solid support. Several peptide conjugates
bearing an N-alkylated 1,2,3,4-tetrahydroisoquinoline moi-
useful building block 3 incorporated Boc-protected amino-
methyl side chains at the α-carbon of N-phthaloyl-β-alanine.
Introduction
Results and Discussion
Branched peptides and peptide-like oligomers have re- Synthesis of Protected Bis(aminomethyl)-β-alanine Building
cently attracted increasing attention owing to their poten- Blocks
tial applications in medical sciences.[1] However, only a lim-
ited number of branching units are available. In fact most
Building block 1 was synthesized from commercially
available 2,2-bis(bromomethyl)-1,3-propanediol (4), as de-
of the syntheses are simply based on the use of lysine for
picted in Scheme 1. Two slightly different routes were em-
branching. We have previously reported on the synthesis of
ployed: either one of the hydroxy functions of 4 was dis-
novel achiral α,α-disubstituted β-alanines, and their use in
placed with a phthalimido group under Mitsunobu condi-
the preparation of linear β-peptide conjugates on a solid
tions[3] without prior protection of the other hydroxy func-
support.[2] In the present study, the methodology is ex-
tion (6), or one of the hydroxy functions was protected with
tended to the preparation of branched β-peptide conjugates.
a monomethoxytrityl group (5) before the Mitsunobu reac-
Three novel achiral branching units (1؊3) derived from
tion (7) and subsequently deprotected (6). The latter route
α,α-bis(aminomethyl)-β-alanine were synthesized (Fig-
hence consists of two additional reaction steps, but 6 can
ure 1). The one bearing Boc-protected aminomethyl side
still be obtained in a far better total yield. Displacement
chains at the α-carbon of N-phthaloyl-β-alanine (3) allowed
of the bromo substituents of 6 with azide ion, and Jones’
convenient solid support preparation of branched β-pep-
oxidation of the hydroxy group to a carboxy group com-
pleted the synthesis of 1.
tides that contained either three identical peptide chains
bound to the α-carbon of the branching unit, or two iden-
The synthesis of building block 2 started from 2-bromo-
tical and one different chain. In both cases achirality is pre-
methyl-2-hydroxymethyl-1,3-propanediol.[4] One of the hy-
served. A set of such β-peptide conjugates containing an N-
droxy functions was protected with a monomethoxytrityl
group (Ǟ 9), and the remaining two were displaced with
alkylated 1,2,3,4-tetrahydroisoquinoline core was prepared.
The purpose of this core structure was to anchor the pep-
tides close to the binding site of the α2-adrenergic receptors
to probe the receptor structure. The conjugate group does
not, however, play any essential role in the assembly of the
branched peptide chain, and 3 can be utilized equally well
in solid phase syntheses of branched β-peptides bearing no
conjugate group.
Figure 1. Building blocks for the synthesis of branched β-peptides
Scheme 1. Synthesis of building blocks 1؊3: (i) MMTrCl, Py;
[a]
Department of Chemistry, University of Turku,
20014 Turku, Finland
Fax: (internat.) ϩ 358-2/333-6700
E-mail: petheino@utu.fi
(ii) phthalimide, PPh3, DEAD, THF; (iii) DCA, CH2Cl2; (iv)
NaN3, LiCl, DMF; (v) CrO3, H2SO4, acetone; (vi) NaBH4,
HS(CH2)3SH, iPrOH; (vii) Boc2O, NaOH, MeCN, H2O; (viii) I2,
MeOH, DCM
Eur. J. Org. Chem. 2000, 3647Ϫ3652
WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
1434Ϫ193X/00/1121Ϫ3647 $ 17.50ϩ.50/0
3647

P. Heinonen, J. Rosenberg, H. Lönnberg
FULL PAPER
phthalimide by Mitsunobu reaction (Ǟ 10). The monome-
thoxytrityl protection was removed (Ǟ 11) under acidic
conditions, and an azido function was brought into the
molecule by displacement of the bromo substituent with az-
ide ion (Ǟ 12). Oxidation of the hydroxy function to a car-
boxy group gave the building block 2.
To obtain building block 3, the two bromo substituents
of 5 were displaced with the azide ion (Ǟ 13), and the azido
functions were reduced with sodium borohydride/propane-
edithiol (Ǟ 14).[5] The amino groups were protected with
Boc anhydride (Ǟ 15), and the phthaloyl protected third
amino function was introduced into the molecule by Mitsu-
nobu reaction (Ǟ 16). The monomethoxytrityl protection
was removed by treatment with iodine in methanol/dichlo-
romethane,[6] and oxidation to acid 3 completed the syn-
thesis.
Figure 2. The model compound 18 analysed by HPLC (Hypersil
Hypurity C18, gradient from aqueous 0.1% TFA to acetonitrile in
30 min, flow 1.0 mL/min, detection at 276 nm); MS (ESI): 18 (peak
at 22.32 min) found 1695.9 [M ϩ H]ϩ and 848.5 [M ϩ 2 H]ϩ,
C84H115N11O26 ϩ H requires 1694.8
Deprotection of the Amino Functions and Coupling of the
Amino Acid Building Blocks 1؊3 on a Solid Support
The amino acid building blocks 1؊3 could be coupled
through their carboxy function almost quantitatively to hy-
droxymethyl polystyrene-supported free amine functions.
On using HATU activation, the peptide coupling of 1 or 2
to the support-bound primary amine was completed in an
hour, and that of 3 in 5 hours. In spite of its slower coup-
The Solid Phase Synthesis of Branched β-Peptide
Conjugates
β-Peptide conjugate 18 was prepared to verify the com-
ling, 3 turned out to be superior to 1 and 2 as a building patibility of building block 3 with the solid phase peptide
block for the assembly of branched β-peptides on a solid synthesis (Figure 2). The synthesis was carried out on hy-
support. The main reason for this was that reduction of the droxymethyl polystyrene, to which the desired conjugate
azido functions of 1 and 2 to amino groups, allowing the group, Boc protected 5-(3-aminopropoxy)-1,2,3,4-tetrahy-
next peptide coupling, turned out to be unexpectedly diffi- droisoquinoline, was tethered through a diethyl sulfone
cult. Most of the methods described in the literature for linker.[2] The support-bound amino group was deprotected
the reduction of an azido to an amino function on a solid and subjected to HATU activated acylation with building
support[7] were tested. The best, but still not satisfactory, block 3. The phthaloyl protection of the introduced branch-
result was achieved with a tin(II) chloride/thiophenol/tri- ing unit was removed by hydrazinolysis, and the β-peptide
ethylamine system. Different concentration ratios and reac- chain was elongated with an achiral N-phthaloyl-β-alanine
tion times were tried without significant improvement of building block. Subsequently, the Boc protection of the
the yield. In the case of 1, the reduction yielded 34% of the branching unit was removed and the exposed amino groups
desired product in 10 minutes. If shorter reaction times were were acylated with a β-alanine unit. Finally, all phthaloyl
used, the deprotection was incomplete. Longer reaction protections were removed and the chain assembly was ac-
times, in turn, gave rise to several side products. Tentative complished by introducing, in a single step, a β-alanine
explanations for the low yields obtained with 1 include the block onto each of the three amino groups. The conjugate
interference of one azido group in the reduction of the 18 was released from the solid support by quaternization of
other, and the instability of the phthaloyl protection under N-2 of the tetrahydroisoquinoline moiety and subsequent
the applied reaction conditions. Removal of the phthaloyl treatment with triethyl amine.
protection from 2 was also problematic. The hydrazinolysis
The compatibility of commercial amino acid building
of the phthaloyl moiety proceeded slowly in the presence of blocks with 3 was checked by the synthesis of peptide con-
an azido group and led to the formation of side products. jugate 19 (Figure 3). After attachment of building block 3
The Boc protections of 3 could be removed cleanly with to the support-bound conjugate group, the phthaloyl pro-
1  HCl in a 1:2 mixture of MeOH and dichloromethane tection was removed and an achiral β-alanine building
(v/v) or with aluminium chloride.[8] The standard TFA block was coupled to the free amino group. The Boc protec-
treatment, in turn, resulted in a marked increase in the tions were then removed and a dipeptide side chain was
number of side products. The removal of the phthaloyl pro- assembled onto each of the exposed amino groups by using
tection also proceeded slowly in this case, but a quantitative standard Boc chemistry. Conjugate 20 was prepared in or-
deprotection was achieved in 6 hours using 2  hydrazine der to illustrate that more than one branching unit can be
hydrate in a 1:2 mixture of DMF and dioxane (v/v) at 80 inserted in a single peptide (Figure 3). Compounds such as
°C.
20 can obviously be used as a scaffold in the preparation of
3648
Eur. J. Org. Chem. 2000, 3647Ϫ3652

Synthesis of Achiral α,α-Bis(aminomethyl)-β-alanines
FULL PAPER
support. The stoppered vessel was held at 55 °C for 3 h and the
mixture was shaken occasionally. The solid support was filtered
off, washed with dichloromethane and methanol, and dried under
reduced pressure.
Peptide Coupling on a Solid Support: 20 mg of the solid support
was suspended in 0.5 mL of DMF. To this suspension was added
the appropriate amino acid (5 mol equiv. in 0.5 mL of DMF), O-
(7-azabenzotriazol-1-yl)-1,1,3,3-tetramethyluronium hexafluoro-
phosphate (HATU) (5 mol equiv. in 0.5 mL of DMF), and diiso-
propyl ethyl amine (10 mol equiv. in 0.1 mL of DMF). The mixture
was shaken for 6 h and the solid support was filtered off, washed
with dichloromethane and methanol, and dried under reduced
pressure.
Cleavage from the Solid Support: The solid support was shaken
with 1.5 mmol of methyl iodide in DMF for 1 h, filtered off,
washed with dichloromethane and methanol, and dried under re-
duced pressure. The solid support was suspended in a mixture of
triethylamine and dichloromethane (1:1, v/v). After 1 h shaking,
the solution was collected by filtration and evaporated under re-
duced pressure.
2,2-Bis(bromomethyl)-3-(4-methoxytrityloxy)propanol (5): 2,2-bis-
(bromomethyl)-1,3-propanediol (5.27 g, 20.1 mmol) was dried by
repeated evaporation with dry pyridine and then dissolved in dry
pyridine (50 mL). 4-Methoxytrityl chloride (6.21 g, 20.1 mmol) was
added to this solution and the reaction mixture was stirred for 20
h. Methanol (10 mL) was added and most of the pyridine was re-
moved by evaporation. The remaining mixture was dissolved in
dichloromethane and the solution was washed with aq NaHCO3
(3 ϫ 20 mL). The organic layer was dried with Na2SO4, evaporated
to dryness, and the oily residue was purified by silica gel chroma-
tography (dichloromethane) to yield 8.0 g (74%) of a foamy prod-
uct. Rf (dichloromethane) ϭ 0.48. Ϫ 1H NMR (200 MHz, CDCl3):
δ ϭ 1.63 (t, J ϭ 5.7 Hz, 1 H, OH), 3.23 (s, 2 H, CH2OMMTr),
3.51 (s, 4 H, CH2Br), 3.61 (d, J ϭ 5.3 Hz, 2 H, CH2OH), 3.78 (s,
3 H, MMTr OCH3), 6.81 (m, 2 H, MMTr CH), 7.1Ϫ7.5 (m, 12 H,
12 ϫ MMTr CH). Ϫ 13C NMR (50 MHz, CDCl3): δ ϭ 35.1
(CH2Br), 44.8 (Cq, pentaerythritol), 55.2 (MMTr OCH3), 62.4, 63.5
(CH2OH, CH2OMMTr), 86.7 (Cq, MMTr), 113.3, 127.1, 128.0,
128.3, 130.3, 134.8, 143.8, 158.7 (MMTr C). Ϫ MS (EIϩ): 534 [Mϩ]
(5), 457 [Mϩ Ϫ Br] (4), 273 (100). Ϫ HRMS (EI): Mϩ found
472.1078. C25H27O481Br requires 472.1072.
Figure 3. The model compounds 19 and 20 analysed by HPLC
(Hypersil Hypurity C18, gradient from aqueous 0.1% TFA to ace-
tonitrile in 30 min, flow 1.0 mL/min, detection at 276 nm); MS
(ESI): 19 (peak at 19.32 min) found 1096.1 [M
ϩ
H]ϩ,
C53H78N10O15 ϩ H requires 1096.3; 20 (peak at 20.08) 1522.4 [M
ϩ H]ϩ, C71H108N16O21 ϩ H requires 1522.8
2,2-Bis(bromomethyl)-3-(4-methoxytrityloxy)-N-phthaloylprop-
ylamine (7): Diethyl azodicarboxylate (1.93 mL, 12.3 mmol) was
added dropwise to a solution of 5 (5.26 g, 9.9 mmol), phthalimide
(1.80 g, 12.3 mmol) and triphenylphosphane (3.22 g, 12.3 mmol) in
THF. The reaction mixture was stirred for 22 h and concentrated
by evaporation. The product was separated by silica gel chromatog-
raphy (5:95 hexane/dichloromethane) to yield 6.0 g (92%) of a pale
yellow foam. Rf (dichloromethane) ϭ 0.79. Ϫ 1H NMR (400 MHz,
CDCl3): δ ϭ 3.31 (s, 2 H, CH2OMMTr), 3.56 (d, J ϭ 10.9 Hz, 2
H, 2 ϫ CHHBr), 3.65 (d, J ϭ 10.9 Hz, 2 H, 2 ϫ CHHBr), 3.77 (s,
3 H, MMTr OCH3), 3.93 (s, 2 H, CH2Npht), 6.8 (m, 2 H, 2 ϫ
MMTr CH), 7.2Ϫ7.4 (m, 12 H, 12 ϫ MMTr CH), 7.72 (dd, J ϭ
5.7 and 2.9 Hz, 2 H, 2 ϫ Npht CH), 7.82 (dd, J ϭ 5.7 and 2.9 Hz,
2 H, 2 ϫ Npht CH). Ϫ MS (EIϩ): 663 (Mϩ, 2), 374 (4), 289 (2),
273 (100), 160 (15). Ϫ HRMS (FAB): MHϩ found 663.0430.
C33H29NO4Br81Br requires 663.0443.
branched peptides by automated solid phase peptide syn-
thesis.
Experimental Section
Spectroscopy: The NMR spectra were recorded on JEOL JNM-
GX 400 or Bruker 200 NMR spectrometers. The chemical shifts
are given in ppm from internal TMS. Ϫ The mass spectra of small
molecular compounds were recorded on a 7070E VG mass spectro-
meter. Ϫ RP HPLC analyses were performed using Hypersil 150
ϫ 4.6 mm, 5 µm HyPurityԹ Elite C18 column, gradient from aque-
ous 0.1% TFA to acetonitrile in 30 min, flow rate 1.0 mL/min, de-
tection at 276 nm. Ϫ LC/ESI-MS analyses were performed on a
PerkinϪElmer Sciex API 365 LC/MS/MS triple quadrupole mass
spectrometer.
2,2-Bis(bromomethyl)-3-phthalimidopropanol (6): Compound 7 (6.0
g, 9.1 mmol) was dissolved in dichloromethane (120 mL) and meth-
anol (15 mL) and dichloroacetic acid (15 mL) were added. After 24
h stirring, the reaction mixture was washed with aqueous NaHCO3
Removal of N-Phthaloyl Protection on a Solid Support: 3 mL of 2
 hydrazine hydrate in a 1:2 mixture of DMF and dioxane (v/v)
was added to a reaction vessel containing 5 to 50 mg of the solid
Eur. J. Org. Chem. 2000, 3647Ϫ3652
3649

P. Heinonen, J. Rosenberg, H. Lönnberg
FULL PAPER
until neutral, dried with Na2SO4 and evaporated to dryness. The
product was purified by silica gel chromatography (5:95 hexane/
2-Bromomethyl-2-(4-methoxytrityloxy)methyl-N,NЈ-diphthaloyl-
propane-1,3-diamine (10): Diethyl azodicarboxylate (4.6 mL,
dichloromethane) to yield 2.9 g (85%) of a colourless oil. Rf 29 mmol) was added dropwise to a solution of 9 (5.2 g, 11.4 mmol),
(dichloromethane) ϭ 0.31. Ϫ 1H NMR (200 MHz, CDCl3): δ ϭ
phthalimide (4.2 g, 29 mmol) and triphenylphosphane (7.6 g, 29
3.50 (d, J ϭ 5.3 Hz, 2 H, CH2OH), 3.58 (d, J ϭ 4.2 Hz, 2 H, 2 ϫ mmol) in THF. The reaction mixture was stirred for 22 h and con-
CHHBr), 3.65 (s, 2 H, CH2Npht), 3.74 (d, J ϭ 4.2 Hz, 2 H, 2 ϫ centrated by evaporation. The product was separated by silica gel
CHHBr), 7.81 (dd, J ϭ 5.3 and 2.6 Hz, 2 H, 2 ϫ Npht CH), 7.90 chromatography (1:99 MeOH/dichloromethane) to yield 5.7 g
1
(dd, J ϭ 5.3 and J ϭ 2.6 Hz, 2 H, 2 ϫ Npht CH). Ϫ 13C NMR
(68%) of white foam. H NMR (200 MHz, CDCl3): δ ϭ 3.42 (s, 2
(50 MHz, CDCl3): δ ϭ 36.1 (CH2Br), 39.9 (CH2Npht), 44.9 (Cq, H, CH2OH), 3.75 (s, 3 H, MMTr OCH3), 3.77 (s, 2 H, CH2Br),
pentaerythritol), 63.3 (CH2OH), 123.8, 131.4, 134.7 (Npht C), 3.80 (d, J ϭ 14.5 Hz, 2 H, 2 ϫ CHHNpht), 3.95 (d, J ϭ 14.5 Hz,
169.4 (CϭO, Npht). Ϫ MS (EIϩ): 391 [Mϩ] (1), 310 (2), 292 (1),
280 (3), 200 (21), 160 (100). Ϫ HRMS (FAB): MHϩ found
391.9333. C13H14NO3Br81Br requires 391.9320.
2 H, 2 ϫ CHHNpht), 6.75 (m, 2 H, 2 ϫ MMTr CH), 7.1Ϫ7.5 (m,
12 H, 12 ϫ MMTr CH), 7.6Ϫ7.9 (m, 4 H, 4 ϫ Npht CH). Ϫ 13C
NMR (50 MHz, CDCl3): δ ϭ 37.4 (CH2Br), 42.5 (CH2Npht), 45.5
(Cq, pentaerythritol), 55.1 (MMTr OCH3), 65.7 (CH2OMMTr),
87.1 (Cq, MMTr), 112.9, 123.4, 126.8, 127.6, 128.7, 130.7, 132.0,
134.0, 134.9, 143.8, 158.5 (MMTr C and Npht C), 168.7 (CϭO,
Npht). Ϫ IR (KBr): ν˜ ϭ 1774, 1716 (s), 1633, 1394, 1251, 718
cmϪ1. Ϫ HRMS (FAB): MHϩ found 731.1602. C41H34N2O681Br
requires 731.1580.
2,2-Bis(azidomethyl)-3-phthalimidopropanol (8): Compound 6 (0.75
g, 1.9 mmol), NaN3 (0.62 g, 9.6 mmol), and a catalytic amount of
LiCl were dissolved in DMF (35 mL). The mixture was refluxed
for 6 h and evaporated to dryness. The residue was dissolved in
dichloromethane and washed with water. After drying with
Na2SO4, and evaporation of the solvent, the oily residue was puri-
fied by silica gel chromatography (3:97 MeOH/dichloromethane)
to yield 0.38 g (63%) of 8 as a colourless oil. H NMR (200 MHz, (5.5 g, 7.5 mmol) was dissolved in dichloromethane (100 mL). Eth-
3-Bromo-2,2-bis(phthalimidomethyl)propanol (11): Compound 10
1
CDCl3): δ ϭ 1.61 (s, 1 H, OH), 3.41 (s, 2 H, CH2OH), 3.45 (qAB
,
anol (20 mL) and trifluoroacetic acid (10 mL) were then added.
After the reaction was complete according to TLC (1:99 MeOH/
J ϭ 14.1 Hz, 4 H, 2 ϫ CH2N3), 3.72 (s, 2 H, CH2Npht), 7.72Ϫ7.95
(m, 4 H, 4 ϫ Npht CH). Ϫ 13C NMR (50 MHz, CDCl3): δ ϭ 38.7 dichloromethane), the solution was evaporated to dryness. The
(CH2Npht), 45.6 (Cq, pentaerythritol), 52.3 (CH2N3), 61.9
(CH2OH), 123.8, 131.6, 134.6 (Npht C), 169.5 (CϭO, Npht).
product was separated by silica gel chromatography (gradient of
MeOH in dichloromethane) to yield 3.5 g (100%) of a colourless
oil. H NMR (200 MHz, CDCl3): δ ϭ 3.52 (s, 2 H, CH2Br), 3.60
1
2,2-Bis(azidomethyl)-3-phthalimidopropanoic Acid (1): A solution of
CrO3 (110 mg, 1.1 mmol) and H2SO4 (0.11 mL) in the minimum
amount of water was added to a solution of 8 (350 mg, 1.1 mmol)
in acetone at 0 °C. After 1 h stirring at 0 °C, and an additional 2
h stirring at room temperature, the mixture was filtered. Methanol
and water were added and the solution was concentrated by evap-
oration. The crude product was extracted with chloroform, dried
with Na2SO4, and evaporated to dryness. Purification by silica gel
chromatography (5:95 MeOH/dichloromethane) yielded 170 mg
(d, J ϭ 7.7 Hz, 2 H, CH2OH), 3.87 (t, J ϭ 8.2 Hz, OH), 3.95 (qAB
,
J ϭ 14.6 Hz, 4 H, 2 ϫ CH2Npht), 7.7Ϫ7.9 (m, 8 H, 8 ϫ Npht
CH). Ϫ 13C NMR (50 MHz, CDCl3): δ ϭ 36.1 (CH2Br), 40.8
(CH2Npht), 45.6 (Cq, pentaerythritol), 123.7, 131.7, 134.4 (Npht
C), 169.3 (CϭO, Npht). Ϫ MS (EIϩ): 458 [Mϩ] (5), 456 [Mϩ] (5),
359 (8), 347 (45), 200 (21), 160 (100).
3-Azido-2,2-bis(phthalimidomethyl)propanol (12): Compound 11
(3.5 g, 7.5 mmol), NaN3 (3.5 g, 54 mmol) and a catalytic amount
(47%) of the product as a white foam. 1H NMR (200 MHz, of LiCl were dissolved in DMF. The mixture was refluxed for 12 h
[D6]DMSO): δ ϭ 3.63 (qAB, J ϭ 12.6 Hz, 4 H, 2 ϫ CH2N3), 3.76
and evaporated to dryness. The product was separated by silica gel
(s, 2 H, CH2Npht), 7.8 (m, 4 H, 4 ϫ Npht CH). Ϫ 13C NMR chromatography (ethyl acetate) to yield 1.0 g (32%) of white foam.
(50 MHz, [D6]DMSO): δ ϭ 50.9 (CH2Npht), 52.3 (CH2N3), 123.2, Ϫ 1H NMR (400 MHz, CDCl3): δ ϭ 1.23 (s, 1 H, OH), 3.45* (s, 2
131.6, 134.6 (Npht C), 168.1 (CϭO, Npht), 172.1 (COOH). Ϫ MS
H, CH2OH), 3.47* (s, 2 H, CH2N3), 3.83 (qAB, J ϭ 14.6 Hz, 4 H,
(FABϩ): 330 (MHϩ, 100). Ϫ IR (KBr): ν˜ ϭ 3430 (br), 3030, 2939, 2 ϫ CH2Npht), 7.7Ϫ7.9 (m, 8 H, 8 ϫ Npht CH); assignments
2114 (s), 1722 (s), 1396, 1298, 717 cmϪ1. Ϫ C13H11N7O4 (329.3) denoted by * may be interchanged. Ϫ 13C NMR (100 MHz,
calcd. C 47.4, H 3.37, N 29.8; found C 47.5, H 3.52, N 29.0.
CDCl3): 40.0 (CH2Npht), 46.3 (Cq, pentaerythritol), 53.6 (CH2N3),
62.4 (CH2OH), 123.7, 131.7, 134.4 (Npht C), 169.3 (CϭO, Npht).
Ϫ MS (EIϩ): 419 [Mϩ] (1), 346 (38), 328 (24), 199 (40), 186 (19),
160 (100). Ϫ IR (KBr): ν˜ ϭ 3356 (br), 2930, 2100 (s), 1730, 1670
2-Bromomethyl-2-(4-methoxytrityloxy)methyl-1,3-propanediol (9):
2-Bromomethyl-2-hydroxymethyl-1,3-propanediol[4]
(4.00
g,
20.1 mmol) was co-evaporated twice with dry pyridine and then
dissolved in the same solvent (50 mL). 4-Methoxytrityl chloride
(6.21 g, 20.1 mmol) was added to this solution and the reaction
mixture was stirred for 20 h. Methanol (10 mL) was added and
most of the pyridine was removed by evaporation. The remaining
mixture was dissolved in dichloromethane and the solution was
washed with aq. NaHCO3 (3 ϫ 20 mL). The organic phase was
dried with Na2SO4, evaporated to dryness, and the oily residue was
purified by silica gel chromatography (1:99 MeOH/dichlorometh-
(s), 1412 cmϪ1
.
3-Azido-2,2-bis(phthalimidomethyl)propanoic Acid (2): A solution of
CrO3 (56 mg, 0.56 mmol) and H2SO4 (0.06 mL, 1.1 mmol) in the
minimum amount of water was added to a solution of 12 (235
mg, 0.56 mmol) in acetone. After 2 h stirring at room temperature,
another portion of oxidizing solution (1/2 of the initial volume
used) was added and the reaction mixture was stirred for an addi-
tional 2 h. The mixture was filtered, methanol and water were ad-
ane) to yield 5.27 g (58%) of white foam. 1H NMR (200 MHz, ded, and the solution was concentrated by evaporation. The crude
CDCl3): δ ϭ 2.05 (br. s, 2 H, OH), 3.21 (s, 2 H, CH2OMMTr), product was extracted into chloroform and the solution was dried
3.61 (s, 2 H, CH2Br), 3.67 (s, 4 H, 2 ϫ CH2OH), 3.79 (s, 3 H, with Na2SO4 and evaporated to dryness. The yield of the crude
MMTr OCH3), 6.82 (m, 2 H, 2 ϫ MMTr CH), 7.1Ϫ7.5 (m, 12 H, product was 190 mg (79%). Purification by silica gel chromatog-
12 ϫ MMTr CH). Ϫ MS (EIϩ): 472 [Mϩ] (3), 470 [Mϩ] (3), 395 raphy (1:9 MeOH/dichloromethane) gave 39% recovery as a white
(3), 393 (3), 273 (100). Ϫ IR (KBr): ν˜ ϭ 3410 (br), 3057, 2930,
1607, 1512, 1251, 1070 cmϪ1. Ϫ HRMS (EI): Mϩ found 470.1093.
C25H27O4Br requires 470.1093.
foam. 1H NMR (200 MHz, CDCl3): δ ϭ 3.65 (s, 2 H, CH2N3),
4.03 (d, J ϭ 14.4 Hz, 2 H, 2 ϫ CHHNpht), 4.25 (d, J ϭ 14.4 Hz,
2 ϫ CHHNpht), 7.70Ϫ7.95 (m, 8 H, 8 ϫ Npht CH). Ϫ 13C NMR
3650
Eur. J. Org. Chem. 2000, 3647Ϫ3652

Synthesis of Achiral α,α-Bis(aminomethyl)-β-alanines
(50 MHz, [D6]DMSO): 40.6 (Cq, pentaerythritol), 51.4
FULL PAPER
12 H, 12 ϫ MMTr CH). Ϫ 13C NMR (50 MHz, CDCl3): δ ϭ
δ
ϭ
(CH2Npht), 54.3 (CH2N3), 123.0, 131.7, 134.3 (Npht C), 168.3 (Cϭ 28.3 (Boc CH3), 39.6 (CH2NHBoc), 46.0 (Cq, pentaerythritol), 55.2
O, Npht), 171.9 (COOH). Ϫ MS (EIϩ): 433 (Mϩ, 1), 299 (41), 227
(MMTr OCH3), 61.4* (CH2OMMTr), 61.7* (CH2OH), 79.5 (Cq,
(100), 160 (24). Ϫ IR (KBr): ν˜ ϭ 3575 (br), 3057, 2932, 2110 (s), Boc), 86.2 (Cq, MMTr), 113.2, 127.0, 128.0, 128.3, 130.2, 135.3,
1776, 1720, 1593, 1390, 1265, 1045, 736 cmϪ1. Ϫ HRMS (FAB):
144.2 (MMTr C), 157.5 (CϭO, Boc), 158.6 (MMTr C); assignments
denoted by * may be interchanged. Ϫ IR (KBr): ν˜ ϭ 3423 (br),
1698, 1510, 1252, 1173, 1036 cmϪ1. Ϫ HRMS (EI): Mϩ found
606.3303. C35H46N2O7 requires 606.3305.
MHϩ found 434.1086. C21H16N5O6 requires 434.1101.
2,2-Bis(azidomethyl)-3-(4-methoxytrityloxy)propanol (13): Com-
pound 5 (8.0 g, 15 mmol), NaN3 (5.0 g, 77 mmol), and a catalytic
amount of LiCl were dissolved in DMF. The reaction mixture was
refluxed for 12 h and most of DMF was removed by evaporation
under vacuum. The residue was dissolved in dichloromethane and
washed with aq NaHCO3. The organic fraction was dried with
Na2SO4, evaporated to dryness, and the residue was purified by
silica gel chromatography (dichloromethane) to yield 3.4 g (49%)
of an off-white foamy product. Ϫ 1H NMR (200 MHz, CDCl3):
N,NЈ-Bis(tert-butoxycarbonyl)-2-(4-methoxytrityloxy)methyl-2-
phthalimidomethylpropane-1,3-diamine (16): Diethyl azodicarboxyl-
ate (2.1 mL, 13.3 mmol) was added dropwise to a solution of 15
(5.34 g, 9.2 mmol), phthalimide (1.95 g, 13.3 mmol) and triphenyl-
phosphane (3.7 g, 13.3 mmol) in THF. The reaction mixture was
stirred overnight and then evaporated to dryness. Purification by
silica gel chromatography (3:7 ethyl acetate/petroleum ether)
1
δ ϭ 1.78 (t, J ϭ 5.9 Hz, 1 H, OH), 3.10 (s, 2 H, CH2OMMTr), yielded 4.36 g (66%) of the product as a yellow foam. Ϫ H NMR
3.44 (s, 4 H, CH2N3), 3.55 (d, J ϭ 6.0 Hz, 2 H, CH2OH), 3.82 (s,
3 H, MMTr OCH3), 6.87 (m, 2 H, 2 ϫ MMTr CH), 7.25Ϫ7.5 (m, 14.5 and 6.5 Hz,
12 H, 12 ϫ MMTr CH). Ϫ 13C NMR (50 MHz, CDCl3): δ ϭ 44.9 CH2OMMTr), 3.25 (dd, J ϭ 14.6 and 6.5 Hz, 2 ϫ CHHNHBoc),
(Cq, pentaerythritol), 51.8 (CH2N3), 55.2 (MMTr OCH3), 62.4* 3.66 (s, 2 H, CH2Npht), 3.75 (s, 3 H, MMTr OCH3), 5.53 (t, J ϭ
(200 MHz, CDCl3): δ ϭ 1.39 [s, 18 H, 2 ϫ C(CH3)3], 3.05 (dd, J ϭ
2
H, CHHNHBoc), 3.20 (s, H,
2
ϫ
2
(CH2OMMTr), 63.5* (CH2OH), 86.8 (Cq, MMTr), 113.2, 127.1, 6.5 Hz, 2 H, NH), 6.76 (m, 2 H, 2 ϫ MMTr CH), 7.1Ϫ7.4 (m, 12
128.0, 128.2, 130.3, 134.8, 143.9, 158.7 (MMTr C); assignments H, 12 ϫ MMTr CH), 7.65Ϫ7.85 (m, 4 H, 4 ϫ Npht CH). Ϫ 13C
denoted by * may be interchanged. Ϫ IR (KBr): ν˜ ϭ 3470 (br),
NMR (50 MHz, CDCl3): δ ϭ 28.2 (Boc CH3), 40.2 (CH2Npht),
2933, 2104 (s), 1608, 1510 cmϪ1. Ϫ MS (EIϩ): 458 [Mϩ] (8), 381 41.7 (CH2Npht), 45.7 (Cq, pentaerythritol), 55.0 (MMTr OCH3),
(3), 273 (100). Ϫ HRMS (EI): Mϩ found 458.2072. C25H26N6O3 64.7 (CH2OMMTr), 78.8 (Cq, Boc), 86.6 (Cq, MMTr), 112.9, 123.2,
requires 458.2066.
126.7, 127.6, 128.3, 130.2, 131.8, 132.8, 133.9, 134.0, 134.8, 143.7
(MMTr C, Npht C), 156.4 (CϭO, Boc), 158.3 (MMTr C), 168.9
(CϭO, Npht).
2,2-Bis(aminomethyl)-3-(4-methoxytrityloxy)propanol (14): Com-
pound 13 (9.3 g, 20.3 mmol), 1,3-propanedithiol (0.2 mL, 2 mmol),
and triethylamine (6 mL, 40 mmol) were dissolved in 2-propanol
(200 mL). NaBH4 (3.8 g, 20 mmol) was added under vigorous stir-
2,2-Bis(tert-butoxycarbonylaminomethyl)-3-phthalimidopropanol
(17): Compound 16 (3.50 g, 4.76 mmol) was dissolved in dichloro-
ring in several portions and the mixture was stirred overnight at methane. A solution of iodine (1%, m/v; 50 mL) was added and
room temperature. The solvent was evaporated and the residue was
dissolved in dichloromethane. The solution was washed with 10%
NaOH in saturated aqueous NaCl, saturated aqueous NaCl, and
then dried with NaSO4. The solvent was evaporated and the re-
sulting oil was separated on a silica gel column (85:5:10 dichloro-
methane/TEA/MeOH). Evaporation of the appropriate fractions
yielded 4.2 g (51%) of the product as an almost colourless oil. Ϫ
the reaction mixture was stirred for 2 h at room temperature. The
reaction solution was washed with aqueous Na2SO3 and brine,
dried with Na2SO4, and evaporated to dryness. Purification by sil-
ica gel chromatography (gradient of MeOH in dichloromethane)
1
yielded 1.9 g (87%) of the product as a yellow foam. Ϫ H NMR
(200 MHz, CDCl3): δ ϭ 1.46 [s, 18 H, 2 ϫ C(CH3)3], 2.98 (dd, J ϭ
14.7 and 6.4 Hz, 2 H, 2 ϫ CHHNHBoc), 3.11 (dd, J ϭ 14.6 and
1H NMR (200 MHz, [D6]DMSO): δ ϭ 2.54 (s, 4 H, 2 ϫ NH2), 7.0 Hz, 2 H, 2 ϫ CHHNHBoc), 3.32 (d, J ϭ 7.2 Hz, 2 H, CH2OH),
2.86 (s, 2 H, CH2OMMTr), 3.40 (s, 2 H, CH2OH), 3.73 (s, 3 H,
3.63 (s, 2 H, CH2Npht), 4.48 (t, J ϭ 7.2 Hz, 1 H, OH), 6.25 (t, J ϭ
MMTr OCH3), 6.87 (m, 2 H, 2 ϫ MMTr CH), 7.15Ϫ7.41 (m, 12
6.4 Hz, 2 H, NH), 7.7Ϫ7.9 (m, 4 H, 4 ϫ Npht CH). Ϫ 13C NMR
H, 12 ϫ MMTr CH). Ϫ 13C NMR (50 MHz, CDCl3): δ ϭ 42.8 (50 MHz, CDCl3): δ ϭ 27.6 (Boc CH3), 38.4* (CH2Npht), 40.0*
(CH2NH2), 43.8 (Cq, pentaerytrithol), 55.0 (MMTr OCH3), 62.6* (CH2NHBoc), 45.4 (Cq, pentaerythritol), 78.5 (Cq, Boc), 122.2,
(CH2OH), 63.1* (CH2OMMTr), 85.0 (Cq, MMTr), 126.7, 127.8,
130.9, 133.1 (Npht C), 156.4 (CϭO, Boc), 168.7 (CϭO, Npht); as-
127.9, 130.0, 135.2, 144.5, 158.0 (MMTr C); assignments denoted signments denoted by * may be interchanged. Ϫ IR (KBr): ν˜ ϭ
by * may be interchanged. Ϫ IR (KBr): ν˜ ϭ 3369, 3306, 3057,
2932, 1607, 1510, 1447, 1252, 1034, 634, 710 cmϪ1. Ϫ HRMS
(FAB): MHϩ found 407.2325. C25H31N2O3 requires 407.2335.
3416, 3208, 3063, 2980, 1744 (s), 1516, 1388, 1308, 1053, 717 cmϪ1
.
Ϫ
HRMS (EI): Mϩ found 463.2311. C23H33N3O7 requires
463.2319.
2,2-Bis(tert-butoxycarbonylaminomethyl)-3-(4-methoxytrityloxy)-
propanol (15): Compound 14 (4.18 g, 10.3 mmol) was dissolved in
aqueous MeCN. NaOH (aq. 2 , 11 mL, 22 mmol) and Boc2O (6.6
g, 30 mmol) were added and the reaction mixture was stirred over-
night. Dichloromethane was added, and the organic fraction was
washed with water and brine, dried with Na2SO4, and evaporated
to dryness. The resulting oil was purified by silica gel chromatog-
raphy (3:97 MeOH/dichloromethane) to yield 5.34 g (86%) of the
product as a white foam. Ϫ 1H NMR (200 MHz, CDCl3): δ ϭ 1.41
2,2-Bis(tert-butoxycarbonylaminomethyl)-3-phthalimidopropanoic
Acid (3): A solution of CrO3 (192 mg, 1.92 mmol) and H2SO4
(0.19 mL) in the minimum amount of water was added to a solu-
tion of 17 (890 mg, 1.92 mmol) in acetone at 0 °C. After 1 h stirring
at 0 °C, and an additional 2 h stirring at room temperature, the
mixture was filtered, methanol and water were added, and the solu-
tion was concentrated by evaporation. The crude product was ex-
tracted with chloroform and the solution was dried with Na2SO4
and evaporated to dryness. Purification by silica gel chromatog-
[s, 18 H, 2 ϫ C(CH3)3], 2.65 (dd, J ϭ 14.3 and 5.1 Hz, 2 H, 2 ϫ raphy (6:94 MeOH/dichloromethane) yielded 0.6 g (65%) of the
CHHNHBoc), 2.99 (s, 2 H, CH2OMMTr), 3.13 (dd, J ϭ 14.3 and product as a pale yellow solid foam. Ϫ 1H NMR (200 MHz,
8.4 Hz, 2 H, 2 ϫ CHHNHBoc), 3.38 (d, J ϭ 7.6 Hz, CH2OH),
CDCl3): δ ϭ 1.42 [s, 18 H, 2 ϫ C(CH3)3], 3.38 (br d, J ϭ 33.7 Hz,
3.79 (s, 3 H, MMTr OCH3), 4.22 (t, J ϭ 7.6 Hz, 1 H, OH), 4.89 4 H, 2 ϫ CH2NHBoc), 3.93 (s, 2 H, CH2Npht), 5.95 (br s, 3 H, 2
(m, 2 H, 2 ϫ NH), 6.8Ϫ6.9 (m, 2 H, 2 ϫ MMTr CH), 7.2Ϫ7.5 (m, ϫ NH and OH), 7.6Ϫ7.8 (m, 4 H, 4 ϫ Npht CH). Ϫ 13C NMR
Eur. J. Org. Chem. 2000, 3647Ϫ3652
3651

P. Heinonen, J. Rosenberg, H. Lönnberg
FULL PAPER
[2]
[3]
P. Heinonen, P. Virta, H. Lönnberg, Tetrahedron 1999, 55,
7613Ϫ7624.
(50 MHz, CDCl3): δ ϭ 28.4 (Boc CH3), 39.6 (CH2NHBoc), 41.4
(Cq, pentaerythritol), 52.4 (CH2Npht), 79.7 (Cq, Boc), 123.5, 131.8,
134.2 (Npht C), 156.8 (CϭO, Boc), 168.9 (CϭO, Npht), 184.9
(COOH). Ϫ IR (KBr): ν˜ ϭ 3416, 3055, 2984, 1776, 1714 (s), 1514,
1394, 1265, 1167, 738 cmϪ1. Ϫ C23H31N3O8 (477.5) Calcd. C 57.9,
H 6.54, N 8.80; found C 57.5, H 6.31, N 8.81.
O. Mitsunobu, M. Yamada, T. Mukaiyama, Bull. Chem. Soc.
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Acknowledgments
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Received February 18, 2000
[O00084]
3652
Eur. J. Org. Chem. 2000, 3647Ϫ3652