Synthesis of asymmetrized 2-benzyl-1,3-diaminopropane by a chemoenzymatic route: A tool for combinatorially developing peptidomimetics

Article abstract of DOI:10.1016/S0957-4166(99)00371-7

Both enantiomers of monoacetamide 5, together with 'dipeptides' 30a,b and monocarbamates 24, (R)-43 and (S)-43, all derived from 2-benzyl-1,3- diaminopropane 4, were synthesized by a chemoenzymatic route starting from the known monoacetate 12. The behaviour of 4 and of the bis(acylated) derivatives 8-11 with respect to hydrolytic enzymes is also presented, together with an extensive study on the configurational stability of monoacylated derivatives of 4.

Full text of DOI:10.1016/S0957-4166(99)00371-7

Pergamon
Tetrahedron: Asymmetry 10 (1999) 3571–3592
Synthesis of asymmetrized 2-benzyl-1,3-diaminopropane by a
chemoenzymatic route: a tool for combinatorially developing
peptidomimetics
Luca Banfi, Giuseppe Guanti ∗ and Renata Riva ∗
Dipartimento di Chimica e Chimica Industriale and C.N.R., Centro di Studio per la Chimica dei Composti Cicloalifatici ed
Aromatici,† via Dodecaneso 31, I-16146 Genova, Italy
Received 30 July 1999; accepted 20 August 1999
Abstract
Both enantiomers of monoacetamide5, together with ‘dipeptides’ 30a,b and monocarbamates24, (R)-43 and (S)-
43, all derived from 2-benzyl-1,3-diaminopropane 4, were synthesized by a chemoenzymatic route starting from
the known monoacetate 12. The behaviour of 4 and of the bis(acylated) derivatives 8–11 with respect to hydrolytic
enzymes is also presented, together with an extensive study on the configurational stability of monoacylated
derivatives of 4. © 1999 Elsevier Science Ltd. All rights reserved.
1. Introduction
The 1,3-diaminopropane unit is incorporated in many biologically active compounds, including
fluorinated phospholipid precursors of liposomes,1 enkephalin (opioid peptides) analogues,2,3 drug
carriers4 and, most of all, enzyme inhibitors.5–8 Among the enzyme inhibitors, many compounds
bearing a 1,3-diaminopropane moiety have been synthesized and tested against HIV protease (aspartyl
protease)5–7 and plasmepsin II (malarial aspartyl protease).8
In many cases the 1,3-diaminopropane unit is substituted on C2 and/or C1 and C3. Moreover, the
two amine functionalities are often alkylated or acylated with different moieties, including amino acids2
or oligopeptides.3 In addition, the presence of a stereogenic centre in position 2 of many of the above-
mentioned compounds, makes the availability of the 1,3-diamino precursor in optically active form a
crucial step in the whole sequence.
∗
†
Corresponding authors. E-mail: guanti@chimica.unige.it and riva@chimica.unige.it
Associated to the National Institute of C.N.R. for the Chemistry of Biological Systems.
0957-4166/99/$ - see front matter © 1999 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(99)00371-7

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A possible application of asymmetrized 1,3-diamino derivatives is in the field of peptidomimetics, one
of the most important classes of enzyme inhibitors.5,9 For this purpose the amine functions most likely
have to be transformed into peptidic derivatives, by acylation with a suitable N-protected amino acid.
As a first goal we needed to prepare simple asymmetrized 2-substituted 1,3-diaminopropanes. One
of the most attractive strategies for the synthesis of small enantiopure molecules is undoubtedly using
enzymes to introduce chirality, particularly if they are employed to asymmetrize prochiral or meso
substrates. Asymmetrization of diols or of the corresponding diacetates catalyzed by lipases is a well-
known and useful procedure, and successfully applied by our group;10 thus, an extension of this protocol
to diamines should be very interesting.
The acylation of primary amino groups in organic solvent has been extensively investigated on α-
amino acids11 or on amines, using lipases,12–37 proteases,38–40 acylases41–45 and aminopeptidases;46
however, only seldom were these reactions performed on diamines. Apart from penicillin G acylase,43–45
the most used enzymes are lipases.12–37 Among the studies with these enzymes, several of them concern
the resolution of racemic amines with achiral14,16,19–25,27–30,32,33,35,36 or chiral13,17,23,26,32,34,37 acylating
agents. Only a few examples of lipase-catalyzed acylation of diamines are known,12,18,24,27,31 but they
involved simple18,24 or double27 resolution reactions of chiral substrates. To the best of our knowledge
the only asymmetrization reactions performed on achiral diamines or diamides did not utilize lipases:
actually, Prinzbach’s group asymmetrized cyclic bis(phenylacet)amides using penicillin G acylase,44
while Wong’s group asymmetrized a diamine using subtilisin.40
2. Results and discussion
Having in mind the preparation of asymmetrized 1,3-diamines, we first focused our attention on the
synthesis of a suitable substrate to be submitted to enzyme-catalyzed acylation. We chose as the first
diamine compound 4 (Scheme 1). A synthesis of 4 by reduction of the corresponding dinitrile has
already been reported.47 However, this reduction gave 4 in about 40% yield, better than that reported,
but still low; this is most likely due to the difficulty of obtaining crude diamine after work up and to the
extensive decomposition during the purification by distillation.‡ We then optimized the synthesis of 4
through a completely different route. Diol 1, readily obtained by reduction of diethyl benzylmalonate,48
was converted into the bis(mesylate) 2, which was submitted to double nucleophilic substitution to give
bis(azide) 3. Crude bis(azide)§ was immediately submitted to a Staudinger reaction50 in order to obtain 4.
The diamine was never isolated as such, but the crude reaction mixture, after selective extraction of excess
PPh3 and of its oxide, was directly acylated under Schotten–Baumann conditions to give bisamides 8 and
11 and carbamates 9¶ and 10. Finally, 4 was obtained on a multigram scale and nearly quantitatively by
hydrogenolysis of both carbamate functionalities.
With diamine 4, we planned to investigate the asymmetrization by acylation in organic solvent using
lipases as catalysts. After a literature survey12–37 we chose lipase from Candida antarctica as the first
enzyme and vinyl acetate as the irreversible acylating agent.|| The acylation was very fast and not
selective to give mixtures of 5 and 8. Moreover, after we found an [α]D value ›0 for 5, we showed
that vinyl acetate also readily reacts with 4 in the absence of enzyme. This fact was already reported in
‡
Considerable and variable amounts of product derived from elimination of ammonia were always obtained.
§
¶
||
Due to the potentially explosive properties of 3, the solvent used for the extraction was not completely evaporated.49
Compound 9 could be stored indefinitely as a readily accessible source of 4.
In our experience vinyl acetate was always the best acylating agent for alcohols.

L. Banfi et al. / Tetrahedron: Asymmetry 10 (1999) 3571–3592
3573
Scheme 1.
the literature,15 although vinyl acetate has been successfully used in the resolution of a primary amine
with moderate enantiomeric excess.35 We avoided the uncatalyzed acylation using ethyl acetate and we
tried different reaction conditions and enzymes.
As summarized in Table 1 the enzymatic direct acylation of 4 showed to be an inadequate procedure
for many reasons: (a) the reaction was always sluggish; (b) it was impossible to quantitatively recover the
unreacted diamine, since it probably tends to bind irreversibly to the enzyme; and (c) the enantiomeric
excess of 5 was absolutely unsatisfactory. Using papain, a thiol protease that can act as an acylase, which
was successfully used by Wong in the synthesis of peptide isosteres,39 we did not observe any reaction
at all. Also diallyl carbonate40 as acylating agent, with CAL as enzyme, did not give any reaction.
Table 1
Acetylation of 4 catalyzed by lipases
From these preliminary and unsuccessful results we concluded that 4 was not a good substrate for

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enzymes, and so we turned our attention to the reverse reaction, that is the transformation of a bisamide
or a biscarbamate into an analogue of 5. In a recent paper Prinzbach44 reported the successful hydrolysis
of cyclic meso-bis(phenylacet)amides catalyzed by penicillin acylase from E. coli (EC 3.5.1.11).
We tried the same protocol on 11, but no reaction at all was observed, even when working under
conditions known to make the reaction faster. Biscarbamate 10 was reacted with pig liver esterase, hoping
to obtain the monocarbamate amine through decomposition of the intermediate monocarbamic acid, but
without success. Eventually, reaction of acylase from Aspergillus melleus was tried on bis(acet)amide
8, but again no hydrolysis was observed. Probably diamine 4 and their derivatives are not able to enter
the catalytic site of enzymes; this fact is most likely due to the relative positions of the two -NHCOR
or -NH2 groups, as it is known that cyclic diamines or bisamides prove to be reactive in the presence of
enzymes.27,40,44
Since we were in any case interested in the preparation of 5 or of similar compounds, we decided to
use monoacetate 12 as a homochiral precursor and to elaborate it via azido derivative 14. The synthesis
of 12 by lipase-catalyzed acylation of the corresponding diol 1 has already been reported;48,52 however,
we optimized its preparation using a 9:1 mixture of iPr2O/vinyl acetate both as solvent and acylating
system and lipase Amano P (from Pseudomonas cepacia) supported on Celite as previously reported.51,53
Following this procedure monoacetate 12 was obtained on a multigram scale as the R enantiomer in
95.9% enantiomeric excess.††
The transformation into azide 14 followed the above reported protocol (Scheme 2). However, treatment
of 14 with triphenylphosphine gave, instead of the desired primary amine, acetamide 15 in a nearly
quantitative yield. This is most likely due to the intramolecular acyl transfer during hydrolysis of the
iminophosphorane intermediate resulting from PPh3 attack on the azido group.
Scheme 2.
Acetamide 15 was then converted as usual into azide 17 but, in contrast to all other cases reported
later in this paper, 17 was obtained only in moderate yield (never more than 45%). We attributed this
fact to the competitive formation of dihydro-1,3-oxazine 18. Although we never succeeded in isolating
18, we detected the formation of considerable amounts of a compound with the same molecular weight
by GC–MS.‡‡ After chromatography we isolated, together with 17, substantial amounts of alcohol 15,
although it was absent in the starting crude mesylate 16. Thus it is likely that intermediate dihydro-
†† In some experiments we obtained up to 98% enantiomeric excess for 12, depending on the degree of conversion.
‡‡ Also, mesylate 16 (MW 249) gave the same result in GC–MS, that is a peak at an unusually low Rt (5.70) with respect to the
corresponding azide (Rt 7.82, MW 232); this can be explained with the thermal decomposition of 16 to give 18 (MW 189).

L. Banfi et al. / Tetrahedron: Asymmetry 10 (1999) 3571–3592
3575
1,3-oxazine 18 is converted back to 15 upon chromatography. It was also observed that, keeping a
sample of crude 17 in solution for a few days, containing 18 (by GC–MS), the latter underwent gradual
and complete hydrolysis to give 15. Finally, azide 17 was reduced and (S)-5 was obtained in nearly
quantitative yield.
For the synthesis of (R)-5 we had to transform the acetate group of 12 into the acetamide. Starting from
the common intermediate 14, we hydrolyzed in nearly quantitative yield the ester function using Amano
P lipase as catalyst in a mixture of THF/H2O at pH 7. Azide reduction gave amino alcohol 20, which
was never isolated but directly acylated under Schotten–Baumann conditions to give 21.§§ Following the
usual protocol we readily obtained amine 24, which, after conventional acetylation and hydrogenolysis
of the benzyl carbamate, gave the desired (R)-5 (Scheme 3).
Scheme 3.
Having in mind the preparation of new peptidomimetics, we then focused our attention on the prepara-
tion of analogues of 5, with one or both amine functionalities acylated with different natural N-protected
amino acids (Scheme 4). For this purpose, we synthesized the two diastereomeric ‘dipeptides’, 30a,b,
starting from (S)-benzyl carbamate 24, which was acylated with L- and D-t-butoxycarbonylalanine,
respectively, using (benzotriazolyl-1-oxy)tripyrrolidinophosphonium hexafluorophosphate as coupling
agent, to give diastereomeric 28a and 28b. After removal of the Z group, followed by acylation of the
amines 29a,b with Z-glycine, compounds 30a and 30b were obtained in good overall yield.
§§ Alcohol 21 and mesylate 22 were indistinguishable by TLC, so we followed the mesylation by GC–MS analysis, which
proved the thermal instability of 22. In fact, 22 was quantitatively transformed into an equimolecular mixture of 26 and 27.

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Scheme 4.
After having set up a simple and efficient preparation of differently mono- and bisacylated compounds
derived from 1,3-diaminopropane, we had to check the enantiomeric excess of the obtained compounds,
knowing the enantiomeric excess of starting chiral building block 12.
First we determined the enantiomeric excesses of both enantiomers of 5, obtained by different
elaborations of 12, by GLC analysis of the corresponding Mosher’s amides 6. We were disappointed
when we noticed an appreciable racemization of about 20%, with respect to the starting enantiomeric
excess of 12 (95.9%). In order to establish the step responsible for such behaviour, we analyzed the
enantiomeric excess of some intermediates, by converting 15, 19 and 21 into the corresponding Mosher’s
1
ester and analyzing their H NMR spectra (Scheme 5). In all cases we observed the maintenance of
the original enantiomeric excess, so we concluded that racemization had occurred in one of the steps
following the formation of azides 17 and 23, respectively.
Scheme 5.
To exclude the responsibility of the Staudinger reaction, different methods for transforming the azide
into the amine were explored, that is treatment of 23 with: (a) triethylphosphite, followed by anhydrous
HCl to give the hydrochloride of 24, which was acetylated with acetic anhydride in aqueous medium at
pH 4.5 to give 25;54 (b) SnCl2 in the presence of thiophenol and triethylamine, followed by conventional
acetylation;55 and (c) thiolacetic acid to give directly 25.56 In all cases we observed the same extent of
racemization on 5, so we could not establish if this step was responsible for the extensive racemization
we observed.

L. Banfi et al. / Tetrahedron: Asymmetry 10 (1999) 3571–3592
3577
We then turned our attention towards the behaviour of 5 and we found some factors which affect the
degree of racemization: (a) the chromatographic eluent, when it contains a small percent of triethylamine;
(b) the use of silica gel as the stationary phase for chromatography; (c) the experimental conditions used
for hydrogenolysis of the benzyl carbamate; and (d) the use of 4-dimethylaminopyridine to catalyze the
acylation with Mosher’s chloride.¶¶ Moreover, we found that 5 itself is configurationally unstable, even
when stored at −20°C in the dry state: the effect of the presence of acidic or basic media, as described
above, makes the racemization much faster.
At this point we also had to check the enantiomeric excess of benzyl carbamate 24: once again we
1
analyzed the H NMR spectrum of the corresponding Mosher’s amides 36 and in this case we did not
detect any appreciable racemization.
Concerning the racemization of 5, this could take place following two different pathways: (a) abs-
traction of the proton bonded to the stereogenic centre, followed by random reprotonation; and (b)
intramolecular acyl transfer from one nitrogen to the other. The acyl transfer in 5 should probably involve
an achiral intermediate such as 38 or 39 (Scheme 6). This process is more favourable in the case of 5,
giving 38, than in the case of 24, giving 39, most likely for electronic reasons. The lower tendency of
benzyl carbamate to migrate with respect to acetamide was confirmed by preparing both enantiomers of
tert-butoxycarbonyl carbamate 43.
Scheme 6.
Actually, 24 was easily transformed into (R)-43, that is a carbamate which, although not being the
enantiomer, had the opposite configuration (Scheme 7). On the other hand, the preparation of (S)-43 was
realized starting from the above prepared aminoalcohol 20. This compound, after transformation into Boc
derivative 30, was elaborated to give (S)-43, following the same protocol described for the Z derivative.
As expected, for both enantiomers of 43 we confirmed that no racemization had occurred during the
whole synthesis, by analysis of the Mosher’s amides.
Disappointed by the relatively low configurational stability of 5, we decided anyway to check the
diastereomeric ratio of ‘dipetides’ 30a,b, a problem that was not trivial. Probably, due to the symmetry
of these compounds, the differences in spectroscopic properties are very low, while they display opposite
signs in optical rotation. Moreover, even HPLC, either in direct or in reverse phase, did not allow any
separation. Surprisingly, after removal of the Boc protecting group with trifluoroacetic acid, we found a
¶¶ Acylation in pyridine without catalyst (see experimental) proved to be less racemizing.
As a consequence of these results the analysis of enzymatic reactions (see Table 1) can only give definite data on the enzyme
ability of catalyzing acylation of 4 to give 5; the reported enantiomeric excesses for 5 are, on the other hand, indicative, since
Mosher’s amides were prepared using DMAP as catalyst and we showed that the latter reagent can cause racemization of 5.
Racemization in the presence of triethylamine should support the first hypothesis, while effect of DMAP should support the
second one.
After we had nearly completed our project an analogous transformation on similar compounds was reported.57

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L. Banfi et al. / Tetrahedron: Asymmetry 10 (1999) 3571–3592
Scheme 7.
small, but meaningful difference in the chemical shift of the methyl derived from alanine (the signal was
differentiated when the spectrum was recorded on an equimolar mixture of 31a,b). From these spectra
we could exclude any racemization higher than 5% in the whole synthesis. A possible explanation for
this different behaviour with respect to acetamide 5 can be given in terms of steric hindrance: passing
from an unsubstituted to a substituted acyl group decreases the propensity of acyl migration from one
amino group to the other. This steric inhibition should be enhanced by using more sterically encumbered
amino acids than alanine (that is, most other proteinogenic amino acids) or bulkier N-protecting groups.
In fact, it is likely that the protection of the amine functionality plays an important role in preventing (or
minimizing) the racemization of monoacylated amines.
3. Conclusions
In this paper we have demonstrated that asymmetrized 2-substituted-1,3-propanediamines, despite
their simple structure, are not easy to obtain and, most of all, their prochiral precursors are not
substrates for enzymes usually able to form or cleave amide bonds. The configurational stability of
these compounds is ensured provided that a carbamate moiety or an acyl derived from an amino acid
is present in the molecule. Although carbamates 24, (R)-43 and (S)-43 could not be obtained by direct
enzyme-catalyzed manipulation of 4, they were, anyway, accessible by a simple synthetic sequence,
characterized by excellent yields in every step, starting from 12. In these compounds the two amino
groups are differentiated and could be elaborated independently. Moreover, since both benzyl and tert-
butoxycarbonyl carbamates (that is, protecting groups with orthogonal properties) are available, a huge
variety of differently N-protected amino acids can be used in the acylation step.
This fact enables the synthesis of compounds like 30 in high enantiomeric excess. The structure
of these compounds, together with the nature of the reactions performed, makes the preparation of
bisacylated amines very attractive from a combinatorial point of view, either in solution or in the solid
phase. In this case, analogues of 24 or 43 had to be employed, most of all for the solid phase approach:
a hydroxy or a 4-hydroxyphenyl group in position 2 with respect to the amino groups seem to be the
most promising for bonding our intermediates to a polymer through a linker. Studies in this field are in
progress and will be presented in due course.

L. Banfi et al. / Tetrahedron: Asymmetry 10 (1999) 3571–3592
3579
4. Experimental
4.1. General
NMR spectra were taken in CDCl3, at 200 MHz (1H), and 50 MHz (13C), using TMS as an internal
standard. Chemical shifts are reported in ppm (δ scale), and coupling constants are reported in hertz.
1
Peak assignment in H NMR spectra was also made with the aid of double resonance experiments. In
ABX systems, the proton A is considered downfield and B upfield. Peak assignment in 13C spectra was
made with the aid of DEPT experiments. GC–MS was carried out on an HP-5971A instrument, using
an HP-1 column (12 m long, 0.2 mm wide), electron impact at 70 eV, and a mass temperature of about
170°C. Unless otherwise indicated analyses were performed with a constant He flow of 0.9 ml/min, init.
temp. 100°C, init. time 2 min, rate 20°C/min, final temp. 260°C, final time 4 min, inj. temp. 250°C, det.
temp. 280°C. IR spectra were measured with a Perkin–Elmer 881 instrument as CHCl3 solutions. Values
of [α]D were determined on a Jasco DIP 181 polarimeter, in CHCl3 (containing 0.75–1% EtOH) solution.
Enantiomeric excesses of 5 as diastereomeric ratios of 7 were determined on the corresponding Mosher’s
amides using a Carlo Erba Fractovap gas chromatograph equipped with an RSL-150 column (25 m long,
0.25 mm wide). Melting points were determined on a Büchi 535 apparatus and are uncorrected. TLC
analyses were carried out on silica gel plates which were developed by these detection methods: (A) UV;
(B) dipping into a solution of (NH4)4MoO4·4H2O (21 g) and Ce(SO4)2·4H2O (1 g) in H2SO4 (31 ml)
and H2O (469 ml) and warming; (C) dipping into 48% aqueous HBr, warming and then dipping into a
solution of ninhydrin [900 mg into n-butanol (300 ml) and acetic acid (9 ml)], followed by warming again;
and (D) dipping into a 2% aqueous KMnO4 solution and warming. Rf was measured after an elution of
7–9 cm. Chromatographies were carried out on 220–400 mesh silica gel (if not otherwise specified)
using the ‘flash’ methodology. Petroleum ether (40–60°C) is abbreviated as PE. In extractive work-up,
aqueous solutions were always re-extracted three times with the appropriate organic solvent. Organic
extracts were washed with brine, dried over Na2SO4 and filtered, before evaporation of the solvent under
reduced pressure. All reactions employing dry solvents were carried out under a nitrogen atmosphere.
1
The purity of all compounds was established by TLC, H NMR, GC–MS. Lipase from recombinant
Candida antarctica was a kind gift from Novo Nordisk. Lipase Amano P and acylase from Aspergillus
melleus were kindly donated by Amano. Penicillin G acylase was kindly given by Recordati. Lipase
from Candida cylindracea, PPL and papain were purchased from Sigma, while PLE was purchased from
Fluka.
4.2. 2-Benzyl-1,3-propanediol 1
This known compound48 was prepared by an improved procedure, as reported by us for similar
compounds in 94% yield.51
4.3. General procedure for the synthesis of mesylates 2, 13, 16, 22 and 41
The appropriate diol 1 or alcohols 12, 15, 21 and 40 (10 mmol) were dissolved in dry CH2Cl2 (25 ml)
and cooled to −30°C. Triethylamine was added (25 mmol for 1, 13 mmol in all other cases), followed
by methanesulfonyl chloride (23 mmol for 1, 12 mmol in all other cases). After stirring at the same
temperature for 2–2.5 h the reaction was quenched by adding saturated aqueous NH4Cl. Extraction with
Et2O and solvent evaporation gave crude mesylates, used as such in the next reaction. Their identity was
proven by GC–MS (when feasible) or 1H NMR or both.

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4.3.1. 2-Benzyl-1,3-bis(methanesulfonyloxy)propane 2
Rf 0.44 (Et2O, A, B). GC–MS: Rt 9.54; m/z: 226 (M+−CH3SO3H, 6.9), 185 (22), 131 (117), 130 (100),
129 (36), 117 (24), 116 (5.2), 115 (22), 107 (6.2), 104 (7.3), 92 (6.3), 91 (62), 79 (20), 65 (9.8). 1H NMR
(on crude 2): 2.42–2.55 (1H, m, >CH(CH2OMs)2), 2.76 (2H, d, -CH2Ph, J=7.7), 3.03 (6H, s, -SO2CH3),
4.19 and 4.28 (4H, AB part of ABX system, -CH2OMs, JAB=10.0, JAX and JBX=4.2, 6.2), 7.17–7.38
(5H, m, aromatics).
4.3.2. (S)-1-Acetoxy-2-benzyl-3-(methanesulfonyloxy)propane 13
Rf 0.52 (PE:AcOEt 4:6, A, B). GC–MS: Rt 8.20; m/z: 226 (M+−CH3CO2H, 2.8), 190 (17), 185 (15),
149 (7.2), 131 (14), 130 (100), 129 (40), 117 (30), 116 (5.5), 115 (22), 107 (8.0), 104 (11), 92 (5.6), 91
(46), 79 (7.6), 65 (6.6), 43 (39).
4.3.3. (R)-(N-Acetyl)-2-benzyl-3-(methanesulfonyloxy)propanamine 16
Rf 0.48 (AcOEt+2% MeOH, A, B). GC–MS: Rt 5.70 (this most likely represents compound 18, formed
by thermal decomposition of 16); m/z: 189 (M+−CH3CO2H, 5.3), 130 (5.7), 119 (5.5), 118 (63), 117
(100), 115 (12), 98 (47), 92 (7.0), 91 (25), 72 (14), 65 (9.3), 56 (13), 51 (5.1), 43 (24), 42 (6.6), 39 (8.4).
1H NMR (on crude 16): 1.97 (3H, s, -COCH3), 2.25–2.41 (1H, m, >CHCH2OMs), 2.58–2.80 (2H, m,
-CH2Ph), 3.02 (3H, s, -SO2CH3), 3.14–3.53 (2H, m, -CH2NHAc), 4.03 and 4.24 (2H, AB part of ABX
system, -CH2OSO2CH3, JAB=10.2, JAX and JBX=3.9, 4.4), 5.93 (1H, br s, -NHAc), 7.11–7.35 (5H, m,
aromatics).
4.3.4. (R)-2-Benzyl-[N-(benzyloxycarbonyl)]-3-(methanesulfonyloxy)propanamine 22
Rf 0.41 (PE:Et2O 3:7, A, B). GC–MS: 21 is not thermally stable and was quantitatively transformed
into 26 (Rt 4.98 min) and 27 (Rt 8.31 min). 1H NMR (on crude 21): 2.20–2.38 (1H, m, >CHCH2OMs),
2.65 and 2.72 (2H, AB part of ABX system, -CH2Ph, JAB=13.2, JAX and JBX=5.4, 9.1), 2.97 (3H, s,
-SO2CH3), 3.14–3.45 (2H, m, -CH2NHZ), 4.05 and 4.23 (2H, AB part of ABX system, -CH2OSO2CH3,
J
AB=10.1, JAX and JBX=3.9, 4.7), 5.02–5.20 (1H, m, -NHZ), 5.08 and 5.11 (2H, AB system, -OCH2Ph,
J=12.3), 5.11 (1H, broad s, -NHZ), 7.16–7.35 (10H, m, aromatics).
4.3.5. (R)-2-Benzyl-3-[(tert-butoxycarbonyl)amino]propanol 41
Rf 0.43 (PE:Et2O 3:7, A, B). GC–MS: 41 is not thermally stable and was quantitatively trans-
1
formed into 27 (Rt 8.31 min). H NMR (on crude 41): 1.44 (9H, s, -C(CH3)3), 2.16–2.34 (1H, m,
>CHCH2OMs), 2.64 and 2.72 (2H, AB part of ABX system, -CH2Ph, JAB=13.6, JAX and JBX=6.5,
8.3), 3.00 (3H, s, -SO2CH3), 3.06–3.44 (2H, m, -CH2NHBoc), 4.06 and 4.23 (2H, AB part of ABX
system, -CH2OSO2CH3, JAB=10.0, JAX and JBX=4.0, 4.5), 4.82 (1H, br t, -NHBoc, J=5.6), 7.17–7.36
(5H, m, aromatics).
4.4. General procedure for the synthesis of azides 3, 14, 17, 23 and 42
The appropriate crude bis(mesylate) 2 or mesylates 13, 16, 22 and 41 (10 mmol) were dissolved in
dry DMF (30–40 ml) and treated with sodium azide (30 mmol for 2, 20 mmol in all other cases, based
on starting alcohol). The resulting suspension was heated at 50°C until reaction was judged complete
by TLC (usually 15–20 h). The crude mixture was then diluted with water and extracted with ether.
Compound 3, due to its potential explosive properties,11 was concentrated carefully, without removing
all the solvent and immediately reduced to diamine 4. Differently, all other azides were purified and
identified as reported.

L. Banfi et al. / Tetrahedron: Asymmetry 10 (1999) 3571–3592
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4.4.1. 2-Benzyl-1,3-diazidopropane 3
Rf 0.55 (PE:Et2O 3:7, A, B). GC–MS: Rt 6.22; m/z: 188 (M+−N2, 0.74), 159 (9.0), 146 (26), 133 (6.0),
132 (28), 131 (13), 130 (53), 119 (5.3), 118 (15), 117 (50), 116 (6.3), 115 (23), 105 (20), 104 (45), 103
(25), 102 (5.0), 92 (12), 91 (100), 89 (8.2), 80 (5.3), 79 (22), 78 (30), 77 (49), 76 (5.0), 69 (5.5), 65 (45),
64 (5.2), 63 (15), 56 (9.2), 54 (8.8), 52 (13), 51 (43), 50 (16), 42 (20), 41 (43), 40 (6.7), 39 (42), 38 (5.6).
4.4.2. (R)-1-Acetoxy-3-azido-2-benzylpropane 14
Chromatography with PE:Et2O 9:1→7:3 gave 14 as a pale yellow oil with 96% overall yield from
12. Rf 0.44 (PE:Et2O 8:2, A, B). [α]D=−9.36 (c 1.66). IR: νmax 2997, 2937, 2862, 2111, 1728, 1602,
1492, 1450, 1389, 1368, 1192, 1037. GC–MS: Rt 6.53; m/z: 205 (M+−N2, 2.2), 146 (30), 145 (6.0),
144 (24), 134 (6.1), 133 (5.7), 132 (15), 130 (10), 118 (8.3), 117 (39), 116 (8.3), 115 (19), 105 (11),
1
104 (11), 92 (9.9), 91 (48), 78 (7.8), 77 (9.2), 65 (13), 51 (6.6), 43 (100), 41 (7.9), 39 (7.2). H NMR:
2.08 (3H, s, -CH3), 2.21 (1H, centre of m, >CHCH2OAc), 2.68 (2H, d, -CH2Ph, J=7.4), 3.32 and 3.37
(2H, AB part of ABX system, -CH2N3, JAB=12.3, JAX and JBX=5.3, 5.8), 4.01 and 4.09 (2H, AB part
of ABX system, -CH2OCOCH3, JAB=11.2, JAX and JBX=5.0, 6.7), 7.15–7.36 (5H, m, aromatics). 13C
NMR: 20.71 (-CH3), 35.14 (-CH2Ph), 39.88 (>CHCH2OAc), 51.86 (-CH2N3), 64.23 (-CH2OAc), 126.49
(>CH- para to -CH2-), 128.59 (2C, >CH- meta to -CH2-), 128.98 (2C, >CH- ortho to -CH2-), 138.52
(>C<, ipso), 170.65 (2C, >C_O).
4.4.3. (R)-(N-Acetyl)-3-azido-2-benzylpropanamine 17
Chromatography with PE:AcOEt 3:7→2:8 gave 17 as a yellow oil in 45% overall yield from 15. Rf
0.27 (PE:AcOEt 3:7, A, B). [α]D=+6.97 (c 1.58). IR: νmax 3446, 2997, 2930, 2861, 2102, 1668, 1603,
1495, 1450, 1266. GC–MS: Rt 7.82; m/z: 204 (M+−N2, 2.7), 146 (8.7), 145 (12), 144 (31), 133 (29), 132
(100), 131 (7.2), 130 (16), 129 (5.5), 128 (5.4), 118 (23), 117 (77), 116 (24), 115 (27), 106 (5.6), 105
(5.7), 104 (7.7), 103 (5.2), 98 (13), 92 (5.4), 91 (50), 84 (22), 77 (8.2), 73 (25), 72 (16), 71 (6.0), 65 (9.1),
1
60 (10), 57 (5.3), 56 (8.6), 43 (31). H NMR: 1.95 (3H, s, -CH3), 2.11 (1H, centre of m, >CHCH2N3),
2.65 (2H, d, -CH2Ph, J=7.5), 3.22–3.40 (4H, m, -CH2N3 and -CH2NHAc), 5.77 (1H, broad s, -NH-),
7.14–7.36 (5H, m, aromatics). 13C NMR: 23.15 (-CH3), 36.46 (-CH2Ph), 40.44 (>CHCH2N3), 41.65
(-CH2N3), 53.03 (-CH2NHAc), 126.45 (>CH- para to-CH2-), 128.62 (2C, >CH- meta to -CH2-), 128.97
(2C, >CH- ortho to -CH2-), 138.94 (>C<, ipso), 170.26 (>C_O).
4.4.4. (R)-3-Azido-2-benzyl-[N-(benzyloxycarbonyl)]propanamine 23
Chromatography with PE:Et2O 6:4→1:1 gave 23 as a pale yellow oil in 92% overall yield from 21. Rf
0.56 (PE:Et2O 1:1, A, B). [α]D=+3.21 (c 4.90). IR: νmax 3447, 3004, 2931, 2101, 1718, 1603, 1501, 1452,
1192. GC–MS: Rt 10.67; m/z: 296 (M+−N2, 0.6), 205 (7.88), 144 (9.3), 133 (8.6), 132 (35), 117 (24),
115 (5.4), 108 (6.1), 92 (9.3), 91 (100), 79 (6.1), 77 (6.5), 74 (7.6), 65 (11). 1H NMR: 2.09 (1H, centre of
m, >CHCH2N3), 2.61 and 2.66 (2H, AB part of ABX system, -CH2Ph, JAB=13.9, JAX and JBX=6.9,
7.9), 3.12–3.40 (4H, m, -CH2N3+-CH2NHZ), 4.92 (1H, broad s, -NH-), 5.10 (2H, s, -CO2CH2Ph),
7.14–7.38 (10H, m, aromatics). 13C NMR: 36.08 (-CH2Ph), 40.75 (>CHCH2N3), 42.94 (-CH2NHZ),
52.60 (-CH2N3), 66.86 (-CO2CH2Ph), 126.46 (>CH- para to -CH2CH<), 128.08 (2C, >CH- ortho to
-CH2O-), 128.13 (>CH- para to -CH2O-), 128.52 (2C, >CH- meta to -CH2O-), 128.62 (2C, >CH- meta
to -CH2CH<), 128.99 (2C, >CH- ortho to -CH2CH<), 136.53 (>C<, ipso of -CO2CH2Ph), 138.84 (>C<,
ipso of -CH2Ph), 156.53 (>C_O).

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4.4.5. (R)-3-Azido-2-benzyl-[N-(tert-butoxycarbonyl)]propanamine 42
Chromatography with PE:Et2O 9:1→100% Et2O gave 42 as a white solid in 91% overall yield from
30. It was crystallized from PE. Mp=56.0–56.3°C (PE). Rf 0.41 (PE:Et2O 7:3, A, C). [α]D=+5.80 (c
3.84). IR: νmax 3451, 2968, 2926, 2098, 1705, 1604, 1491, 1448, 1390, 1197, 1162, 850. GC–MS: Rt
8.45; m/z: 262 (M+−N2, 0.23), 146 (6.3), 144 (5.6), 133 (8.5), 132 (45), 130 (6.5), 118 (8.5), 117 (15),
116 (22), 115 (7.1), 105 (5.5), 102 (12), 91 (24), 74 (7.0), 65 (5.2), 59 (9.8), 58 (6.4), 57 (100), 41 (22),
39 (6.3). 1H NMR: 1.44 (9H, s, -C(CH3)3), 1.96–2.17 (1H, m, >CHCH2N3), 2.61 and 2.66 (2H, AB part
of ABX system, -CH2Ph, JAB=13.9, JAX and JBX=6.6, 8.2), 3.04–3.27 (2H, m, -CH2NHBoc), 3.27 and
3.34 (2H, AB part of ABX system, -CH2N3, JAB=12.6, JAX and JBX=5.7, 5.7), 4.68 (1H, broad s, -NH-),
7.13–7.35 (5H, m, aromatics). 13C NMR: 28.35 (3C, -C(CH3)3), 36.01 (-CH2Ph), 40.79 (>CHCH2N3),
42.34 (-CH2NHBoc), 52.44 (-CH2N3), 79.42 (-C(CH3)3), 126.34 (>CH- para to -CH2-), 128.55 (2C,
>CH- meta to -CH2-), 129.00 (2C, >CH- ortho to -CH2-), 138.98 (>C<, ipso), 156.01 (>C_O).
4.5. 2-Benzyl-1,3-propanediamine 4
(a) From bis(azide) 3: The above prepared solution of 3 in ether (about 20 ml) was diluted with THF (34
ml) and treated with water (2 ml) and triphenylphosphine (7.87 g, 30.0 mmol) at room temperature. After
the development of nitrogen ceased (a few minutes required) the solution was stirred at 50°C for about 20
h. After cooling to room temperature, the pH was adjusted to 1 by careful addition of 1N HCl. Non-basic
organic compounds were extracted with CH2Cl2; since 4 has a great affinity for water it was not possible
to quantitatively extract the diamine from aqueous solution. Solutions of 4 as bis(hydrochloride) were
then directly used for bisacylation reactions, leading to 8, 9, 10 and 11, as described later.
(b) From bis(benzyloxycarbonyl) derivative 9: Compound 9 (1.00 g, 2.31 mmol) was dissolved in
methanol (15 ml), treated with Pd/C (10%, 150 mg) and hydrogenated at 1 atm for 30 min. The catalyst
was filtered and the solvent was removed in vacuo. The resulting diamine, obtained in quantitative yield
as a pale yellow oil, was very pure and was used without further purification. Rf≈0.15 (MeOH:Et3N
9:1, elongated spot, A, C). IR: νmax 3386, 3319, 2926, 2864, 1601, 1492, 1453. GC–MS: Rt 5.28;
1
m/z: 164 (M+, 0.026), 118 (14), 117 (27), 91 (14), 65 (5.1), 56 (100). H NMR: 1.75 (1H, centre of
m, -CH(CH2NH2)2), 2.61 (2H, d, -CH2Ph, J=7.3), 2.67–2.80 (4H, m, -CH2NH2), 7.16–7.32 (5H, m,
aromatics). 13C NMR: 36.67 (-CH2Ph), 43.30 (2C, -CH2NH2), 44.91 (>CHCH2Ph), 125.90 (>CH-, para
to -CH2), 128.31 (2C, >CH-, meta to -CH2), 128.96 (2C, >CH-, ortho to -CH2), 140.33 (>C<, ipso).
4.6. (N-Acetyl)-2-benzyl-1,3-propanediamine 5
(a) (R)-5 and (S)-5 by enzyme-catalyzed acylation: Diamine 4 (100 mg, 609 µmol) was dissolved in 5
ml of the suitable solvent (see Table 1) and stirred at room temperature for 15 min in the presence of 15
mg of powdered 3 Å molecular sieves. The mixture was cooled to the desired reaction temperature and,
if not used as cosolvent, the acylating agent was added, followed by the enzyme. After stirring for the
desired time, the enzyme was filtered and the solution concentrated in vacuo. Chromatography (for this
compound 70–230 mesh silica was used) with AcOEt:MeOH 1:1→AcOEt:MeOH 1:1+10% Et3N gave
pure 5 slightly enriched in the (R)- or (S)-enantiomer as a pale yellow oil.
(b) (S)-5 from 17: Compound 17 (737 mg, 3.17 mmol) was dissolved in THF (16 ml) and treated with
water (1.2 ml) and triphenylphosphine (1.25 g, 4.77 mmol). After the development of nitrogen ceased
(some minutes required) the solution was stirred at 50°C for about 6 h. The pH was adjusted to 10 by
addition of 1N NaOH and the extraction was performed with AcOEt. The crude product was purified by
chromatography and 600 mg of (S)-5 were obtained (92% yield). Due to the configurational instability

L. Banfi et al. / Tetrahedron: Asymmetry 10 (1999) 3571–3592
3583
of 5 no [α]D was reported, although it is possible to say that the (R)-enantiomer is dextrorotatory, while
the (S)-enantiomer is levorotatory.
(c) (R)-5 from 25: Compound 25 (102 mg, 300 µmol) was hydrogenated as described above for
preparation of 4 from 9. After chromatography, 58 mg of pure (R)-5 were obtained in 94% yield.
Rf 0.39 (elongated spot, AcOEt:MeOH 1:1+8% Et3N, A, C). IR: νmax 3605, 3449, 2993, 2922, 1660,
1601, 1511, 1452, 1370, 1217. GC–MS: Rt 7.43; m/z: 206 (M+, 4.8), 177 (23), 134 (35), 132 (5.4), 130
(9.7), 129 (5.3), 118 (49), 117 (100), 116 (8.6), 115 (40), 98 (12), 92 (5.0), 91 (42), 86 (5.1), 77 (5.1),
1
73 (99), 72 (8.4), 65 (12), 60 (30), 56 (70), 44 (12), 43 (42), 42 (5.0), 39 (6.4). H NMR: 1.83–2.00
(1H, m, >CHCH2NH2), 1.93 (3H, s, -CH3), 2.59 (2H, d, -CH2Ph, J=7.4), 2.62 and 2.82 (2H, AB part
of ABX system, -CH2NH2, JAB=12.8, JAX and JBX=4.1, 7.4), 3.15–3.48 (2H, m, -CH2NHAc, became
AB part of ABX system after irradiating at 1.93; δ: νA 3.23 and νB 3.42, JAB=13.7, JAX and JBX=5.3,
6.0), 6.66 (1H, broad s, -NH-), 7.15–7.34 (5H, m, aromatics). 13C NMR: 23.08 (-CH3), 36.98 (-CH2Ph),
41.04 (>CHCH2Ph), 41.36 (-CH2NH2), 42.78 (-CH2NHAc), 126.31 (>CH-, para to -CH2-), 128.52 (2C,
>CH-, meta to -CH2-), 128.92 (2C, >CH-, ortho to -CH2-), 139.33 (>C<, ipso), 171.22 (>C_O).
4.7. Acylation of crude enzymatic reaction mixture by Mosher’s chloride to give 6, 7 and 8
Crude 5 (about 10 mg), in a mixture with diacetamide 8 and unreacted diamine 4, as derived from
enzymatic reactions, was dissolved in dry CH2Cl2 (1 ml) and treated with 4-dimethylaminopyridine
(14 mg, 121 µmol) and (R)- or (S)-Mosher’s chloride (23 µl, 121 µmol). After 1.5 h the mixture was
concentrated and rapidly purified, without separation of the components, by filtration over silica gel,
using AcOEt:MeOH 9:1 as eluent. The mixture was then analyzed by GLC (He pressure: 1.7 kg/cm2;
split ratio: 41:1; inj. 250°C; det. 250°C; init. temp.: 200°C for 40 min and then raising the temperature
by 10°C/min until 290°C; final time 10 min), giving the following: Rt: 6.12 min for 8; 38.92 min for 6
(R,R- or S,S-diastereoisomers) and 40.42 for 6 (R,S- or S,R-diastereoisomers) and 51.90 min for 7.
4.8. 2-Benzyl-(N,N0-diacetyl)-1,3-propanediamine 8
An acidic aqueous solution of 4 (3.00 mmol based on starting diol 1), obtained from 3 after work-up,
was treated with 6N NaOH until pH 5 and mixed with AcONa·3H2O (6.81 g, 50.0 mmol), in order to
maintain pH ›4.5. After cooling to 0°C acetic anhydride (850 µl, 9.01 mmol) was added and, after 5 min,
the reaction was allowed to stir at room temperature. Since the reaction was slow, two further portions
of acetic anhydride (850 µl each) were added, and finally the pH was adjusted to 7 by addition of 6N
NaOH and the mixture stirred again overnight. Extraction was performed with AcOEt and the crude
product was purified by chromatography using AcOEt:MeOH 98:2→9:1 as eluent. In this way, 551 mg
of 8 were obtained as a colourless oil in 74% overall yield from 1. Rf 0.46 (AcOEt:MeOH 8:2, A). IR:
νmax 3446, 2994, 2931, 1659, 1515, 1437, 1369, 1281. GC–MS: Rt 8.87; m/z: 248 (M+, 8.9), 177 (6.7),
176 (49), 157 (15), 146 (8.0), 134 (8.1), 132 (5.1), 130 (6.1), 118 (25), 117 (100), 116 (5.8), 115 (13),
98 (28), 91 (32), 73 (47), 72 (34), 65 (7.1), 60 (19), 56 (36), 44 (8.3), 43 (56). 1H NMR: 1.97–2.04 (1H,
m, -CH(CH2NHAc)2), 2.00 (6H, s, -CH3), 2.56 (2H, d, -CH2Ph, J=7.5), 2.97–3.41 (4H, m, -CH2NHAc,
became AB part of ABX system after irradiating at 6.38; δ: νA 3.04 and νB 3.34, JAB=14.0, JAX and
J
BX=4.1, 7.1), 6.38 (2H, broad t, -NHAc, J=4.9), 7.14–7.35 (5H, m, aromatics). 13C NMR: 23.07 (2C,
-CH3), 39.76 (2C, -CH2NHAc), 36.82 (-CH2Ph), 39.76 (2C, -CH2NHAc), 41.04 (-CH(CH2NHAc)2),
126.22 (>CH- para to -CH2-), 128.46 (2C, >CH- meta to -CH2-), 128.78 (2C, >CH- ortho to -CH2-),
139.40 (>C< ipso), 171.02 (2C, >C_O).

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L. Banfi et al. / Tetrahedron: Asymmetry 10 (1999) 3571–3592
4.9. Acylation of 4 under Schotten–Baumann conditions to give 9, 10 and 11
An acidic aqueous solution of 4 (3.00 mmol based on starting diol 1), obtained from 3 after work-up,
was treated with 6N NaOH until pH ›9. After cooling to 0°C the appropriate acylating agent was added
(benzyl chloroformate to obtain 9, methyl chloroformate to obtain 10, phenylacetyl chloride to obtain
11, 7.5 mmol), and after 10 min the reaction was allowed to stir at room temperature, while pH was
maintained at 9 by occasional addition of 1N NaOH. The reaction was usually complete in 2–6 h. After
saturation with solid NaCl, the organic compounds were extracted with AcOEt.
4.9.1. 2-Benzyl-[N,N0-bis(benzyloxycarbonyl)]-1,3-propanediamine 9
Chromatography with PE:Et2O 65:35→1:1 gave pure 9 (80% overall yield from 1), which was
crystallized from Et2O/ETP to give a pale yellow solid. Mp=87.9–88.4°C (PE/Et2O). Rf 0.54 (PE:Et2O
4:6, A, B). IR: νmax 3448, 2998, 2940, 1713, 1503, 1453, 1248. GC–MS: 9 decomposes in the
chromatographic column. 1H NMR: 1.95–2.09 (1H, m, -CH(CH2NHZ)2), 2.55 (2H, d, -CH2Ph, J=7.6),
2.92–3.39 (4H, m, -CH2NHZ, became AB part of ABX system after irradiating at 5.35; δ: νA 2.99
and νB 3.32, JAB=14.4, JAX and JBX=4.0, 7.0), 5.10 (4H, s, 2 -CO2CH2Ph), 5.35 (2H, broad t, -NH-,
J=5.9), 7.13–7.35 (15H, m, aromatics). 13C NMR: 36.22 (-CH2Ph), 41.25 (2C, -CH2NHZ), 41.35
(-CH(CH2NHZ)2), 66.74 (2C, -OCH2Ph), 126.27 (>CH- para to -CH2CH<), 127.97 (4C, >CH- ortho
to -CH2O-), 128.02 (2C, >CH- para to -CH2O-), 128.44 (4C, >CH- meta to -CH2O-), 128.55 (2C, >CH-
meta to -CH2CH<), 128.81 (2C, >CH- ortho to -CH2CH<), 136.58 (2C, >C< ipso of -CO2CH2Ph),
139.31 (>C< ipso of -CH2Ph), 157.07 (2C, >C_O).
4.9.2. 2-Benzyl-[N,N0-bis(methoxycarbonyl)]-1,3-propanediamine 10
Chromatography with PE:Et2O 2:8→Et2O gave pure 10 (80% overall yield from 1), which was
crystallized from CH2Cl2/Et2O to give a white solid. Mp=100.0–100.4°C (CH2Cl2/Et2O). Rf 0.60 (Et2O,
A, C, D). IR: νmax 3450, 2953, 1711, 1601, 1510, 1450, 1193, 906. GC–MS: Rt 8.87; m/z: 280 (M+,
6.3), 205 (5.7), 192 (7.2), 160 (30), 131 (6.1), 130 (34), 129 (6.4), 118 (41), 117 (47), 116 (7.6), 115
(16), 114 (44), 104 (5.1), 102 (6.7), 92 (6.9), 91 (42), 89 (12), 88 (100), 76 (18), 74 (5.4), 65 (8.6), 59
1
(22), 56 (5.3), 44 (33), 42 (5.1). H NMR: 1.93–2.07 (1H, m, -CH(CO2CH3)2), 2.56 (2H, d, -CH2Ph,
J=7.6), 2.93–3.36 (2H, m, -CH2CO2CH3, became AB part of ABX system after irradiating at 5.33;
δ: νA 3.00 and νB 3.29, JAB=14.4, JAX and JBX=3.8, 7.1), 3.67 (6H, s, 2 -CH3), 5.33 (2H, broad t,
-NH-, J=5.1), 7.14–7.32 (5H, m, aromatics). 13C NMR: 36.18 (-CH2Ph), 41.08 (2C, -CH2NHCO2CH3),
41.40 (-CH(CH2NHCO2CH3)2), 52.06 (2C, -CH3), 126.22 (>CH- para to -CH2CH<), 128.49 (2C, >CH-
meta to -CH2CH<), 128.79 (2C, >CH- ortho to -CH2CH<), 139.34 (>C< ipso of -CH2Ph), 157.75 (2C,
>C_O).
4.9.3. 2-Benzyl-[N,N0-bis(phenylacetyl)]-1,3-propanediamine 11
Crude 11 was directly crystallized from AcOEt/Et2O, giving a white solid (53% overall yield from
1). Mp=137.3–138.1°C (AcOEt/Et2O). Rf 0.34 (PE:AcOEt 3:7, A, D). IR: νmax 3423, 2996, 2942,
1658, 1602, 1507, 1436, 1191, 1014. GC–MS: Rt 14.69 (usual conditions but with a final temp. of
290°C and final time of 4 min); m/z: 400 (M+, 6.7), 309 (12), 252 (15), 191 (27), 174 (6.3), 149 (7.4),
1
148 (6.4), 146 (5.7), 118 (9.8), 117 (23), 115 (5.9), 92 (12), 91 (100), 65 (9.1), 56 (17), 44 (8.2). H
NMR: 1.84–2.01 (1H, m, -CH(CH2NHCOCH2Ph)2), 2.32 (2H, d, -CH2Ph, J=7.7), 2.75–3.31 (4H, m,
-CH2NH-), 3.56 (4H, s, -COCH2Ph), 6.19 (2H, broad t, -NH-, J=6.1), 6.84–7.42 (15H, m, aromatics).
13C NMR: 36.40 (-CH2Ph), 39.52 (2C, -CH2NHCOCH2Ph), 40.84 (-CH(CH2NHCOCH2Ph)2), 43.82
(2C, -COCH2Ph), 126.19 (>CH- para to -CH2CH<), 127.12 (>CH- para to -CH2CO-), 128.48 (2C,

L. Banfi et al. / Tetrahedron: Asymmetry 10 (1999) 3571–3592
3585
>CH- meta to -CH2CH<), 128.61 (2C, >CH- ortho to -CH2CH<), 128.82 (2C, >CH- meta to-CH2CO-),
129.16 (2C, >CH- ortho to -CH2CO-), 135.14 (>C< ipso of -CH2CO-), 139.12 (>C< ipso of -CH2Ph),
171.80 (2C, >C_O).
4.10. (R)-3-Acetoxy-2-benzyl-1-propanol 12
A slightly different procedure was followed with respect to a literature report in order to prepare the
known 12.51 A suspension of crystallized diol 1 (5.10 g, 30.7 mmol) in a mixture of isopropyl ether (117
ml) and vinyl acetate (8 ml) was treated with powdered 3 Å molecular sieves (520 mg) and stirred at
25°C for 15 min. Then lipase Amano P supported on Celite (5.10 g), following our reported protocol for
PPL,51 was added and the mixture stirred at the same temperature for 5.7 h. The enzyme was filtered,
washed with CH2Cl2 and the organic solution was concentrated in vacuo. Chromatography with PE:Et2O
4:6→Et2O gave 12 as a pale yellow oil (6.05 g, 95% yield) with 95.9% enantiomeric excess.
4.11. (R)-3-(N-Acetylamino)-2-benzyl-1-propanol 15
Azide 14 was transformed into 15 following the same procedure used for diazide 3, using in this
case 1.5 mmol of PPh3/mmol of 14. After 6 h at 50°C the product was extracted with AcOEt and
purified by chromatography with AcOEt→AcOEt:MeOH 9:1 to give 15 in 97% overall yield from
12. This compound was crystallized from CH2Cl2/Et2O to give a pale yellow solid. Mp=75.6–76.9°C
(CH2Cl2/Et2O). Rf 0.33 (AcOEt+3% MeOH, A, B). [α]D=−24.21 (c 1.59). IR: νmax 3450, 2995, 2933,
2992, 1657, 1603, 1510, 1439, 1273, 1044, 992. GC–MS: Rt 7.55; m/z: 207 (M+, 1.7), 189 (33), 132
(5.1), 131 (7.8), 130 (61), 129 (13), 118 (27), 117 (82), 116 (10), 115 (18), 104 (8.1), 98 (46), 92 (12), 91
(59), 85 (24), 78 (6.7), 77 (9.6), 74 (12), 73 (100), 72 (40), 65 (17), 60 (22), 57 (6.3), 56 (32), 51 (7.9),
45 (9.6), 44 (10), 43 (73), 42 (6.3), 41 (5.3), 39 (9.0). 1H NMR: 1.83–1.99 (1H, m, >CH(CH2OH)), 2.01
(3H, s, -CH3), 2.53 and 2.67 (2H, AB part of ABX system, -CH2Ph, JAB=13.6, JAX and JBX=7.3, 7.8),
3.17–3.38 (2H, m, -CH2NHAc), 3.39 and 3.56 (2H, AB part of ABX system, -CH2OH, JAB=12.3, JAX
and JBX=3.6, 6.7), 3.80 (1H, broad s, -OH), 5.87 (1H, broad s, -NH-), 7.15–7.35 (5H, m, aromatics).
13C NMR: 22.87 (-CH3), 35.63 (-CH2Ph), 40.32 (-CH2NH-), 42.91 (>CH(CH2OH)), 62.16 (-CH2OH),
126.09 (>CH- para to -CH2CH<), 128.40 (2C, >CH- meta to -CH2CH<), 128.86 (2C, >CH -ortho to
-CH2CH<), 139.78 (>C< ipso), 171.80 (>C_O).
4.12. (R)-3-Azido-2-benzyl-1-propanol 19
Azide 14 (4.40 mg, 18.9 mmol) was dissolved in THF (45 ml); then 135 ml of 0.067 M pH 7 buffer
solution were added, followed by unsupported lipase Amano P (1.51 g). The resulting biphasic system
was stirred at room temperature for about 22 h, while the pH was adjusted to 7, when necessary, by
addition of 1N NaOH. The enzyme was filtered over a Celite pad, and an extraction with Et2O was
performed. The crude compound was then purified by chromatography, using PE:Et2O 8:2→Et2O as
eluent to give 19 as a yellow oil (3.58 g, 99% yield). Rf 0.27 (PE:Et2O 6:4, A, B). [α]D=−35.16 (c 1.06).
IR: νmax 3622, 3007, 2930, 2100, 1602, 1492, 1450, 1285, 1029. GC–MS: Rt 5.96; m/z: 163 (M+−N2,
3.9), 162 (8.5), 146 (9.7), 144 (7.9), 133 (5.8), 132 (25), 130 (6.4), 118 (7.6), 117 (21), 115 (14), 106 (10),
105 (28), 104 (19), 103 (7), 92 (29), 91 (100), 79 (10), 78 (18), 77 (17), 65 (22), 63 (5.2), 51 (11), 41 (5.3),
1
39 (9.1). H NMR: 2.06 (1H, centre of m, >CHCH2OH), 2.65 and 2.71 (2H, AB part of ABX system,
-CH2Ph, JAB=13.8, JAX and JBX=7.46, 7.50), 3.37 and 3.44 (2H, AB part of ABX system, -CH2N3,
J
AB=12.3, JAX and JBX=5.1, 6.5), 3.60 and 3.68 (2H, AB part of ABX system, -CH2OH, JAB=10.8,

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L. Banfi et al. / Tetrahedron: Asymmetry 10 (1999) 3571–3592
JAX and JBX=4.5, 6.3, determined after exchange with D2O), 7.15–7.36 (5H, m, aromatics). 13C NMR:
34.98 (-CH2Ph), 42.58 (>CHCH2OH), 52.16 (-CH2N3), 62.86 (-CH2OH), 126.29 (>CH- para to -CH2),
128.50 (2C, >CH- meta to -CH2), 129.00 (2C, >CH- ortho to -CH2), 139.20 (>C< ipso).
4.13. (R)-3-Amino-2-benzyl-1-propanol 20
The same procedure described above for compound 15 was followed. At the end of the reaction, the
pH was adjusted to 1 by addition of 1N HCl and the non-basic products were extracted with CH2Cl2. It
was not possible to extract 20 from the basic aqueous solution and so it was used as such for the next
reaction. Rf 0.33 (elongated spot, MeOH:Et3N 9:1, A).
4.14. Acylation of 20 under Schotten–Baumann conditions to give 21 and 40
The same procedure reported above for compounds 9, 10 and 11 was followed, using, respectively,
benzyl chloroformate to obtain 21 and di-tert-butyl dicarbonate to obtain 40.
4.14.1. (R)-2-Benzyl-3-[N-(benzyloxycarbonyl)amino]-1-propanol 21
Chromatography with PE:Et2O 6:4→2:8 gave 21 as a pale yellow oil (94% overall yield from 19). Rf
0.41 (PE:Et2O 3:7, A, B). [α]D=−23.51 (c 1.83). IR: νmax 3449, 3000, 2928, 1702, 1602, 1505, 1452,
1195, 1028. GC–MS: Rt 10.54; m/z: 299 (M+, 0.097), 190 (10), 178 (9.0), 129 (7.8), 118 (9.5), 117 (67),
108 (14), 107 (9.8), 100 (6.3), 92 (19), 91 (100), 79 (15), 77 (11), 74 (13), 65 (12), 51 (5.8), 39 (6.0). 1H
NMR: 1.86–2.03 (1H, m, >CHCH2OH), 2.52 and 2.65 (2H, AB part of ABX system, -CH2Ph, JAB=13.7,
JAX and JBX=7.6, 7.7), 3.11–3.39 (2H, m, -CH2NHZ), 3.42 and 3.59 (2H, AB part of ABX system,
-CH2OH, JAB=11.8, JAX and JBX=3.6, 6.2, determined after exchange with D2O), 5.03 (1H, broad dt,
-NH-, J=2.2, 6.4), 5.11 (2H, s, -CO2CH2Ph), 7.14–7.35 (10H, m, aromatics). 13C NMR: 35.42 (-CH2Ph),
41.49 (-CH2NHZ), 43.33 (>CHCH2OH), 62.50 (-CH2OH), 67.09 (-CO2CH2Ph), 126.24 (>CH- para to
-CH2CH<), 128.12 (2C, >CH- ortho to -CH2O-), 128.22 (>CH- para to -CH2O-), 128.58 (4C, >CH-
meta to -CH2CH< and meta to -CH2O-), 128.97 (2C, >CH- ortho to -CH2CH<), 136.48 (>C< ipso of
-CO2CH2Ph), 139.77 (>C< ipso of -CH2Ph), 157.72 (>C_O).
4.14.2. (R)-2-Benzyl-3-[N-(tert-butoxycarbonyl)amino]-1-propanol 40
Chromatography with PE:Et2O 6:4→3:7 gave 40 (96% overall yield from 19), which was crystallized
from i-Pr2O/PE to give a white solid. Mp=70.4–70.7°C (i-Pr2O/PE). Rf 0.58 (PE:Et2O 3:7, A, C).
[α]D=−26.24 (c 2.22). IR: νmax 3453, 3039, 2931, 1686, 1602, 1494, 1444, 1367, 1157. GC–MS: Rt
8.20; m/z: 265 (M+, 0.059), 209 (5.2), 192 (8.7), 191 (38), 131 (16), 130 (100), 118 (29), 117 (33), 115
(5.2), 104 (6.2), 100 (6.5), 92 (11), 91 (36), 74 (15), 65 (5.7), 59 (19), 58 (5.0), 57 (99), 56 (6.8), 41
1
(22), 39 (6.6). H NMR: 1.45 (9H, s, -C(CH3)3), 1.84–1.98 (1H, m, >CHCH2OH), 2.51 and 2.64 (2H,
AB part of ABX system, -CH2Ph, JAB=13.7, JAX and JBX=7.5, 8.0), 3.02–3.32 (2H, m, -CH2NHBoc),
3.40 and 3.58 (2H, AB part of ABX system, -CH2OH, JAB=11.9, JAX and JBX=3.8, 6.3, determined
after exchange with D2O), 4.79 (1H, broad t, -NH-, J=6.6), 7.15–7.34 (5H, m, aromatics). 13C NMR:
28.34 (3C, -C(CH3)3), 35.35 (-CH2Ph), 40.31 (-CH2NHBoc), 43.58 (>CHCH2OH), 61.99 (-CH2OH),
79.94 (-C(CH3)3), 126.13 (>CH- para to -CH2CH<), 128.49 (2C, >CH- meta to -CH2CH<), 128.95
(2C, >CH- ortho to -CH2CH<), 139.92 (>C< ipso of -CH2Ph), 157.60 (>C_O).

L. Banfi et al. / Tetrahedron: Asymmetry 10 (1999) 3571–3592
3587
4.15. (S)-2-Benzyl-[N-(benzyloxycarbonyl)]-1,3-propanediamine 24
The same procedure described above for compound 15 was followed. In this case non-basic products
could not be extracted selectively, probably due to the low basicity of 24. The crude reaction mixture
was then directly extracted with AcOEt. Chromatography (70–230 mesh silica was used) with AcOEt,
AcOEt:MeOH 1:1→AcOEt:MeOH 1:1+2% Et3N gave pure 24 as a pale yellow oil (98% yield). Rf 0.40
(AcOEt:MeOH 1:1+2% Et3N, A, B). [α]D=−15.78 (c 1.56). IR: νmax 3448, 3312, 3029, 2929, 1712,
1600, 1497, 1453, 1372, 1245. GC–MS: Rt 10.45 (usual conditions but with a final temp. of 290°C and a
final time of 4 min); m/z: 298 (M+, 3.8), 207 (5.4), 190 (9.5), 178 (8.6), 146 (11), 134 (10), 118 (9.5), 117
(37), 116 (5.6), 115 (5.5), 108 (9.3), 107 (6.8), 99 (8.2), 92 (12), 91 (100), 79 (11), 77 (8.3), 74 (19), 65
(11), 56 (17). 1H NMR: 1.82–1.99 (1H, m, >CHCH2NH2), 2.58 (2H, d, -CH2Ph, J=7.4), 2.63–2.91 (2H,
m, -CH2NH2), 3.10–3.42 (2H, m, -CH2NHZ), 5.09 (2H, s, -CO2CH2Ph), 5.60 (1H, broad t, -NH-, J=5.4),
7.13–7.35 (10H, m, aromatics). 13C NMR: 36.77 (-CH2Ph), 42.71 (>CHCH2NH2), 43.18 and 43.57 (2C,
-CH2NH2 and -CH2NHZ), 66.65 (-CO2CH2Ph), 126.18 (>CH- para to -CH2CH<), 128.01, 128.48 and
128.92 (9C, >CH- aromatics), 136.75 (>C< ipso of -CO2CH2Ph), 139.78 (>C< ipso of -CH2Ph), 156.78
(2C, >C_O).
4.16. (S)-(N-Acetyl)-2-benzyl-[N0 -(benzyloxycarbonyl)]-1,3-propanediamine 25
A solution of 24 (207 mg, 751 µmol) in dry pyridine (2 ml) was treated with acetic anhydride (106 µl,
1.13 mmol) and stirred at room temperature for 1.5 h. The solution was diluted with water and extracted
with ether. The combined organic layers were washed with 0.7 M H2SO4 solution to remove pyridine
and then with 5% aqueous NH4H2PO4 and brine. The crude product was purified by chromatography
with PE:AcOEt 7:3→AcOEt to give 25 (207 mg, 88%). Crystallization from CH2Cl2 gave a pale yellow
solid. Mp=115.7–116.5°C (CH2Cl2/Et2O). Rf 0.39 (AcOEt:ETP 8:2, A, B). [α]D=+4.49 (c 2.08). IR:
νmax 3447, 3001, 2935, 1710, 1664, 1601, 1507, 1244. GC–MS: Rt 12.42 (12 tends to decompose in
the GC column); m/z: 340 (M+, 3.2), 249 (8.8), 178 (6.4), 176 (22), 160 (12), 146 (28), 130 (5.0),
129 (23), 118 (12), 117 (49), 116 (5.3), 115 (7.4), 108 (6.3), 107 (5.2), 92 (9.6), 91 (100), 79 (7.1),
1
77 (6.7), 74 (12), 73 (21), 72 (30), 65 (12), 60 (8.2), 56 (6.6), 43 (18). H NMR: 1.92–2.09 (1H, m,
>CHCH2NHAc), 1.98 (3H, s, -CH3), 2.52 and 2.59 (2H, AB part of ABX system, -CH2Ph, JAB=13.9,
JAX and JBX=7.4, 7.8), 2.92–3.46 (4H, m, -CH2NHZ and -CH2NHAc), 5.11 (2H, s, -CO2CH2Ph), 5.37
(1H, broad t, -NHZ, J=6.4), 6.27 (1H, broad s, -NHAc), 7.14–7.36 (10H, m, aromatics). 13C NMR:
23.04 (-CH3), 36.47 (-CH2Ph), 39.84 (-CH2NHAc), 41.13 (2C, >CHCH2NHAc and -CH2NHZ), 66.64
(-CO2CH2Ph), 126.20 (>CH- para to -CH2CH<), 127.82 (2C, >CH- ortho to -CH2O-), 127.97 (>CH-
para to -CH2O-), 128.39 (2C, >CH- meta to -CH2O-), 128.46 (2C, >CH- meta to -CH2CH<), 128.77
(2C, >CH- ortho to -CH2CH<), 136.49 (>C<, ipso of -CO2CH2Ph), 139.36 (>C<, ipso of -CH2Ph),
157.26 (-CO2CH2Ph), 170.81 (-COCH3).
4.17. General procedure for the acylation of monoprotected 2-benzyl-1,3-propanediamines with N-
protected amino acids to give 28a,b and 30a,b
A solution of amine 24, 29a or 29b (amines 29a and 29b were obtained from 28a,b by hydrogenolysis
of the N-benzyloxycarbonyl group, as described above for compound 4 from 9; they were used as such for
the following coupling reaction) (459 µmol) was dissolved in dry CH2Cl2 (10 ml) and cooled to 0°C. The
desired amino acid (N-tert-butoxycarbonyl-L-alanine for the synthesis of 28a, N-tert-butoxycarbonyl-
D-alanine for the synthesis of 28b, N-benzyloxycarbonylglycine for the synthesis of 30a,b, 689 µmol)

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L. Banfi et al. / Tetrahedron: Asymmetry 10 (1999) 3571–3592
was added, followed by (benzotriazolyl-1-oxy)tripyrrolidinophosphonium hexafluorophosphate (PyBOP,
287 mg, 551 µmol) and 4-methylmorpholine (73 µl, 661 µmol). The resulting solution was stirred at the
same temperature until complete (3–12 h). After dilution with water, the mixture was extracted with ethyl
acetate. Combined organic layers were washed with a diluted solution of H2SO4 (pH 2–3), then with a
diluted solution of Na2CO3 (pH 10) and, finally with brine. After solvent removal, crude products were
obtained.
4.17.1. (S)-2-Benzyl-[N-(benzyloxycarbonyl)]-[N0 -(tert-butoxycarbonyl)-L-alanyl]-1,3-propanedi-
amine 28a
Chromatography with PE:AcOEt 7:3→2:8 gave 28a as a white solid (77% yield), which was triturated
with ether. Mp=144.4–145.2°C (Et2O). Rf 0.42 (PE:AcOEt 1:1, A, C). [α]D=−33.26 (c 1.08). IR: νmax
3435, 2970, 2929, 1707, 1488, 1445, 1368, 1194, 1158. GC–MS: this compound decomposes in the
1
GC column. H NMR (DMSO-d6, temp. 100°C): 1.22 (3H, d, CH3CH(NHBoc)-, J=7.1), 1.40 (9H, s,
-C(CH3)3), 1.98 (1H, quintuplet, >CHCH2NHZ, J=6.3), 2.55 (2H, d, -CH2Ph, J=7.0), 2.89–3.11 (4H,
m, -CH2NHZ and -CH2NHAla), 3.97 (1H, quintuplet, CH3CH(NHBoc)-, J=7.2), 5.04 (2H, apparent
s, -CO2CH2Ph), 6.38 (1H, broad s (broad d at 6.94, J=7.0, temp. 22°C), -NHBoc), 6.83 (1H, broad
s, -NHZ), 7.12–7.38 (10H, m, aromatics), 7.47 (1H, broad s (broad t at 7.78, J=5.5, temp. 22°C),
-NHAla). 13C NMR (DMSO-d6, temp. 22°C): 18.01 (CH3CH(NHBoc)-), 28.09 (3C, -C(CH3)3), 35.30
(-CH2Ph), 39.42 (-CH2NHAla), 40.78 (-CHCH2NHZ), 41.11 (-CH2NHZ), 49.89 (CH3CH(NHBoc)-),
65.17 (-CO2CH2Ph), 77.91 (-C(CH3)3), 125.74 (>CH- para to -CH2CH<), 127.61, 127.68, 128.08,
128.27, 128.98 (9C, >CH-, aromatics), 137.15 (>C<, ipso of -CO2CH2Ph), 140.01 (>C<, ipso of
-CH2Ph), 155.02 (-CO2tBu), 156.29 (-CO2CH2Ph), 173.11 (-COCH(CH3)-).
4.17.2. (S)-2-Benzyl-[N-(benzyloxycarbonyl)]-[N0 -(tert-butoxycarbonyl)-D-alanyl]-1,3-propanedi-
amine 28b
Chromatography with PE:AcOEt 6:4→1:9 gave 28b as a white foam (85% yield). Rf 0.38 (PE:AcOEt
1:1, A, C). [α]D=+24.52 (c 0.52). IR: νmax 3432, 2972, 2929, 1704, 1490, 1444, 1367, 1201, 1162.
1
GC–MS: this compound decomposes in the GC column. H NMR (DMSO-d6, temp. 100°C): 1.23
(3H, d, CH3CH(NHBoc)-, J=7.3), 1.41 (9H, s, -C(CH3)3), 2.00 (1H, quintuplet, >CHCH2NHZ,
J=6.4), 2.56 (2H, d, -CH2Ph, J=7.0), 2.92–3.17 (4H, m, -CH2NHZ and -CH2NHAla), 3.98 (1H,
centre of m, CH3CH(NHBoc)-), 5.05 (2H, apparent s, -CO2CH2Ph), 6.38 (1H, broad s (broad d at
6.98, J=7.0, temp. 22°C), -NHBoc), 6.83 (1H, broad s, -NHZ), 7.14–7.37 (10H, m, aromatics), 7.48
(1H, broad t (broad t at 7.83, J=5.5, temp. 22°C), -NHAla, J=4.8). 13C NMR (DMSO-d6, temp.
22°C): 18.00 (CH3CH(NHBoc)-), 28.09 (3C, -C(CH3)3), 35.29 (-CH2Ph), 39.45 (-CH2NHAla), 40.66
(-CHCH2NHZ), 40.94 (-CH2NHZ), 49.94 (CH3CH(NHBoc)-), 65.18 (-CO2CH2Ph), 77.91 (-C(CH3)3),
125.74 (>CH- para to -CH2CH<), 127.61, 127.69, 128.07, 128.27, 128.98 (9C, >CH-, aromatics), 137.15
(>C<, ipso of -CO2CH2Ph), 140.03 (>C<, ipso of -CH2Ph), 155.04 (-CO2tBu), 156.34 (-CO2CH2Ph),
173.13 (-COCH(CH3)-).
4.17.3. (R)-2-Benzyl-[N-(benzyloxycarbonyl)glycyl]-[N0-(tert-butoxycarbonyl)-L-alanyl]-1,3-propane-
diamine 30a
Chromatography with AcOEt:CH2Cl2 8:2→AcOEt:CH2Cl2 8:2+2% MeOH gave 30a as a thick
colourless oil (78% yield). Rf 0.45 (AcOEt:CH2Cl2 8:2+2% MeOH, A, C). [α]D=−11.54 (c 1.78). IR:
ν
max 3433, 2967, 2920, 1705, 1662, 1486, 1445, 1367, 1158. GC–MS: this compound decomposes in the
1
GC column. H NMR (DMSO-d6, temp. 100°C): 1.23 (3H, d, CH3CH(NHBoc)-, J=7.2), 1.40 (9H, s,
-C(CH3)3), 1.97 (1H, quintuplet, >CHCH2NHAla, J=6.4), 2.54 (2H, d, -CH2Ph, J=7.0), 3.04–3.10 (4H,

L. Banfi et al. / Tetrahedron: Asymmetry 10 (1999) 3571–3592
3589
m, 2 -CH2NHCO-), 3.65 (2H, d, -CH2CO2CH2Ph, J=6.0), 3.98 (1H, centre of m, CH3CH(NHBoc)-),
5.04 (2H, apparent s, -CO2CH2Ph), 6.37 (1H, broad d (broad d at 6.97, J=6.9, temp. 22°C), -NHBoc,
J=6.5), 6.98 (1H, broad s, (broad t at 7.51, J=5.0, temp. 22°C) -NHZ), 7.12–7.38 (10H, m, aromatics),
7.50 (2H, centre of m (2 broad t at 7.82, J=6.6 and 7.89, J=6.6, temp. 22°C), 2 -CH2NHCO-). 13C
NMR (DMSO-d6, temp. 22°C): 18.01 (CH3CH(NHBoc)-), 28.10 (3C, -C(CH3)3), 35.40 (-CH2Ph),
39.10 (-CH2NHAla), 40.70 (-CHCH2NHZ), 43.61 (-CH2NHGly), 49.95 (CH3CH(NHBoc)-), 65.43
(-CO2CH2Ph), 77.93 (-C(CH3)3), 125.74 (>CH- para to -CH2CH<), 127.64, 128.08, 128.24, 128.98
(9C, >CH-, aromatics), 136.93 (>C<, ipso of -CO2CH2Ph), 140.05 (>C<, ipso of -CH2Ph), 155.03
(-CO2tBu), 156.41 (-CO2CH2Ph), 169.26 (-COCH2NHZ), 173.12 (-COCH(CH3)-).
4.17.4. (R)-2-Benzyl-[N-(benzyloxycarbonyl)glycyl]-[N0-(tert-butoxycarbonyl)-D-alanyl]-1,3-propane-
diamine 30b
Chromatography with AcOEt:CH2Cl2 7:3→AcOEt:CH2Cl2 8:2+1% MeOH gave 30b as a thick
colourless oil (83% yield). Rf 0.45 (AcOEt:CH2Cl2 8:2+2% MeOH, A, C). [α]D=+8.27 (c 0.44). IR:
νmax 3430, 2979, 2929, 1727, 1671, 1492, 1452, 1370, 1194. GC–MS: this compound decomposes in
1
the GC column. H NMR (DMSO-d6, temp. 100°C): 1.23 (3H, d, CH3CH(NHBoc)-, J=7.0), 1.40 (9H,
s, -C(CH3)3), 1.97 (1H, centre of m, >CHCH2NHAla), 2.53 (2H, d, -CH2Ph, J=7.0), 2.84–3.21 (4H,
m, 2 -CH2NHCO-), 3.65 (2H, d, -CH2CO2CH2Ph, J=6.0), 3.98 (1H, centre of m, CH3CH(NHBoc)-),
5.07 (2H, apparent s, -CO2CH2Ph), 6.37 (1H, broad d (broad d at 6.98, J=7.0, temp. 22°C), -NHBoc,
J=7.2), 6.97 (1H, broad s, (broad t at 7.51, J=6.0, temp. 22°C) -NHZ), 7.14–7.38 (10H, m, aromatics),
7.50 (2H, centre of m (2 broad t at 7.85, J=4.6 and 7.89, J=5.9, temp. 22°C), 2 -CH2NHCO-). 13C
NMR (DMSO-d6, temp. 22°C): 18.01 (CH3CH(NHBoc)-), 28.09 (3C, -C(CH3)3), 35.40 (-CH2Ph),
39.20 (-CH2NHAla), 40.60 (-CHCH2NHZ), 43.56 (-CH2NHGly), 50.02 (CH3CH(NHBoc)-), 65.42
(-CO2CH2Ph), 77.93 (-C(CH3)3), 125.74 (>CH- para to -CH2CH<), 127.64, 128.07, 128.24, 128.97
(9C, >CH-, aromatics), 136.94 (>C<, ipso of -CO2CH2Ph), 140.06 (>C<, ipso of -CH2Ph), 155.03
(-CO2tBu), 156.40 (-CO2CH2Ph), 169.27 (-COCH2NHZ), 173.12 (-COCH(CH3)-).
4.18. General procedure for tert-butoxycarbonyl group removal
Compound 30a,b (10 mg) was dissolved in dry CH2Cl2 (1 ml), cooled to 0°C and treated with
trifluoroacetic acid (0.5 ml). After 20 min stirring at 0°C, solvent was removed in vacuo. Traces of
acid were azeotropically removed with heptane and the oily residue was kept at 8×10−2 mbar overnight.
The crude product was directly dissolved in methanol-d4 for 1H NMR spectrum recording.
4.18.1. Characterization of 31a
1H NMR (methanol-d4): 1.50 (3H, d, CH3CH(NH3 )-, J=7.0), 2.08 (1H, centre of m, >CHCH2NHZ),
+
2.48–2.69 (2H, m, -CH2Ph), 3.07–3.58 (4H, m, 2 -CH2NHCO-), 3.75 (2H, s, -CH2NHZ), 3.91 (1H, q,
+
CH3CH(NH3 )-, J=7.0), 5.11 (2H, apparent s, -CO2CH2Ph), 7.18–7.42 (10H, m, aromatics).
4.18.2. Characterization of 31b
1H NMR (methanol-d4): 1.49 (3H, d, CH3CH(NH3 )-, J=7.1), 2.06 (1H, centre of m, >CHCH2NHZ),
+
2.48–2.69 (2H, m, -CH2Ph), 3.07–3.42 (4H, m, 2 -CH2NHCO-), 3.76 (2H, s, -CH2NHZ), 3.91 (1H, q,
+
CH3CH(NH3 )-, J=7.0), 5.11 (2H, apparent s, -CO2CH2Ph), 7.14–7.42 (10H, m, aromatics).

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4.19. (R)- and (S)-2-Benzyl-[N-(tert-butoxycarbonyl)]-1,3-propanediamine 43
(a) (R)-43 from 44: A solution of 42 (272 mg, 0.68 mmol) in methanol (10 ml) was treated with Pd/C
(10%, 54 mg) and hydrogenated at room temperature and 1 atm pressure for 6 h. The catalyst was filtered
off and the solvent was removed in vacuo. Chromatography (70–230 mesh) with AcOEt, AcOEt:MeOH
1:1→AcOEt:MeOH 1:1+1% Et3N gave (R)-41 (152 mg) as a pale yellow oil in 85% yield.
(b) (S)-43 from 42: The same procedure described above for compounds 15 and 24 was followed. After
chromatography, pure (S)-41 was obtained in 95% yield. Rf 0.30 (elongated spot, AcOEt:MeOH 1:1+1%
Et3N, A, C). [α]D [(R)-41]=+19.87 (c 2.56); [α]D [(S)-41]=−17.77 (c 2.05). IR: νmax 3451, 3039, 2933,
1692, 1603, 1492, 1452, 1367, 1192. GC–MS: 8.17; m/z: 264 (M+, 3.0), 208 (17), 191 (26), 179 (7.1),
173 (6.4), 156 (7.3), 146 (23), 134 (26), 132 (5.4), 131 (6.0), 130 (31), 119 (9.8), 118 (100), 117 (76),
116 (8.8), 115 (9.8), 100 (19), 92 (13), 91 (41), 74 (9.0), 65 (7.9), 59 (19), 58 (5.3), 57 (94), 56 (67), 44
1
(8.4), 43 (8.4), 41 (32), 39 (10). H NMR: 1.43 (9H, m, -C(CH3)3), 2.19–2.31 (1H, m, >CHCH2NH2),
2.58–3.40 (4H, m, -CH2NH2 and -CH2NHBoc), 2.59 and 2.67 (2H, AB part of ABX system, -CH2Ph,
J
AB=13.7, JAX and JBX=7.3, 7.6), 4.95 (2H, broad s, -NH2), 5.12 (1H, broad t, -NH-, J=5.4), 7.16–7.33
(5H, m, aromatics). 13C NMR: 28.28 (3C, -C(CH3)3), 36.24 (-CH2Ph), 40.51 (>CHCH2NH2), 40.79
(-CH2NHBoc), 41.36 (-CH2NH2), 79.61 (-C(CH)3), 126.26 (>CH- para to -CH2CH<), 128.50 (2C,
>CH- meta to -CH2CH<), 128.88 (2C, >CH- ortho to -CH2CH<), 138.89 (>C< ipso of -CH2Ph), 156.93
(>C_O).
4.20. (S)-2-Benzyl-[N-(benzyloxycarbonyl)]-[N0 -(tert-butoxycarbonyl)]-1,3-propanediamine 44
A solution of 24 (226 mg, 758 µmol) in THF (0.5 ml) was diluted with water (4.5 ml), then the pH was
adjusted to 9 by addition of 1N NaOH. Di-tert-butyl dicarbonate (261 ml, 1.16 mmol) was added and
the reaction was stirred at room temperature for 2.5 h. The reaction was diluted with water and extracted
with Et2O. The crude product was chromatographed with PE:Et2O 7:3→3:7 to give a thick pale yellow oil
(259 mg, 86% yield). Rf 0.40 (PE:Et2O 1:1, A, B, C). [α]D=−0.15 (c 2.21). IR: νmax 3450, 3024, 2930,
1
1703, 1603, 1494, 1443, 1189, 991. GC–MS: this compound decomposes in the GC column. H NMR:
1.43 (9H, s, -C(CH3)3), 1.91–2.04 (1H, m, >CHCH2NHAc), 2.54 (2H, d, -CH2Ph, J=7.7), 2.84–3.38
(4H, m, -CH2NHZ and -CH2NHBoc), 5.00 (1H, broad t, -NHZ, J=6.5), 5.09 and 5.12 (2H, AB system,
-CO2CH2Ph, J=12.4), 5.56 (1H, broad t, -NHAc, J=6.1), 7.14–7.38 (10H, m, aromatics). 13C NMR:
28.39 (3C, -C(CH3)3), 36.22 (-CH2Ph), 40.55 (-CH2NHBoc), 41.28 (-CH2NHZ), 41.55 (-CHCH2NHZ),
66.68 (-CO2CH2Ph), 79.43 (-C(CH3)3), 126.27 (>CH- para to -CH2CH<), 128.02, 128.49, 128.59 and
128.87 (9C, >CH-, aromatics), 136.67 (>C<, ipso of -CO2CH2Ph), 139.48 (>C<, ipso of -CH2Ph),
156.74 and 157.05 (2C, >C_O).
4.21. General method for the preparation of Mosher’s esters 32, 33, 34 and 35
About 15 µmol of alcohol (15, 19, 21 and 40, respectively) were dissolved in dry CH2Cl2 (0.5 ml) and
treated with 4-dimethylaminopyridine (6 mol equivalents) and Mosher’s chloride (3 mol equivalents).
After 1 h crude mixture was directly purified by preparative thin layer chromatography to give the
corresponding esters in 70–92% yield.
4.21.1. (R,R)- and (R,S)-Esters (from 15) 32
Eluent for chromatography: PE:AcOEt 1:9. Rf 0.48 (PE:AcOEt 1:9, A, B).

L. Banfi et al. / Tetrahedron: Asymmetry 10 (1999) 3571–3592
3591
4.21.2. (R,R)- and (R,S)-Esters (from 19) 33
Eluent for chromatography: PE:Et2O 8:2. Rf 0.48 (PE:Et2O 8:2, A, B).
4.21.3. (R,R)- and (R,S)-Esters (from 21) 34
Eluent for chromatography: PE:Et2O 1:1. Rf 0.32 (PE:Et2O 6:4, A, B).
4.21.4. (R,R)- and (R,S)-Esters (from 30) 35
Eluent for chromatography: PE:Et2O 6:4 Rf 0.37 (PE:Et2O 7:3, A, C).
4.22. General method for the preparation of Mosher’s amides 36, 37
About 15 µmol of amine (24 and 43, respectively) were dissolved in dry pyridine (0.5 ml) and treated
with Mosher’s chloride (3 mol equivalents). After 2–3 h the crude mixture was diluted with water
and extracted with ether. After solvent evaporation residual pyridine was azeotropically removed with
heptane. Purification was performed by preparative thin layer chromatography to give the corresponding
amides in 66–84% yield.
4.22.1. (R,R)- and (R,S)-Amides (from 24) 36
Eluent for chromatography: PE:Et2O 1:1. Rf 0.38 (PE:Et2O 1:1, A, B).
4.22.2. (R,R)- and (R,S)-Amides (from 43) 37
Eluent for chromatography: PE:Et2O 1:1. Rf 0.39 (PE:Et2O 1:1, A, C).
Acknowledgements
We wish to thank Amano, Novo Nordisk and Recordati (Unità Biochimici De.Bi) for the generous
gift of some enzymes, and Mr. Silvio Carrettin for his collaboration to this work. We also wish to thank
M.U.R.S.T. (COFIN 98), Università di Genova and C.N.R. for financial support to this project.
References
1. Clary, L.; Santaella, C.; Vierling, P. Tetrahedron 1995, 51, 13073–13088.
2. Jacobson, A. R.; Gintzler, A. R.; Sayre, L. M. J. Med. Chem. 1989, 32, 1708–1717.
3. Stepinski, J.; Tam, S. W. Z. Naturforsch. 1994, 49b, 407–411.
4. Lambert, D. M.; Neuvens, L.; Mergen, F.; Gallez, B.; Poupaert, J. H.; Ghysel-Burton, J.; Maloteaux, J.-M.; Dumont, P. J.
Pharm. Pharmacol. 1993, 45, 186–191.
5. Gante, J. Angew. Chem., Int. Ed. Engl. 1994, 33, 1699–1720.
6. Martin, J. A.; Redshaw, S.; Thomas, G. J. Progress in Medicinal Chemistry 1995, 32, 239–287.
7. Wonacott, A.; Cooke, R.; Hayes, F. R.; Hann, M. M.; Jhoti, H.; McMeekin, P.; Mistry, A.; Murray-Rust, P.; Singh, O. M.
P.; Weir, M. P. J. Med. Chem. 1993, 36, 3113–3119.
8. Haque, T. S.; Skillman, A. G.; Lee, C. E.; Habashita, H.; Gluzman, I. Y.; Ewing, T. J. A.; Goldberg, D. E.; Kuntz, I. D.;
Ellman, J. A. J. Med. Chem. 1999, 42, 1428–1440.
9. Giannis, A.; Kolter, T. Angew. Chem., Int. Ed. Engl. 1993, 32, 1244–1267.
10. Banfi, L.; Guanti, G.; Mugnoli, A.; Riva, R. Tetrahedron: Asymmetry 1998, 9, 2481–2492, and references cited therein.
11. Wong, C.-H.; Whitesides, G. M. Enzymes in Synthetic Organic Chemistry. Tetrahedron Organic Chemistry Series; Elsevier
Science: Oxford, 1994.
12. Adamczyk, M.; Grote, J. Tetrahedron: Asymmetry 1997, 8, 2099–2100.

3592
L. Banfi et al. / Tetrahedron: Asymmetry 10 (1999) 3571–3592
13. Adamczyk, M.; Grote, J.; Rege, S. Tetrahedron: Asymmetry 1997, 8, 2509–2512.
14. Chamorro, C.; Gonzales-Muñiz, R.; Conde, S. Tetrahedron: Asymmetry 1995, 6, 2343–2352.
15. Djeghaba, Z.; Deleuze, H.; De Jeso, B.; Messadi, D.; Maillard, B. Tetrahedron Lett. 1991, 32, 761–762.
16. Gotor, V.; Brieva, R.; Rebolledo, F. J. Chem. Soc., Chem. Commun. 1988, 957–958.
17. Brieva, R.; Rebolledo, F.; Gotor, V. J. Chem. Soc., Chem. Commun. 1990, 1386–1387.
18. Gotor, V.; García, M. J.; Rebolledo, F. Tetrahedron: Asymmetry 1990, 1, 277–278.
19. Fernández, S.; Brieva, R.; Rebolledo, F.; Gotor, V. J. Chem. Soc., Perkin Trans. 1 1992, 2885–2889.
20. Gotor, V.; Menéndez, E.; Mouloungui, Z.; Gaset, A. J. Chem. Soc., Perkin Trans. 1 1993, 2453–2456.
21. Puertas, S.; Brieva, R.; Rebolledo, F.; Gotor, V. Tetrahedron 1993, 49, 4007–4014.
22. Pozo, M.; Gotor, V. Tetrahedron 1993, 49, 4321–4326.
23. García, M. J.; Rebolledo, F.; Gotor, F. Tetrahedron 1994, 50, 6935–6940.
24. Astorga, C.; Rebolledo, F.; Gotor, V. J. Chem. Soc., Perkin Trans. 1 1994, 829–832.
25. Puertas, S.; Rebolledo, F.; Gotor, F. Tetrahedron 1995, 51, 1495–1502.
26. Pozo, M.; Gotor, V. Tetrahedron: Asymmetry 1995, 6, 2797–2802.
27. Alfonso, I.; Astorga, C.; Rebolledo, F.; Gotor, V. J. Chem. Soc., Chem. Commun. 1996, 2471–2472.
28. Sánchez, V. M.; Rebolledo, F.; Gotor, V. Tetrahedron: Asymmetry 1997, 8, 37–40.
29. Iglesias, L. E.; Sánchez, V. M.; Rebolledo, F.; Gotor, V. Tetrahedron: Asymmetry 1997, 8, 2675–2677.
30. Maestro, A.; Astorga, C.; Gotor, V. Tetrahedron: Asymmetry 1997, 8, 3153–3159.
31. Gutman, A. L.; Meyer, E.; Yue, X.; Abell, C. Tetrahedron Lett. 1992, 33, 3943–3946.
32. Vörde, C.; Högberg, H.-E.; Hedenström, E. Tetrahedron: Asymmetry 1996, 7, 1507–1513.
33. Kanerva, L. T.; Csomós, P.; Sundholm, O.; Bernáth, G.; Fülöp, F. Tetrahedron: Asymmetry 1996, 7, 1705–1716.
34. Margolin, A. L.; Klibanov, A. M. J. Am. Chem. Soc. 1987, 109, 3802–3804.
35. Yang, F.; Hoenke, C.; Prinzbach, H. Tetrahedron Lett. 1995, 36, 5151–5154.
36. De Castro, M. S.; Sinisterra Gago, J. V. Tetrahedron 1998, 54, 2877–2892.
37. West, J. B.; Wong, C.-H. Tetrahedron Lett. 1987, 28, 1629–1632.
38. Gutman, A. L.; Meyer, E.; Kalerin, E.; Polyak, F.; Sterling, J. Biotech. and Bioeng. 1992, 40, 760–767.
39. Schuster, M.; Munoz, B.; Yuan, W.; Wong, C.-H. Tetrahedron Lett. 1993, 34, 1247–1250.
40. Orsat, B.; Alper, P. B.; Moree, W.; Mak, C.-P.; Wong, C.-H. J. Am. Chem. Soc. 1996, 118, 712–713.
41. Bommarius, A. S.; Drauz, K.; Günther, K.; Kanup, G.; Schwarm, M. Tetrahedron: Asymmetry 1997 8, 3197–3200.
42. Easton, C. J.; Harper, J. B. Tetrahedron Lett. 1998, 39, 5269–5272.
43. Cainelli, G.; Giacomini, D.; Galletti, P.; DaCol, M. Tetrahedron: Asymmetry 1997, 8, 3231–3235.
44. Grabowski, S.; Armbruster, J.; Prinzbach, H. Tetrahedron Lett. 1997, 38, 5485–5488.
45. Waldmann, H.; Reidel, A. Angew. Chem., Int. Ed. Engl. 1997, 36, 647–649.
46. Roos, E. C.; Mooiweer, H. H.; Hiemstra, H.; Speckamp, W. N.; Kaptein, B.; Boesten, W. H. J.; Kamphuis, J. J. Org. Chem.
1992, 57, 6769–6778.
47. Whitmore, B. C.; Eisenberg, R. Inorg. Chem. 1983, 22, 1–3.
48. Mori, K.; Chiba, N. Liebigs Ann. Chem. 1989, 957–962.
49. Biffin, M. E. C.; Miller, J.; Paul, D. B. In The Chemistry of the Azido Group; S. Patai, Ed.; Wiley: London, 1971; pp.
57–181.
50. Vaultier, M.; Knouzi, N.; Carrié, R. Tetrahedron Lett. 1983, 24, 763–764.
51. Guanti, G.; Banfi, L.; Riva, R. Tetrahedron: Asymmetry 1995, 6, 1345–1356, and references cited therein.
52. Tsuji, K.; Terao, Y.; Achiwa, K. Tetrahedron Lett. 1989, 30, 6189–6192.
53. Secundo, F.; Riva, S.; Carrea, G. Tetrahedron: Asymmetry 1992, 3, 267–280.
54. Koziara, A.; Osowska-Pacewicka, K.; Zawadzki, S.; Zwierzak, A. Synthesis 1985, 202–204.
55. Bartra, M.; Romea, P.; Urpí, F.; Vilarrasa, J. Tetrahedron 1990, 46, 587–594.
56. Rosen, T.; Lico, I. M.; Chu, D. T. W. J. Org. Chem. 1988, 53, 1580–1582.
57. Yokomatsu, T.; Minowa, T.; Murano, T.; Shibuya, S. Tetrahedron 1998, 54, 9341–9356.