A convenient synthesis of amino acid-derived precursors to the important wine aroma 3-sulfanylhexan-1-ol (3SH)

Article abstract of DOI:10.1016/j.tetlet.2020.151663

A convenient, straightforward synthesis of the important amino acid-derived aroma precursors, 3-S-cysteinylhexan-1-ol (Cys-3SH) and 3-S-glutathionylhexan-1-ol (GSH-3SH) from commercially available butan-1-ol is reported. The versatility of this approach to include deuterium labelling is also demonstrated.

Full text of DOI:10.1016/j.tetlet.2020.151663

Journal Pre-proofs
A convenient synthesis of amino acid-derived precursors to the important wine
aroma 3-sulfanylhexan-1-ol (3SH)
Rebecca E. Jelley, Nina Duhamel, David Barker, Bruno Fedrizzi
PII:
S0040-4039(20)30082-4
DOI:
https://doi.org/10.1016/j.tetlet.2020.151663
TETL 151663
Reference:
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
29 November 2019
16 January 2020
21 January 2020
Please cite this article as: Jelley, R.E., Duhamel, N., Barker, D., Fedrizzi, B., A convenient synthesis of amino acid-
derived precursors to the important wine aroma 3-sulfanylhexan-1-ol (3SH), Tetrahedron Letters (2020), doi: https://
doi.org/10.1016/j.tetlet.2020.151663
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover
page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will
undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing
this version to give early visibility of the article. Please note that, during the production process, errors may be
discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
©
2020 Published by Elsevier Ltd.

A convenient synthesis of amino acid-derived precursors to the important
wine aroma 3-sulfanylhexan-1-ol (3SH)
a*,
a
a,b,
a,b,
Rebecca E. Jelley , Nina Duhamel , David Barker *, Bruno Fedrizzi *
aSchool of Chemical Sciences, University of Auckland, 23 Symonds St, Auckland, New
Zealand
bCentre for Green Chemical Science, School of Chemical Sciences, University of Auckland.
Private Bag 92019, Auckland, New Zealand.
*
Corresponding Authors
Tel: + 64 9 923 8473 (BF)
E-mail: rebecca.jelley@auckland.ac.nz (REJ), d.barker@auckland.ac.nz (DB),
b.fedrizzi@auckland.ac.nz (BF),
Abstract
A convenient, straightforward synthesis of the important amino acid-derived aroma precursors,
3
-S-cysteinylhexan-1-ol (Cys-3SH) and 3-S-glutathionylhexan-1-ol (GSH-3SH) from
commercially available butan-1-ol is reported. The versatility of this approach to include
deuterium labelling is also demonstrated.
Keywords
Wine aroma; Aroma precursors; 3-sulfanylhexan-1-ol (3SH); Isotopic labelling.

Introduction
The varietal thiol 3-sulfanylhexan-1-ol (3SH, 1) is an important aroma compound responsible
for the desirable fruity notes associated with white wines, particularly Sauvignon Blanc. Two
key amino acid-derived precursors to 1 have previously been identified, namely 3-S-
cysteinylhexan-1-ol (Cys-3SH, 2) and 3-S-glutathionylhexan-1-ol (GSH-3SH, 3).1,2 The
bioconversion of these amino acid-derived precursors, 2 and 3, to 3SH (1), which is known to
occur during fermentation, is therefore of considerable interest as it becomes desirable to
maximise the concentration of 3SH (1) in wine for its sought after sensory properties. Studies
of these transformations often require the use of deuterated analogues followed by mass
spectrometry detections.3
O
H N
2
OH
S
OH
(
R/S)-Cys-3SH (2)
SH
OH
(R/S)-3SH (1)
Yeast activity
HO
O
H N
2
O
O
HN
N
OH
O
H
S
OH
(
R/S)-GSH-3SH (3)
Figure 1. Structures of the amino acid-derived precursors to the aroma compound 1.

Previous approaches to the synthesis of these amino acid-derived precursors involve the
conjugate addition of glutathione or cysteine to a very reactive species, hex-2-enal (4).1,2,4,5 In
addition to the difficulties arising from the susceptibility of volatile 4 to readily oxidise, it has
been documented that the addition reaction does not stop at the mono-adduct but proceeds to
the di-adduct giving an unwanted side product containing a thiazolidine moiety 5 and under
some conditions thiazepane 6 (Fig. 2).5,6
O
O
HS
OH
NH Cl
4
3
Cys
Conjugate Addition
O
H N
2
OH
S
OH
O
S
S
OH
NH
N
H
O
5
6
Figure 2. Structures of reported byproducts obtained during the conjugate addition of 4 and
cysteine.5,6
Changes to this approach involved the inclusion of protecting groups on cysteine before the
conjugate addition with hex-2-enal (4), to prevent the unwanted cyclisation.7,8 However, this
adds further synthetic steps. We encountered difficulties with the reproducibility of the
9
aforementioned strategies to obtain GSH-3SH (3), as did Roland and co-workers. Therefore,
in an attempt to improve the reproducibility of the syntheses of these compounds, avoiding the
problematic use of hex-2-enal (4) and protecting amino acid derivatives, it was envisaged that
the two aroma precursors could be prepared from a common starting material derived from
commercially available butan-1-ol (7). This approach follows those of Luisier and co-
1
0
4
11
workers, Pardon and co-workers, and Duhamel and co-workers, where the intermediate

ethyl hex-2-enoate (8) has been employed, and can provide access to both aroma precursors
with the inclusion of up to eight deuterium labels, depending on the degree of deuteration of
butan-1-ol (7) (Fig. 3).
D
D
D
D
D
D
D
D
D
D
O
D
R
D
D
D
D
D
D
D
D
D
D
D
OD
D
D
O
OH
D
d -7
d8-8
R = cysteine or glutathione
1
0
Figure 3. Proposed pathway to deuterated Cys-3SH (2) and GSH-3SH (3) from
commercially available deuterated butan-1-ol (7).
Results and Discussion
Butanal (9) was obtained from the Swern oxidation of butan-1-ol (7) using oxalyl chloride and
DMSO and the crude aldehyde 9, retained in the reaction solvents, was used immediately
without further purification due to its high volatility. Butanal (9) was then converted to ethyl
(E)-hex-2-enoate in 88% yield (from butan-1-ol), through a Wittig reaction using
1
1
Ph P=CHCO Et. This gave exclusive formation of the desired (E)-alkene product, which was
3
2
confirmed by NMR analysis. In contrast to hex-2-enal (4), (E)-hex-2-enoate (8) could be easily
purified using normal-phase silica gel chromatography under ambient conditions as it is not
readily oxidised.
A conjugate addition was then employed to add the desired amino acid to α,β-unsaturated ester
1
0
8
using similar reported reaction conditions, for the synthesis of Cys-3SH (2). However,
difficulties were encountered when the reported purification procedure was followed.
Purification was found to be improved through the use of reversed-phase C18 column
chromatography using pre-packed cartridges, especially when working on smaller scales.

Addition of single enantiomers of cysteine or glutathione to ethyl (E)-hex-2-enoate (8) gave an
inseparable mixture of two diastereomers (of 10 and 11), in an approximately 1:1 mixture in
both cases, as determined by NMR analysis.
The reduction of an ester in the presence of a carboxylic acid moiety is potentially problematic,
particularly when the compound of interest has poor solubility in organic solvents. The most
commonly used reducing agents, sodium borohydride and lithium aluminium hydride, exhibit
different reactivities towards the reduction of esters; the former is often unreactive towards
esters, while reduction of both the ester and the carboxylic acid is generally observed with the
1
0
latter. However, additives have been shown to enhance the reactivity of NaBH towards
4
esters,12,13 and a simple one-pot sodium borohydride-MeOH system in THF has been shown to
be effective for a range of different esters.13
This methodology was therefore employed and proved to be successful in selectively reducing
the ethyl esters of both Cys-3SH and GSH-3SH to their desired alcohol functionality. This
approach utilised less expensive regents and solvents than those employed previously to reduce
1
0
8
. By employing reversed-phase C18 column chromatography, using pre-packed cartridges,
to purify the final products, the issues with removing the inorganic salts from the products were
eliminated.
Following optimisation of the above synthetic procedures, they were then used to prepare d8-
Cys-3SH (d -2) and d -GSH-3SH (d -3), and d -Cys-3SH (d -2), from d -butan-1-ol and
8
8
8
5
5
10
3
,3,4,4,4-d -butan-1-ol respectively (Fig. 3). The general reaction pathway, conditions and
5
yields (for both labelled and unlabelled compounds) are shown in Scheme 1. All products and
intermediates were fully characterised using NMR spectroscopy and high resolution mass
1
spectrometry. H NMR analysis of the deuterated deuterated final products provided no
evidence that unwanted deuterium-proton exchange occurred during the synthetic

transformations. Therefore, d -2, d -3 and d -2 retain the >99% labelling found in the
8
8
5
commercial precursors.
HO
O
H N
2
O
O
O
S
O
H N
H N
2
2
HN
OH
OH
D
OH
N
H
O
D
D
S
D
D
D D
D
S
D
D
D
D
D
D
D
D
D
D
OH
OH
OH
D
D
D
d8-3
d8-2
d5-2
Figure 3. Structures of the deuterated analogues prepared of precursors 2 and 3.

D
D
D
D
D
D
D
D
D
OD
7
a
D
D
D
D
D
D
O
D
D
9
b
D
D
O
D
D
D
O
HO
O
D
d8-6
D
D
H N
2
c
d
O
O
O
HN
OH
H N
2
N
H
OH
O
D
S
D
O
D
D
S
D
O
D
D
D
D
D
D
D
D
D
D
O
O
D
d8-10
d8-11
HO
O
e
f
H N
2
O
O
O
H N
2
OH
D
HN
D
OH
N
H
D
D
S
D
O
D
D
S
D
D
D
D
D
D
OH
D
OH
D
D
d8-3
d8-2
Scheme 1 Synthesis of d -Cys 3SH d -2 and d -GSH-3SH d -3. Reagents and conditions; (a)
8
8
8
8
oxalyl chloride, DMSO, CH Cl, −78 °C; (b) Ph P=CHCO Et, CH Cl, room temperature, 50%
3
3
2
3
yield over two steps; (c) glutathione; H O, pH 7.5, 3 days, room temperature, 44% yield; (d)
2
cysteine; H O, pH 7.5, 3 days, room temperature, 43% yield; (e) NaBH , MeOH, THF, reflux,
2
4
1
h, 49% yield; (f) NaBH , MeOH, THF, reflux, 1 h, 47% yield. Yields for synthetic steps to
4

the unlabelled precursors, 2 and 3, were as follows; (b) 88% over two steps; (c) 50%; (d) 69%;
(
e) 33%; (f) 48%. Yields for synthetic steps to d -2 were as follows; (b) 62% over two steps;
5
(c) 42%; (e) 58%.
In conclusion, a convenient, versatile and reproducible synthetic procedure to access the
important aroma precursors Cys-3SH (2) and GSH-3SH (3) has been established. Three new
deuterated analogues of these precursors were synthesised and fully characterised using this
methodology, d -Cys-3SH, d -Cys-3SH and d -GSH-3SH. Isotopically labelled analogues of
5
8
8
the natural aroma precursors, allow for mass spectrometry based stable isotope dilution
analyses (SIDA) to be developed. In this case, such analogues can be employed in studies to
better understand the accumulation of these precursors in different grape and grapevine tissues
as well as to study their bioconversion into the desirable wine aroma compound, 3-
sulfanylhexan-1-ol (3SH).
Acknowledgements
This research was supported by the Bioresource Processing Alliance, established by the New
Zealand Ministry of Business, Innovation and Employment to generate innovative products
from primary sector by-products.
Supplementary Information
Full experimental procedures, characterisation and NMR spectra can be found in the
Supplementary Information document.

References
1
2
. Tominaga T, Peyrot des Gachons C, Dubourdieu D. J Agric Food Chem. 1998; 46: 5215–
219.
. Peyrot des Gachons C, Tominaga T, Dubourdieu D. J Agric Food Chem. 2002; 50: 4076–
079.
5
4
3
4
. Roland A, Schneider R, Razungles A, Cavelier F. Chem Rev. 2011; 111: 7355–7376.
. Pardon KH, Graney SD, Capone DL, Swiegers JH, Sefton MA, Elsey GM. J Agric Food
Chem. 2008; 56: 3758–3763.
5
6
. Starkenmann C. J Agric Food Chem. 2003; 51: 7146–7155.
. Wakabayashi H, Wakabayashi M, Eisenreich W, Engel K-H. J Agric Food Chem. 2004;
5
2: 110–116.
7
8
9
. Grant-Preece PA, Pardon KH, Capone DL, Cordente AG, Sefton MA, Jeffery DW, Elsey
GM. J Agric Food Chem. 2010; 58: 1383–1389.
. Roland A, Schneider R, Le Guerneve C, Razungles A, Cavelier F. Food Chem. 2010;
1
21: 847–855.
. Roland A, Schneider R, Razungles A, Le GC, Cavelier F. J Agric Food Chem. 2010; 58:
0684–9.
1
1
1
0. Luisier J-L, Veyrand J, Piantini U. Chim Int J Chem. 2007; 61: 533–535.
1. Duhamel N, Piano F, Davidson SJ, Larcher R, Fedrizzi B, Barker D. Tetrahedron Lett.
2
015; 56: 1728–1731.
1
1
2. Periasamy M, Thirumalaikumar M. J Organomet Chem. 2000; 609: 137–151.
3. da Costa JCS, Pais KC, Fernandes EL, de Oliveira PSM, Mendonca JS, de Souza MVN,
Peralta MA, Vasconcelos TRA. Arkivoc. 2005; 2006: 128.
Highlights
-
-
Convenient and reproducible synthetic route to Cys-3SH and GSH-3SH
Method easily adapted to allow for the preparation of deuterium-labelled
compounds
-
Straightforward purification of products using SPE pre-packed C18
cartridges
Declaration of interests

☒
The authors declare that they have no known competing financial interests or
personal relationships that could have appeared to influence the work reported
in this paper.
☐
The authors declare the following financial interests/personal relationships
which may be considered as potential competing interests: