Synthesis and analysis of stable isotope-labelled: N -acyl homoserine lactones

Article abstract of DOI:10.1039/c6ra17797b

Aliphatic aldehydes were deuterated at the α-position via a base-catalyzed exchange reaction with D₂O. These deuterated building blocks were used for the synthesis of labelled analogues of quorum sensing signal molecules belonging to the three major classes of naturally occurring N-acylated homoserine lactones (AHLs), with the label on a non-enolizable and therefore stable position. Besides the application of these stable isotope-labelled AHLs as a labelled standard for analysis via isotope dilution mass spectrometry, these compounds can be used to study the metabolic fate of the fatty acid tail of the AHL-molecule. These isotope-labelled compounds were fully characterized and used to synthesize the deuterated analogues of two commonly occurring AHL-degradation products, a tetramic acid and a ring opened N-acyl homoserine.

Full text of DOI:10.1039/c6ra17797b

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Synthesis and analysis of stable isotope-labelled N-acyl homoserine lactones
DOI: 10.1039/C6RA17797B
Ewout Ruysbergh, Christian V. Stevens, Norbert De Kimpe and Sven Mangelinckx*
Department of Sustainable Organic Chemistry and Technology, Faculty of Bioscience
Engineering, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium
* Corresponding Author: E-Mail: Sven.Mangelinckx@UGent.be; Tel.: +32-(0)9-264.59.51;
Fax +32-(0)9-264.62.21.
Received: / Accepted: / Published:
Keywords: AHL, quorum sensing, isotope labelling, tetramic acid, isotope dilution, GC-MS
Graphical abstract
Abstract
Aliphatic aldehydes were deuterated at the -position via a base-catalyzed exchange reaction
with D2O. These deuterated building blocks were used for the synthesis of labelled analogues
of quorum sensing signal molecules belonging to the three major classes of naturally occurring
N-acylated homoserine lactones (AHLs), with the label on a non-enolizable and therefore
stable position. Besides the application of these stable isotope-labelled AHLs as labelled
standard for analysis via isotope dilution mass spectrometry, these compounds can be used
to study the metabolic fate of the fatty acid tail of the AHL-molecule. These isotope-labelled
compounds were fully characterized and used to synthesize the deuterated analogues of two
commonly occurring AHL-degradation products, a tetramic acid and a ring opened N-acyl
homoserine.
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DOI: 10.1039/C6RA17797B
Introduction
For many years, researchers thought of bacteria as individual cells, unable to interact with one
another. However, this view changed dramatically with the discovery of population density
dependent light production by the marine bacterium Vibrio fischeri.1 Because this type of gene
regulation is linked to the population density or quorum, the term ‘quorum sensing’ (QS) was
used to describe this phenomenon.2 To communicate with each other, bacteria rely on small,
diffusible molecules. Since these molecules can upregulate their own production, they are
commonly referred to as autoinducers. In Gram-negative bacteria these autoinducers are N-
acylated homoserine lactones (AHLs).3, 4 The structure of an AHL consists of a homoserine
lactone ring coupled with a variable N-acyl chain. This acyl chain can vary in length from four
to eighteen carbon atoms, and the chain can contain an oxo or hydroxy group at the third
carbon of the acyl chain. AHLs with an unsaturated or branched side chain have also been
detected in nature.5-7 Very recently, a new class of AHLs, containing a p-coumaryl or a
cinnamoyl group instead of an acyl chain, was discovered in nature, extending the range of
possible occurring AHLs.8, 9 Many diverse bacterial phenotypes such as bioluminescence,
enzyme secretion, virulence expression and biofilm formation are regulated by QS.3 Besides
intraspecies communication, AHL-molecules are also involved in interspecies and even
interkingdom signaling.10-12
Although the AHL-concentration inside a biofilm can reach as high as 600 µM, only
concentrations in the nM range are encountered in the effluent.13 To detect these trace
amounts of AHLs, sensitive detection methods are needed. One possible method is via the
application of biosensors, such as Agrobacterium tumefaciens NT1,14 Chromobacterium
violaceum CV02615 and Escherichia coli JB523.16 The detection relies on a phenotypic response
such as enzyme secretion, pigment production or bioluminescence when the threshold
concentration of AHLs is exceeded.17 Although detection of sub-picomole amounts of AHLs is
feasible, the possibility of artefacts, such as medium-derived diketopiperazines,18 and the
need to use multiple biosensor strains in parallel for complete coverage of all AHLs, has
prompted researchers to develop multiple techniques for instrumental AHL-detection and
identification.19-23 To obtain reliable results and exact quantification, an internal standard
needs to be included in these analyses. The use of odd-chain AHLs as internal standard was
abandoned after the discovery of odd-chain AHL-producing bacteria.24, 25 Several groups have
reported the synthesis of isotope-labelled AHLs 1-10 (Figure 1) which can be used as internal
standards.13, 26-33 In the case of isotope dilution mass spectrometry (IDMS), the spike
compound should be chemically identical with the analyte. As the isotope-labelled compound
acts as an internal standard, compensating for losses during sample isolation and analysis, the
mass difference between the isotope and the analyte should not be too high, to avoid possible
isotope effects.34 Besides the application as standard, isotope-labelled molecules are often
used in absorption, distribution, metabolism and excretion (ADME) studies and to study
reaction mechanisms.35 Hereby, mostly a 1:1 mixture of non-labelled and isotope-labelled
compounds is used, to create a recognizable mass spectral ion pattern to study the in vitro
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and in vivo metabolic dispersion.35-38 However, no methodology is available to syntDhOeI:s1i0z.e10A39H/CL6sRA17797B
belonging to the major different classes with an isotope label in the acyl chain, starting from
one, easily available deuterated building block.
View Article Online
In this work, a convenient synthesis of several deuterium-labelled AHLs is reported. D2O is
used to introduce the deuterium label in aldehydes, which are used as building blocks to
synthesize AHLs belonging to the three major classes of naturally occurring AHLs.
Figure 1: Isotope-labelled AHL-analogues 1,13 2,26 3a-c,27 4a-h,28 5a-c,29 6a-e,30 7,31 8, 932 and
1033 described in the literature.
Results and discussion
Since secondary metabolites are quite expensive to synthesize in terms of energy and used
materials, it is tempting to speculate that certain elements of these metabolites are reused.
Several enzymes are known that are able to degrade AHLs.39 Acylases catalyze the hydrolysis
of the amide bond, thereby releasing a fatty acid and homoserine lactone.40-42
Haloperoxidases are able to halogenate N-(3-oxoacyl)-L-homoserine lactones in a hydrogen
peroxide-dependent manner.43-45 Subsequent cleavage of the halogenated acyl chain yields
N-(α,α-dihaloacetyl)-L-homoserine lactone and a fatty acid.44 Therefore, to study the
metabolic fate of the fatty acid side chains, we decided to include the isotope label in the acyl
side chain of the AHL-molecule. When the isotope label is included in the lactone ring
(analogues 3 and 4), all classes of AHLs can easily be accessed.27, 28 However, studies to
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investigate the metabolization of the fatty acid side chain are impossible with these analogues.
DOI: 10.1039/C6RA17797B
To include the label in the side chain (analogues 2, 5 and 10), most synthetic routes rely on
the use of rather expensive deuterated fatty acids.26, 29, 33 A metal-catalyzed reduction of
terminally unsaturated AHLs with sodium borodeuteride to include the isotope label
(analogues 6), has been reported as well.30
To the best of our knowledge, no analogues of N-(3-hydroxyacyl)-L-homoserine lactones with
an isotope label in the acyl chain have been synthesized yet. The synthesis of this type of
compounds was therefore our first goal. In a first approach, -ketoester 13 was synthesized
in excellent yield by reacting undecanone 11 with diethyl carbonate 12 in the presence of
sodium hydride, followed by a sodium hydroxide-mediated hydrolysis to yield 3-
oxododecanoic acid 14 (Scheme 1).46 The deuterium label was introduced via a reduction of
the keto function with sodium borodeuteride to give deuterated -hydroxy fatty acid 15 with
a deuterium incorporation of 89% at the carbon atom bearing the hydroxy moiety.47 1-Ethyl-
3-(3-dimethylaminopropyl)carbodiimide (EDC)-mediated coupling with L-homoserine lactone
hydrobromide 16 yielded the desired N-(3-hydroxydodecanoyl-[3-2H])-L-homoserine lactone
17.48 Only the class of AHLs bearing the hydroxy group is accessible via this route. The
introduction of only one deuterium atom causes a mass shift of one unit. The natural presence
of the heavy isotopes of mainly carbon, oxygen, nitrogen and hydrogen, gives rise to the
presence of a mass (M+1) one unit higher than the expected parental mass (M). The
abundance of this M+1 can be as high as 20% of the parental mass M for molecules with a
molecular weight of 300 Da, hindering the application of these monodeuterated molecules as
standards, but they can be useful to study the fragmentation patterns during GC/MS-analysis.
Although M+2 is naturally present as well, even for the AHLs with the highest mass, the
abundancy never exceeds 3% of the presence of the parental mass M, resulting in less
interference with peaks of a dideuterated labeled compound. Noteworthy, dideuterated AHL-
analogues 4a-h were applied as internal standards in an isotope dilution tandem mass
spectrometric method.28 Therefore, a more general route was developed to gain access to the
dideuterated analogues of all different types of AHLs.
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DOI: 10.1039/C6RA17797B
Scheme 1: Synthesis of N-(3-hydroxydodecanoyl-[3-2H])-L-homoserine lactone 17. The
deuterium content was determined by ESI-MS.
Aliphatic aldehydes 18a-c were deuterated at the -position via
a
4-(N,N-
dimethylamino)pyridine (DMAP)-catalyzed H/D-exchange reaction with D2O (Scheme 2).49
This mild catalysis only allows selective deuterium introduction at the acidic -position. Due
to the formation of HDO and H2O during this exchange reaction, complete deuteration is
impossible. Therefore, to get a higher degree of deuterium incorporation than 68-82%,
obtained after one iteration, a second treatment with D2O was applied, yielding aldehydes
19a-c with a satisfactory deuterium incorporation of 93-95%. To achieve a deuterium
incorporation higher than 95%, a third iteration with D2O should be included. However, as in
IDMS, one is rather interested in the alteration of the ratio of two isotopes (labelled compared
to non-labelled), the incomplete deuterium incorporation will not hinder the applicability, as
long as the isotope ratio of the standard is determined in a parallel analysis.34, 50, 51
Scheme 2: Synthesis of ,-dideuterated aldehydes 19a-c as deuterated building blocks. The
deuterium content was determined via 1H NMR.
These ,-dideuterated aldehydes 19a-c were transformed to the corresponding -hydroxy
esters 21a-c via a Reformatsky reaction with ethyl bromoacetate 20 (Scheme 3). Hydrolysis of
-hydroxy esters 21a-c gave the [4-2H2]--hydroxy fatty acids 22a-c in excellent yields.52
Alternatively, further elaboration of these deuterated aldehydes 19a-c towards
unfunctionalized fatty acids 24a-c was also possible. Because the -position of a carbonyl
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group is quite acidic, a chain extension was needed to shift the deuterium label to the -
DOI: 10.1039/C6RA17797B
position of the carbonyl and avoid deuterium loss due to a deuterium-hydrogen exchange.
The labelled aldehydes 19a-c were reduced to the alcohols after reaction with two equivalents
of sodium borohydride in ethereal methanol. Mesylation,53 followed by substitution with
potassium cyanide and alkaline hydrolysis yielded the [3-2H2]-fatty acids 24a-c (Scheme 3).54
These labelled fatty acids 24a-c were coupled with L-homoserine lactone hydrobromide 16 to
give N-(acyl-[3-2H2])-L-homoserine lactones 27a-c (Scheme 4). A similar reaction with [4-2H2]-
-hydroxy fatty acids 22a-c gave N-(3-hydroxyacyl-[4-2H2])-L-homoserine lactones 26a-c, as a
mixture of diastereomers. As expected, no separation of both diastereomers was observed
during both HPLC and GC-analysis, allowing this mixture to be used as such as labelled spike
for IDMS, utilizing a common analytical equipment. For the N-(3-oxoacyl-[5-2H2])-L-
homoserine lactones 28a-c, [3-2H2]-fatty acids 24a-c were reacted with Meldrum’s acid to
introduce the oxo functionality (Scheme 3), followed by amidation with L-homoserine lactone
hydrobromide 16 (Scheme 4).55 No significant loss of deuterium was observed during this
synthetic route.
Scheme 3: Transformation of ,-dideuterated aldehydes 19a-c into deuterated fatty acid
derivatives 22a-c, 24a-c and 25a-c.
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DOI: 10.1039/C6RA17797B
Scheme 4: Synthesis of N-(3-hydroxyacyl-[4-2H2])-L-homoserine lactones 26a-c, N-(acyl-[3-
2H2])-L-homoserine lactones 27a-c and N-(3-oxoacyl-[5-2H2])-L-homoserine lactones 28a-c
starting from deuterated precursors 22a-c, 24a-c and 25a-c. The deuterium content was
determined by ESI-MS.
This methodology allows the convenient and straightforward synthesis of AHLs with different
functionalities, starting from one easily available deuterated building block without the use of
deuterium gas or expensive catalysts. The presence of two deuterium atoms causes a mass
shift of two units, making these isotope-labelled analogues easily distinguishable from the
naturally occurring 13C-containing AHLs, with a mass one unit higher than the regular AHLs. All
deuterated AHLs 26a-c, 27a-c and 28a-c were fully characterized.
The degree of deuterium incorporation in the synthesized AHLs 17, 26a-c, 27a-c and 28a-c was
determined via HPLC-MS. To confirm the position of the isotope label, 1H and 13C NMR spectra
were recorded and compared with those of the unlabelled AHLs. The presence of deuterium
atoms at the -position of the acyl chain in N-(acyl-[3-2H2])-L-homoserine lactones 27a-c was
confirmed by the transformation of the signal of the -protons of the acyl chain from a triplet
to a singlet and the disappearance of the quintet at 1.64 ppm (in CDCl3). A similar alteration
was observed in the spectra of N-(3-oxoacyl-[5-2H2])-L-homoserine lactones 28a-c. For N-(3-
hydroxydodecanoyl-[3-2H])-L-homoserine lactone 17, the signal at  4.0 ppm (CDCl3), linked
with the CHOH-unit logically disappeared, while for N-(3-hydroxyacyl-[4-2H2])-L-homoserine
lactones 26a-c the signal at  1.45 ppm (CDCl3) was absent. The expected quintet associated
with a dideuterated carbon atom, was not always clearly visible in the 13C NMR spectrum due
to excessive signal splitting and increased relaxation times.56 A small isotope effect, resulting
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in an upfield shift of 0.1 to 0.2 ppm, was observed for the flanking carbons, while this was
DOI: 10.1039/C6RA17797B
negligible for the other carbon atoms.
Several methods have been developed to analyze AHLs with GC-MS.13, 19, 57 Therefore, the
suitability of the synthesized AHLs for this type of analysis was evaluated by studying the
electron impact (EI) mass fragmentation pattern (Table 1). The retention times of labelled and
unlabelled AHL were identical.
Table 1: GC-MS data of discussed AHL-molecules. EI MS spectra can be found in SI.
EI-MS m/z (rel. int.)
AHL
N-Dodecanoyl-L-homoserine lactone
283 [M] (4), 156 (21), 143 (100), 125 (17),
102 (18), 83 (15), 57 (41), 55 (19), 43 (21), 41
(17)
285 [M] (4), 158 (15), 143 (100), 125 (17),
102 (14), 83 (13), 57 (44), 55 (11), 43 (21), 41
(14)
N-(Dodecanoyl-[3-2H2])-L-homoserine
lactone 27c
N-(3-Hydroxydodecanoyl)-L-homoserine
lactone
299 [M] (2), 281 (3), 214 (11), 197 (19), 172
(100), 144 (18), 143 (40), 125 (11), 102 (85),
83 (18), 69 (12), 57 (51), 56 (19), 55 (21), 43
(36), 41 (21)
300 [M] (2), 282 (3), 215 (8), 197 (16), 173
(100), 145 (15), 143 (46), 125 (13), 102 (86),
83 (16), 69 (12), 57 (55), 56 (28), 55 (19), 43
(37), 41 (22)
301 [M] (2), 283 (2), 216 (11), 199 (17), 172
(100), 144 (24), 143 (28), 125 (9), 102 (79),
83 (12), 69 (9), 57 (48), 56 (22), 55 (14), 43
(33), 41 (17)
N-(3-Hydroxydodecanoyl-[3-2H])-L-
homoserine lactone 17
N-(3-Hydroxydodecanoyl-[4-2H2])-L-
homoserine lactone 26b
N-(3-Hydroxydodecanoyl)-L-homoserine
lactone + BSTFA-TMCS
371 [M+TMS] (1), 356 (100), 244 (40), 228
(10), 215 (5), 200 (14), 186 (8), 174 (8), 160
(6), 143 (23), 130 (11), 103 (6), 83 (9), 73
(27), 57 (5), 55 (5), 43 (7), 41 (6)
372 [M+TMS] (1), 357 (100), 245 (42), 229
(10), 215 (6), 200 (14), 187 (7), 175 (6), 160
(7), 144 (18), 130 (13), 103 (6), 84 (6), 75
(16), 73 (33), 57 (5), 55 (5), 43 (8), 41 (6)
373 [M+TMS] (1), 358 (100), 244 (40), 228
(11), 215 (5), 200 (14), 186 (8), 174 (8), 160
(6), 143 (18), 130 (9), 103 (6), 85 (6), 73 (31),
57 (5), 55 (4), 43 (7), 41 (6)
N-(3-Hydroxydodecanoyl-[3-2H])-L-
homoserine lactone 17 + BSTFA-TMCS
N-(3-Hydroxydodecanoyl-[4-2H2])-L-
homoserine lactone 26b + BSTFA-TMCS
N-(3-Oxodecanoyl)-L-homoserine lactone + 341 [M+TMS] (11), 326 (72), 270 (21), 257
BSTFA-TMCS
(49), 241 (94), 215 (17), 169 (65), 150 (25),
125 (15), 73 (100), 57 (11), 43 (12)
343 [M+TMS] (9), 328 (60), 272 (16), 257
(44), 243 (81), 215 (16), 171 (57), 152 (24),
125 (12), 73 (100), 57 (11), 43 (15)
N-(3-Oxodecanoyl-[5-2H2])-L-homoserine
lactone 28a + BSTFA-TMCS
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The characteristic mass fragment of N-acyl homoserine lactones is situated at m/z 143,
DOI: 10.1039/C6RA17797B
corresponding to a McLafferty rearrangement. Since the synthesized deuterium-labelled
derivatives 27a-c have the deuterium atoms located at the -carbon, the label is lost and the
ion with m/z 143 is formed as well (Scheme 5). To distinguish between the native and labelled
AHLs, the higher mass fragments, corresponding to different alkyl chain losses, but retaining
the isotope label, should be targeted. The ion with m/z 158 (corresponding to m/z 156 in
unlabelled AHLs) was detected with sufficient intensity in all N-(acyl-[3-2H2])-L-homoserine
lactones 27a-c and can be used in a SIM-method to detect only labelled analogues. In all
compounds analyzed, the molecular ion was detected, albeit with low intensities.
Scheme 5: Main mass fragment formed via a McLafferty rearrangement during EI-ionization
induced fragmentation of N-(acyl-[3-2H2])-L-homoserine lactones 27a-c.
The characteristic ion formed during fragmentation of N-(3-hydroxyacyl)-L-homoserine
lactones is located at m/z 172. This fragment arises from an -cleavage next to the hydroxy
group. Not surprisingly, this fragment can be observed in both unlabelled and -dilabelled N-
(3-hydroxyacyl)-L-homoserine lactones 26a-c (Scheme 6). However, in case of the
monolabelled analogue 17, with the deuterium label at the -position, a fragment with one
mass unit higher (m/z 173) results. Another characteristic ion is formed by the McLafferty
rearrangement. While the mass fragment of m/z 143 is observed in all N-(3-hydroxyacyl)-L-
homoserine lactones, the ion with m/z 144 is observed with an elevated intensity in case of
the N-(3-hydroxyacyl-[4-2H2])-L-homoserine lactones 26a-c. This can be explained via an
alternative McLafferty rearrangement, in which not the proton of the hydroxy group is
abstracted, but rather the -proton (or deuterium in case of analogues 26a-c) of the alkyl
chain, causing a mass shift of one unit for analogues 26a-c. As only a minor (37-43%) increase
in abundance of m/z 144 is observed, a preference towards abstraction of the hydroxy proton
can be concluded. Unfortunately, an alternative fragmentation, a hydrogen rearrangement
followed by a McLafferty rearrangement, also leads to m/z 144 in both the unlabelled and
dilabelled analogues, rendering this mass fragment not very useful to be targeted in a SIM-
method. In the case of the monolabelled analogue 17 this fragmentation leads to a fragment
with m/z 145, indicating that mainly the -hydrogen (or deuterium) atom is abstracted
(Scheme 6). Once again, the molecular ion itself was detected, albeit with low intensities.
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DOI: 10.1039/C6RA17797B
Scheme 6: Main mass fragments formed during the fragmentation of isotope-labelled N-(3-
hydroxyacyl)-L-homoserine lactones 17 and 26b.
Due to the lability of N-(3-oxoacyl)-L-homoserine lactones during chromatographic analysis, a
derivatization step needs to be included. When N,O-bis(trimethylsilyl)trifluoroacetamide
(BSTFA) is used as silylation agent, detection via GC-MS becomes possible. The molecular ion
and the mass fragment resulting from the loss of one methyl group are detected with
satisfying intensities. The ion at m/z 257 is formed via a McLafferty rearrangement (Scheme
7). -Cleavage, with loss of the lactone unit, results in an alkyl chain fragment with m/z 243
for N-(3-oxodecanoyl)-L-homoserine lactone 28a. A possible marker fragment with m/z 171,
common to all N-(3-oxoacyl-[5-2H2])-L-homoserine lactones 28a-c and with full retention of
the isotope label, is obtained after a H-rearrangement, followed by the expulsion of a neutral
homoserine lactone molecule.
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Scheme 7: Formalisms for the main mass fragments formed during the fragmentation of
isotope-labelled N-(3-oxodecanoyl)-L-homoserine lactone 28a after derivatization with
BSTFA.
When labelled N-(3-hydroxyacyl)-L-homoserine lactones 17 and 26a-c are treated with BSTFA,
the fragment observed with the highest intensity is the silylated molecule minus a methyl
group (Scheme 8). Due to the high intensity and full retention of the isotope label, this
fragment can be used to detect specific labelled N-(3-hydroxyacyl)-L-homoserine lactones 17
and 26a-c in a reliable manner.
Scheme 8: Main mass fragments formed during the fragmentation of isotope-labelled N-(3-
hydroxyacyl)-L-homoserine lactones 17 and 26b after derivatization with BSTFA.
The presence of deuterium atoms is also obvious from the infrared spectrum by the
occurrence of CD2-vibrations. The small peaks around 2200 and 2100 cm-1 correspond to
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antisymmetric and symmetric CD2-vibrations. These signals can be used toDOsIt: u10d.1y039t/Ch6eRA17797B
integration of deuterated AHLs in supported bilayers.29, 58
To demonstrate and further extend the possible applications of these deuterated compounds,
two AHL-degradation products, which occur in nature, were synthesized. The hydrolysis of the
lactone ring of AHLs towards N-acyl homoserines, occurs in a temperature, pH and chain
length dependent way and results in a loss of QS-activity.59, 60 N-(3-Oxoacyl)-L-homoserine
lactones can form another type of degradation product. Via an intramolecular Claisen-type
rearrangement, a tetramic acid can be formed. Fascinating biological properties such as
antibacterial activity and iron chelation are associated with this type of molecules.61 Methods
have been developed to detect both degradation products as well.32, 62 However, to the best
of our knowledge, no deuterium-labelled N-acyl homoserines nor deuterated tetramic acids
have been reported yet, although these compounds could be used as internal standards for
IDMS.
The corresponding tetramic acid 29 and the ring opened product 30, were synthesized in good
yield and full retention of the deuterium label was observed during these transformations
(Scheme 9).
Scheme 9: Synthesis of deuterated analogues tetramic acid 29 and ring opened AHL 30. The
deuterium content was determined by ESI-MS.
Conclusion
An easy, reliable manner to make suitable, deuterated standards of AHL-molecules belonging
to all three important classes of AHLs is presented, starting from a cheap and commercially
available deuterium source. Deuterium loss via D/H-exchange is avoided by the introduction
of the isotope label on a non-enolizable position. All synthesized analogues were fully
characterized. These deuterated analogues of the major classes of AHLs can also be used to
synthesize the labelled analogues of the naturally occurring degradation products, without a
significant loss of deuterium. These labelled AHLs and degradation products can be used to
study the metabolization of AHLs in nature.
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DOI: 10.1039/C6RA17797B
Acknowledgements
The authors thank Ghent University (BOF 14/DOC_V/285) for financial support of this
research.
Experimental section
General
Solvents and chemicals used were bought from commercial suppliers and used as such, unless
stated otherwise. Sodium borodeuteride (98% D) and D2O (99.9% D) were purchased form
Sigma-Aldrich. 1H (400 MHz) and 13C (100.6 MHz) NMR spectra were recorded on a Bruker
Avance III Nano-bay 400 at room temperature. IR spectra were recorded in neat form with a
Perkin-Elmer Spectrum One FTIR spectrometer. High-resolution mass spectra were
determined with an Agilent 1100 series HPLC coupled to an Agilent 6210 TOF mass
spectrometer, equipped with an ESI/APCI multimode source. GC spectra were recorded on a
Agilent HP 6890 series with a DB-5 MS fused-silica capillary column (30 m; 0.25 mm, film
thickness = 0.25 µm). Electron Impact (EI) mass spectra were obtained with an Agilent HP 5973
series MSD mass spectrometer.
GC-MS conditions
GC-MS analyses were carried out according to the procedure developed by Cataldi et al. with
minor modifications.19 Conditions applied were: inlet pressure 77.1 kPa; He: 23.3 mL/min;
injection volume: 1 μL; injector temperature: 250 °C; transfer line: 300 °C; electron energy: 70
eV. The oven temperature program was: initial temperature and hold for 5 min at 100 °C, then
increasing at a ramp of 10 °C per min to 300 °C. The injector was operated in splitless mode
(60 s valve time). The carrier gas used was helium with a constant flow of 1 mL/min. AHLs were
dissolved in dichloromethane. For the derivatization, 100 µL of 99:1 BSTFA-TMCS [N,O-
bis(trimethylsilyl) trifluoroacetamide-trimethylchlorosilane] was added to 100 µL of
dichloromethane containing the AHL and the mixture was allowed to stand for 10 min at room
temperature prior to injection.
Synthesis of deuterium-labelled analogues
Synthesis of [3-2H]-3-hydroxydodecanoic acid 15
Diethyl carbonate 12 (2.1 equiv, 22 mmol, 2.5 mL) and sodium hydride (60% dispersion in
mineral oil, 3 equiv, 30 mmol, 1.2 g) were stirred at reflux in 20 mL of dry THF under a nitrogen
atmosphere. Undecanone 11 (1 equiv, 10 mmol, 2.1 mL) was added dropwise and the resulting
mixture was stirred at reflux overnight. After cooling down, the suspension was poured into a
mixture of saturated aq. NH4Cl, 5% aq. HCl and ice. Extraction (three times 50 mL of diethyl
ether) and washing of the combined organic phases, followed by drying over MgSO4 and
removal of the solvent in vacuo, afforded ethyl 3-oxododecanoate 13 as a yellow oil in 94%
yield. This crude -ketoester 13 was used for the next step without further purification.
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To a stirred solution of ethyl 3-oxododecanoate 13 (1 equiv, 8.5 mmol, 2.0 g) in 25 mL of
DOI: 10.1039/C6RA17797B
methanol was added 22 mL of 2M NaOH (5 equiv, 44 mmol, 1.7 g). The resulting mixture was
stirred overnight at room temperature, after which it was extracted with 50 mL of diethyl
ether. The organic phase was discarded and the aqueous phase was acidified to pH 2 by
addition of 2M HCl, and extracted three times with 50 mL of diethyl ether. The combined
organic phases were dried over MgSO4 and the solvent was removed in vacuo.
Recrystallization from hexane afforded 3-oxododecanoic acid 14 as a colorless powder (1.4 g,
75%).
Sodium borodeuteride (1.5 equiv, 7.5 mmol, 0.31 g) was added to a solution of 3-
oxododecanoic acid 14 (1 equiv, 5 mmol, 1.1 g) in diethyl ether:methanol 1:1 (10 mL) at 0 °C.
The ice bath was removed and the mixture was stirred at room temperature for 2 h. The
mixture was diluted with 10 mL of 2M HCl and 10 mL of diethyl ether. After phase separation,
the aqueous phase was extracted twice with 10 mL of diethyl ether. The combined extracts
were washed with 20 mL of brine and dried over MgSO4. Filtration and evaporation of the
solvent in vacuo yielded pure [3-2H]-3-hydroxydodecanoic acid 15 (98%, 1.1 g) as a colorless
powder.
[3-2H]-3-Hydroxydodecanoic acid 15 (89% D) 1H NMR (400 MHz, CDCl3):  = 0.88 (3H, t, J = 6.9
Hz, CH3), 1.20-1.61 (16H, m, (CH2)8CH3), 2.47 (1H, d, J = 16.6 Hz, CHH’COOH), 2.58 (1H, d, J =
16.6 Hz, CHH’COOH), 4.00-4.11 (0.1H, m, CHOH) ppm. 13C NMR (100 MHz, CDCl3):  = 14.1
(CH3), 22.7, 25.4, 29.3, 29.5, 29.6 (2C), 31.9, 36.3 ((CH2)8CH3), 41.0 (CH2COOH), 67.4-68.3 (m,
+
CDOH), 68.2 (CHOH), 177.8 (COOH) ppm. MS (ESI): m/z (%): 218 (M+H+, 7), 235 (M+NH4 , 100).
-
HRMS mass expected: C12H22DO3 216.1715; found: 216.1721. IR (cm-1): max 913, 1226, 1680,
2130, 2848, 2915, 2953, 3050, 3534. Melting Point: 72-74 °C. Colorless powder. Yield: 98%.
General procedure for the synthesis of deuterated aldehydes 19a-c
As described by Ariza et al.,49 freshly distilled aldehyde 18a-c (1 equiv, 13 mmol), 4-(N,N-
dimethylamino)pyridine (0.1 equiv, 1.3 mmol, 0.16 g) and D2O (10 equiv, 130 mmol, 2.3 mL)
were added to a septum sealed flask and heated at 100 °C for 1 h. Then 20 mL of
dichloromethane and 5 mL of 1M aq. HCl were added. The organic phase was washed with 15
mL of saturated aq. NaHCO3 and 15 mL of brine. Drying over MgSO4, filtration and removal of
the solvent in vacuo yielded the deuterated aldehyde 19a-c (71-97% yield). To obtain a higher
degree of deuterium incorporation, the obtained deuterated aldehyde was subjected to a
second iteration with fresh D2O.
General procedure for the synthesis of deuterated -hydroxy fatty acids 22a-c
To a stirred suspension of activated zinc dust (acid-washed and dried) (1.3 equiv, 6.5 mmol,
0.43 g) in 20 mL of anhydrous diethyl ether in a flame-dried bulb, was added
chlorotrimethylsilane (0.1 equiv, 0.5 mmol, 65 µL). The mixture was stirred at room
temperature for 15 min and then heated at reflux for 10 min. The suspension was allowed to
cool down and a mixture of ethyl bromoacetate 20 (1 equiv, 5 mmol, 0.57 mL) and deuterated
14

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aldehyde 19a-c (1 equiv, 5 mmol) was added dropwise in such a pace that a gentle reflux was
DOI: 10.1039/C6RA17797B
obtained. The resulting mixture was further heated at reflux for 1 h, after which it was cooled
down and 20 mL of 2M aq. HCl was added. After stirring for 15 min, the layers were separated
and the aqueous phase was extracted two times with 20 mL of diethyl ether. The combined
organic phases were washed with 20 mL of saturated aq. NaHCO3 and 20 mL of brine. Drying
over MgSO4 and removal of the solvent in vacuo yielded the desired -hydroxy ethyl ester 21a-
c as a colorless oil in 92-97% yield.
The obtained ester 21a-c was dissolved in 30 mL of a 2:1 mixture of tetrahydrofuran:methanol
and placed in an ice bath. Then, 10 mL of 1M aq. LiOH (2 equiv, 10 mmol, 0.24 g) was added
and the stirring continued for 2 h at 0 °C. Subsequently, the ice bath was removed and the
hydrolysis continued at room temperature overnight. The mixture was extracted once with 20
mL of diethyl ether to remove unreacted ester. The aqueous phase was acidified with 2M aq.
HCl to pH 2 and extracted three times with 20 mL of diethyl ether. Drying over MgSO4,
filtration and rotary evaporation in vacuo of the solvent yielded crude -hydroxy fatty acid
22a-c. Recrystallization from diethyl ether gave the pure fatty acid 22a-c as a colorless powder
(84-95% yield).
[4-2H2]-3-Hydroxynonanoic acid 22a (93% D) 1H NMR (400 MHz, CDCl3):  = 0.88 (3H, t, J = 6.8
Hz, CH3), 1.21-1.50 (8H, m, (CH2)4CH3), 2.48 (1H, dd, J = 16.6 Hz, 8.8 Hz, CHH’COOH), 2.58 (1H,
dd, J = 16.6 Hz, 3.1 Hz, CHH’COOH), 4.03 (1H, dd, J = 8.8 Hz, 3.1 Hz, CHOH) ppm. 13C NMR (100
MHz, CDCl3):  = 14.1 (CH3), 22.6, 25.2, 29.1, 31.8 ((CH2)4CH3), 35.7 (quintet, JC-D = 19.4 Hz,
CD2), 41.0 (CH2COOH), 68.0 (CHOH), 178.0 (COOH) ppm. MS (ESI): m/z (%): 176 (M+H+, 26),
+
-
194 (M+NH4 , 100). HRMS mass expected: C9H16D2O3 175.1309; found: 175.1311. IR (cm-1):
max 913, 1218, 1681, 2103, 2174, 2856, 2916, 2952, 3050, 3536. Melting Point: 61-63 °C.
Colorless powder. Yield: 84%.
[4-2H2]-3-Hydroxydodecanoic acid 22b (95% D) 1H NMR (400 MHz, CDCl3):  = 0.87 (3H, t, J =
7.0 Hz, CH3), 1.21-1.50 (14H, m, (CH2)7CH3), 2.48 (1H, dd, J = 16.5 Hz, 8.9 Hz, CHH’COOH), 2.58
(1H, dd, J = 16.5 Hz, 3.2 Hz, CHH’COOH), 4.05 (1H, dd, J = 8.9 Hz, 3.2 Hz, CHOH) ppm. 13C NMR
(100 MHz, CDCl3):  = 14.1 (CH3), 22.7, 25.3, 29.3, 29.4, 29.5, 29.6, 31.9 ((CH2)7CH3), 35.7
(quintet, JC-D = 19.8 Hz, CD2), 41.1 (CH2COOH), 68.0 (CHOH), 178.0 (COOH) ppm. MS (ESI): m/z
+
(%): 201 (M-H2O, 80), 219 (M+H+, 6), 241 (M+Na, 100). HRMS mass expected: C12H22D2O3NH4
236.2189; found: 236.2181. IR (cm-1): max 914, 1228, 1677, 2102, 2179, 2848, 2915, 2953,
3063, 3534. Melting Point: 73-74 °C. Colorless powder. Yield: 89%.
1
[4-2H2]-3-Hydroxytridecanoic acid 22c (93% D) H NMR (400 MHz, CDCl3):  = 0.88 (3H, t, J =
6.8 Hz, CH3), 1.20-1.48 (16H, m, (CH2)8CH3), 2.47 (1H, dd, J = 16.6 Hz, 8.9 Hz, CHH’COOH), 2.58
(1H, dd, J = 16.5 Hz, 3.1 Hz, CHH’COOH), 4.02 (1H, dd, J = 8.9 Hz, 3.1 Hz, CHOH) ppm. 13C NMR
(100 MHz, CDCl3):  = 14.1 (CH3), 22.7, 25.2, 29.3, 29.4, 29.56, 29.58, 29.60, 31.9 ((CH2)8CH3),
35.4-36.2 (m, CD2), 41.0 (CH2COOH), 67.9 (CHOH), 178.0 (COOH) ppm. MS (ESI): m/z (%): 233
+
+
(M+H+, 7), 250 (M+NH4 , 100). HRMS mass expected: C13H24D2O3NH4 250.2346; found:
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250.2340. IR (cm-1): max 915, 1219, 1681, 2100, 2182, 2847, 2914, 2952, 3031, 3534. Melting
DOI: 10.1039/C6RA17797B
Point: 78-80 °C. Colorless powder. Yield: 95%.
General procedure for the synthesis of deuterated fatty acids 24a-c
-Dideuterated aldehyde 19a-c (1 equiv, 10 mmol) was dissolved in 20 mL of a 1:1
methanol:diethyl ether mixture whereafter sodium borohydride (2 equiv, 20 mmol, 0.76 g)
was added portion-wise. The reaction was stirred for 2 h at room temperature and quenched
by the dropwise addition of water. The mixture was acidified by the addition of 2M aq. HCl
and the aqueous layer was extracted three times with 20 mL of ethyl acetate. The combined
organic phases were washed with 30 mL of brine and dried over MgSO4. Removal of the drying
agent by filtration and evaporation of the solvent in vacuo gave the -dideuterated alcohol
(88-96% yield).
The obtained crude -dideuterated alcohol (1 equiv, 10 mmol) was dissolved in 30 mL of dry
diethyl ether and triethylamine (1.4 equiv, 14 mmol, 2.0 mL) was added. The resulting solution
was placed in an ice bath and methanesulfonyl chloride (1.15 equiv, 11.5 mmol, 1.1 mL) was
added dropwise. The stirring was continued for 2 h at room temperature, then 25 mL of water
was added to the resulting turbid suspension. The phases were separated and the organic
phase was washed with 15 mL of saturated aq. NaHCO3. Drying over MgSO4, filtration and
removal of the solvent in vacuo gave the desired alkyl methanesulfonate 23a-c (77-96% yield).
To obtain the alkyl nitrile, the mesylate 23a-c (1 equiv, 10 mmol) was dissolved in dimethyl
sulfoxide (30 mL), followed by the addition of potassium cyanide (2.5 equiv, 25 mmol, 1.63 g).
Stirring overnight at 120 °C resulted in the formation of a thick precipitate. The reaction
mixture was cooled down and partitioned between water (20 mL) and diethyl ether (20 mL).
The aqueous layer was extracted three times with diethyl ether (3 x 20 mL) and the combined
organic phases were dried over MgSO4. Removal of the solvent in vacuo yielded the alkyl
nitriles (86-95% yield).
To a solution of the nitrile (1 equiv, 10 mmol) in 40 mL of methanol was added 4 mL of 10M
aq. NaOH (4 equiv, 40 mmol, 1.60 g) and the resulting mixture was stirred at reflux overnight.
After cooling down, methanol was removed under reduced pressure and the remaining
heterogeneous mixture was heated at reflux for a further 2 h. The suspension was extracted
with 20 mL of diethyl ether to remove impurities and unreacted nitrile, followed by
acidification with 2M aq. HCl and extraction with diethyl ether (3 x 50 mL). Drying over MgSO4
and removal of the solvent in vacuo yielded the desired deuterium-labelled fatty acids 24a-c
(58-80% yield).
[3-2H2]-Octanoic acid 24a (93% D) 1H NMR (400 MHz, CDCl3):  = 0.88 (3H, t, J = 6.9 Hz, CH3),
1.20-1.38 (8H, m, (CH2)4CH3), 2.33 (2H, s, CH2COOH), 11.56 (1H, br s, COOH) ppm. 13C NMR
(100 MHz, CDCl3):  = 14.1 (CH3), 22.6, 28.80, 28.84, 31.6 ((CH2)4CH3), 23.5-24.5 (m, CD2), 34.0
(CH2COOH), 180.6 (COOH) ppm. IR (cm-1): max 934, 1230, 1275, 1412, 1705, 2857, 2925.
Colorless oil. Yield: 58%.
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[3-2H2]-Undecanoic acid 24b (95% D) 1H NMR (400 MHz, CDCl3):  = 0.88 (3H, t, J = 6.9 Hz, CH3),
DOI: 10.1039/C6RA17797B
1.18-1.37 (14H, m, (CH2)7CH3), 2.33 (2H, s, CH2COOH), 11.31 (1H, br s, COOH) ppm. 13C NMR
(100 MHz, CDCl3):  = 14.1 (CH3), 22.7, 28.9, 29.2, 29.3, 29.4, 29.6, 31.9 ((CH2)7CH3), 23.5-24.7
(m, CD2), 33.9 (CH2COOH), 180.0 (COOH) ppm. IR (cm-1): max 927, 1252, 1692, 2111, 2201,
2850, 2918, 2955, 3019. Colorless oil. Yield: 80%.
[3-2H2]-Dodecanoic acid 24c (92% D) 1H NMR (400 MHz, CDCl3):  = 0.88 (3H, t, J = 6.6 Hz, CH3),
1.18-1.37 (16H, m, (CH2)8CH3), 2.32 (2H, s, CH2COOH), 9.34 (1H, br s, COOH) ppm. 13C NMR
(100 MHz, CDCl3):  = 14.1 (CH3), 22.7, 28.9, 29.2, 29.3, 29.4, 29.6 (2C), 31.9 ((CH2)8CH3), 23.6-
24.8 (m, CD2), 34.0 (CH2COOH), 179.9 (COOH) ppm. IR (cm-1): max 931, 1275, 1429, 1695, 2848,
2912. Colorless powder. Melting Point: 40-41 °C. Yield: 70%.
General procedure for the synthesis of deuterated AHLs 17, 26a-c and 27a-c
The deuterated analogues of N-acyl-L-homoserine lactones and N-(3-hydroxyacyl)-L-
homoserine lactones were synthesized following the procedure described by Chhabra et al.48
Triethylamine (1 equiv, 2 mmol, 0.28 mL) was added to a stirred solution of L-homoserine
lactone hydrobromide 16 (1 equiv, 2 mmol, 0.36 g) in 5 mL of water, followed by the addition
of the appropriate deuterated fatty acid (15, 22a-c or 24a-c, 1 equiv, 2 mmol) and 1-ethyl-3-
(3-dimethylaminopropyl)carbodiimide hydrochloride (1 equiv, 2 mmol, 0.38 g). After stirring
for 3 h or overnight at room temperature, 15 mL of water was added and the aqueous phase
was extracted three times with 20 mL of ethyl acetate. The combined organic phases were
washed with 30 mL of saturated aq. NaHCO3 and 30 mL of brine. Drying over MgSO4, followed
by filtration and evaporation of the solvent in vacuo gave the crude product. Purification via
column chromatography on silica gel (ethyl acetate/petroleum ether 3:2 to 4:1) yielded the
desired deuterated AHLs 17, 26a-c and 27a-c as a colorless powder.
N-(3-Hydroxydodecanoyl-[3-2H])-L-homoserine lactone 17 (89% D) 1H NMR (400 MHz, CDCl3):
 = 0.88 (3H, t, J = 6.9 Hz, CH3, isomer 1 and 2), 1.19-1.57 (16H, m, (CH2)8CH3, isomer 1 and 2), 2.13-2.26
(1H, m, OCH2CHH'isomer 1 and 2), 2.33 (0.5H, d, J = 15.4 Hz, CHH’CDOHisomer 1), 2.35 (0.5H, d, J =
15.4 Hz, CHH’CDOHisomer 2), 2.44 (0.5H, d, J = 15.4 Hz, CHH’CDOHisomer 2), 2.46 (0.5H, d, J = 15.4
Hz, CHH’CDOHisomer 1), 2.81 (1H, dddd, J = 12.5 Hz, 8.6 Hz, 5.9 Hz, 1.2 Hz, OCH2CHH'isomer 1 and 2),
3.13 (1H, br s, OHisomer 1 and 2), 4.0 (0.1H, m, CHOHisomer 1 and 2), 4.29 (1H, ddd, J = 11.2 Hz, 9.3 Hz,
6.0 Hz, OCHH’isomer 1 and 2), 4.480 (0.5H, td, J = 9.1 Hz, 1.3 Hz, OCHH'isomer 1), 4.483 (0.5H, td, J =
9.1 Hz, 1.4 Hz, OCHH'isomer 2), 4.56 (0.5H, ddd, J = 11.7 Hz, 8.6 Hz, 6.2 Hz, CHNisomer 1), 4.59 (0.5H,
ddd, J = 11.8 Hz, 8.7 Hz, 6.3 Hz, CHNisomer 2), 6.60 (0.5H, d, J = 5.8 Hz, NHisomer 1), 6.65 (0.5H, d,
J = 5.7 Hz, NHisomer 2) ppm. 13C NMR (100 MHz, CDCl3):  = 14.1 (CH3, isomer 1 and 2), 22.7, 25.5,
29.3, 29.5, 29.56, 29.59, 31.9, 36.8, 36.9 ((CH2)8CH3, isomer 1 and 2), 29.9 (CH2CHNisomer 1), 30.0
(CH2CHNisomer 2), 42.5 (CH2CONHisomer 1), 42.6 (CH2CONHisomer 2), 49.0 (CHNisomer 1), 49.2
(CHNisomer 2), 66.1 (CH2Oisomer 1), 66.2 (CH2Oisomer 2), 68.2 (t, JC-D = 21.6 Hz, CDOHisomer 1), 68.3 (t,
JC-D = 21.7 Hz, CDOHisomer 2), 68.6 (COHisomer 1 unlabelled), 68.7 (COHisomer 2 unlabelled), 173.0
(CONHisomer 1), 173.1 (CONHisomer 2), 175.70 (COOisomer 1), 175.74 (COOisomer 2) ppm. MS (ESI): m/z
(%): 301 (M+H+, 100). HRMS mass expected: C16H29DNO4H+ 301.2232; found: 301.2237. IR (cm-
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1): max 951, 1008, 1178, 1548, 1627, 1768, 2850, 2919, 3315, 3494. ChromatograDpOhI:y1:0.E10t3O9/ACc6R:A17797B
Petroleum ether 4:1 Rf = 0.16. Melting Point: 107-108 °C. Colorless powder. Yield: 65%.
N-(3-Hydroxynonanoyl-[4-2H2])-L-homoserine lactone 26a (93% D) 1H NMR (400 MHz, CDCl3):
 = 0.88 (3H, t, J = 6.8 Hz, CH3, isomer 1 and 2), 1.20-1.45 (8H, m, (CH2)4CH3, isomer 1 and 2), 2.13-2.26
(1H, m, OCH2CHH'isomer 1 and 2), 2.33 (0.4H, dd, J = 15.5 Hz, 8.9 Hz, CHH’CHOHisomer 1), 2.35 (0.6H,
dd, J = 15.5 Hz, 8.9 Hz, CHH’CHOHisomer 2), 2.44 (0.6H, dd, J = 15.5 Hz, 2.8 Hz, CHH’CHOHisomer
2), 2.46 (0.4H, dd, J = 15.5 Hz, 2.8 Hz, CHH’CHOHisomer 1), 2.82 (1H, dddd, J = 12.6 Hz, 8.6 Hz, 5.9
Hz, 1.1 Hz, OCH2CHH'isomer 1 and 2), 3.10 (1H, br s, OHisomer 1 and 2), 3.99-4.06 (1H, m, CHOHisomer 1
and 2), 4.29 (1H, ddd, J = 11.3 Hz, 9.3 Hz, 5.9 Hz, OCHH’isomer 1 and 2), 4.45-4.51 (1H, m, OCHH'isomer
1 and 2), 4.56 (0.4H, ddd, J = 11.5 Hz, 8.7 Hz, 6.1 Hz, CHNisomer 1), 4.58 (0.6H, ddd, J = 11.6 Hz, 8.7
Hz, 6.2 Hz, CHNisomer 2), 6.55 (0.4H, d, J = 5.6 Hz, NHisomer 1), 6.60 (0.6H, d, J = 5.6 Hz, NHisomer 2
)
ppm. 13C NMR (100 MHz, CDCl3):  = 14.1 (CH3, isomer 1 and 2), 22.6, 25.3, 29.1, 31.8 ((CH2)4CH3,
isomer 1 and 2), 29.7 (CH2CHNisomer 1), 29.8 (CH2CHNisomer 2), 35.8-36.7 (m, CD2, isomer 1 and 2), 42.6
(CH2CONHisomer 1), 42.7 (CH2CONHisomer 2), 48.9 (CHNisomer 1), 49.1 (CHNisomer 2), 66.15 (CH2Oisomer
1), 66.18 (CH2Oisomer 2), 68.5 (COHisomer 1), 68.6 (COHisomer 2), 173.0 (CONHisomer 1), 173.1
(CONHisomer 2), 175.8 (COOisomer 1), 175.9 (COOisomer 2) ppm. MS (ESI): m/z (%): 260 (M+H+, 100).
HRMS mass expected: C13H21D2NO4H+ 260.1831; found: 260.1832. IR (cm-1): max 950, 1012,
1174, 1382, 1543, 1645, 1768, 2103, 2184, 2855, 2920, 2956, 3302. Chromatography:
EtOAc:Petroleum ether 4:1 Rf = 0.18. Melting Point: 97-98 °C. Colorless powder. Yield: 58%.
1
N-(3-Hydroxydodecanoyl-[4-2H2])-L-homoserine lactone 26b (95% D) H NMR (400 MHz,
CDCl3):  = 0.88 (3H, t, J = 6.9 Hz, CH3, isomer 1 and 2), 1.19-1.43 (14H, m, (CH2)7CH3, isomer 1 and 2),
2.13-2.26 (1H, m, OCH2CHH'isomer 1 and 2), 2.33 (0.44H, dd, J = 15.3 Hz, 8.9 Hz, CHH’CHOHisomer 1),
2.35 (0.56H, dd, J = 15.4 Hz, 8.9 Hz, CHH’CHOHisomer 2), 2.43 (0.44H, dd, J = 15.4 Hz, 2.8 Hz,
CHH’CHOHisomer 2), 2.46 (0.44H, dd, J = 15.4 Hz, 2.7 Hz, CHH’CHOHisomer 1), 2.77-2.86 (1H, m,
OCH2CHH'isomer 1 and 2), 3.11 (1H, br s, OHisomer 1 and 2), 3.98-4.05 (1H, m, CHOHisomer 1 and 2), 4.29
(1H, ddd, J = 11.2 Hz, 9.3 Hz, 5.9 Hz, OCHH’isomer 1 and 2), 4.43-4.51 (1H, m, OCHH'isomer 1 and 2),
4.56 (0.44H, ddd, J = 11.6 Hz, 8.7 Hz, 6.1 Hz, CHNisomer 1), 4.59 (0.56H, ddd, J = 11.6 Hz, 8.8 Hz,
6.1 Hz, CHNisomer 2), 6.53-6.64 (1H, m, NHisomer 1 and 2) ppm. 13C NMR (100 MHz, CDCl3):  = 14.1
(CH3, isomer 1 and 2), 22.7, 25.3, 29.3, 29.5, 29.56, 29.60, 31.9 ((CH2)7CH3, isomer 1 and 2), 29.98
(CH2CHNisomer 1), 30.04 (CH2CHNisomer 2), 35.8-36.8 (m, CD2, isomer 1 and 2), 42.5 (CH2CONHisomer 1),
42.6 (CH2CONHisomer 2), 49.0 (CHNisomer 1), 49.2 (CHNisomer 2), 66.1 (CH2Oisomer 1), 66.2 (CH2Oisomer
2), 68.5 (COHisomer 1), 68.6 (COHisomer 2), 173.01 (CONHisomer 1), 173.05 (CONHisomer 2), 175.67
(COOisomer 1), 175.75 (COOisomer 2) ppm. MS (ESI): m/z (%): 302 (M+H+, 100). HRMS mass
expected: C16H27D2NO4H+ 302.2300; found: 302.2300. IR (cm-1): max 952, 1014, 1177, 1382,
1549, 1625, 1766, 2082, 2185, 2851, 2919, 2956, 3326, 3461. Chromatography:
EtOAc:Petroleum ether 4:1 Rf = 0.15. Melting Point: 107-108 °C. Colorless powder. Yield: 63%.
1
N-(3-Hydroxytridecanoyl-[4-2H2])-L-homoserine lactone 26c (93% D) H NMR (400 MHz,
CDCl3):  = 0.88 (3H, t, J = 6.9 Hz, CH3, isomer 1 and 2), 1.19-1.43 (16H, m, (CH2)8CH3, isomer 1 and 2),
2.13-2.25 (1H, m, OCH2CHH'isomer 1 and 2), 2.33 (0.44H, dd, J = 15.5 Hz, 9.0 Hz, CHH’CHOHisomer 1),
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2.35 (0.56H, dd, J = 15.4 Hz, 8.7 Hz, CHH’CHOHisomer 2), 2.43 (0.54H, dd, J = 15.4DHOIz: ,102.10.839/HC6zR,A17797B
CHH’CHOHisomer 2), 2.46 (0.44H, dd, J = 15.3 Hz, 2.8 Hz, CHH’CHOHisomer 1), 2.79-2.87 (1H, m,
OCH2CHH'isomer 1 and 2), 3.04 (1H, br s, OHisomer 1 and 2), 3.98-4.04 (1H, m, CHOHisomer 1 and 2), 4.29
(1H, ddd, J = 11.2 Hz, 9.3 Hz, 5.9 Hz, OCHH’isomer 1 and 2), 4.45-4.51 (1H, m, OCHH'isomer 1 and 2),
4.56 (0.44H, ddd, J = 11.6 Hz, 8.6 Hz, 5.9 Hz, CHNisomer 1), 4.57 (0.56H, ddd, J = 11.6 Hz, 8.6 Hz,
5.7 Hz, CHNisomer 2), 6.46-6.57 (1H, m, NHisomer 1 and 2) ppm. 13C NMR (100 MHz, CDCl3):  = 14.1
(CH3, isomer 1 and 2), 22.7, 25.3, 29.3, 29.5, 29.6 (3C), 31.9 ((CH2)8CH3, isomer 1 and 2), 29.9
(CH2CHNisomer 1), 30.0 (CH2CHNisomer 2), 35.7-36.8 (m, CD2, isomer 1 and 2), 42.5 (CH2CONHisomer 1),
42.6 (CH2CONHisomer 2), 49.0 (CHNisomer 1), 49.1 (CHNisomer 2), 66.1 (CH2Oisomer 1), 66.2 (CH2Oisomer
2), 68.5 (COHisomer 1), 68.6 (COHisomer 2), 173.02 (CONHisomer 1), 173.05 (CONHisomer 2), 175.7
(COOisomer
2) ppm. MS (ESI): m/z (%): 316 (M+H+, 100). HRMS mass expected:
1
and
C17H29D2NO4H+ 316.2457; found: 316.2448. IR (cm-1): max 948, 1022, 1177, 1382, 1549, 1641,
1770, 2102, 2177, 2849, 2917, 2953, 3312, 3490. Chromatography: EtOAc:Petroleum ether
4:1 Rf = 0.16. Melting Point: 110-112 °C. Colorless powder. Yield: 42%.
1
N-(Octanoyl-[3-2H2])-L-homoserine lactone 27a (92% D) H NMR (400 MHz, CDCl3):  = 0.88
(3H, t, J = 6.9 Hz, CH3), 1.20-1.36 (8H, m, (CH2)4CH3), 2.12 (1H, dddd, J = 12.5 Hz, 11.5 Hz, 11.5
Hz, 8.8 Hz, OCH2CHH'), 2.23 (2H, s, CH2CONH), 2.88 (1H, dddd, J = 12.5 Hz, 8.5 Hz, 5.8 Hz, 1.2
Hz, OCH2CHH'), 4.28 (1H, ddd, J = 11.3 Hz, 9.3 Hz, 5.8 Hz, OCHH'), 4.47 (1H, td, J = 9.1 Hz, 1.0
Hz, OCHH'), 4.54 (1H, ddd, J = 11.6 Hz, 8.5 Hz, 5.6 Hz, CHN), 5.94 (1H, s, NH) ppm. 13C NMR
(100 MHz, CDCl3):  = 14.1 (CH3), 22.6, 28.9, 29.0, 31.6 ((CH2)4CH3), 24.4-25.4 (m, CD2), 30.6
(CH2CHN), 36.0 (CH2CONH), 49.2 (CHN), 66.1 (CH2O), 173.8 (CONH), 175.7 (COO) ppm. MS
(ESI): m/z (%): 230 (M+H+, 100). HRMS mass expected: C12H19D2NO3H+ 230.1725; found:
230.1709. IR (cm-1): max 1010, 1170, 1545, 1643, 1774, 2107, 2194, 2852, 2920, 3314.
Chromatography: EtOAc:Petroleum ether 3:2 Rf = 0.19. Melting Point: 130-132 °C. Colorless
powder. Yield: 55%.
N-(Undecanoyl-[3-2H2])-L-homoserine lactone 27b (95% D) 1H NMR (400 MHz, CDCl3):  = 0.88
(3H, t, J = 6.9 Hz, CH3), 1.21-1.32 (14H, m, (CH2)7CH3), 2.12 (1H, dddd, J = 12.5 Hz, 11.5 Hz, 11.5
Hz, 8.8 Hz, OCH2CHH'), 2.23 (2H, s, CH2CONH), 2.88 (1H, dddd, J = 12.6 Hz, 8.5 Hz, 5.8 Hz, 1.1
Hz, OCH2CHH'), 4.29 (1H, ddd, J = 11.3 Hz, 9.3 Hz, 5.9 Hz, OCHH'), 4.47 (1H, td, J = 9.1 Hz, 1.0
Hz, OCHH'), 4.54 (1H, ddd, J = 11.6 Hz, 8.5 Hz, 5.6 Hz, CHN), 5.96 (1H, d, J = 5.6 Hz, NH) ppm.
13C NMR (100 MHz, CDCl3):  = 14.1 (CH3), 22.7, 29.0, 29.28, 29.30, 29.5, 29.6, 31.9 ((CH2)7CH3),
24.7 (quintet, JC-D = 19.2 Hz, CD2), 30.5 (CH2CHN), 36.0 (CH2CONH), 49.2 (CHN), 66.1 (CH2O),
173.8 (CONH), 175.7 (COO) ppm. MS (ESI): m/z (%): 272 (M+H+, 100). HRMS mass expected:
C15H25D2NO3H+ 272.2195; found: 272.2182. IR (cm-1): max 1010, 1171, 1547, 1643, 1779, 2113,
2205, 2851, 2919, 3315. Chromatography: EtOAc:Petroleum ether 3:2 Rf = 0.21. Melting Point:
135-136 °C. Colorless powder. Yield: 69%.
N-(Dodecanoyl-[3-2H2])-L-homoserine lactone 27c (92% D) 1H NMR (400 MHz, CDCl3):  = 0.88
(3H, t, J = 6.9 Hz, CH3), 1.19-1.35 (16H, m, (CH2)8CH3), 2.12 (1H, dddd, J = 12.5 Hz, 11.5 Hz, 11.5
Hz, 8.8 Hz, OCH2CHH'), 2.23 (2H, s, CH2CONH), 2.88 (1H, dddd, J = 12.6 Hz, 8.5 Hz, 5.8 Hz, 1.1
19

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Hz, OCH2CHH'), 4.28 (1H, ddd, J = 11.3 Hz, 9.3 Hz, 5.8 Hz, OCHH'), 4.47 (1H, td, J = 9.1 Hz, 1.0
DOI: 10.1039/C6RA17797B
Hz, OCHH'), 4.53 (1H, ddd, J = 11.6 Hz, 8.5 Hz, 5.6 Hz, CHN), 5.93 (1H, d, J = 4.8 Hz, NH) ppm.
13C NMR (100 MHz, CDCl3):  = 14.1 (CH3), 22.7, 29.0, 29.27, 29.32, 29.5, 29.6 (2C), 31.9
((CH2)8CH3), 24.3-25.4 (m, CD2), 30.4 (CH2CHN), 36.0 (CH2CONH), 49.1 (CHN), 66.1 (CH2O),
173.8 (CONH), 175.8 (COO) ppm. MS (ESI): m/z (%): 286 (M+H+, 100). HRMS mass expected:
C16H27D2NO3H+ 286.2351; found: 286.2335. IR (cm-1): max 1010, 1171, 1546, 1643, 1775, 2110,
2194, 2850, 2918, 3315. Chromatography: EtOAc:Petroleum ether 3:2 Rf = 0.23. Melting Point:
137-139 °C. Colorless powder. Yield: 52%.
General procedure for the synthesis of deuterated AHLs 28a-c
To a stirred solution of ,-dideuterated fatty acid 24a-c (1 equiv, 2 mmol) in 20 mL of dry
dichloromethane, was added 4-(N,N-dimethylamino)pyridine (2.1 equiv, 4.2 mmol, 0.51 g), 1-
ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (1.1 equiv, 2.2 mmol, 0.42 g) and
Meldrum’s acid (1 equiv, 2 mmol, 0.29 g). The resulting clear yellow solution was stirred for
20 h at room temperature. The solvent was removed by rotary evaporation in vacuo, the
residue was redissolved in ethyl acetate (50 mL) and washed with 30 mL of 2M aq. HCl. Drying
over MgSO4, followed by filtration to remove the drying agent and evaporation of the solvent
in vacuo yielded acylated Meldrum’s acid 25a-c quantitatively, which was used without further
purification. The deuterium-labelled, acylated Meldrum’s acid 25a-c was dissolved in
acetonitrile (30 mL), after which triethylamine (1.2 equiv, 2.4 mmol, 0.33 mL) and L-
homoserine lactone hydrobromide 16 (1 equiv, 2 mmol, 0.36 g) were added. The mixture was
stirred at room temperature for 2 h and then heated at reflux overnight. The solvent was
removed in vacuo and the resulting residue was dissolved in 30 mL of ethyl acetate and 30 mL
of water. After separation of both layers, the aqueous phase was extracted two times with 30
mL of ethyl acetate. The combined organic phases were washed with 60 mL of saturated aq.
NaHCO3 and 60 mL of brine. Drying over MgSO4 and removal of the solvent in vacuo yielded
crude deuterated AHL 28a-c. Purification via column chromatography on silica gel (ethyl
acetate/petroleum ether 3:2 to 4:1) gave the pure product as a colorless powder.
N-(3-Oxodecanoyl-[5-2H2])-L-homoserine lactone 28a (93% D) 1H NMR (400 MHz, CDCl3):  =
0.88 (3H, t, J = 6.8 Hz, CH3), 1.20-1.32 (8H, m, (CH2)4CH3), 2.23 (1H, dddd, J = 12.5 Hz, 11.3 Hz,
11.3 Hz, 8.9 Hz, OCH2CHH'), 2.51 (2H, s, CH2CONH), 2.76 (1H, dddd, J = 12.6 Hz, 8.7 Hz, 6.0 Hz,
1.4 Hz, OCH2CHH'), 3.47 (2H, s, COCH2CO), 4.28 (1H, ddd, J = 11.0 Hz, 9.3 Hz, 6.1 Hz, OCHH'),
4.47 (1H, td, J = 9.1 Hz, 1.3 Hz, OCHH'), 4.59 (1H, ddd, J = 11.5 Hz, 8.7 Hz, 6.6 Hz, CHN), 7.66
(1H, d, J = 5.6 Hz, NH) ppm. 13C NMR (100 MHz, CDCl3):  = 14.1 (CH3), 22.6, 28.7, 28.9, 31.6
((CH2)4CH3), 22.2-23.4 (m, CD2), 29.6 (CH2CHN), 43.6 (CD2CH2CO), 48.4 (COCH2CO), 49.0 (CHN),
65.9 (CH2O), 166.5 (CONH), 175.0 (COO), 206.5 (CH2COCH2) ppm. MS (ESI): m/z (%): 272
+
(M+H+, 100), 289 (M+NH4 , 20). HRMS mass expected: C14H21D2NO4H+ 272.1831; found:
272.1833. IR (cm-1): max 1010, 1023, 1165, 1356, 1548, 1646, 1712, 1776, 2112, 2193, 2851,
2918, 2957, 3081, 3284. Chromatography: EtOAc:Petroleum ether 3:2 Rf = 0.21. Melting Point:
81-82 °C. Colorless powder. Yield: 49%.
20

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N-(3-Oxotridecanoyl-[5-2H2])-L-homoserine lactone 28b (95% D) 1H NMR (400 MHz, CDCl3): 
DOI: 10.1039/C6RA17797B
= 0.88 (3H, t, J = 6.8 Hz, CH3), 1.19-1.33 (14H, m, (CH2)7CH3), 2.24 (1H, dddd, J = 12.5 Hz, 11.3
Hz, 11.3 Hz, 9.0 Hz, OCH2CHH'), 2.51 (2H, s, CH2CONH), 2.76 (1H, dddd, J = 12.5 Hz, 8.7 Hz, 6.1
Hz, 1.4 Hz, OCH2CHH'), 3.47 (2H, s, COCH2CO), 4.28 (1H, ddd, J = 11.0 Hz, 9.3 Hz, 6.1 Hz, OCHH'),
4.48 (1H, td, J = 9.1 Hz, 1.3 Hz, OCHH'), 4.60 (1H, ddd, J = 11.5 Hz, 8.7 Hz, 6.6 Hz, CHN), 7.67
(1H, d, J = 5.7 Hz, NH) ppm. 13C NMR (100 MHz, CDCl3):  = 14.1 (CH3), 22.7, 28.8, 29.3, 29.4,
29.5, 29.6, 31.9 ((CH2)7CH3), 22.2-23.4 (m, CD2), 29.7 (CH2CHN), 43.7 (CD2CH2CO), 48.2
(COCH2CO), 49.0 (CHN), 65.9 (CH2O), 166.4 (CONH), 174.7 (COO), 206.6 (CH2COCH2) ppm. MS
+
(ESI): m/z (%): 314 (M+H+, 100), 331 (M+NH4 , 21). HRMS mass expected: C17H27D2NO4H+
314.2295; found: 314.2305. IR (cm-1): max 1006, 1016, 1176, 1356, 1544, 1642, 1716, 1776,
2092, 2164, 2850, 2919, 3071, 3294. Chromatography: EtOAc:Petroleum ether 4:1 Rf = 0.37.
Melting Point: 86-88 °C. Colorless powder. Yield: 66%.
N-(3-Oxotetradecanoyl-[5-2H2])-L-homoserine lactone 28c (93 %D) 1H NMR (400 MHz, CDCl3):
 = 0.88 (3H, t, J = 6.9 Hz, CH3), 1.20-1.32 (16H, m, (CH2)8CH3), 2.23 (1H, dddd, J = 12.5 Hz, 11.3
Hz, 11.3 Hz, 9.0 Hz, OCH2CHH'), 2.51 (2H, s, CH2CONH), 2.76 (1H, dddd, J = 12.6 Hz, 8.7 Hz, 6.1
Hz, 1.4 Hz, OCH2CHH'), 3.47 (2H, s, COCH2CO), 4.28 (1H, ddd, J = 11.1 Hz, 9.3 Hz, 6.1 Hz, OCHH'),
4.48 (1H, td, J = 9.1 Hz, 1.3 Hz, OCHH'), 4.59 (1H, ddd, J = 11.5 Hz, 8.7 Hz, 6.6 Hz, CHN), 7.66
(1H, d, J = 5.4 Hz, NH) ppm. 13C NMR (100 MHz, CDCl3):  = 14.1 (CH3), 22.7, 28.8, 29.30, 29.32,
29.4, 29.6, 29.8, 31.9 ((CH2)8CH3), 22.3-23.2 (m, CD2), 29.6 (CH2CHN), 43.7 (CD2CH2CO), 48.2
(COCH2CO), 49.0 (CHN), 65.9 (CH2O), 166.4 (CONH), 174.9 (COO), 206.6 (CH2COCH2) ppm. MS
+
(ESI): m/z (%): 328 (M+H+, 100), 345 (M+NH4 , 19). HRMS mass expected: C18H29D2NO4H+
328.2457; found: 328.2446. IR (cm-1): max 1007, 1016, 1176, 1356, 1544, 1641, 1716, 1775,
2101, 2192, 2850, 2918, 2954, 3073, 3294. Chromatography: EtOAc:Petroleum ether 3:2 Rf =
0.24. Melting Point: 94-95 °C. Colorless powder. Yield: 54%.
Synthesis of tetramic acid 29
313 mg of N-(3-oxotridecanoyl-[5-2H2])-L-homoserine lactone 28b (1 equiv, 1 mmol) was
dissolved in 3 mL of dry methanol under a nitrogen atmosphere. Then 1 equiv of NaOMe in
methanol (0.5M, 54 mg in 2 mL) was added and the mixture was stirred at reflux for 3 h.
Subsequently, the reaction mixture was poured into 10 mL of water and extracted with 10 mL
of diethyl ether. The organic phase was discarded and the aqueous phase was acidified with
2M aq. HCl and extracted three times with 10 mL of diethyl ether. Drying of the combined
organic phases over MgSO4, evaporation of the solvent in vacuo and recrystallization form
hexane yielded 250 mg of tetramic acid 29 as a colorless powder.
1
3-(1-Hydroxyundecylidene-[5-2H2])-5-(2-hydroxyethyl)pyrrolidine-2,4-dione 29 (95% D) H
NMR (400 MHz, CD3OD):  = 0.88 (3H, t, J = 6.8 Hz, CH3), 1.20-1.37 (14H, m, (CH2)7CH3), 1.68-
1.79 (1H, m, HOCH2CHH'), 1.96-2.05 (1H, m, HOCH2CHH'), 2.80 (2H, s, CH2CONH), 3.62-3.73
(2H, m, HOCH2), 3.96 (1H, m, CHN) ppm. 13C NMR (100 MHz, CD3OD):  = 14.4 (CH3), 23.7, 30.1,
30.3, 30.4, 30.6, 30.7, 33.1 ((CH2)7CH3), 26.2 (quintet, JC-D = 19.1 Hz, CD2), 33.9 (CD2CH2CO),
35.7 (CH2CHN), 59.3 (CH2OH), 60.0-61.5 (m, CHN), 101.5-102.3 (m, COCCO), 175.5-177.1 (m,
21

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CONH), 191.0-191.6 (m, CD2CH2CHOH), 197.8-198.5 (m, NHCHCO) ppm. MS (ESI): m/z (%): 314
DOI: 10.1039/C6RA17797B
(M+H+, 100). HRMS mass expected: C17H27D2NO4H+ 314.2295; found: 314.2297. Melting Point:
80-81 °C. Colorless powder. Yield: 80%.
Synthesis of ring opened AHL 30
200 mg of N-(undecanoyl-[3-2H2])-L-homoserine lactone 27b (1 equiv, 0.74 mmol) was
dissolved in 2 mL of acetonitrile at 0 °C. Then 2 mL of 2M aq. NaOH (5 equiv, 3.7 mmol, 0.15
g) was added and the mixture was stirred overnight at room temperature. The reaction
mixture was extracted with 5 mL of ethyl acetate. The organic phase was discarded and the
aqueous phase acidified to pH 2 with 2M aq. HCl. Extraction with ethyl acetate (3 x 5 mL),
followed by drying over MgSO4 and evaporation of the combined organic phases in vacuo and
recrystallization from acetone gave 188 mg of ring opened AHL 30 as a colorless powder.
N-(Undecanoyl-[3-2H2])-L-homoserine 30 (95% D) 1H NMR (400 MHz, CD3OD):  = 0.91 (3H, t,
J = 6.8 Hz, CH3), 1.23-1.40 (14H, m, (CH2)7CH3), 1.81-1.91 (1H, m, HOCH2CHH'), 2.05-2.15 (1H,
m, HOCH2CHH'), 2.24 (2H, s, CH2CONH), 3.57-3.71 (2H, m, HOCH2), 4.52 (1H, dd, J = 9.3 Hz, 4.6
Hz, CHN) ppm. 13C NMR (100 MHz, CD3OD):  = 14.4 (CH3), 23.7, 30.1, 30.43, 30.46, 30.65,
30.71, 33.1 ((CH2)7CH3), 26.0-27.0 (m, CD2), 35.3 (CH2CHN), 36.7 (CH2CONH), 50.9 (CHN), 59.3
(CH2OH), 175.5 (CONH), 176.5 (COOH) ppm. MS (ESI): m/z (%): 290 (M+H+, 100), 312 (M+Na,
38). HRMS mass expected: C15H27D2NO4H+ 290.2295; found: 290.2296. Melting Point: 114-115
°C. Colorless powder. Yield: 88%.
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