Synthesis and sensory studies of umami-active scaffolds

Article abstract of DOI:10.1002/cbdv.201400113

The class of 2-isopropyl-5-methylbicyclo[4.1.0]heptane-7-carboxamides, 1-4, has been identified as potent umami-tasting molecules. A scalable synthesis of this challenging scaffold and new sensory insights will be presented. Interestingly, the umami chara

Full text of DOI:10.1002/cbdv.201400113

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Synthesis and Sensory Studies of Umami-Active Scaffolds
by Michael Backes*, Susanne Paetz, Tobias Vçssing, and Jakob Peter Ley
Symrise AG, Mꢀhlenfeldstraße 1, D-37603 Holzminden
The class of 2-isopropyl-5-methylbicyclo[4.1.0]heptane-7-carboxamides, 1–4, has been identi-
fied as potent umami-tasting molecules. A scalable synthesis of this challenging scaffold and new
sensory insights will be presented. Interestingly, the umami characteristics differ remarkably, depend-
ing on constitutional and stereochemical features of the parent scaffold. During our studies, we
could identify the carboxamide moiety as a crucial factor to influence the umami intensity of these
scaffolds. In addition, the configuration of the cyclopropyl moiety exerts some influence, whereas
the absolute configuration of the menthyl scaffold, at least the tested d- and l-configuration, is less
important.
Introduction. – After introduction of the concept of umami as a distinctive fifth
taste quality triggered by monosodium glutamate (MSG) by Ikeda in 1908 [1], it took
another 60 years, until Yamaguchi could scientifically establish that certain nucleotides
(naturally occurring in various food sources) were able to act synergistically to the
umami sensation of MSG [2]. Surprisingly, during the next decades only very few new
natural umami-tasting compounds with a weaker sensory profile have been identified,
which are only of limited use for flavoring purposes [3][4].
Whereas there are no scientifically sound constraints to use MSG in food [5], the
public perception of added MSG is nowadays very poor. Hence, the food industry
constantly strives to develop new solutions to meet consumer expectations. Due to the
identification of the heterodimeric T1R1/T1R3 G protein-coupled receptor as being
mainly responsible for the umami perception in the early 2000s [6], a high throughput
screening of pharmaceutical compound libraries was started, resulting in amides and
related structures showing potent umami activities [7]. Subsequently, the oxalic acid-
derived compounds, A–D (Fig. 1), and amide E have been registered for the use in
food in several countries. In parallel, structureꢀactivity-based concepts led to the
identification of several other structural spaces [8][9], resulting in the registration of
spilanthol derived amides, F–H, amide I, and the urea derivative J.
All of the above mentioned molecules bear some kind of an amide functionality
in their core structure. Interestingly, I and J are the only registered ones so far
which possess stereogenic centers. More recently, the dihydrochalcones K and L have
been introduced, which do not follow this general observation [10]. However, they
contain a pyridine substructure, which is a very common motive for umami-active
scaffolds as well.
Within our sensory screening program directed towards the identification of
umami-active scaffolds, we identified diastereoisomeric mixtures of 2-isopropyl-5-
ꢁ 2014 Verlag Helvetica Chimica Acta AG, Zꢀrich

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Fig. 1. Artificial umami compounds currently registered for the use in food
methylbicyclo[4.1.0]heptane-7-carboxamides, 1 and 2, as very potent umami-tasting
candidates (Fig. 2) [11].
We could demonstrate that the amide moiety plays an important role for the umami
perception [12]. However, the influence of the configuration of the core structure had
not been investigated in detail. For this purpose, a scalable synthetic route to highly
enantiomerically enriched 2-isopropyl-5-methylbicyclo[4.1.0]heptane-7-carboxamides
1–4 had to be established, envisaging fractional crystallization of the corresponding N-
methyl carboxamide as the key step for the separation of the diastereoisomeric
mixtures obtained from the addition of ethyl diazoacetate (N2CHCOOEt) to p-menth-
2-ene. Sensory evaluation via a descriptive expert panel and a ranking test revealed the
influence of the amide moiety and the configuration of the core scaffold for the umami
sensation.

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Fig. 2. Evaluated structures based on the 2-isopropyl-5-methylbicyclo[4.1.0]heptane-7-carboxamide
scaffold
Results and Discussion. – Synthesis. An optimized synthetic route to four different
stereoisomers of the 2-isopropyl-5-methylbicyclo[4.1.0]-heptane-7-carboxamide scaf-
folds, 1–4, comprising a linear sequence of ten linear steps could be developed
(Scheme 1). The synthesis of 1 and 2 starting from l-menthol (5a) will be described in
detail later, however, the same methods can be applied for the synthesis of the
corresponding enantiomeric scaffolds 3 and 4 with d-menthol (5b) and (3R,6S)-p-
menth-2-ene (6b) as starting material, respectively. Although being described in the
literature abundantly, the regioselective elimination of l-menthol (5a) and its
derivatives to (3S,6R)-p-menth-2-ene (6a) in larger scale proved to be challenging.
Finally, by slightly modifying a literature protocol [13] the elimination of the
t
corresponding p-toluenesulfonate employing BuOK in N-methylpyrrolidin-2-one at
elevated temperatures furnished the desired (3S,6R)-p-menth-2-ene (6a) in acceptable
yield and purity.
The subsequent cyclopropanation employing ethyl diazoacetate resulted in the
formation of the expected diastereoisomeric esters 7a and 8a, and some undesired by-
products. Diethyl malonate and diethyl fumarate both result from the self-condensa-
tion of ethyl diazoacetate and by-product 9a is generated from the insertion of ethyl
diazoacetate to HꢀC(6) of (3S,6R)-p-menth-2-ene (6a). Besides the well-established
chlorinated solvents, we obtained conversions of nearly 35% (based on ethyl
diazoacetate) by using a large excess of 6a without any additional solvent, employing
[Cu(acac)2] as metal source. Interestingly, it was not possible to avoid or even
significantly decrease the formation of by-product 9a by using an additional solvent.
The diastereoselectivity of this reaction (6 :4 in favor of 7a) is set by the stereogenic
centers present in (3S,6R)-p-menth-2-ene (6a). To influence this diastereoselectivity,
the use of a chiral l-valine-based bis(oxazoline) ligand with a tartaric acid-derived
backbone was investigated [14]. However, no change in diastereoselectivity could be
observed, and the yield decreased dramatically. Furthermore, l- and d-menthyl
diazoacetate were employed for an auxiliary-based approach [15]. However, the yield
dropped significantly, the products were difficult to hydrolyze, and the diastereoiso-

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Scheme 1. Synthesis of N-Methylcarboxamides 1a and 2a Starting from l-Menthol (5a)
t
i) TsCl, 3-methylpyridine. ii) BuOK, NMP (¼ N-methylpyrrolidin-2-one; 66% over two steps). iii)
N2CHCOOEt, [Cu(acac)2] (acac, acetylacetonate). iv) H2O2, HCOOH, NaOH, EtOH. v) MeNH2,
THF/H2O (18% over four steps).
meric distribution of the addition products was not affected. In addition, several
attempts to separate the diastereoisomers via enzymatic resolution or preparative flash
chromatography failed. In previous studies, it was found that the corresponding N-
methyl carboxamides 1a and 2a, in contrast to all other synthesized carboxamides,
could be separated via fractional crystallization. To facilitate this crystallization step,
by-product 9a has to be removed from the mixture. This was achieved by epoxidation of
the remaining C¼C bond with subsequent ring opening to the corresponding diol,
which could easily be separated via column chromatography. The obtained pure
carboxylic acids 7a and 8a were converted to their corresponding acid chlorides with
(COCl)2. Subsequent reaction with aqueous MeNH2 under SchottenꢀBaumann
conditions led to the desired N-methyl carboxamides 1a and 2a in 18% over four
steps starting from 6a. The separation of this diastereoisomeric mixture was
accomplished by fractional crystallization in acetone, with isomer 1a being the one to
crystallize first (Scheme 2).
After concentration of the mother liquor, the second isomer 2a started to
crystallize, the addition of seed crystals obtained via preparative HPLC facilitated the
crystallization process significantly. In case of the fractional crystallization of the
enantiomeric amide mixture 3a/4a, the diastereoisomeric excess (de) of the latter was
not as high as expected, which might be the result of not using a seed crystal in this step.
The diastereoisomers 1a, 2a, and 3a could be obtained with ꢁ94% de, whereas
diastereoisomer 4a could be obtained with only 68% de. N-Methyl carboxamides 1a–
4a were hydrolyzed to the corresponding acids, which could be transformed to different
carboxamides, 1b–1g, 2b–2g, 3b–3g, and 4b–4g, via chlorination and subsequent
amidation using variations of the SchottenꢀBaumann reaction.

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Scheme 2. Fractional Crystallization and Synthesis of the Corresponding Diastereoisomerically Enriched
Carboxamides 1a–1g and 2a–2g
i) Acetone (48% yield, 93% de regarding 1a; 37% yield, 93% de regarding 2a). ii) Aq. KOH,
HOCH2CH2OH. iii) (COCl)2, NMFA (N-methylformanilide), CH2Cl2. iv) RꢀNH2, NaHCO3 (yield 63–
78% over three steps, ꢁ98% de). v) aq. KOH, HOCH2CH2OH. vi) (COCl)2, NMFA, CH2Cl2. vii)
RꢀNH2, KOH, THF/H2O (26–80% over three steps, ꢁ98% de).
Sensory Evaluation. Prior to sensory testing, the safety profile of the corresponding
N-cyclopentyl carboxamide 1f as representative example for this group of compounds
was evaluated. The LD50 value in rats (according to OECD guideline 423) was
determined to be above 2,000 mgkgꢀ1, and a Salmonella typhimurium reverse-
mutation assay with and without metabolic activation showed no mutagenic effects.
Based on these results, the evaluation of this class of compounds using the sip-and-spit
method could be performed. In a first step, all synthesized amides were pre-evaluated
by an expert panel for their intrinsic umami activity in a dosage of 5 ppm in a 0.5% salt
and a 5% sucrose solution (Table).
Interestingly, besides the already described pronounced effect of the different
amide residues, the l-menthol (5a)-derived scaffolds 1 seem to be preferred. To
validate this first impression and to gain more detailed information, three ranking tests

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Table. Sensory Evaluation Regarding the Intrinsic Umami Activity of the 2-Isopropyl-5-methylbicy-
clo[4.1.0]heptan-7-carboxamides in a 0.5% Salt and 5% Glucose Solution Using the Sip-and-Spit Method
(number of panelists 5–8)
Scaffold 1
Scaffold 2
Scaffold 3
ꢁ95% de
Scaffold 4
ꢁ67% de
a
b
c
ꢁ93% dea)
ꢁ93% dea)
very slightly umami
ꢁ99% de
ꢁ99% de
ꢁ99% de
ꢁ66% de
ꢁ68% de
ꢁ62% de
ꢁ64% de
umami
slightly umami
ꢁ99% de
ꢁ98% de
ꢁ99% de
umami
slightly umami
umami
d
ꢁ99% de
ꢁ99% de
ꢁ99% de
ꢁ99% de
ꢁ99% de
slightly umami
e
f
ꢁ99% de
ꢁ99% de
ꢁ99% de
ꢁ98% de
ꢁ66% de
umami
umami
umami
g
ꢁ99% de
ꢁ98% de
ꢁ98% de
ꢁ65% de
slightly umami
umami
slightly umami
a) de, Diastereoisomeric excess. Can be purified to ꢁ99% de via second crystallization using seed
crystals.
(ISO 8587:2006) with a larger trained panel on different aspects of this class of
compounds were conducted [16]. It is important to note that this kind of test is used to
highlight differences of the tested samples regarding one descriptor. However, no
conclusions on the overall intensity or the degree of difference can be drawn. In
addition, the class of compounds with the poorest score might only be very slightly
active or even show no activity at all. In a first attempt the l-menthol (5a)-derived
scaffolds 1a–1g showing the most potent umami activities, were selected to evaluate
the effect of the amide moieties (Fig. 3).
Scaffolds 1a, 1g, and 1d were identified as the least active compounds, followed by
1e and 1b, being medium active, and two highly active compounds 1c and 1f. This is in
accordance with the observations reported earlier stating that the N-cyclopentyl
carboxamides 1f and 2f are very active compounds at levels as low as 300 ppb, and the
corresponding N-methyl carboxamides 1a and 2a have virtually no effect at a dosage of
5 ppm [12]. To further investigate the influence of the configuration, strongly active N-
cyclopentyl carboxamides 1f–4f, and less active N-cyclohexyl carboxamides 1g–4g,
were selected. As expected, for both series the same ranking of the scaffolds could be
observed (Fig. 4).
The l-menthyl-derived configuration with the cyclopropa part pointing down, i.e.,
in 1f and 1g, always provided the strongest effect, whereas the l-menthyl-derived
configuration with the cyclopropa moiety pointing up, i.e., in 2f and 2g, always leads to
the less active scaffold. The umami intensity of the corresponding d-menthol (5b)-
derived scaffolds lies in between. However, in case of the highly active N-cyclopentyl
carboxamides 3f and 4f, the scaffold with the cyclopropa motive pointing down, i.e., 4f,

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Fig. 3. Ranking of the carboxamide moieties 1a–1g according to their umami intensity employing the ISO
8587:2006 method (number of panelists 14–18; level of significance for the mean rank (LSD <10%)
shows stronger umami activity, compared to the stereoisomer with the cyclopropa
moiety pointing up, i.e., 3f. In case of the only slightly active N-cyclohexyl
carboxamides 3g and 4g, both compounds are rated equally active. It has to be
considered that for the d-menthol-derived scaffolds with the cyclopropa motive
pointing down (4a–4g), only compounds with de values of ꢁ62% were used for the
ranking tests. However, even this supports the findings, as the pure compounds with the
cyclopropa motive pointing up (i.e., 3a–3g) are weaker in their umami activities.
Conclusions. – In total, 28 different 2-isopropyl-5-methylbicyclo[4.1.0]heptane-7-
carboxamides starting from l-menthol (5a) and d-menthol (5b) have been prepared in
yields ranging from 1.1–4.5% following a ten-step synthetic protocol employing
fractional crystallization of the corresponding N-methyl carboxamides 1a–4a as key
step. The umami activities of all compounds have been evaluated, and correlations for
structural requirements have been postulated. The amide moiety is the most relevant
factor to influence the umami intensity of these scaffolds. In addition, the configuration
of the cyclopropa moiety plays a significant role as well, whereas the absolute
configuration of the menthyl part, at least the tested d- and l-configuration, is of little
importance.
Experimental Part
General. Reagents and solvents were purchased from commercial suppliers (Acros Organics, BE-
Geel; SigmaꢀAldrich, DE-Steinheim; Alfa Aesar GmbH & Co KG, DE-Karlsruhe) or prepared by
Symrise, and used without further purification or drying. M.p.: LICO 500 (Hach Lange GmbH, DE-
Berlin); uncorrected. Monitoring of the reaction was accomplished by TLC on silica gel GF254 plates
(SiO2) with either UV detection or by using a staining reagent consisting of ammonium molybdate,

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Fig. 4. Ranking of the N-cyclopentyl carboxamides 1f–4f and N-cyclohexyl carboxamides 1g–4g
according to their umami intensity employing the ISO 8587:2006 method (number of panelists 14–18;
level of significance for the mean rank (LSD) <10%)
Ce(SO4)2, and H2SO4. Purity and diastereoselectivity were determined using either an Agilent 6890N or
Agilent 7890N system (Agilent Technologies, Santa Clara, USA) equipped with DB-WAX and DB-1
columns (length, 20 m; i.d., 0.18 mm; film, 0.18 mm); flow rate, 0.5–3.0 mlminꢀ1; injector split ratio 1:70;
80–2508 (rate 128/s); carrier gas, H2; detector, FID, 2758 (Agilent Technologies, Santa Clara, USA). The
purity of all reported compounds is ꢁ98.0% according to GC unless otherwise stated. Optical rotations:
Unipol L 1000 (SchmidtþHaensch GmbH & Co., DE-Berlin). 1H- and 13C-NMR spectra: Varian
Mercury Plus or Varian Unity Innova spectrometer (Varian, DE-Darmstadt); d in ppm rel. to Me4Si as
internal standard, J in Hz. GC/EI-MS: Shimadzu GC2010/QP2010 (Shimadzu Corporation, Kyoto,

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Japan) or Agilent 6890N system (Agilent Technologies, Santa Clara, USA); 70 eV; detector, quadrupole.
HR-EI-MS: coupled system consisting of an Agilent 7890A and a Waters GTC Premier (Waters, DE-
Eschborn); 70 eV; detector, TOF.
Chemistry. General Procedure A (GP A): Selected Carboxamides from Corresponding N-Methyl
Carboxamides. One equiv. of the corresponding N-methyl carboxamide and 10–15 equiv. KOH were
stirred at r.t. in HOCH2CH2OH (7.5 ml/mmol substrate) for 12 h before heating under reflux for
additional 4 h. Subsequently, ice-water (30 ml/mmol substrate) was added, and the aq. phase was washed
two times with tBuOMe (6 ml/mmol substrate). After adjusting the aq. soln. to pH 1 with 1m H2SO4, the
product was extracted with AcOEt (7.5 ml/mmol substrate). The org. phase was washed two times with
H2O and once with brine before drying (Na2SO4). After evaporation of the solvent, the crude carboxylic
acid was recrystallized from H2O/EtOH 2 :1 and used in the next step without any further purification.
One equiv. of the corresponding acid and a catalytic amount of N-methylformanilide (NMFA) were
suspended in CH2Cl2 (1 ml/mmol substrate) before 1.1 equiv. (COCl)2 were added slowly to the soln. The
mixture was stirred for 1 h at r.t. and additional 30 min at reflux temp. After evaporation of the solvent,
the crude product was resolved in THF (2.4 ml/mmol substrate) and slowly added to a mixture of 1.2
equiv. of the corresponding amide dissolved in a mixture of THF (2 ml/mmol substrate), H2O (2 ml/
mmol substrate), and 1.2 equiv. of KOH at r.t. Subsequently, the mixture was heated under reflux for
15 min before adding H2O (10 ml/mmol substrate) to precipitate the formed carboxamide. The product
was separated by filtration, washed with H2O, and further purified via recrystallization from EtOH/H2O.
Finally, the product was dried in a vacuum oven at 758.
General Procedure B (GP B): Selected Carboxamides from Corresponding N-Methyl Carboxamides.
One equiv. of the corresponding N-methyl carboxamide and 5 equiv. KOH were heated under reflux in
HOCH2CH2OH (4 ml/mmol substrate) for 6 h. Subsequently, ice water (12 ml/mmol substrate) was
added, and the aq. phase was washed two times with AcOEt (10 ml/mmol substrate). After adjusting the
aq. soln. to pH 1 with 1m H2SO4, the product was extracted two times with AcOEt (10 ml/mmol
substrate). The org. phase was washed (4ꢂ ) with H2O before drying (Na2SO4). After evaporation of the
solvent, the crude carboxylic acid product was used in the next step without any further purification.
One equiv. of the corresponding acid and a cat. amount of NMFA were suspended in CH2Cl2 (3–
4 ml/mmol substrate) before 1.3 equiv. (COCl)2 were added slowly, and the mixture was stirred for 3 h
under reflux. After evaporation of the solvent, the crude product was resolved in acetone (2.5–4.0 ml/
mmol substrate) and slowly added to a mixture of 1.5 equiv. of the corresponding amine dissolved in a
mixture of aq. 5% NaHCO3 soln. (7–10 ml/mmol substrate) and H2O (6–8 ml/mmol substrate) at r.t.
Subsequently, the mixture was stirred for 70 h, while the resulting carboxamides started to crystallize. The
products were separated by filtration, washed with H2O, and further purified via recrystallization from
H2O/acetone. Finally, the products were dried in a vacuum oven at 508.
General Procedure C (GP C): Selected Carboxamides from Corresponding N-Methyl Carboxamides.
One equiv. of the corresponding N-methyl carboxamide and 5 equiv. KOH were heated under reflux in
HOCH2CH2OH (3.5 ml/mmol substrate) for 6 h. Subsequently, ice water (10 ml/mmol substrate) was
added, and the aq. phase was washed two times with AcOEt (3 ml/mmol substrate). After adjusting the
aq. soln. to pH 1 with 1m H2SO4, the product was extracted two times with AcOEt (5 ml/mmol substrate).
The org. phase was washed (5ꢂ ) with H2O before drying (Na2SO4). After evaporation of the solvent, the
crude carboxylic acid product was used in the next step without further purification.
One equiv. of the corresponding acid and a cat. amount of NMFAwere suspended in CH2Cl2 (2.5 ml/
mmol substrate) before 1.3 equiv. (COCl)2 were added slowly, and the mixture was stirred for 3 h under
reflux. After evaporation of the solvent, the crude product was resolved in acetone (2.5 ml/mmol
substrate) and slowly added to a mixture of 2.0 equiv. of the corresponding amine and 2.0 equiv. of
NaHCO3 dissolved in H2O/acetone 1:1 (7.5–14.0 ml/mmol substrate) at r.t. Subsequently, the mixture
was stirred for 24 h while some of the resulting carboxamides started to crystallize. After addition of H2O
(15.0 ml/mmol substrate), all carboxamides participated and were separated by filtration, washed with
H2O, and further purified via recrystallization from EtOH/H2O. Finally, the product was dried in a
vacuum oven at 508.
(3R,6S)-3-Methyl-6-(1-methylethyl)cyclohexene (¼(3S,6R)-p-Menth-2-ene; 6a). A soln. of 600.0 g
(3.8 mol) l-menthol in 500 ml 3-methylpyridine was slowly added to a suspension of 805.2 g (4.2 mol)

CHEMISTRY & BIODIVERSITY – Vol. 11 (2014)
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TsCl in 500 ml 3-methylpyridine, while maintaining the temp. below 308. The mixture was stirred for 4 h
at r.t. before 365 ml 3-methylpyridine were removed via distillation, until the mixture nearly became
solid. The residue was dissolved in 3500 ml AcOEt, and the org. phase was extracted two times with 1m
H2SO4 and once with sat. aq. NaHCO3 soln. After evaporation of the solvent, 1184.4 g of the
corresponding l-menthyl p-toluenesulfonate were obtained as colorless solid.
A mixture of 1.0 equiv. of the l-menthyl p-toluenesulfonate and 1.5 equiv. tBuOK were suspended in
N-methylpyrrolidin-2-one (0.5–0.8 ml/mmol substrate), and the mixture was heated at 1408 for 3 h.
After cooling to 808, H2O (0.5 ml/mmol substrate) was added, and the org. phase was separated,
subsequently washed with H2O, and dried (Na2SO4). The residue contained 89.6–92.4% of 6a besides
other regioisomers and unreacted l-menthol.
This reaction sequence was repeated several times and in total the reaction of 4.102 kg (26.2 mol) l-
menthol (5a) resulted in 2.745 kg of 6a (purity 91.2%). Final purification via distillation (52–558/
18 mbar) led to 2.460 kg (97.0%, 17.3 mol) 6a in an overall yield of 66%. [a]2D3 ¼ þ149.6 (c¼1.0, EtOH);
[17]: [a]2D4 ¼ þ115.3 (c¼2.2, benzene).
(3S,6R)-3-Methyl-6-(1-methylethyl)cyclohexene (¼(3R,6S)-2-p-menthene (6b)). As described for
6a, 247.8 g (1.59 mol) d-menthol were converted to the corresponding p-toluenesulfonate. The
elimination was affected with 2.5 equiv. KOH (85% aq. soln.) in polyethylene glycol 400 (0.5–1.5 ml/
mmol substrate) at 1308 for 3 h. After workup and final distillation, 100.0 g (95.1%, 0.69 mol) 6b were
obtained in an overall yield of 43%. [a]D23 ¼ ꢀ147.1 (c¼1.0, EtOH); [18]: [a]1D5 ¼ ꢀ139.5 (c¼2.0,
benzene).
(1S,2R,5S,6R,7R)- and (1R,2R,5S,6S,7S)-N,2-Dimethyl-5-(1-methylethyl)bicyclo[4.1.0]heptane-7-
carboxamide (1a and 2a, resp.). A mixture of 2.61 g (10.0 mmol) [Cu(acac)2] and 236.0 g (97.0%,
1.656 mmol) of 6a was heated to 958 before 100.0 g (90%, 0.79 mol) ethyl diazoacetate were added during
5.5 h maintaining the same temp. After further stirring for 1 h at 958, the mixture was cooled and filtered
over a plug of Celiteꢂ. After distillation (78–1008/2 mbar), 85.5 g of the corresponding esters, 7a (41.8%),
8a (29.2%), and 9a (15.5%), were obtained, and they were dissolved in 100 ml of HCOOH.
Subsequently, 28.3 g (30%, 0.25 mol) of aq. H2O2 were slowly added over a period of 2 h keeping the
temp. at 70–808. After the addition, the mixture was stirred for 2 h, before a mixture of HCOOH and
H2O was removed by distillation. The residue was suspended in 200 ml (15%, 0.75 mol) of NaOH, and
the mixture was stirred at r.t. for additional 6 h. After addition of 100 ml of H2O, the aq. phase was
washed with tBuOMe, before it was adjusted to pH 1 by addition of 2m H2SO4 and extracted AcOEt (2ꢂ
100 ml). The combined org. phases were washed with H2O, dried (Na2SO4), and, after evaporation, the
crude mixture was further purified via column chromatography (CC; hexane/tBuOMe 3 :1). The
resulting 44.0 g and a cat. amount of NMFA were dissolved in 150 ml of CH2Cl2 at r.t., before 19.9 ml
(235.2 mmol) (COCl)2 were added during 2 h. After the mixture was subsequently heated under reflux
for 1 additional h, the solvent was removed, and the residue was dissolved in 50 ml of THF. This soln. was
slowly added to a mixture of 56.8 ml (41%, 672.5 mmol) of MeNH2, 100 ml of H2O, and 300 ml of THF,
maintaining the temp. below 258. Subsequently, the mixture was stirred for 30 min at r.t. and additional
30 min under reflux, before 900 ml of H2O were added to the hot mixture to effect the complete
precipitation of 1a and 2a. The suspension was cooled to r.t., and the products were filtered off, washed
extensively with H2O, and dried at 758 in a vacuum oven to yield 30.9 g (58.0% 1a, 37.8% 2a; 141.4 mmol)
of an off-white solid which corresponded to an overall yield of 18% (based on ethyl diazoacetate) over
five steps.
Fractional Crystallization. The mixture 1a/2a was dissolved in 1000 ml of acetone under reflux, and
the unsolved material was removed by hot filtration. While slowly cooling to r.t., 1a started to precipitate,
was filtered off after 20 min, and dried to furnish 8.9 g (42.5 mmol) of a colorless solid with a
diastereoselectivity of ꢁ93% and a yield of 48% based on the available amount of the relevant
diastereoisomer 1a. The mother liquor was concentrated at 508 to 600 ml and, after cooling to r.t., 2a
started to precipitate. After filtration and drying, 4.4 g (21.0 mmol) of a colorless solid with a
diastereoselectivity of ꢁ93% and a yield of 37% based on the available amount of the relevant
diastereoisomer 2a could be achieved.
Compound 1a (ꢁ 93% de). M.p. 201.28. [a]2D3 ¼ þ37.0 (c¼1.0, EtOH). 1H-NMR (400 MHz, CDCl3):
0.56 (tdd, J¼13.5, 11.5, 1.9, 1 H); 0.79 (m, 1 H); 0.91 (d, J¼6.7, 3 H); 0.93 (d, J¼6.7, 3 H); 1.02 (t, J¼4.5,

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CHEMISTRY & BIODIVERSITY – Vol. 11 (2014)
1 H); 1.08 (d, J¼6.7, 3 H); 1.31 (ddd, J¼9.3, 4.1, 1.8, 1 H); 1.37 (dsept., J¼7.9, 6.7, 1 H); 1.40–1.58 (m,
3 H); 1.57–1.67 (m, 2 H); 2.28 (d, J¼4.9, 3 H); 5.48 (s, 1 H). 13C-NMR (100 MHz, CDCl3): 20.5 (Me);
20.7 (Me); 23.4 (Me); 24.8 (CH2); 25.5 (CH); 26.0 (CH); 26.5 (Me); 27.5 (CH); 30.4 (CH); 32.7 (CH2);
.
33.6 (CH); 39.9 (CH); 174.2 (C¼O). GC/EI-MS: 209 (5, Mþ ), 166 (100), 136 (40), 124 (73), 113 (45),
.
109 (66), 81 (36), 74 (42), 73 (84), 67 (47), 58 (55). HR-MS: 209.1785 (Mþ , C13H23NOþ ; calc. 209.1780).
Compound 2a (ꢁ 93% de). M.p. 156.88. [a]2D3 ¼ þ63.4 (c¼1.0, EtOH). 1H-NMR (400 MHz, CDCl3):
0.52 (tdd, J¼13.4, 11.9, 2.2, 1 H); 0.90 (m, 1 H); 0.91 (d, J¼6.8, 3 H); 0.93 (d, J¼6.8, 3 H); 0.96 (d, J¼
6.6, 3 H); 0.99 (t, J¼4.4, 1 H); 1.24 (dtd, J¼12.6, 5.4, 2.1, 1 H); 1.36–1.54 (m, 3 H); 1.58 (dt, J¼9.3, 5.2,
4.4, 1 H); 1.66 (dsept., J¼6.8, 5.4, 1 H); 1.90 (m, 1 H); 2.82 (d, J¼4.9, 3 H); 5.58 (s, 1 H). 13C-NMR
(100 MHz, CDCl3): 19.3 (Me); 19.9 (Me); 21.4 (Me); 25.27 (CH); 25.29 (CH); 26.2 (CH2); 26.5 (Me);
.
28.3 (CH); 28.81 (CH2); 28.82 (CH); 33.3 (CH); 41.9 (CH); 174.4 (C¼O). GC/EI-MS: 209 (11, Mþ ), 166
(100), 136 (15), 124 (70), 109 (29), 95 (24), 93 (15), 81 (31), 73 (39), 67 (19), 58 (28). HR-MS: 209.1771
.
(Mþ , C13H23NOþ ; calc. 209.1780).
(1R,2S,5R,6S,7S)- and (1S,2S,5R,6R,7R)-N,2-Dimethyl-5-(1-methylethyl)bicyclo[4.1.0]heptane-7-
carboxamide (3a and 4a, resp.). A mixture of 2.60 g (8.4 mmol) [Cu(acac)2], 98.0 g (95.1%, 0.67 mol)
of 6b, and 100 ml of PhCl was heated up to 958, before 100.0 g (85%, 0.745 mol) ethyl diazoacetate were
added during 7 h maintaining the same temp. After further stirring for 1 h at 958, the mixture was cooled
and filtered over a plug of Celiteꢂ. After distillation (78–1008/2 mbar), 97.5 g of the corresponding esters
7b (41.8%), 8b (29.4%), and 9b (15.3%) were obtained and dissolved in 100 ml of HCOOH.
Subsequently, 28.3 g (30%, 0.25 mol) of aq. H2O2 were slowly added over a period of 2 h keeping the
temp. at 70–808. After the addition, the mixture was stirred for 2 h, before a mixture of HCOOH and
H2O was removed by distillation. The residue was suspended in 270 ml (15%, 1.0 mol) of NaOH and
stirred at r.t. for additional 6 h. After addition of 100 ml of H2O, the aq. phase was washed with tBuOMe
before being adjusted to pH 1 by the addition of 2m H2SO4 and extracted two times with tBuOMe. The
combined org. phases were washed with H2O, dried (Na2SO4), and, after evaporation, the crude mixture
was further purified via CC (hexane/tBuOMe 3 :1). The resulting 55.0 g and a cat. amount of NMFAwere
dissolved in 250 ml of CH2Cl2 at r.t., before 25.7 ml (0.3 mol) (COCl)2 were added during 1 h. After the
mixture was stirred for 1 h at r.t. and subsequently refluxed for 1 h, the solvent was removed, and the
residue was dissolved in 100 ml of acetone. This soln. was slowly added to a mixture of 76.0 ml (41%,
0.9 mol) of MeNH2, 350 ml of H2O, and 100 ml of acetone maintaining the temp. below 108.
Subsequently, the mixture was stirred for 1 h at r.t. and 1 h under reflux, before 200 ml of H2O were
added to the hot mixture to effect the complete precipitation of 3a and 4a. The suspension was cooled to
r.t., and the products were filtered off, washed extensively with H2O, and dried at 758 in a vacuum oven to
yield 36.2 g (56.4% 3a, 41.7% 4a; 169.6 mmol) of an off-white solid which corresponded to an overall
yield of 25% (based on 6b) over five steps.
Fractional Crystallization. The mixture 3a/4a was dissolved in 1200 ml of acetone under reflux,
unsolved material was removed by hot filtration, and the mixture was slowly cooled to r.t. Amide 3a
started to precipitate, was filtered off after 20 min, and dried to give 11.0 g (52.5 mmol) of a colorless
solid with a diastereoselectivity of ꢁ94% and a yield of 52% based on the available amount of the
relevant diastereoisomer 3a. The mother liquor was concentrated to dryness, and the residue was
recrystallized from H2O/EtOH 2 :1. After filtration and drying, 17.2 g (82.2 mmol) of a colorless solid
with a diastereoselectivity of ꢁ67% and a yield of 95% based on the available amount of the relevant
diastereoisomer 4a could be achieved.
Compound 3a (ꢁ 95% de). [a]2D3 ¼ ꢀ31.6 (c¼0.9, EtOH). The spectroscopic data corresponded to
those of 1a.
Compound 4a (ꢁ66% de). [a]2D3 ¼ ꢀ62.1 (c¼1.0, EtOH). The spectroscopic data corresponded to
those of enantiomer 2a.
(1S,2R,5S,6R,7R)-N-Ethyl-2-methyl-5-(1-methylethyl)bicyclo[4.1.0]heptane-7-carboxamide (1b).
According to GP A, 2.15 g (10.3 mmol) of 1a were reacted with 0.82 ml (70%, 10.2 mmol) of aq.
EtNH2. After crystallization from EtOH/H2O (2 :1), 1.46 g (6.5 mmol, 63%) of 1b were obtained as
colorless solid (ꢁ 99% de). M.p. 195.48. [a]2D3 ¼ þ31.4 (c¼1.0, EtOH). 1H-NMR (400 MHz, CDCl3): 0.56
(tdd, J¼13.4, 11.6, 1.9, 1 H); 0.79 (m, 1 H); 0.91 (d, J¼6.6, 3 H); 0.94 (d, J¼6.7, 3 H); 1.00 (t, J¼4.5,
1 H); 1.09 (d, J¼6.7, 3 H); 1.14 (t, J¼7.3, 3 H); 1.31 (ddd, J¼9.2, 4.2, 1.9, 1 H); 1.37 (dsept., J¼7.9, 6.7,

CHEMISTRY & BIODIVERSITY – Vol. 11 (2014)
1793
1 H); 1.44–1.55 (m, 3 H); 1.57–1.64 (m, 2 H); 3.30 (dq, J¼7.3, 5.6, 2 H); 5.41 (s, 1 H). 13C-NMR
(100 MHz, CDCl3): 15.1 (Me); 20.5 (Me); 20.7 (Me); 23.4 (Me); 24.8 (CH2); 25.6 (CH); 26.1 (CH); 27.4
.
(CH); 30.4 (CH); 32.7 (CH2); 33.6 (CH); 34.5 (CH2); 39.9 (CH); 173.4 (C¼O). GC/EI-MS: 223 (7, Mþ ),
180 (78), 138 (52), 109 (58), 88 (39), 87 (100), 81 (28), 72 (45), 67 (33), 55 (28), 29 (33). HR-MS:
.
223.1935 (Mþ , C14H25NOþ ; calc. 223.1936).
(1R,2R,5S,6S,7S)-N-Ethyl-2-methyl-5-(1-methylethyl)bicyclo[4.1.0]heptane-7-carboxamide (2b).
According to GP B, 0.86 g (4.1 mmol) of 2a were reacted with 0.39 g (70%, 6.1 mmol) aq. EtNH2.
After crystallization from H2O/acetone (4 :5), 0.73 g (3.2 mmol, 80%) of 2b were obtained as colorless
solid (ꢁ 99% de). M.p. 1448. [a]2D3 ¼ þ54.9 (c¼1.0, EtOH). 1H-NMR (400 MHz, CDCl3): 0.52 (tdd, J¼
13.5, 11.9, 2.2, 1 H); 0.90 (m, 1 H); 0.91 (d, J¼6.8, 3 H); 0.93 (d, J¼6.8, 3 H); 0.95 (m, 1 H); 0.97 (d, J¼
6.5, 3 H); 1.15 (t, J¼7.3, 3 H); 1.25 (dtd, J¼12.7, 5.4, 2.1, 1 H); 1.35–1.54 (m, 3 H); 1.57 (m, 1 H); 1.66 (m,
1 H); 1.90 (m, 1 H); 3.18–3.42 (m, 2 H); 5.41 (s, 1 H). 13C-NMR (100 MHz, CDCl3): 14.9 (Me); 19.2
(Me); 19.9 (Me); 21.4 (Me); 25.2 (CH); 25.3 (CH); 26.1 (CH2); 28.2 (CH); 28.67 (CH); 28.74 (CH2);
.
33.2 (CH); 34.4 (CH2); 41.8 (CH); 173.6 (C¼O). GC/EI-MS: 223 (13, Mþ ), 180 (100), 138 (72), 109
.
(32), 95 (25), 88 (16), 87 (52), 81 (29), 72 (25), 67 (18), 55 (16). HR-MS: 223.1936 (Mþ , C14H25NOþ
;
calc. 223.1936).
(1R,2S,5R,6S,7S)-N-Ethyl-2-methyl-5-(1-methylethyl)bicyclo[4.1.0]heptane-7-carboxamide (3b).
According to GP B, 1.50 g (7.2 mmol) of 3a were reacted with 0.58 g (70%, 9.0 mmol) of aq. EtNH2.
After crystallization from H2O/acetone (5 :9), 0.97 g (4.3 mmol, 59%) of 3b could be obtained as
colorless solid (ꢁ 99% de). [a]2D3 ¼ ꢀ27.6 (c¼1.0, EtOH). The spectroscopic data corresponded to those
of 1b.
(1S,2S,5R,6R,7R)-N-Ethyl-2-methyl-5-(1-methylethyl)bicyclo[4.1.0]heptane-7-carboxamide (4b).
According to GP C, 1.67 g (8.0 mmol) of 4a were reacted with 0.84 g (70% in H2O, 13.0 mmol) of
EtNH2. After crystallization from EtOH/H2O 2 :5, 0.77 g (purity 97.8%; 3.4 mmol, 43%) of 4b could be
obtained as colorless solid (ꢁ66% de). [a]2D3 ¼ ꢀ38.2 (c¼1.1, EtOH). The spectroscopic data
corresponded to those of 2b.
(1S,2R,5S,6R,7R)-2-Methyl-N,5-bis(1-methylethyl)bicyclo[4.1.0]heptane-7-carboxamide (1c). Ac-
i
cording to GP A, 2.15 g (10.3 mmol) of 1a were reacted with 0.88 ml (10.2 mmol) of PrNH2. After
crystallization from EtOH/H2O (2 :1), 1.83 g (7.7 mmol, 75%) of 1c could be obtained as colorless solid
(ꢁ 99% de). M.p. 198.38. [a]2D3 ¼ þ30.2 (c¼1.0, EtOH). 1H-NMR (400 MHz, CDCl3): 0.55 (tdd, J¼13.4,
11.6, 1.8, 1 H); 0.79 (m, 1 H); 0.91 (d, J¼6.6, 3 H); 0.93 (d, J¼6.6, 3 H); 0.97 (t, J¼4.5, 1 H); 1.09 (d, J¼
6.7, 3 H); 1.14 (d, J¼6.5, 3 H); 1.16 (d, J¼6.5, 3 H); 1.31 (ddd, J¼9.2, 4.2, 2.0, 1 H); 1.36 (dsept., J¼7.9,
6.7, 1 H); 1.43–1.55 (m, 3 H); 1.56–1.65 (m, 2 H); 4.09 (dsept., J¼8.0, 6.6, 1 H); 5.26 (d, J¼7.0, 1 H).
13C-NMR (100 MHz, CDCl3): 20.5 (Me); 20.6 (Me); 22.9 (Me); 23.1 (Me); 23.4 (Me); 24.9 (CH2); 25.6
(CH); 26.1 (CH); 27.2 (CH); 30.4 (CH); 32.7 (CH2); 33.7 (CH); 39.9 (CH); 41.4 (CH); 172.6 (C¼O).
.
GC/EI-MS: 237 (12, Mþ ), 194 (84), 152 (55), 109 (55), 102 (34), 101 (100), 95 (34), 86 (45), 67 (30), 43
.
(65), 41 (30). HR-MS: 237.2076 (Mþ , C15H27NOþ ; calc. 237.2093).
(1R,2R,5S,6S,7S)-2-Methyl-N,5-bis(1-methylethyl)bicyclo[4.1.0]heptane-7-carboxamide (2c). Ac-
cording to GP B, 0.86 g (4.1 mmol) of 2a were reacted with 0.35 g (5.9 mmol) of iPrNH2. After
crystallization from H2O/acetone (1:10), 0.57 g (2.4 mmol, 59%) of 2c could be obtained as colorless
solid (ꢁ 98% de). M.p. 1608. [a]2D3 ¼ þ47.7 (c¼1.0, EtOH). 1H-NMR (400 MHz, CDCl3): 0.52 (tdd, J¼
13.6, 12.0, 2.0, 1 H); 0.84–0.95 (m, 2 H); 0.91 (d, J¼6.8, 3 H); 0.93 (d, J¼6.8, 3 H); 0.96 (d, J¼6.6, 3 H);
1.14 (d, J¼6.6, 3 H); 1.15 (d, J¼6.6, 3 H); 1.25 (m, 1 H); 1.34–1.45 (m, 2 H); 1.49 (m, 1 H); 1. 56 (m,
1 H); 1.67 (dsept., J¼6.7, 5.9, 1 H); 1.90 (m, 1 H); 4.07 (dsept., J¼8.0, 6.5, 1 H); 5.27 (d, J¼7.8, 1 H).
13C-NMR (100 MHz, CDCl3): 19.2 (Me); 19.9 (Me); 21.4 (Me); 23.0 (Me); 23.1 (Me); 25.3 (CH); 25.5
(CH); 26.1 (CH2); 28.3 (CH); 28.6 (CH); 28.8 (CH2); 33.3 (CH); 41.4 (CH); 41.9 (CH); 172.8 (C¼O).
.
GC/EI-MS: 237 (17, Mþ ), 194 (100), 152 (68), 109 (32), 101 (47), 95 (29), 86 (23), 81 (26), 55 (18), 43
.
(30), 41 (20). HR-MS: 237.2073 (Mþ , C15H27NOþ ; calc. 237.2093).
(1R,2S,5R,6S,7S)-2-Methyl-N,5-bis(1-methylethyl)bicyclo[4.1.0]heptane-7-carboxamide (3c). Ac-
cording to GP B, 1.50 g (7.2 mmol) of 3a were reacted with 0.53 g (9.0 mmol) of iPrNH2. After
crystallization from H2O/acetone 5 :11, 0.89 g (3.8 mmol, 53%) of 3c could be obtained as colorless solid
(ꢁ 99% de). [a]2D3 ¼ ꢀ20.0 (c¼1.0, EtOH). The spectroscopic data corresponded to those of 1c.

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CHEMISTRY & BIODIVERSITY – Vol. 11 (2014)
(1S,2S,5R,6R,7R)-2-Methyl-N,5-bis(1-methylethyl)bicyclo[4.1.0]heptane-7-carboxamide (4c). Ac-
i
cording to GP C, 1.67 g (8.0 mmol) of 4a were reacted with 0.77 g (13.0 mmol) of PrNH2. After
crystallization from EtOH/H2O (1:2), 0.61 g (purity 97.6%; 2.5 mmol, 31%) of 4c could be obtained as
colorless solid (ꢁ66% de). [a]2D3 ¼ ꢀ35.1 (c¼0.8, EtOH). The spectroscopic data corresponded to those
of enantiomer 2c.
(1S,2R,5S,6R,7R)-N-(2-Hydroxyethyl)-2-methyl-5-(1-methylethyl)bicyclo[4.1.0]heptane-7-carbox-
amide (1d). According to GP A, 2.15 g (10.3 mmol) of 1a were reacted with 0.61 ml (10.2 mmol) of
HOCH2CH2NH2. After crystallization from EtOH/H2O 4 :3, 1.35 g (5.6 mmol, 54%) of 1d were obtained
1
as colorless solid (ꢁ 99% de). M.p. 1948. [a]2D3 ¼ þ22.5 (c¼1.0, EtOH). H-NMR (400 MHz, CDCl3):
0.57 (tdd, J¼13.3, 11.6, 2.0, 1 H); 0.79 (m, 1 H); 0.92 (d, J¼6.6, 3 H); 0.94 (d, J¼6.7, 3 H); 1.08 (t, J¼4.5,
1 H); 1.09 (d, J¼6.7, 3 H); 1.33 (m, 1 H); 1.37 (m, J¼7.9, 6.7, 1 H); 1.44–1.57 (m, 3 H); 1.58–1.68 (m,
2 H); 2.83 (br. s, 1 H); 3.44 (m, 2 H); 3.73, (t, J¼4.4, 2 H); 5.98 (s, 1 H). 13C-NMR (100 MHz, CDCl3):
20.5 (Me); 20.7 (Me); 23.4 (Me); 24.7 (CH2); 25.8 (CH); 26.1 (CH); 27.9 (CH); 30.3 (CH); 32.6 (CH2);
.
33.6 (CH); 39.9 (CH); 42.9 (CH2); 63.1 (CH2); 172.6 (C¼O). GC/EI-MS: 239 (5, Mþ ), 196 (63), 154
.
(40), 135 (49), 109 (47), 103 (100), 95 (48), 85 (37), 81 (42), 67 (36), 55 (48). HR-MS: 239.1881 (Mþ
C14H25NOþ2 ; calc. 239.1885).
,
(1R,2R,5S,6S,7S)-N-(2-Hydroxyethyl)-2-methyl-5-(1-methylethyl)bicyclo[4.1.0]heptane-7-carbox-
amide (2d). According to GP B, 1.30 g (6.2 mmol) of 2a were reacted with 0.55 g (9.0 mmol) of
HOCH2CH2NH2. After crystallization from H2O/acetone 6 :2, 0.37 g (1.6 mmol, 26%) of 2d could be
1
obtained as colorless solid (ꢁ 99% de). M.p. 1348. [a]2D3 ¼ þ48.4 (c¼1.0, EtOH). H-NMR (400 MHz,
CDCl3): 0.53 (tdd, J¼13.0, 12.1, 2.2, 1 H); 0.90 (m, 1 H); 0.92 (d, J¼6.7, 3 H); 0.93 (d, J¼6.7, 3 H); 0.98
(d, J¼6.6, 3 H); 1.03 (t, J¼4.4, 1 H); 1.27 (m, 1 H); 1.46–1.49 (m, 2 H); 1.51 (m, 1 H); 1.60 (m, 1 H); 1.67
(dsept., J¼6.9, 5.7, 1 H); 1.91 (m, 1 H); 2.80 (br. s, 1 H); 3.43 (m, 2 H); 3.74 (t, J¼4.9, 2 H); 5.92 (s, 1 H).
13C-NMR (100 MHz, CDCl3): 19.2 (Me); 19.9 (Me); 21.4 (Me); 25.2 (CH); 25.8 (CH); 26.0 (CH2); 28.3
(CH); 28.7 (CH2); 29.3 (CH); 33.3 (CH); 41.8 (CH); 43.0 (CH2); 63.1 (CH2); 175.3 (C¼O). GC/EI-MS:
.
239 (14, Mþ ), 196 (100), 154 (68), 136 (35), 135 (38), 109 (36), 103 (46), 95 (48), 93 (32), 81 (42), 55
.
(30). HR-MS: 239.1887 (Mþ , C14H25NO2þ ; calc. 239.1885).
(1R,2S,5R,6S,7S)-N-(2-Hydroxyethyl)-2-methyl-5-(1-methylethyl)bicyclo[4.1.0]heptane-7-carbox-
amide (3d). According to GP B, 2.00 g (9.6 mmol) of 3a were reacted with 0.73 g (12.0 mmol) of
HOCH2CH2NH2. After crystallization from H2O/acetone 10 :11, 0.60 g (2.5 mmol, 26%) of ethanola-
mide 3d could be obtained as colorless solid (ꢁ 99% de). [a]2D3 ¼ ꢀ20.5 (c¼1.0, EtOH). The
spectroscopic data corresponded to those of 1d.
(1S,2S,5R,6R,7R)-N-(2-Hydroxyethyl)-2-methyl-5-(1-methylethyl)bicyclo[4.1.0]heptane-7-carbox-
amide (4d). According to GP C, 1.67 g (8.0 mmol) of 4a were reacted with 0.79 g (13.0 mmol) of
HOCH2CH2NH2. After crystallization from EtOH/H2O 1 :2, 0.75 g (purity 97.4%; 3.1 mmol, 39%) of
4d could be obtained as colorless solid (ꢁ62% de). [a]2D3 ¼ ꢀ37.5 (c¼0.8, EtOH). The spectroscopic
data corresponded to those of 2d.
(1S,2R,5S,6R,7R)-N-Cyclopropyl-2-methyl-5-(1-methylethyl)bicyclo[4.1.0]heptane-7-carboxamide
(1e). According to GP A, 2.15 g (10.3 mmol) of 1a were reacted with 0.71 ml (10.2 mmol) of
cyclopropylamine. After crystallization from EtOH/H2O 3 :1, 1.69 g (7.1 mmol, 69%) of 1e could be
1
obtained as colorless solid (ꢁ 99% de). M.p. 2278. [a]2D3 ¼ þ26.7 (c¼1.0, EtOH). H-NMR (400 MHz,
CDCl3): 0.43–0.66 (m, 3 H); 0.70–0.87 (m, 3 H); 0.90 (d, J¼6.6, 3 H); 0.93 (d, J¼6.7, 3 H); 1.08 (d, J¼
6.7, 3 H); 1.11 (m, 1 H); 1.27–1.42 (m, 2 H); 1.42–1.56 (m, 3 H); 1.56–1.66 (m, 2 H); 2.72 (dddd, J¼10.9,
7.0, 3.8, 3.0, 1 H); 5.66 (s, 1 H). 13C-NMR (100 MHz, CDCl3): 6.67 (CH2); 6.73 (CH2); 20.5 (Me); 20.7
(Me); 22.8 (CH); 23.4 (Me); 24.8 (CH2); 25.8 (CH); 25.9 (CH); 27.6 (CH); 30.4 (CH); 32.6 (CH2); 33.6
.
(CH); 39.9 (CH); 174.9 (C¼O). GC/EI-MS: 235 (18, Mþ ), 135 (56), 95 (100), 93 (79), 81 (59), 69 (29),
.
67 (24), 57 (27), 55 (47), 43 (29), 41 (36). HR-MS: 235.1925 (Mþ , C15H25NOþ ; calc. 235.1936).
(1R,2R,5S,6S,7S)-N-Cyclopropyl-2-methyl-5-(1-methylethyl)bicyclo[4.1.0]heptane-7-carboxamide
(2e). According to GP B, 0.86 g (4.1 mmol) of 2a were reacted with 0.34 g (6.0 mmol) cyclopropylamine.
After crystallization from H2O/acetone 4 :7, 0.48 g (2.0 mmol, 49%) of 2e could be obtained as colorless
solid (ꢁ 98% de). M.p. 1858. [a]2D3 ¼ þ46.9 (c¼1.0, EtOH). 1H-NMR (400 MHz, CDCl3): 0.43–0.59 (m,
3 H); 0.69–0.98 (m, 4 H); 0.91 (d, J¼6.7, 3 H); 0.93 (d, J¼6.8, 3 H); 0.95 (d, J¼6.6, 3 H); 1.23 (m, 1 H);
1.36–1.64 (m, 4 H); 1.66 (m, 1 H); 1.90 (m, 1 H); 2.72 (m, 1 H); 5.69 (s, 1 H). 13C-NMR (100 MHz,

CHEMISTRY & BIODIVERSITY – Vol. 11 (2014)
1795
CDCl3): 6.6 (CH2); 6.7 (CH2); 19.2 (Me); 19.9 (Me); 21.4 (Me); 22.8 (CH); 25.2 (CH); 25.6 (CH); 26.1
(CH2); 28.3 (CH); 28.8 (CH2); 29.0 (CH); 33.3 (CH); 41.9 (CH); 175.1 (C¼O). GC/EI-MS: 235 (35, Mþ
.
), 179 (51), 135 (56), 109 (28), 95 (100), 93 (67), 81 (54), 69 (30), 55 (41), 41 (28). HR-MS: 235.1934
.
(Mþ , C15H25NOþ ; calc. 235.1936).
(1R,2S,5R,6S,7S)-N-Cyclopropyl-2-methyl-5-(1-methylethyl)bicyclo[4.1.0]heptane-7-carboxamide
(3e). According to GP B, 1.50 g (7.2 mmol) of 3a were reacted with 0.51 g (9.0 mmol) of cyclopropyl-
amine. After crystallization from H2O/acetone 5 :11, 1.01 g (4.3 mmol, 60%) of 3e could be obtained as
colorless solid (ꢁ 99% de). [a]2D3 ¼ ꢀ22.5 (c¼1.0, EtOH). The spectroscopic data corresponded to those
of 1e.
(1S,2S,5R,6R,7R)-N-Cyclopropyl-2-methyl-5-(1-methylethyl)bicyclo[4.1.0]heptane-7-carboxamide
(4e). According to GP C, 1.67 g (8.0 mmol) of 4a were reacted with 0.77 g (13.0 mmol) of cyclopropyl-
amine. After crystallization from EtOH/H2O 1:2, 0.59 g (purity 97.5%; 2.5 mmol, 40%) of 4e could be
obtained as colorless solid (ꢁ63% de). [a]2D3 ¼ ꢀ38.1 (c¼0.8, EtOH). The spectroscopic data
corresponded to those of 2e.
(1S,2R,5S,6R,7R)-N-Cyclopentyl-2-methyl-5-(1-methylethyl)bicyclo[4.1.0]heptane-7-carboxamide
(1f). According to GP A, 2.15 g (10.3 mmol) of 1a were reacted with 1.01 ml (10.2 mmol) of
cyclopentylamine. After crystallization from EtOH/H2O 5 :2, 2.04 g (7.7 mmol, 75%) of 1f could be
1
obtained as colorless solid (ꢁ 99% de). M.p. 2008. [a]2D3 ¼ þ29.7 (c¼1.0, EtOH). H-NMR (400 MHz,
CDCl3): 0.55 (tdd, J¼13.4, 11.5, 1.8, 1 H); 0.79 (m, 1 H); 0.91 (d, J¼6.6, 3 H); 0.93 (d, J¼6.6, 3 H); 0.98
(t, J¼4.5, 1 H); 1.09 (d, J¼6.8, 3 H); 1.31 (m, 1 H); 1.34–1.42 (m, 3 H); 1.44–1.71 (m, 9 H); 1.99 (m,
2 H); 4.22 (m, 1 H); 5.42 (d, J¼7.1, 1 H ) . 13C-NMR (100 MHz, CDCl3): 20.5 (Me); 20.6 (Me); 23.4 (Me);
23.7 (CH2); 23.8 (CH2); 24.8 (CH2); 25.6 (CH); 26.1 (CH); 27.3 (CH); 30.4 (CH); 32.7 (CH2); 33.2
.
(CH2); 33.5 (CH2); 33.7 (CH); 39.9 (CH); 51.3 (CH); 173.1 (C¼O). GC/EI-MS: 263 (17, Mþ ), 220 (100),
.
178 (45), 127 (98), 109 (51), 95 (39), 69 (58), 67 (33), 60 (67), 55 (37), 41 (41). HR-MS: 263.2244 (Mþ
C17H29NOþ ; calc. 263.2249).
,
(1R,2R,5S,6S,7S)-N-Cyclopentyl-2-methyl-5-(1-methylethyl)bicyclo[4.1.0]heptane-7-carboxamide
(2f). According to GP B, 0.75 g (3.6 mmol) of 2a were reacted with 0.45 g (5.3 mmol) of cyclopentyl-
amine. After crystallization from H2O/acetone 4 :7, 0.67 g (2.5 mmol, 69%) of 2f could be obtained as
colorless solid (ꢁ 98% de). M.p. 1648. [a]D23 ¼ þ42.6 (c¼1.0, EtOH). 1H-NMR (400 MHz, CDCl3): 0.52
(tdd, J¼13.5, 11.9, 2.0, 1 H); 0.88 (m, 1 H); 0.91 (d, J¼6.8, 3 H); 0.93 (d, J¼6.8, 3 H); 0.93 (m, 1 H); 0.96
(d, J¼6.6, 3 H); 1.25 (m, 1 H); 1.31–1.45 (m, 3 H); 1.49 (m, 1 H); 1.53–1.72 (m, 7 H); 1.89 (m, 1 H); 1.99
(m, 2 H); 4.20 (m, 1 H); 5.49 (d, J¼7.1, 1 H ) . 13C-NMR (100 MHz, CDCl3): 19.2 (Me); 19.9 (Me); 21.4
(Me); 23.8 (2 CH2); 25.3 (CH); 25.5 (CH); 26.1 (CH2); 28.3 (CH); 28.7 (CH); 28.8 (CH2); 33.26 (CH);
.
33.33 (CH2); 33.4 (CH2); 41.9 (CH); 51.2 (CH); 173.2 (C¼O). GC/EI-MS: 263 (18, Mþ ), 220 (100), 178
.
(55), 127 (35), 109 (26), 95 (30), 81 (24), 69 (34), 67 (20), 55 (22), 41 (24). HR-MS: 263.2230 (Mþ
C17H29NOþ ; calc. 263.2249).
,
(1R,2S,5R,6S,7S)-N-Cyclopentyl-2-methyl-5-(1-methylethyl)bicyclo[4.1.0]heptane-7-carboxamide
(3f). According to GP B, 1.50 g (7.2 mmol) of 3a were reacted with 0.77 g (9.0 mmol) of cyclopentyl-
amine. After crystallization from H2O/acetone 5 :11, 1.12 g (4.3 mmol, 60%) of 3f could be obtained as
colorless solid (ꢁ 98% de). [a]2D3 ¼ ꢀ29.3 (c¼1.0, EtOH). The spectroscopic data corresponded to those
of 1f.
(1S,2S,5R,6R,7R)-N-Cyclopentyl-2-methyl-5-(1-methylethyl)bicyclo[4.1.0]heptane-7-carboxamide
(4f). According to GP C, 1.67 g (8.0 mmol) of 4a were reacted with 0.77 g (13.0 mmol) of cyclopentyl-
amine. After crystallization from EtOH/H2O 1:2, 0.40 g (1.5 mmol, 19%) of 4f could be obtained as
colorless solid (ꢁ66% de). [a]2D3 ¼ ꢀ40.4 (c¼0.8, EtOH). The spectroscopic data corresponded to those
of 2f.
(1S,2R,5S,6R,7R)-N-Cyclohexyl-2-methyl-5-(1-methylethyl)bicyclo[4.1.0]heptane-7-carboxamide
(1g). According to GP A, 2.15 g (10.3 mmol) of 1a were reacted with 1.17 ml (10.2 mmol) of
cyclohexylamine. After crystallization from EtOH/H2O 5 :2, 2.24 g (8.0 mmol, 78%) of 1c could be
1
obtained as colorless solid (ꢁ 99% de). M.p. 2208. [a]2D3 ¼ þ22.6 (c¼1.0, EtOH). H-NMR (400 MHz,
CDCl3): 0.55 (m, 1 H); 0.79 (m, 1 H); 0.91 (d, J¼6.6, 3 H); 0.93 (d, J¼6.6, 3 H); 0.98 (t, J¼4.5, 1 H); 1.09
(d, J¼6.8, 3 H); 1.05–1.21 (m, 3 H); 1.28–1.42 (m, 4 H); 1.45–1.74 (m, 8 H); 1.91 (m, 2 H); 3.77 (m,
1 H); 5.35 (d, J¼7.9, 1 H). 13C-NMR (100 MHz, CDCl3): 20.56 (Me); 20.58 (Me); 23.4 (Me); 24.87

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CHEMISTRY & BIODIVERSITY – Vol. 11 (2014)
(CH2); 24.91 (CH2); 25.0 (CH2); 25.6 (CH2); 25.6 (CH); 26.2 (CH); 27.2 (CH); 30.4 (CH); 32.7 (CH2);
.
33.4 (CH2); 33.6 (CH2); 33.7 (CH); 39.9 (CH); 48.2 (CH); 172.5 (C¼O). GC/EI-MS: 277 (20, Mþ ), 234
(100), 192 (37), 141 (88), 109 (45), 95 (38), 83 (48), 81 (31), 60 (66), 55 (69), 41 (32). HR-MS: 277.2403
.
(Mþ , C18H31NOþ ; calc. 277.2406).
(1R,2R,5S,6S,7S)-N-Cyclohexyl-2-methyl-5-(1-methylethyl)bicyclo[4.1.0]heptane-7-carboxamide
(2g). According to GP B, 0.75 g (3.6 mmol) of 2a were reacted with 0.52 g (5.3 mmol) of cyclohexyl-
amine. After crystallization from H2O/acetone 4 :7, 0.49 g (1.8 mmol, 50%) of 2g could be obtained as
colorless solid (ꢁ 98% de). M.p. 196.48. [a]2D3 ¼ þ41.9 (c¼1.0, EtOH). 1H-NMR (400 MHz, CDCl3): 0.52
(m, 1 H); 0.86–0.98 (m, 2 H); 0.91 (d, J¼6.7, 3 H); 0.93 (d, J¼6.7, 3 H); 0.96 (d, J¼6.6, 3 H); 1.06–1.28
(m, 3 H); 1.29–1.45 (m, 3 H); 1.45–1.75 (m, 8 H); 1.84–1.98 (m, 3 H); 3.75 (m, 1 H); 5.35 (d, J¼7.9,
1 H). 13C-NMR (100 MHz, CDCl3): 19.2 (Me); 19.9 (Me); 21.4 (Me); 25.0 (2 CH2); 25.3 (CH); 25.58
(CH); 25.62 (CH2); 26.1 (CH2); 28.3 (CH); 28.7 (CH); 28.9 (CH2); 33.3 (CH); 33.4 (CH2); 33.5 (CH2);
.
41.9 (CH); 48.2 (CH); 172.7 (C¼O). GC/EI-MS: 277 (21, Mþ ), 234 (100), 192 (48), 141 (32), 109 (24),
.
95 (30), 83 (24), 81 (24), 55 (34), 41 (19). HR-MS: 277.2405 (Mþ , C18H31NOþ ; calc. 277.2406).
(1R,2S,5R,6S,7S)-N-Cyclohexyl-2-methyl-5-(1-methylethyl)bicyclo[4.1.0]heptane-7-carboxamide
(3g). According to GP B, 1.50 g (7.2 mmol) of 3a were reacted with 0.89 g (9.0 mmol) of cyclohexyl-
amine. After crystallization from H2O/acetone 5 :15, 1.22 g (4.4 mmol, 61%) of 3g could be obtained as
colorless solid (ꢁ 98% de). [a]2D3 ¼ ꢀ18.9 (c¼1.0, EtOH). The spectroscopic data corresponded to those
of 1g.
(1S,2S,5R,6R,7R)-N-Cyclohexyl-2-methyl-5-(1-methylethyl)bicyclo[4.1.0]heptane-7-carboxamide
(4g). According to GP C, 1.67 g (8.0 mmol) of 4a were reacted with 0.77 g (13.0 mmol) of cyclohexyl-
amine. After crystallization from EtOH/H2O 1:2, 0.39 g (1.4 mmol, 18%) of 4g could be obtained as
colorless solid (ꢁ64% de). [a]2D3 ¼ ꢀ28.0 (c¼1.1, EtOH). The spectroscopic data corresponded to those
of 2g.
Sensory Analysis. Sensory tests were carried out with healthy and trained panelists without known
taste disorders. Panelists were fully informed about procedure and intention of the project and had given
written consent. They were advised not to swallow the samples, and samples were tested using the sip-
and-spit method. The samples were tested in sensory panel rooms under standardized conditions, and
they were given blind and randomized. For the preparation of the test solns., Vittelꢂ water was used. The
panelists had participated earlier at regular intervals in sensory work and were, therefore, familiar with
the techniques applied.
Pre-Evaluation. A number of 5–8 trained panelists received each compound in a dosage of 5 ppm in
a 0.5% salt and a 5.0% sugar soln., and was asked to describe the sample and give a qualitative statement
for the umami intensity. No additional reference (e.g., MSG) was presented during the session.
Ranking Test (ISO 8587:2006). A panel of 14–18 trained panelists received at least three samples
containing a 0.5% salt soln. plus 5 ppm of the corresponding test compounds. The panelist were asked to
rank the samples according to the descriptor umami. The rank sums were determined, and statistical
comparisons were made employing least significant difference (LSD) post hoc test, and the level of
significance for the mean rank was set to <10%. This test could be used to determine differences
between the samples, but not to quantify the degree of difference.
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Received March 13, 2014