Optically active juvenoids derived from 2-substituted cyclopentanol and their biological activity on Tenebrio molitor

Article abstract of DOI:10.1016/S0957-4166(98)00369-3

Optically active juvenoids 1c-4c were synthesised using chiral precursors prepared by biotransformation reactions of suitable substrates. Biological activity of these juvenoids on Tenebrio molitor is reported.

Full text of DOI:10.1016/S0957-4166(98)00369-3

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 9 (1998) 3657–3665
Optically active juvenoids derived from 2-substituted
cyclopentanol and their biological activity on Tenebrio molitor
Martin Rejzek,a Zdeneˇk Wimmer,a,∗ Marie Zarevúcka,a Jelena Kuldová,a David Šaman a and
Miroslav Vacek b
aInstitute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo námeˇstí 2,
166 10 Prague 6, Czech Republic
bInstitute of Chemical Technology, Technická 5, 160 28 Prague 6, Czech Republic
Received 27 July 1998; accepted 14 September 1998
Abstract
Optically active juvenoids 1c–4c were synthesised using chiral precursors prepared by biotransformation
reactions of suitable substrates. Biological activity of these juvenoids on Tenebrio molitor is reported. © 1998
Elsevier Science Ltd. All rights reserved.
1. Introduction
Although the mechanism of insect juvenile hormones (JH) reception has not been elucidated, it is
generally accepted that the receptor is chiral. Considerable differences in biological activity observed
for the optical isomers of compounds imitating the action of insect JH have been presented.1 This fact
implies that a chiral receptor system (and possibly more than one such site) is involved in the insect JH
response. It is supposed that the optically active centre of the juvenoid molecule takes a direct part in, or
is very close to the part of the molecule interacting with the receptor site.2
In our previous paper3 we reported on the biological activity of optically active juvenoids derived from
2-substituted cyclohexanol. The biological activity of these compounds was strongly influenced by the
spatial arrangement of the cyclohexane ring substituents. Moreover, in the case of the six-membered ring
it was shown that biological activity was much more strongly influenced by C(2) configuration (carbon
atom bearing the hydroxyl group) than by the C(1) one.
In this paper we wish to report on the preparation and biological activity of optically active juvenoids
1c–4c derived from 2-substituted cyclopentanol (Fig. 1).
∗
Corresponding author. Tel: 0420 2/201 83 281; fax: 0420 2/24 31 01 77; e-mail: wimmer@uochb.cas.cz
0957-4166/98/$ - see front matter © 1998 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(98)00369-3

3658
M. Rejzek et al. / Tetrahedron: Asymmetry 9 (1998) 3657–3665
Fig. 1.
2. Results and discussion
Biotransformation was chosen as a technique for the introduction of the chiral information. Substrates
5–7 (Fig. 2) used for the biotransformation were prepared (Scheme 1) from 2-(4-hydroxybenzyl)-1-
cyclopentanone.4 A sodium salt of this compound was treated with chloromethyl methyl ether5 in
benzene yielding the racemic substrate 5. The ketone 5 was reduced by LiAlH4 and a mixture of
corresponding isomeric alcohols 8 and 9 was separated on silica gel. An acetylation6 of the respective
isomeric alcohols 8 and 9 yielded the racemic substrates 6 or 7 respectively (Scheme 1).
Fig. 2.
An enzymatic reduction of the substrate 5 in aqueous media (Scheme 1, Tables 1 and 2) using
Saccharomyces cerevisiae7 yielded a mixture of diastereomeric alcohols 1b and 3b that were separated by
column chromatography on silica gel. The chemical yield was improved by dissolving the substrate with
a small amount of acetone. An enzymatic hydrolysis of 6 and 7 in aqueous media (Scheme 1, Tables 1
and 2) using porcine pancreatic lipase yielded stereoisomers 2b or 4b, respectively. Again, the solubility
of the substrates was improved by the addition of a small amount of acetone.
Absolute configuration of the biotransformation products 1b–4b was assigned8 using 1H and 19F NMR
(Table 3) spectra of the corresponding MTPA9–13 esters.
The enantiomeric excess of the alcohols 1b–4b was determined on the basis of HPLC data of the
corresponding MTPA esters (Tables 1 and 4). The MOM protecting group proved to be stable on the
HPLC columns. This fact simplified considerably the evaluation of a broad biotransformation screening
leading to a selection of optimal biocatalyst and reaction conditions.
Although CD spectra of 1b–4b and 1c–4c were measured, no Cotton effect was found. The analogous
six-membered compounds showed very tiny Cotton effects3 and probably their five-membered analogues

M. Rejzek et al. / Tetrahedron: Asymmetry 9 (1998) 3657–3665
3659
Scheme 1.
Table 1
Biotransformation of substrates 5–7
Table 2
Biotransformation conditions

3660
M. Rejzek et al. / Tetrahedron: Asymmetry 9 (1998) 3657–3665
Table 3
1H and 19F NMR data of MTPA esters derived from 1b–4b and the assignment of absolute configura-
tion
Table 4
MTPA esters of alcohols 1b–4b, HPLC data
show only immeasurable values. Specific rotations of compounds 1b–4b and 1c–4c are summarised in
Table 5.
For the following synthesis of the target optically active juvenoids 1c–4c, chiral precursors 1a–4a
prepared by deprotection of 1b–4b were used. The chiral precursors 1a–4a defined by their as-
signed absolute configuration and enantiomeric excess were alkylated14 (Scheme 2) using ethyl N-(2-
bromoethyl)carbamate15 in the presence of dry powdered potassium carbonate in refluxing 2-butanone.
Table 5
Specific rotation of alcohols 1b–4b and 1c–4c

M. Rejzek et al. / Tetrahedron: Asymmetry 9 (1998) 3657–3665
3661
Scheme 2.
The optically active juvenoids 1c–4c were obtained in chemical yields exceeding 87% (when using
acetone as a solvent the yields were much lower). The absolute configuration of the asymmetric carbon
atoms of the juvenoids 1c–4c corresponds to that of the starting chiral precursors 1a–4a. It should be
pointed out that according to the IUPAC nomenclature system, the numbering of the saturated ring of the
juvenoids 1c–4c differs from that of compounds 1a–4a. This is due to the side chain directive carbamate
moiety of the compounds 1c–4c (Scheme 2). Analogously to our previous work3 we assume that both
the deprotection of 1b–4b and the alkylation of the chiral phenolic precursors 1a–4a did not influence
any of the asymmetric carbon atoms, and it is to be expected that the reaction proceeds with retention of
both absolute configuration and enantiomeric excess. Moreover, retention of the absolute configuration
was confirmed by specific rotation (Table 5) of the juvenoids 1c–4c. To summarise, the optically active
juvenoids 1c–4c defined by their assigned absolute configuration of the asymmetric carbon atoms and by
their enantiomeric excess were prepared.
The biological assay of compounds 1c–4c and the respective racemates (Table 6) was performed by
a standard method described by Sláma et al.16 The compounds were applied topically on the ventral
body part of freshly moulted pupae of the yellow mealworm (Tenebrio molitor). The yellow mealworm
proved to be a suitable species for a fast and sensitive screening bioassay of compounds showing the
juvenilising activity. Biological activity is given in ID50 values (an inhibitory dose) that gives a dose of
an active compound causing changes of 50% of observed morphological features. In other words, the
less the ID50 value, the better the activity. For comparison, the biological activity of racemic mixtures
of 1c and 2c (cis-1,2-relative configuration) or 3c and 4c (trans-1,2-relative configuration), respectively,
prepared earlier,17 was used.
Table 6
Biological activity of optically active juvenoids 1c–4c in comparison with the racemic forms
Results of the bioassays are summarised in Table 6. The (1R,2S)-stereoisomer 3c generally shows the

3662
M. Rejzek et al. / Tetrahedron: Asymmetry 9 (1998) 3657–3665
best activity when compared with the other stereoisomers 1c, 2c, 4c, and the racemic compounds 1c/2c
and 3c/4c. The differences in biological activity of the respective stereoisomers 1c–4c show clearly that
the cyclopentane ring (the spatial arrangement of its substituents on C(1) and C(2), respectively) plays a
role in molecular recognition in the interaction of these juvenoids with the receptor site(s). The receptor
decides clearly in favour of juvenoids 1c and 3c with the (S)-absolute configuration of C(2). On the other
hand, the absolute configuration of C(1) seems to influence the biological activity (Table 6) much less,
a phenomenon which also occurs in the case of the cyclohexane analogues.3 To conclude, even though
we did not work with optically pure compounds (ee of compounds 1c–4c was in the range 90–>99%),
we have found considerable differences in biological activity of the particular stereoisomers 1c–4c. (S)-
Absolute configuration of C(2) is essential for high biological activity, whereas the configuration of
carbon atom C(1) does not influence biological activity of these compounds decidedly.
3. Experimental
The 1H NMR spectra were recorded on a Varian UNITY-200 spectrometer at 200.06 MHz frequency
in deuteriochloroform, using tetramethylsilane as an internal reference. The 13C NMR spectra were
recorded on a Varian UNITY-500 spectrometer at 125.7 MHz frequency in deuteriochloroform, using the
central line of the solvent as an internal reference (δ=77.0 ppm). The 19F NMR spectra were recorded
on a Varian UNITY-200 spectrometer at 188.15 MHz in deuteriochloroform, with a capillary containing
hexafluorobenzene as an external reference (δ=−162.9 ppm), unless stated otherwise. The IR spectra
were recorded on a Perkin–Elmer 580 instrument in tetrachloromethane, unless stated otherwise. HPLC
analyses were carried out on a Knauer instrument. Detection was carried out at 220, 230, 240, 265 nm
wavelength by means of an ultraviolet deuterium lamp; integration was carried out at 220 nm. A column
250×4 (i.d.) mm, filled with Separon SGX (particle size 7 mm) as stationary phase, was used for the
analysis. Light petroleum (40–68°C fraction) with 3% ether was used as mobile phase, flow rate 1.4 (cis)
or 1.2 (trans samples) ml min−1, respectively. Column chromatography was carried out on silica gel
(Gebr. Herrman, Köln–Ehrenfeld). Optical rotations were measured on a Perkin–Elmer 241 polarimeter.
The CD spectra were obtained from a Jobin Yvon Mark V instrument in methanol. Microanalyses were
performed using a Perkin–Elmer 240 C elemental analyser.
3.1. 2-(4-Methoxymethoxybenzyl)-1-cyclopentanone, 5
To a stirred suspension of NaH (3.94 g, 81.8 mmol, 50% disp. in mineral oil) in dry benzene (50 ml), a
solution of 2-(4-hydroxybenzyl)-1-cyclopentanone (22.0 g, 0.126 mol) in dry benzene (50 ml) was added
under Ar, and the mixture was refluxed for 1 h. The mixture was cooled to 0°C and chloromethyl methyl
ether (30.64 g, 0.379 mmol) was added. The mixture was stirred for 9 h at 0°C. Water (50 ml) was added
and the mixture was extracted with diethyl ether (3×100 ml), washed with NaOH/H2O 5% solution (50
ml), with water (2×100 ml), and the organic layer was dried over MgSO4. The volatiles were evaporated
in vacuo and the residue (475 mg) was purified by column chromatography on silica gel (100 g) to yield
pure 5 (12.4 g, 41.9%). IR: 2959, 2933, 1742, 1712, 1511, 1236, 1200, 1176, 1154, 1081, 1017, 1012,
925 cm−1; 1H NMR: δ 7.08 (m, 2H), 6.95 (m, 2H), 5.15 (s, 2H), 3.47 (s, 3H), 3.07 (dd, J=13.9, 4.2, 1H),
2.51 (dd, J=13.9, 9.3, 1H), 2.34–2.08 (m, 2H), 2.32–1.51 (m, 7H); 13C NMR: δ 220.2 (C-1), 51.1 (C-2),
29.1 (C-3), 20.5 (C-4), 38.2 (C-5), 34.8 (C-6), 133.4 (C-7), 129.9 (C-8,80), 116.3 (C-9,90), 155.7 (C-10),
94.6 (C-11), 55.9 (C-12); MS: m/z 234 (M+, 35), 151 (30), 121 (29), 107 (5), 81 (3), 77 (3), 55 (3), 45
(100). Anal. calcd for C14H18O3 (234.28): C, 71.82; H, 7.74. Found: C, 71.87; H, 7.77.

M. Rejzek et al. / Tetrahedron: Asymmetry 9 (1998) 3657–3665
3663
3.2. cis- and trans-2-(4-Methoxymethoxybenzyl)-1-cyclopentanol, 8 and 9
To a cooled (0°C) and stirred suspension of LiAlH4 (2.66 g, 70.96 mmol) in dry diethyl ether (100
ml) ketone 5 (8.31 g, 35.48 mmol) in dry diethyl ether (100 ml) was added dropwise. After 7 h of
stirring, potassium sodium tartrate tetrahydrate 25% aq. solution (10.8 ml) was added. The mixture was
extracted with diethyl ether (4×100 ml), the combined organic extracts were dried over MgSO4 and the
solvent was evaporated in vacuo. The crude mixture of isomeric alcohols (9 g) was separated by column
chromatography on silica gel (100 g) to give 1.35 g (16.1%) of pure 8 and 4.20 g (50.0%) of pure 9.
1
8: IR: 2957, 2934, 1511, 1232, 1198, 1175, 1154, 1081, 1018, 1013, 924 cm−1; H NMR: δ 7.14 (m,
2H), 6.96 (m, 2H), 5.15 (s, 2H), 4.08 (dt, J=2×1.5, 4.4, 1H), 3.48 (s, 3H), 2.75 (dd, J=13.8, 7.8, 1H),
2.63 (dd, J=13.8, 7.8, 1H), 1.97 (m, 1H), 1.88–1.44 (m, 6H); 13C NMR: δ 74.4 (C-1), 34.9 (C-2), 28.7
(C-3), 21.8 (C-4), 34.6 (C-5), 47.7 (C-6), 135.3 (C-7), 129.6 (C-8,80), 116.2 (C-9,90), 155.4 (C-10), 94.6
(C-11), 55.9 (C-12); MS: m/z 236 (M+, 22), 218 (10), 188 (13), 151 (14), 121 (20), 107 (10), 91 (6), 77
(5), 45 (100). Anal. calcd for C14H20O3 (236.30): C, 71.16; H, 8.53. Found: C, 71.12; H, 8.51. 9: IR:
2956, 2931, 2898, 1233, 1511, 1233, 1199, 1176, 1154, 1081, 1018, 1012, 924 cm−1; 1H NMR: δ 7.11
(m, 2H), 6.96 (m, 2H), 5.15 (s, 2H), 3.90 (dt, J=2×5.6, 6.8, 1H), 3.48 (s, 3H), 2.69 (dd, J=13.7, 6.8, 1H),
2.49 (dd, J=13.7, 8.3, 1H), 1.99 (m, 1H), 1.88–1.20 (m, 6H); 13C NMR: δ 78.5 (C-1), 38.9 (C-2), 29.8
(C-3), 21.5 (C-4), 34.2 (C-5), 50.0 (C-6), 134.5 (C-7), 129.7 (C-8,80), 116.3 (C-9,90), 155.5 (C-10), 94.6
(C-11), 55.9 (C-12); MS: m/z 236 (M+, 34), 218 (2), 206 (2), 188 (3), 174 (4), 151 (14), 121 (30), 107
(18), 91 (5), 77 (4), 45 (100). Anal. calcd for C14H20O3 (236.30): C, 71.16; H, 8.53. Found: C, 71.12; H,
8.50.
3.3. cis- and trans-2-(4-Methoxymethoxybenzyl)-1-acetoxycyclopentane, 6 and 7
To a stirred mixture of the cis-alcohol 8 (0.438 g, 1.9 mmol) and 4-dimethylaminopyridine (1.2 mg,
0.01 mmol) in dry triethylamine (14 ml), acetic anhydride (0.272 ml, 2.88 mmol) was added through a
septum in portions and at room temperature. After 5 h of stirring, the reaction mixture was poured into a
cooled saturated potassium bicarbonate solution (6 ml). The mixture was extracted with light petroleum
(3×20 ml), the combined organic extracts were dried over potassium carbonate and the solvents were
evaporated under reduced pressure. The crude product (0.6 g) was purified by column chromatography
on silica gel (50 g) affording the pure acetate 6 (0.410 g, 78.8%). IR: 2956, 2933, 2897, 2875, 1736, 1612,
1511, 1450, 1441, 1373, 1311, 1239, 1199, 1176, 1154, 1081, 1032, 1017, 1012, 924 cm−1; 1H NMR: δ
7.05 (m, 2H), 6.94 (m, 2H), 5.14 (s, 2H), 5.08 (dt, J=1.9, 2×5.1, 1H), 3.47 (s, 3H), 2.75 (dd, J=6.8, 13.7,
1H), 2.52 (dd, J=8.6, 13.7, 1H), 2.09 (m, 1H), 2.07 (s, 3H), 1.95–1.44 (m, 6H); 13C NMR: δ 77.7 (C-1),
34.6 (C-2), 29.5 (C-3), 21.9 (C-4), 32.4 (C-5), 46.3 (C-6), 134.8 (C-7), 129.5 (C-8,80), 116.2 (C-9,90),
155.4 (C-10), 94.6 (C-11), 55.9 (C-12), 170.8 (C-13), 21.3 (C-14); MS: m/z 278 (M+, 21), 218 (46), 188
(20), 151 (7), 121 (14), 107 (13), 45 (100). Anal. calcd for C16H22O4 (278.34): C, 69.04; H, 7.97. Found:
C, 69.01; H, 7.94. The same procedure was used for the preparation of trans-acetate 7 starting from the
corresponding alcohol 9 (0.765 g, 3.24 mmol). The reaction yielded 7 (0.889 g, 98.7%). IR: 2957, 2933,
2897, 2877, 1734, 1613, 1511, 1442, 1376, 1363, 1254, 1199, 1176, 1154, 1081, 1018, 1012, 924 cm−1
;
1H NMR: δ 7.07 (m, 2H), 6.94 (m, 2H), 5.15 (s, 2H), 4.83 (ddd, J=4.4, 5.2, 7.32, 1H), 3.47 (s, 3H),
2.76 (dd, J=6.1, 13.8, 1H), 2.44 (dd, J=9.1, 13.8, 1H), 2.20 (m, 1H), 1.96 (s, 3H), 1.83–1.22 (m, 6H);
13C NMR: δ 80.6 (C-1), 38.4 (C-2), 29.5 (C-3), 22.1 (C-4), 31.6 (C-5), 46.9 (C-6), 134.1 (C-7), 129.8
(C-8,80), 116.1 (C-9,90), 155.5 (C-10), 94.6 (C-11), 55.9 (C-12), 171.0 (C-13), 21.2 (C-14); MS: m/z 278
(M+, 18), 218 (51), 188 (18), 151 (9), 121 (14), 107 (14), 45 (100). Anal. calcd for C16H22O4 (278.34):
C, 69.04; H, 7.97. Found: C, 69.03; H, 7.98.

3664
M. Rejzek et al. / Tetrahedron: Asymmetry 9 (1998) 3657–3665
3.4. cis-(1S,2S)-, cis-(1R,2R)-, trans-(1S,2R)- and trans-(1R,2S)-2-(4-Methoxymethoxybenzyl)-
1-cyclopentanol, 1b–4b
The optically active alcohols 1b–4b were obtained by biotransformation reactions of substrates 5–7.
The biotransformation reactions are described in Table 2 in detail. Specific rotation of the respective
alcohols 1b–4b are summarised in Table 5. Chemical yields of the biotransformations are summarised in
Table 1. IR, 1H NMR, 13C NMR spectra, MS and microanalyses of stereoisomers 1b and 2b or 3b and
4b were in good accord with data found for the racemic alcohols 8 or 9, respectively.
3.5. MTPA esters of alcohols 1b–4b
A general procedure used for the preparation of the MTPA esters in a milligram scale starting from
the chloride of MTPA has already been described in detail.16 The characterisation of the MTPA esters by
spectral data is summarised in Table 3. The HPLC determination of optical purity of the alcohols 1b–4b
using the corresponding MTPA esters is presented in Table 4.
3.6. (1S,2S)-cis-, (1R,2R)-cis-, (1R,2S)-trans- and (1S,2R)-trans-Ethyl N-{2-[4-(2-hydroxy-1-cyclo-
pentylmethyl)phenoxy]ethyl}carbamate, 1c–4c
After deprotection of 1b–4b by conc. HCl in a benzene:ethanol (1:1) solution, the respective chi-
ral precursor 1a–4a (0.6 mmol) defined by its assigned absolute configuration and optical purity
(Table 6) was dissolved in 2-butanone (15 ml). Dry powdered potassium carbonate (1 g) and ethyl
N-(2-bromoethyl)carbamate (1 g, 5.0 mmol) were added, and the mixture was refluxed for 16 h. The
mixture was cooled and filtered. The solid was washed with diethyl ether (30 ml) and the filtrate was
washed with water (10 ml) and dried over MgSO4. The volatiles were evaporated under reduced pressure
and the residue was purified by column chromatography on silica gel. The chromatography yielded the
compound 1c (99.1%), 2c (86.8%), 3c (91.6%) or 4c (89.4%). Specific rotations of 1c–4c are summarised
in Table 5. The following data are common for both 1c and 2c. IR (CCl4): 3617, 3465, 1728, 1521, 1244,
1112, 987 cm−1; 1H NMR: δ 7.14 (m, 2H), 6.81 (m, 2H), 5.12 (br. s, 1H), 4.13 (q, J=7.3, 2H), 4.07 (m,
1H), 4.01 (t, J=5.1, 2H), 3.57 (br. q, J=5.4, 1H), 2.79 (dd, J=7.8, 13.7, 1H), 2.61 (dd, J=7.6, 13.7, 1H),
1.62–1.38 (m, 7H), 1.24 (t, J=7.3, 3H); 13C NMR: δ 74.3 (C-1), 47.8 (C-2), 28.7 (C-3), 21.8 (C-4), 34.5
(C-5), 34.8 (C-6), 134.5 (C-7), 129.6 (C-8,80), 114.3 (C-9,90), 156.6 (C-10), 67.0 (C-11), 40.5 (C-12),
156.7 (C-13), 60.9 (C-14), 14.6 (C-15); MS: m/z 307 (M+, 10), 116 (100), 107 (16), 88 (44). Anal. calcd
for C17H25O4N (307.38): C, 66.42; H, 8.20; N, 4.56. Found for 1c: C, 66.39; H, 8.15; N, 4.49; and for
2c: C, 66.37; H, 8.22; N, 4.51. The following data are common for both 3c and 4c. IR (CCl4): 3611,
3470, 1731, 1523, 1249, 1112, 1071 cm−1; 1H NMR: δ 7.14 (m, 2H), 6.81 (m, 2H), 5.16 (bs, 1H), 4.12
(q, J=7.2, 2H), 4.01 (t, J=5.4, 2H), 3.88 (bq, J=3×6.9, 1H), 3.56 (br. q, J=5.3, 2H), 2.70 (dd, J=6.9,
13.7, 1H), 2.47 (dd, J=8.1, 13.7, 1H), 1.86–1.40 (m, 7H), 1.25 (t, J=7.2, 3H); 13C NMR: δ 78.4 (C-1),
49.9 (C-2), 29.7 (C-3), 21.4 (C-4), 34.2 (C-5), 38.8 (C-6), 133.7 (C-7), 129.8 (C-8,80), 114.4 (C-9,90),
156.7 (C-10), 67.0 (C-11), 40.5 (C-12), 156.7 (C-13), 60.9 (C-14), 14.6 (C-15); MS: m/z 307 (M+, 8),
116 (100), 107 (18), 88 (40). Anal. calcd for C17H25O4N (307.38): C, 66.42; H, 8.20; N, 4.56. Found for
3c: C, 66.38; H, 8.26; N, 4.57; and for 4c: C, 66.39; H, 8.22; N, 4.51.

M. Rejzek et al. / Tetrahedron: Asymmetry 9 (1998) 3657–3665
3665
Acknowledgements
Financial support from several sources is gratefully acknowledged: the Ministry of Education of the
Czech Republic (COST projects D10.10(D10/005/98) and D12.10) and the Grant Agency of the Czech
Republic (project 203/96/1617).
References
1. Henrick, C. A.; Anderson, R. J.; Staal, G. B.; Ludvik, G. F. J. Agric. Food Chem. 1978, 26, 542.
2. Wimmer, Z.; Romanˇuk, M. Collect. Czech. Chem. Commum. 1989, 54, 2302.
ˇ
3. Rejzek, M.; Wimmer Z.; Zarevúcka, M.; Šaman, D.; Pavlík, M.; Rícˇánková, M. Tetrahedron: Asymmetry 1994, 5, 1501.
4. Wimmer, Z.; Streinz, L.; Romanˇuk, M. Collect. Czech. Chem. Commun. 1985, 50, 2453.
5. Kluge, A. F.; Untch, K. G.; Fried, J. H. J. Am. Chem. Soc. 1972, 94, 7827.
6. Zarevúcka, M.; Rejzek, M.; Wimmer, Z.; Šaman, D.; Streinz, L. Tetrahedron 1993, 49, 5305.
7. Wimmer, Z.; Budeˇšínský, M.; Macek, T.; Svatoš, A.; Šaman, D.; Vašícˇková, S.; Romanˇuk, M. Collect. Czech. Chem.
Commun. 1987, 52, 2326.
8. Zarevúcka, M.; Rejzek, M.; Šaman, D.; Wimmer, Z.; Vaneˇk, T.; Zhao, Q.; Legoy M. D. Enantiomer 1996, 1, 227.
9. Rinaldi, P. L. Prog. Nucl. Magn. Reson. Spectrosc. 1982, 15, 291.
10. Dale, J. A.; Dull, D. L.; Mosher, H. S. J. Org. Chem. 1969, 34, 2543.
11. Dale, J. A.; Mosher, H. S. J. Am. Chem. Soc. 1973, 95, 512.
12. Sullivan, G. R.; Dale, J. A.; Mosher, H. S. J. Org. Chem. 1973, 38, 2143.
13. Dale, J. A.; Mosher, H. S. J. Org. Chem. 1970, 35, 4002.
14. Rejzek, M. Dissertation thesis, IOCHB Prague, 1994.
15. Rejzek, M.; Zarevúcka, M.; Wimmer, Z. Bioorg. Med. Chem. Lett. 1992, 2, 963.
16. Minamikawa, J.; Brossi, A. Tetrahedron Lett. 1978, 3085.
ˇ
17. Rejzek, M.; Wimmer, Z.; Šaman, D.; Rícˇánková, M. Helv. Chim. Acta 1994, 77, 1241.