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13C and 1H chemical shift assignments and conformation confirmation of trimedlure-Y via 2-D NMR
Spectrochimica Acta, Vol. 43A, No. 7, pp. 895-899, 1987.
0584-8539/87 $3.00 + 0.00 Pergamon Journals Ltd.
Printed in Great Britain.
13 C
and ~H chemical shift assignments and conformation confirmation of trimedlare-Y via 2-D NMR*
J. D. WARTHEN, JR,~" R. M. WATERS and T. P. McC-nDVERN United States Department of Agriculture, Agricultural Research Service, Agricultural Environmental Quality Institute, Insect Chemical Ecology Laboratory, Beltsville, Maryland 20705, U.S.A. (Received 11 September 1986; in final form 19 November 1986; accepted 4 December 1986)
Abstract--The conformation of 1,1-dimethylethyl 5-chloro-cis-2-methylcyclohexane-l-carboxylate (trimedlure-Y) was confirmed as 1,2,5 equatorial, axial, equatorial via taC, tH, APT, CSCM and COSY NMR analyses. The carbon and proton nuclei in trimedlure-Y and the previously unassigned eight cyclohexyl protons (1.50-2.60 ppm) in 1,1-dimethylethyl 5-chioro-trans-2-methylcyclohexane-l-carboxyiate (trimedlure-B~; 1,2,5equatorial, equatorial, equatorial) were also characterized by these methods. The effects of the 2-CH3 in the axial or equatorial conformation upon the chemical shifts of the other nuclei in the molecule are discussed.
Table 1. Conformation* of trans- and cis-trimedlure racemates [6, 9]
INTRODUCTION
Trimedlure (TM L), 1,1-dimethylethyl 4- and 5-chloro2-methylcyclohexane-l-carboxylate, is a potent synthetic attractant mixture which is used for detecting and monitoring infestations of the Mediterranean fruit fly (medfly), Ceratitis capitata (Wiedemann): this insect is a worldwide pest of fruits, nuts and vegetables [,1, 2]. Commercial T M L is prepared by a four-step procedure [-3] that results in 16 enantiomers, four pairs of which are trans racemates and four pairs of which are cis racemates (see Table 1). The trans and cis designations refer to the geometry of the vicinal carboxylic ester and methyl groups. The four t r a n s - T M L racemates, arbitrarily designated A, BI (structure in Fig. 1), B2 and C [-4], have a 1carboxyl-2-methyl diequatoriai conformation and make up 90--95 % of the commercial T M L mixture [5]. The four t r a n s - T M L racemates were isolated, and stereochemical and conformationai assignments were made by chemical and spectral analyses [-6]. The most biologically active racemate is T M L - C [,7], with the 1 S , 2 S , 4 R - T M L - C enantiomer being the more active [-8]. Structural assignments for three c i s - T M L racemates (designated V, W and X, with a 1-carboxyl-l-methyl axial-equatorial conformation) were made by discovering their epimeric relationships to t r a n s - T M L racemates of known conformation [-9, 10]. The stereochemistry of the other c i s - r a c e m a t e (TML-Y, structure in Figs 2 and 3) was also assigned by its relationship to TML-A; however, its conformation was postulated as the interconverted 1,2,5 equatorial, axial, equatorial form, to relieve 1,3-diaxial strain, rather than the one that would result from epimerization. This hypothesis was supported by the resistance of TML-Y to elimination of hydrogen chloride, * Mention of a commercial or proprietary product in this paper does not constitute a recommendation or endorsement of the product by the U.S. Department of Agriculture. fTo whom correspondence should be addressed.
TML racemates A Bt
B2 C V W X Y
1-CO2C(CH3)3:2-CH3 4 - 0 trans e:e* trans e:e trans e: e trans e: e cis a:e cis a:e cis a:e cis e:af
5-C1
---
a e
e a
---
-a e --
e --ef
*e = equatorial; a = axial. $Conformation postulated in [9]. compared with the other c i s - T M L racemates, and by i.r. absorption at 760 c m - t, which is characteristic of an equatorial C-CI stretching band [-9]. c i s - T M L , containing four racemates, is 14-26 % as attractive to medflies [-9] as t r a n s - T M L , containing four racemates; however, c i s - T M L makes up only 5--10% of the commercial T M L mixture [-5]. There is therefore a need for structure--activity relationship studies on each c i s - T M L racemate [,11] to determine whether one racemate has significantly higher attractiveness. The conformations of c/s-TML racemates were confirmed except for TML-Y [-9]. Thus, to confirm the postulated conformation of TML-Y [,9], we utilized two-dimensional (2-D) nuclear magnetic resonance (NMR) analyses of this c i s - r a c e m a t e and the TML-BI racemate, which differs from Y only by its equatorial 2CHs. EXPERIMENTAL
trans-TML was synthesized by the addition of hydrogen chloride to the double bond of trans-6-methyl-3-cyclohexene1-carboxylic acid followed by condensation with isobutylene [6]. TML-B t was then concentrated from the trans-TML mixture [6"]; followed by saponification, TML-Bt was recrystallized via its acid, regenerated as its t-butyl ester, and distilled [12]. The purity of TML-Bt was 97.4% by
895
896
J.D. WARTHENJR et al. Table 2. ~3CNMR and ~HNMR chemical shifts of trimedlure-Bl and -Y*
gas-liquid chromatographic analysis (GLC) [13]. cis-TML was prepared by the addition of hydrogen chloride to the double bond of methyl cis-6-methyl-3-cyclobexene-lcarboxylate and condensation with isobutylene [9]; TML-Y was separated from other cis isomers by repeated distillations for enrichment. The purity of TML-Y was 89.6 % by GLC analysis [13]. The NMR spectra were recorded with a General Electric QE-300 NMR spectrometer in the Fourier transform mode with a 5 mm dual tH/13C probe. All spectra were run in CDC13 solution (100 rag/0.4 ml) and chemical shifts were measured in ppm from TMS as an internal reference. ~H, ~3C, attached proton test (APT) [14], and a t Hlac proton decoupled chemical shift correlation map (CSCM) [15, 16] were obtained for TML-B~ and -Y. A correlation spectroscopy (COSY) [15-17] spectrum was obtained for TML-Y.
C-1 C-2 C-3 C-4 C-5 C-6 1-CO 1-CO2C_(CH3)3 1-CO2C(C_H3)a 2-C._H3 1-H 2-H 3-2H 4-2H 5-H 6-2H 1-CO2C(CH__3)3 2-CH__3
RESULTS AND DISCUSSION Our 13C N M R chemical shift assignments for C-2 and C-3 of TML-B1 are reversed from those previously reported [8]. However, the previously calculated chemical shifts [8] for these carbons agreed with our observed assignments. The A P T results in Fig. 1 clearly show the negative deflection of the odd C H of C-2 at 33.484 ppm and the positive deflection of the even CHz of C-3 at 34.004 ppm (see Table 2). The rest of the taC reported assignments [8] were confirmed by the A P T studies with negative deflections for the carbons with odd numbers of protons [C-5, C-l, 2-CH3, and 1CO2C(CH3)3], and with the positive deflections for the carbons with even numbers of protons (C-6 and C4). The quaternary I-COzC(CH3)3 and 1-CO in Table 2 were assigned in a separate ~3C survey. It is
!
TML-BI
TML-Y
52.206 33.484 34.004 36.944 58.141 39.927 173.746 80.746 28.186 19.638 1.935 (d,t) 1.675 (m) 1.780 (m) 2.175 (d,m) 3.798 (t,t) 2.310 (d,q) 1.449 (s) 0.889 (d) 0.911
46.989 28.797 32.167 31.050 58.910 32.766 172.555 80.373 28.089 13.020 2.444 2.320 1.651 1.931 3.781 2.172 1.445 0.912 0.936
(d,
(t,t) (d,q)
(s) (d)
*Chemical shifts in ppm downfieid from TMS. CDCI a solvent. (s = singlet; d = doublet; t = triplet; q = quartet; m = multiplet.) noted that the relative positions of the chemical shifts of even C H 2 are C-6 > C-4 > C-3 for TML-BI, which are the same as those [8] for T M L - A (differing from BI only by an axial chlorine); however, the relative position of the chemical shift of C-2 falls between C-6 and C-4 for A and less than C-3 for B t.
APT
~
~/C-5
cl-~,
CH~
" ,-r(-co,c(c.,), TML- B 1
C-1
CSCM -C-6 -C-4 -C-3 V",~ C _ 2
t 1-CO'CC~.H 3)3
1"CO2C(CH~)3
2-CH 3
IH
2-CHa
2-H
4-21~
3-2H
5-H o i i , ,
' 3 . 5
3.0
t)
(m) (m) (t)
I
2.5
'
'
'
'
I
2.0
'
'
'
'
I
l.S
'
'
'
'
I
'
1.0
Fig. 1. Iac, 1H, APT and CSCM NMR analyses of TML-Bt, 100 mg/0.4 ml CDCIa.
'
PPM
l aC and t H assignments of trimedlure-Y
By examining the COSY of TML-Y, one can see that the 5-H is coupled with 6-2H and 4-2H (see Fig. 3). The remaining unassigned 3-2H is thus assigned by elimination. Of 6-2H and 4-2H, the two-proton peak at the higher chemical shift could not be 4-2H becaase it is not correlated with 3-2H; therefore, 6-2H is at a higher chemical shift than 4-2H. It would be expected that 62H between 5-OH--el and I - C H - C O would be more deshielded and at a higher chemical shift than 4-2H which lies between 5-CH-CI and 3-CH2. The relative positions of the chemical shifts for the remaining unassigned carbons can then be assigned as C-6 > C-3 > C-4 > via CSCM in Fig. 2. Because of the number of contour levels necessary to reveal one-proton centers in the presence of the nine protons of the tbutyl group, some long-range coupling was observed in the COSY experiment between 1-H and 4-2H, 6-2H and 4-2H, and 6-2H and 1-CO2C(CH_j)3. The conformation of TML-Y as 1,2,5 equatorial, axial, equatorial is supported by: the resistance of this racemate to elimination of hydrogen chloride, compared with other cis-TML racemates [9]; the i.r. absorption at 760 c m - 1 characteristic of an equatorial C-CI stretching hand, opposed to 684-692 cm-1 for an axial C-Cl in TML-A and -C [9]; the chemical shift of 3.798ppm for an axial 5-H, opposed to a 4.40--4.45 ppm for an equatorial 5-H in TML-A and -C [6, 18]; the deshieided shift of the equatorial 2-H in the deshielding cone, compared to the axial 2-H outside the deshielding cone in TML-B t [18]; the upfield shift
As the chemical shifts for I-CO2C(CH_~)3, 2-C]_~t, and 5-H protons of TML-B1 had been assigned previously [6], we assigned chemical shifts for the remaining eight cyclohexyi protons (1.50-2.60 ppm) via CSCM (Fig. 1). The relative positions of the chemical shifts of these eight protons arc 6-2H > 4-2H > 1-H > 3-2H > 2-H (Table 2). The small proton signals at -,, 1.1 and ~ 3.5 ppm in Fig. 1 are due to small traces of ethanol in the sample. The assignments in Table 2 for the mcthylenic protons on carbons 3, 4 and 6 were made at the centers of the multiplets even though the axial and equatorial protons on each of those carbons were non-equivalent. It was not the aim of this work to distinguish axial and equatorial methylenic protons. The tH and 13CNMR assignments for TML-Y, postulated to differ from TM L-Br only by the conformation of the 2-CH3, were determined by 1H, 13C, APT, CSCM, and COSY NMR analyses (see Figs 2 and 3, Table 2). It is reasonable to conclude that the relative positions for the chemical shifts for negative deflections of carbons with odd numbers of protons in APT are C-5 > C-1 > C-2 > 1-CO2C(CH3) 3 > 2CH 3 by comparison with the APT for TML-B t. This evidence assigns the protons on these carbons via CSCM and leaves the remaining 6-2H, 4-2H and 3-2H unassigned. The quaternary 1-CO2C(CHa)3 and 1CO, in Table 2, were assigned in a separate t3C survey. The small proton signals at ... 1.1 and ~ 3.5 ppm in Fig. 2 are due to small traces of ethanol in the sample.
uc
897
APT CH=
OD.
TML-Y
C-S CSCM O
C-1
g.
C-6
_~.k...-C - 3 g. ~X'~1-CO,C~H 3)3
1 - Co,c(cH,)~ IH
v", I
2-CH~
m
n
3-,.
II
II
l
S-H
o
,a~ z-
2-CH~
[ , , , , 5.0
', 4.
,
,
,
[ 4.0
,
,
~_ ,
i
| 3.5
, ,
,
'
'
I 3.0
'
'
'
'
I 2.5
'
'
'
'
I 2.0
. . . .
I 1.5
'
'
'
'
I 1.0
'
'
'
'
I 0.5
Fig. 2. t3C, 1H, APT and CSCM NMR analyses of TML-Y, 100 mg/0.4 ml C D C ! 3.
' PPM
898
J.D. WAR'mENJR et al.
i-co~c(c.J~ CH3
cl.-~~co,c(c.,),
2-CH 3 6-2H
TML-Y
2-H
3-2H [ 4-2H
5-H I
' ' ' I ' '
4
--'
3
'
'
I '
'
1
o
m
i~:.~
J
i
0
II
Fig. 3. COSY of TML-Y, 100 mg/0.4 ml CDCI3.
of the axial 2-CH3 (not as deshielded), compared to the equatorial 2-CH3 of all four t r a n s - T M L racemates; an upfield shift of C-4 and C-6 due to y-gauche steric compression caused by the axial 2-CH3 [18-1, compared to TML-Bt; and an approximate J value of 3.37 for 2-H in a 1,2 axial, equatorial proton relationship with l-H, opposed to an approximate J value of 10.74 in TML-B~ for 2-H in a 1,2 axial, axial proton relationship with 1-H [18]. In addition to this evidence for the 1,2,5 equatorial, axial, equatorial conformation for TML-Y, we observed that TML-Y is the only racemate of the eight TML racemates that does not fall into a specific molecular polarity/conformation/configuration pattern when eluted from silicic acid [11-1. We also observed that changing an equatorial methyl or chlorine to the axial conformation, as from TML-B1 to TML-Y or TML-BI to TML-A [8-1, respectively, results in a shielded shift for carbons 1--4and 6, except for C-2 in the latter case. SUMMARY
The postulated conformation of TML-Y has been confirmed by tH, t3C, APT, CSCM and COSY NMR analyses as 1,2,5 equatorial, axial, equatorial. The carbon and proton nuclei for TML-Y have also been
assigned by these methods as have the previously unassigned eight cyclohexyl protons (1.50-2.60 ppm) in TML-B,. The effects of the axial 2-CH 3 in TML-Y upon the chemical shifts of other nuclei in this molecule in comparison to the effects of an equatorial 2-CH3 in TML-B1 upon its nuclei are discussed.
REFERENCES
[1] K. S. HAGEN,W. W. ALLENand R. L. TASSAN,Calif. Agr. 35, 5 (1981). [2] D. S. JACKSONandB. G. LEE,Bull. entomol. Soc. Am. 31, 29 (1985). [3] M. BEROZA, N. GREEN, S. 1. GERTLER, U F. STEINER and D. H. MIYASHITA,J. Agric. Food Chem. 9, 361 (1961). [4"] M. BEROZAand R. SARMIENTO,J. Ass. Off. Agr. Chem. 47, 838 (1964). [5"] R. T. CUNNINGHAM, B. A. LEONHARDT, T. P. McGoVERN and R. E. RICE, in preparation. [6"] T. P. MCGOVERN and M. BEROZA, J. org. Chem. 31, 1472 (1966). E7"] T. P. McGOVERN, M. BEROZA, g . OHINATA, D. MIYASHITAand L. F. STEINER,J. econ. Entomol. 59,
1450 (1966). [8] P. E. SONNET, T. P. McGOVERN and R. T. CUNNINGHAM,d. org. Chem. 49, 4639 (1984). [9] T. P. McGOVERN, R. T. CUNNINGHAMand B. A. LEONHARDT,J. econ. Entomol. 79, 98 (1986).
13C and 1H assignments of trimedlure-Y [10] B.A. LEONHARDT,T. P. McGOVERNand J. R. PLIMMER, J. High Resol. Chromatogr. Chromatogr. Commun. 5, 430 (1982). I l l ] J. D. WARTHEN, JR. and T. P. McGoVERN, in preparation. [12] T. P. McGoVERN, R. T. CUNNINGHAMand B. A. LEONHARDT,ill preparation. [13] B. A. LEONHARDT, T. P. McGovERN arid J. R. PLIMMER, J. High ResoL Chromatogr. Chromatogr. Commun, 5, 430 (1982).
899
[14] S. L. PATTand J. N. SHOOLERY,J. raagn. Resort. 46, 535 (1982). [15] R. BENNand H. GUNTHER,Angew. Chem. Int. Ed. Engl. 22, 350 (1983). [16] G. H. LEE, J. Agric. Food. Chem. 33, 499 (1985). [17] A. BAX, R. FREEMANand G. MORRIS,J. magn. Reson. 42, 164 (1981). [18] R. M. SILVERSTEIN,G. C. BASSLERand T. C. MORRILL, Spectrometric Identification of Organic Compounds, 4th edn, pp. 189, 206, 235, 261. Wiley, New York (1981).
0584-8539/87 $3.00 + 0.00 Pergamon Journals Ltd.
Printed in Great Britain.
13 C
and ~H chemical shift assignments and conformation confirmation of trimedlare-Y via 2-D NMR*
J. D. WARTHEN, JR,~" R. M. WATERS and T. P. McC-nDVERN United States Department of Agriculture, Agricultural Research Service, Agricultural Environmental Quality Institute, Insect Chemical Ecology Laboratory, Beltsville, Maryland 20705, U.S.A. (Received 11 September 1986; in final form 19 November 1986; accepted 4 December 1986)
Abstract--The conformation of 1,1-dimethylethyl 5-chloro-cis-2-methylcyclohexane-l-carboxylate (trimedlure-Y) was confirmed as 1,2,5 equatorial, axial, equatorial via taC, tH, APT, CSCM and COSY NMR analyses. The carbon and proton nuclei in trimedlure-Y and the previously unassigned eight cyclohexyl protons (1.50-2.60 ppm) in 1,1-dimethylethyl 5-chioro-trans-2-methylcyclohexane-l-carboxyiate (trimedlure-B~; 1,2,5equatorial, equatorial, equatorial) were also characterized by these methods. The effects of the 2-CH3 in the axial or equatorial conformation upon the chemical shifts of the other nuclei in the molecule are discussed.
Table 1. Conformation* of trans- and cis-trimedlure racemates [6, 9]
INTRODUCTION
Trimedlure (TM L), 1,1-dimethylethyl 4- and 5-chloro2-methylcyclohexane-l-carboxylate, is a potent synthetic attractant mixture which is used for detecting and monitoring infestations of the Mediterranean fruit fly (medfly), Ceratitis capitata (Wiedemann): this insect is a worldwide pest of fruits, nuts and vegetables [,1, 2]. Commercial T M L is prepared by a four-step procedure [-3] that results in 16 enantiomers, four pairs of which are trans racemates and four pairs of which are cis racemates (see Table 1). The trans and cis designations refer to the geometry of the vicinal carboxylic ester and methyl groups. The four t r a n s - T M L racemates, arbitrarily designated A, BI (structure in Fig. 1), B2 and C [-4], have a 1carboxyl-2-methyl diequatoriai conformation and make up 90--95 % of the commercial T M L mixture [5]. The four t r a n s - T M L racemates were isolated, and stereochemical and conformationai assignments were made by chemical and spectral analyses [-6]. The most biologically active racemate is T M L - C [,7], with the 1 S , 2 S , 4 R - T M L - C enantiomer being the more active [-8]. Structural assignments for three c i s - T M L racemates (designated V, W and X, with a 1-carboxyl-l-methyl axial-equatorial conformation) were made by discovering their epimeric relationships to t r a n s - T M L racemates of known conformation [-9, 10]. The stereochemistry of the other c i s - r a c e m a t e (TML-Y, structure in Figs 2 and 3) was also assigned by its relationship to TML-A; however, its conformation was postulated as the interconverted 1,2,5 equatorial, axial, equatorial form, to relieve 1,3-diaxial strain, rather than the one that would result from epimerization. This hypothesis was supported by the resistance of TML-Y to elimination of hydrogen chloride, * Mention of a commercial or proprietary product in this paper does not constitute a recommendation or endorsement of the product by the U.S. Department of Agriculture. fTo whom correspondence should be addressed.
TML racemates A Bt
B2 C V W X Y
1-CO2C(CH3)3:2-CH3 4 - 0 trans e:e* trans e:e trans e: e trans e: e cis a:e cis a:e cis a:e cis e:af
5-C1
---
a e
e a
---
-a e --
e --ef
*e = equatorial; a = axial. $Conformation postulated in [9]. compared with the other c i s - T M L racemates, and by i.r. absorption at 760 c m - t, which is characteristic of an equatorial C-CI stretching band [-9]. c i s - T M L , containing four racemates, is 14-26 % as attractive to medflies [-9] as t r a n s - T M L , containing four racemates; however, c i s - T M L makes up only 5--10% of the commercial T M L mixture [-5]. There is therefore a need for structure--activity relationship studies on each c i s - T M L racemate [,11] to determine whether one racemate has significantly higher attractiveness. The conformations of c/s-TML racemates were confirmed except for TML-Y [-9]. Thus, to confirm the postulated conformation of TML-Y [,9], we utilized two-dimensional (2-D) nuclear magnetic resonance (NMR) analyses of this c i s - r a c e m a t e and the TML-BI racemate, which differs from Y only by its equatorial 2CHs. EXPERIMENTAL
trans-TML was synthesized by the addition of hydrogen chloride to the double bond of trans-6-methyl-3-cyclohexene1-carboxylic acid followed by condensation with isobutylene [6]. TML-B t was then concentrated from the trans-TML mixture [6"]; followed by saponification, TML-Bt was recrystallized via its acid, regenerated as its t-butyl ester, and distilled [12]. The purity of TML-Bt was 97.4% by
895
896
J.D. WARTHENJR et al. Table 2. ~3CNMR and ~HNMR chemical shifts of trimedlure-Bl and -Y*
gas-liquid chromatographic analysis (GLC) [13]. cis-TML was prepared by the addition of hydrogen chloride to the double bond of methyl cis-6-methyl-3-cyclobexene-lcarboxylate and condensation with isobutylene [9]; TML-Y was separated from other cis isomers by repeated distillations for enrichment. The purity of TML-Y was 89.6 % by GLC analysis [13]. The NMR spectra were recorded with a General Electric QE-300 NMR spectrometer in the Fourier transform mode with a 5 mm dual tH/13C probe. All spectra were run in CDC13 solution (100 rag/0.4 ml) and chemical shifts were measured in ppm from TMS as an internal reference. ~H, ~3C, attached proton test (APT) [14], and a t Hlac proton decoupled chemical shift correlation map (CSCM) [15, 16] were obtained for TML-B~ and -Y. A correlation spectroscopy (COSY) [15-17] spectrum was obtained for TML-Y.
C-1 C-2 C-3 C-4 C-5 C-6 1-CO 1-CO2C_(CH3)3 1-CO2C(C_H3)a 2-C._H3 1-H 2-H 3-2H 4-2H 5-H 6-2H 1-CO2C(CH__3)3 2-CH__3
RESULTS AND DISCUSSION Our 13C N M R chemical shift assignments for C-2 and C-3 of TML-B1 are reversed from those previously reported [8]. However, the previously calculated chemical shifts [8] for these carbons agreed with our observed assignments. The A P T results in Fig. 1 clearly show the negative deflection of the odd C H of C-2 at 33.484 ppm and the positive deflection of the even CHz of C-3 at 34.004 ppm (see Table 2). The rest of the taC reported assignments [8] were confirmed by the A P T studies with negative deflections for the carbons with odd numbers of protons [C-5, C-l, 2-CH3, and 1CO2C(CH3)3], and with the positive deflections for the carbons with even numbers of protons (C-6 and C4). The quaternary I-COzC(CH3)3 and 1-CO in Table 2 were assigned in a separate ~3C survey. It is
!
TML-BI
TML-Y
52.206 33.484 34.004 36.944 58.141 39.927 173.746 80.746 28.186 19.638 1.935 (d,t) 1.675 (m) 1.780 (m) 2.175 (d,m) 3.798 (t,t) 2.310 (d,q) 1.449 (s) 0.889 (d) 0.911
46.989 28.797 32.167 31.050 58.910 32.766 172.555 80.373 28.089 13.020 2.444 2.320 1.651 1.931 3.781 2.172 1.445 0.912 0.936
(d,
(t,t) (d,q)
(s) (d)
*Chemical shifts in ppm downfieid from TMS. CDCI a solvent. (s = singlet; d = doublet; t = triplet; q = quartet; m = multiplet.) noted that the relative positions of the chemical shifts of even C H 2 are C-6 > C-4 > C-3 for TML-BI, which are the same as those [8] for T M L - A (differing from BI only by an axial chlorine); however, the relative position of the chemical shift of C-2 falls between C-6 and C-4 for A and less than C-3 for B t.
APT
~
~/C-5
cl-~,
CH~
" ,-r(-co,c(c.,), TML- B 1
C-1
CSCM -C-6 -C-4 -C-3 V",~ C _ 2
t 1-CO'CC~.H 3)3
1"CO2C(CH~)3
2-CH 3
IH
2-CHa
2-H
4-21~
3-2H
5-H o i i , ,
' 3 . 5
3.0
t)
(m) (m) (t)
I
2.5
'
'
'
'
I
2.0
'
'
'
'
I
l.S
'
'
'
'
I
'
1.0
Fig. 1. Iac, 1H, APT and CSCM NMR analyses of TML-Bt, 100 mg/0.4 ml CDCIa.
'
PPM
l aC and t H assignments of trimedlure-Y
By examining the COSY of TML-Y, one can see that the 5-H is coupled with 6-2H and 4-2H (see Fig. 3). The remaining unassigned 3-2H is thus assigned by elimination. Of 6-2H and 4-2H, the two-proton peak at the higher chemical shift could not be 4-2H becaase it is not correlated with 3-2H; therefore, 6-2H is at a higher chemical shift than 4-2H. It would be expected that 62H between 5-OH--el and I - C H - C O would be more deshielded and at a higher chemical shift than 4-2H which lies between 5-CH-CI and 3-CH2. The relative positions of the chemical shifts for the remaining unassigned carbons can then be assigned as C-6 > C-3 > C-4 > via CSCM in Fig. 2. Because of the number of contour levels necessary to reveal one-proton centers in the presence of the nine protons of the tbutyl group, some long-range coupling was observed in the COSY experiment between 1-H and 4-2H, 6-2H and 4-2H, and 6-2H and 1-CO2C(CH_j)3. The conformation of TML-Y as 1,2,5 equatorial, axial, equatorial is supported by: the resistance of this racemate to elimination of hydrogen chloride, compared with other cis-TML racemates [9]; the i.r. absorption at 760 c m - 1 characteristic of an equatorial C-CI stretching hand, opposed to 684-692 cm-1 for an axial C-Cl in TML-A and -C [9]; the chemical shift of 3.798ppm for an axial 5-H, opposed to a 4.40--4.45 ppm for an equatorial 5-H in TML-A and -C [6, 18]; the deshieided shift of the equatorial 2-H in the deshielding cone, compared to the axial 2-H outside the deshielding cone in TML-B t [18]; the upfield shift
As the chemical shifts for I-CO2C(CH_~)3, 2-C]_~t, and 5-H protons of TML-B1 had been assigned previously [6], we assigned chemical shifts for the remaining eight cyclohexyi protons (1.50-2.60 ppm) via CSCM (Fig. 1). The relative positions of the chemical shifts of these eight protons arc 6-2H > 4-2H > 1-H > 3-2H > 2-H (Table 2). The small proton signals at -,, 1.1 and ~ 3.5 ppm in Fig. 1 are due to small traces of ethanol in the sample. The assignments in Table 2 for the mcthylenic protons on carbons 3, 4 and 6 were made at the centers of the multiplets even though the axial and equatorial protons on each of those carbons were non-equivalent. It was not the aim of this work to distinguish axial and equatorial methylenic protons. The tH and 13CNMR assignments for TML-Y, postulated to differ from TM L-Br only by the conformation of the 2-CH3, were determined by 1H, 13C, APT, CSCM, and COSY NMR analyses (see Figs 2 and 3, Table 2). It is reasonable to conclude that the relative positions for the chemical shifts for negative deflections of carbons with odd numbers of protons in APT are C-5 > C-1 > C-2 > 1-CO2C(CH3) 3 > 2CH 3 by comparison with the APT for TML-B t. This evidence assigns the protons on these carbons via CSCM and leaves the remaining 6-2H, 4-2H and 3-2H unassigned. The quaternary 1-CO2C(CHa)3 and 1CO, in Table 2, were assigned in a separate t3C survey. The small proton signals at ... 1.1 and ~ 3.5 ppm in Fig. 2 are due to small traces of ethanol in the sample.
uc
897
APT CH=
OD.
TML-Y
C-S CSCM O
C-1
g.
C-6
_~.k...-C - 3 g. ~X'~1-CO,C~H 3)3
1 - Co,c(cH,)~ IH
v", I
2-CH~
m
n
3-,.
II
II
l
S-H
o
,a~ z-
2-CH~
[ , , , , 5.0
', 4.
,
,
,
[ 4.0
,
,
~_ ,
i
| 3.5
, ,
,
'
'
I 3.0
'
'
'
'
I 2.5
'
'
'
'
I 2.0
. . . .
I 1.5
'
'
'
'
I 1.0
'
'
'
'
I 0.5
Fig. 2. t3C, 1H, APT and CSCM NMR analyses of TML-Y, 100 mg/0.4 ml C D C ! 3.
' PPM
898
J.D. WAR'mENJR et al.
i-co~c(c.J~ CH3
cl.-~~co,c(c.,),
2-CH 3 6-2H
TML-Y
2-H
3-2H [ 4-2H
5-H I
' ' ' I ' '
4
--'
3
'
'
I '
'
1
o
m
i~:.~
J
i
0
II
Fig. 3. COSY of TML-Y, 100 mg/0.4 ml CDCI3.
of the axial 2-CH3 (not as deshielded), compared to the equatorial 2-CH3 of all four t r a n s - T M L racemates; an upfield shift of C-4 and C-6 due to y-gauche steric compression caused by the axial 2-CH3 [18-1, compared to TML-Bt; and an approximate J value of 3.37 for 2-H in a 1,2 axial, equatorial proton relationship with l-H, opposed to an approximate J value of 10.74 in TML-B~ for 2-H in a 1,2 axial, axial proton relationship with 1-H [18]. In addition to this evidence for the 1,2,5 equatorial, axial, equatorial conformation for TML-Y, we observed that TML-Y is the only racemate of the eight TML racemates that does not fall into a specific molecular polarity/conformation/configuration pattern when eluted from silicic acid [11-1. We also observed that changing an equatorial methyl or chlorine to the axial conformation, as from TML-B1 to TML-Y or TML-BI to TML-A [8-1, respectively, results in a shielded shift for carbons 1--4and 6, except for C-2 in the latter case. SUMMARY
The postulated conformation of TML-Y has been confirmed by tH, t3C, APT, CSCM and COSY NMR analyses as 1,2,5 equatorial, axial, equatorial. The carbon and proton nuclei for TML-Y have also been
assigned by these methods as have the previously unassigned eight cyclohexyl protons (1.50-2.60 ppm) in TML-B,. The effects of the axial 2-CH 3 in TML-Y upon the chemical shifts of other nuclei in this molecule in comparison to the effects of an equatorial 2-CH3 in TML-B1 upon its nuclei are discussed.
REFERENCES
[1] K. S. HAGEN,W. W. ALLENand R. L. TASSAN,Calif. Agr. 35, 5 (1981). [2] D. S. JACKSONandB. G. LEE,Bull. entomol. Soc. Am. 31, 29 (1985). [3] M. BEROZA, N. GREEN, S. 1. GERTLER, U F. STEINER and D. H. MIYASHITA,J. Agric. Food Chem. 9, 361 (1961). [4"] M. BEROZAand R. SARMIENTO,J. Ass. Off. Agr. Chem. 47, 838 (1964). [5"] R. T. CUNNINGHAM, B. A. LEONHARDT, T. P. McGoVERN and R. E. RICE, in preparation. [6"] T. P. MCGOVERN and M. BEROZA, J. org. Chem. 31, 1472 (1966). E7"] T. P. McGOVERN, M. BEROZA, g . OHINATA, D. MIYASHITAand L. F. STEINER,J. econ. Entomol. 59,
1450 (1966). [8] P. E. SONNET, T. P. McGOVERN and R. T. CUNNINGHAM,d. org. Chem. 49, 4639 (1984). [9] T. P. McGOVERN, R. T. CUNNINGHAMand B. A. LEONHARDT,J. econ. Entomol. 79, 98 (1986).
13C and 1H assignments of trimedlure-Y [10] B.A. LEONHARDT,T. P. McGOVERNand J. R. PLIMMER, J. High Resol. Chromatogr. Chromatogr. Commun. 5, 430 (1982). I l l ] J. D. WARTHEN, JR. and T. P. McGoVERN, in preparation. [12] T. P. McGoVERN, R. T. CUNNINGHAMand B. A. LEONHARDT,ill preparation. [13] B. A. LEONHARDT, T. P. McGovERN arid J. R. PLIMMER, J. High ResoL Chromatogr. Chromatogr. Commun, 5, 430 (1982).
899
[14] S. L. PATTand J. N. SHOOLERY,J. raagn. Resort. 46, 535 (1982). [15] R. BENNand H. GUNTHER,Angew. Chem. Int. Ed. Engl. 22, 350 (1983). [16] G. H. LEE, J. Agric. Food. Chem. 33, 499 (1985). [17] A. BAX, R. FREEMANand G. MORRIS,J. magn. Reson. 42, 164 (1981). [18] R. M. SILVERSTEIN,G. C. BASSLERand T. C. MORRILL, Spectrometric Identification of Organic Compounds, 4th edn, pp. 189, 206, 235, 261. Wiley, New York (1981).