organic compounds
(RSS)-[N-Hydroxyethyloxy]-hexafluoroVal–MeLeu–Ala tert-butyl ester
aDepartment of Chemistry and Biochemistry, University Bern, Freiestrasse 3, CH-3012 Bern, Switzerland, and bInstitute of Physics, University of Neuchâtel, rue Emile-Argand 11, CH-2009 Neuchâtel, Switzerland
*Correspondence e-mail: reinhart.keese@ioc.unibe.ch
The title compound [systematic name: (2S,5S,8R)-tert-butyl 8-(1,1,1,3,3,3-hexafluoropropan-2-yl)-12-hydroxy-5-isobutyl-2,6-dimethyl-4,7-dioxo-10-oxa-3,6,9-triazadodecanoate], C21H36F6N3O6, is a tripeptide crystallizing in the chiral orthorhombic spacegroup P212121. The (R) of the chiral center in the hexafluorovaline unit is based on the known stereochemistry of MeLeu and Ala (SS). The N-hydroxyethyloxy substituent of hexafluorovaline is positionally disordered [occupancy ratio 0.543 (9):0.457 (9)]. In the solid state structure there are N—H⋯F and N—H⋯O intramolecular hydrogen bonds supporting the coiled structure of this tripeptide with the three hydrophobic substituents on the outside.
Related literature
For biomolecules with fluoro substituents, see: Kirsch (2004); Mikol et al. (1997); Eberle et al. (1998); Zhang et al. (1998); Eberle & Keese (2009). For the tripeptide Val-MeLeu-Ala in cyclosporine, an undecapeptide, and the fact that it can be extracted and reintroduced in the remaining octapeptide, see: Eberle et al. (1994).
Experimental
Crystal data
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Data collection
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Refinement
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Data collection: EXPOSE in IPDS-I (Stoe & Cie, 2000); cell CELL in IPDS-I; data reduction: INTEGRATE in IPDS-I; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: SHELXL97.
Supporting information
https://doi.org/10.1107/S1600536809042974/im2143sup1.cif
contains datablocks I, global. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536809042974/im2143Isup2.hkl
The synthesis of the title compound is summerized in Fig. 2, and full details will be published elsewhere (Eberle & Keese, 2009). In order to replace Val by hexafluoro-valine in the tripeptide Val-MeLeu-Ala, the depsipeptide (3), and subsequently the tripeptide (RS)-(5) containing an N-functionalized 4,4,4,4',4',4'-hexafluorovaline, were prepared. Compound (3) was obtained from (S)-N-methylleucine-(S)-alanine-O-tert-butylester (1) by acylation with 4,4,4,4',4',4'-hexafluoro acrylic acid (2). The subsequent addition of 2-hydroxyethyloxyamine (4) to the α-position of the hexafluoroacrylic moiety in (3) gave two of the title tripeptide (RS)-(5). One of these solidified and crystals, suitable for X-ray analysis, were obtained as colourless rods from ether-hexane (1:5) on slow evaporation at room temperature.
In the final cycles of
in the absence of significant effects, the 2234 Friedel pairs were merged and Δf " set to zero. The coordinates correspond to the of the molecule in the crystal assigned with reference to the known stereospecific centers in the molecule. The –NH—O—CH2—CH2OH side chain is disordered over two positions (occupancies A:B = 0.6:0.4). One methyl group (C23) of the isopropyl substituent is also disordered over two positions (occupancies A:B = 0.5:0.5). During a certain number of restraints were applied: ADP's of the pairs of atoms C23A & C21, C23B & C21, C24B & C24A, C25B & C25A were made equal; bonds C22—C23A, C22—C23B, C24B—C25B, C24A—C25A were refined with distance restraints of 1.54 (2) Å and bonds C25A—O6A, C25B—O6B with distant restraints of 1.44 (2) Å. The N—H hydrogen atoms could be located in difference Fourier syntheses. N1—H1N was freely refined (N—H = 0.88 (4) Å), while N3a—H3a was included in the calculated position and treated as riding: N—H = 0.88 Å with Uiso(H) = 1.2Ueq(N-atom). The O– and C-bound H-atoms were included in calculated positions and treated as riding atoms: O—H = 0.84 Å, C—H = 0.98 - 1.00 Å with Uiso(H) = 1.5Ueq(parent O-atom) and = 1.2Ueq(parent C-atom).Biomolecules with fluoro substituents differ in their properties compared to their congeners by a variety of properties. For example, they tend to be more lipophilic, exhibit a higher stability and may excert specific medicinal effects (Kirsch, 2004; Mikol et al., 1997). As part of our interest in fluorinated biomolecules we have prepared (R)- and (S)-4,4,4,4',4',4'-hexafluorovaline (Eberle et al., 1998; Eberle & Keese, 2009) and (S)-5,5,5,5',5,'5'-hexafluoroleucine (Zhang et al., 1998). Our interest was further stimulated when we realised that cyclosporine, an undecapeptide and an important immunosuppressant, contains (S)-valine as one of the 11 aminoacids (Mikol et al., 1997). Furthermore, earlier work had shown that the tripeptide Val-MeLeu-Ala can be chemically cut out of the undecapeptide and reintroduced eventually into the remaining octapeptide (Eberle et al., 1994).
In order to replace Val in the tripeptide Val-MeLeu-Ala by hexafluoro-valine the depsipeptide, (S)-1N-methyl-leucine-(S)-alanine-O-tert-butylester-1N-(3,3-bistrifluoromethyl-acryloylamide, was prepared and subsequently the title tripeptide containing an N-functionalized 4,4,4,4',4',4'-hexafluorovaline. The depsipeptide was obtained from (S)-N-methylleucine-(S)-alanine-O-tert-butylester by acylation with 4,4,4,4',4',4'-hexafluoro acrylic acid. Subsequent addition of 2-hydroxyethyloxyamine in α-position of the hexafluoroacrylic moiety in the depsipeptide gave two of the title tripeptide. One of these solidified and gave crystals suitable for an X-ray structure analysis, and we describe its herein.
Based on the known
of MeLeu and Ala, (SS), used in the synthesis, the hexafluoro-valine moiety in the title compound has (R)-configuration (Fig. 1). The geometrical parameters are available in the archived The –NH—O—CH2—CH2OH side chain of the hexafluoro Valine is disordered over two positions [occupancies A:B = 0.6:0.4]. One methyl group (C23) of the isopropyl substituent in the central amino acid MeLeu is also disordered over two positions [occupancies A:B = 0.5:0.5]. The bond angle in the hexafluoroisopropyl group (C17—C16—C18) in hexafluoro valine is 109.3 (6)°, whereas the bond angles in the isopropyl group of MeLeu within the two orientations (C21—C22—C23A and C21—C22—C23B) are 107.5 (9)° and 111.8 (10)°, respectively. The bond angle C9—C20—C22 of the leucine side chain is 114.7 (4)°. The bond angles at the acylated N-atoms, N1 and N2, are close to 120°, the value expected for tricoordinate sp2 hybridized N-atoms. The torsional angles around the two amide groups [2.2 (10)° for C2—N1—C8—O3, 178.7 (6) ° for C2—N1—C8—C9, and -1.8 (9) ° for C9—N2—C14—O4, 173.6 (5) ° for C9—N2—C14—C15] are within the normal range and provide the evidence for almost planar arrangements (Fig. 1).In the
there is a three-centered hydrogen bond located between N3—H3N···F5, whereas a bifurcated hydrogen bond O2—H1N—O5 leads to interactions between the N1—H and atom O5, the N-bonded O-atom of the hydroxyethyloxy side chain, and the carbonyl group of the BOC protecting group (Table 1 and Fig. 1). These intramolecular hydrogen bonds support the coiled structure of this tripeptide with the three hydrophobic substituents on the outside.For biomolecules with fluoro substituents, see: Kirsch (2004); Mikol et al. (1997); Eberle et al. (1998); Zhang et al. (1998); Eberle & Keese (2009). For the tripeptide Val-MeLeu-Ala in cyclosporine, an undecapeptide, and the fact that it can be extracted and reintroduced in the remaining octapeptide, see: Eberle et al. (1994).
Data collection: EXPOSE in IPDS-I (Stoe & Cie, 2000); cell
CELL in IPDS-I (Stoe & Cie, 2000); data reduction: INTEGRATE in IPDS-I (Stoe & Cie, 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).C21H35F6N3O6 | F(000) = 1136 |
Mr = 539.52 | Dx = 1.348 Mg m−3 |
Orthorhombic, P212121 | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: P 2ac 2ab | Cell parameters from 8000 reflections |
a = 11.1608 (7) Å | θ = 2.1–25.9° |
b = 11.2088 (7) Å | µ = 0.12 mm−1 |
c = 21.2562 (15) Å | T = 153 K |
V = 2659.1 (3) Å3 | Rod, colourless |
Z = 4 | 0.50 × 0.50 × 0.40 mm |
Stoe IPDS diffractometer | 2554 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.063 |
Graphite monochromator | θmax = 25.9°, θmin = 2.1° |
phi oscillation scans | h = −13→13 |
18889 measured reflections | k = −13→13 |
2917 independent reflections | l = −26→25 |
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.077 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.201 | w = 1/[σ2(Fo2) + (0.0533P)2 + 7.6569P] where P = (Fo2 + 2Fc2)/3 |
S = 1.14 | (Δ/σ)max < 0.001 |
2917 reflections | Δρmax = 0.54 e Å−3 |
358 parameters | Δρmin = −0.37 e Å−3 |
8 restraints | Extinction correction: SHELXL, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.010 (2) |
C21H35F6N3O6 | V = 2659.1 (3) Å3 |
Mr = 539.52 | Z = 4 |
Orthorhombic, P212121 | Mo Kα radiation |
a = 11.1608 (7) Å | µ = 0.12 mm−1 |
b = 11.2088 (7) Å | T = 153 K |
c = 21.2562 (15) Å | 0.50 × 0.50 × 0.40 mm |
Stoe IPDS diffractometer | 2554 reflections with I > 2σ(I) |
18889 measured reflections | Rint = 0.063 |
2917 independent reflections |
R[F2 > 2σ(F2)] = 0.077 | 8 restraints |
wR(F2) = 0.201 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.14 | Δρmax = 0.54 e Å−3 |
2917 reflections | Δρmin = −0.37 e Å−3 |
358 parameters |
Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and torsion angles |
Refinement. In the final cycles of refinement, in the absence of significant anomalous scattering effects, the 2234 Friedel pairs were merged and Δf " set to zero. The –NH—O—CH2CH2OH side chain is disordered over two positions (A & B: occupancies 0.6 / 0.4). One methyl group (C23) of the isopropyl substituent is disordered over two positions (A & B: occupancies 0.5 / 1/2). The coordinates correspond to the absolute structure of the molecule in the crystal, assigned with reference to the known stereospecific centers in the molecule. During refinement a certain number of restraints were applied, for example, EADP N3A N3B; EADP C23A C21 EADP C23B C21; EADP C25A C25B C24B C24A; DFIX 1.54 .02 C22 C23A C22 C23B C24B C25B C24A C25A; DFIX 1.44 .02 C25A O6A C25B O6B; DFIX 0.88 .02 N1 H1N; DFIX -2.2 .02 H9 H23A; DFIX -3.0 .02 C23A O6B. |
x | y | z | Uiso*/Ueq | Occ. (<1) | |
F1 | 0.8576 (6) | 0.5625 (5) | 0.7742 (2) | 0.0700 (19) | |
F2 | 1.0348 (6) | 0.6382 (5) | 0.7580 (2) | 0.083 (2) | |
F3 | 0.9114 (5) | 0.7225 (4) | 0.82195 (18) | 0.0505 (14) | |
F4 | 0.9183 (4) | 0.3504 (4) | 0.8362 (2) | 0.0513 (16) | |
F5 | 1.0984 (5) | 0.3567 (4) | 0.8715 (3) | 0.0623 (18) | |
F6 | 1.0617 (5) | 0.4058 (4) | 0.7766 (2) | 0.0670 (19) | |
O1 | 0.9061 (4) | 0.6526 (4) | 1.24644 (19) | 0.0343 (12) | |
O2 | 0.9956 (5) | 0.6041 (6) | 1.1539 (3) | 0.0573 (19) | |
O3 | 0.7713 (5) | 0.9284 (4) | 1.0905 (2) | 0.0357 (14) | |
O4 | 1.0307 (4) | 0.7163 (4) | 0.9528 (2) | 0.0403 (17) | |
O5A | 0.9190 (14) | 0.4938 (14) | 1.0180 (7) | 0.042 (4) | 0.543 (9) |
O6A | 0.6768 (14) | 0.4094 (14) | 1.0107 (12) | 0.127 (8) | 0.543 (9) |
N1 | 0.8327 (6) | 0.7356 (5) | 1.0887 (3) | 0.0387 (19) | |
N2 | 0.8262 (5) | 0.7377 (5) | 0.9574 (2) | 0.0270 (16) | |
N3A | 0.982 (2) | 0.473 (3) | 0.9578 (16) | 0.031 (6) | 0.543 (9) |
C1 | 0.9169 (7) | 0.6529 (6) | 1.1836 (3) | 0.0350 (19) | |
C2 | 0.8107 (6) | 0.7148 (6) | 1.1547 (3) | 0.0337 (19) | |
C3 | 0.6980 (7) | 0.6393 (8) | 1.1630 (3) | 0.045 (3) | |
C4 | 0.9872 (7) | 0.5833 (7) | 1.2875 (3) | 0.039 (2) | |
C5 | 1.1153 (8) | 0.6268 (9) | 1.2817 (4) | 0.061 (3) | |
C6 | 0.9761 (9) | 0.4527 (7) | 1.2725 (4) | 0.060 (3) | |
C7 | 0.9347 (8) | 0.6062 (8) | 1.3525 (3) | 0.050 (3) | |
C8 | 0.8089 (5) | 0.8426 (6) | 1.0615 (3) | 0.0260 (17) | |
C9 | 0.8399 (6) | 0.8523 (5) | 0.9904 (3) | 0.0293 (17) | |
C14 | 0.9274 (7) | 0.6796 (6) | 0.9424 (3) | 0.0337 (19) | |
C15 | 0.9200 (7) | 0.5526 (6) | 0.9140 (3) | 0.0330 (19) | |
C16 | 1.0017 (7) | 0.5429 (6) | 0.8559 (3) | 0.036 (2) | |
C17 | 1.0167 (7) | 0.4139 (7) | 0.8347 (4) | 0.041 (2) | |
C18 | 0.9518 (8) | 0.6150 (7) | 0.8028 (3) | 0.044 (2) | |
C19 | 0.7068 (6) | 0.6926 (7) | 0.9431 (4) | 0.044 (2) | |
C20 | 0.7694 (7) | 0.9544 (6) | 0.9583 (3) | 0.0357 (19) | |
C21 | 0.7368 (9) | 1.0861 (8) | 0.8671 (4) | 0.056 (3) | |
C22 | 0.8160 (9) | 0.9903 (7) | 0.8948 (4) | 0.059 (3) | |
C23A | 0.9457 (15) | 1.0506 (16) | 0.9098 (8) | 0.056 (3) | 0.500 |
C23B | 0.9385 (14) | 1.0120 (17) | 0.8825 (8) | 0.056 (3) | 0.500 |
C24A | 0.8850 (19) | 0.3851 (14) | 1.0521 (10) | 0.080 (4) | 0.543 (9) |
C25A | 0.7784 (17) | 0.3265 (15) | 1.0138 (12) | 0.080 (4) | 0.543 (9) |
N3B | 0.947 (3) | 0.465 (4) | 0.966 (2) | 0.031 (6) | 0.457 (9) |
O5B | 0.8575 (18) | 0.4829 (19) | 1.0142 (11) | 0.059 (6) | 0.457 (9) |
O6B | 0.9684 (16) | 0.2308 (12) | 1.0006 (7) | 0.073 (6) | 0.457 (9) |
C24B | 0.803 (2) | 0.3747 (19) | 1.0197 (15) | 0.080 (4) | 0.457 (9) |
C25B | 0.882 (2) | 0.2763 (17) | 1.0439 (11) | 0.080 (4) | 0.457 (9) |
H3A1 | 1.04260 | 0.42520 | 0.95020 | 0.0380* | 0.543 (9) |
H3C | 0.67350 | 0.64060 | 1.20730 | 0.0680* | |
H5A | 1.11730 | 0.71370 | 1.28630 | 0.0920* | |
H1N | 0.860 (7) | 0.667 (4) | 1.075 (3) | 0.0470* | |
H2 | 0.79870 | 0.79330 | 1.17620 | 0.0400* | |
H6A1 | 0.61320 | 0.37270 | 1.01920 | 0.1510* | 0.543 (9) |
H3A | 0.63350 | 0.67190 | 1.13690 | 0.0680* | |
H3B | 0.71470 | 0.55700 | 1.15020 | 0.0680* | |
H7A | 0.85130 | 0.57900 | 1.35360 | 0.0760* | |
H7B | 0.93780 | 0.69180 | 1.36170 | 0.0760* | |
H7C | 0.98130 | 0.56260 | 1.38410 | 0.0760* | |
H9 | 0.92660 | 0.87400 | 0.98770 | 0.0350* | |
H15 | 0.83580 | 0.52690 | 0.90530 | 0.0400* | |
H16 | 1.08230 | 0.57540 | 0.86710 | 0.0430* | |
H19A | 0.69300 | 0.69650 | 0.89760 | 0.0660* | |
H19B | 0.64680 | 0.74140 | 0.96480 | 0.0660* | |
H19C | 0.70030 | 0.60970 | 0.95730 | 0.0660* | |
H20A | 0.68480 | 0.92950 | 0.95380 | 0.0430* | |
H20B | 0.77110 | 1.02510 | 0.98630 | 0.0430* | |
H21A | 0.65580 | 1.05440 | 0.86110 | 0.0840* | |
H21B | 0.73380 | 1.15450 | 0.89580 | 0.0840* | |
H21C | 0.76950 | 1.11160 | 0.82650 | 0.0840* | |
H22A | 0.82370 | 0.92020 | 0.86600 | 0.0710* | 0.500 |
H22B | 0.80410 | 0.91870 | 0.86740 | 0.0710* | 0.500 |
H23A | 1.00580 | 0.98780 | 0.91550 | 0.0840* | 0.500 |
H23B | 0.94010 | 1.09830 | 0.94840 | 0.0840* | 0.500 |
H23C | 0.96930 | 1.10210 | 0.87470 | 0.0840* | 0.500 |
H23D | 0.96630 | 1.07870 | 0.90850 | 0.0840* | 0.500 |
H23E | 0.94910 | 1.03180 | 0.83800 | 0.0840* | 0.500 |
H23F | 0.98520 | 0.94050 | 0.89260 | 0.0840* | 0.500 |
H24A | 0.85890 | 0.40490 | 1.09540 | 0.0950* | 0.543 (9) |
H24B | 0.95370 | 0.32950 | 1.05460 | 0.0950* | 0.543 (9) |
H25A | 0.80560 | 0.30680 | 0.97070 | 0.0950* | 0.543 (9) |
H25B | 0.75300 | 0.25160 | 1.03460 | 0.0950* | 0.543 (9) |
H5B | 1.14720 | 0.60460 | 1.24040 | 0.0920* | |
H5C | 1.16430 | 0.59010 | 1.31480 | 0.0920* | |
H6A | 1.00380 | 0.43820 | 1.22940 | 0.0900* | |
H6B | 0.89210 | 0.42830 | 1.27640 | 0.0900* | |
H6C | 1.02510 | 0.40650 | 1.30200 | 0.0900* | |
H3B1 | 1.00600 | 0.41330 | 0.96670 | 0.0380* | 0.457 (9) |
H6B1 | 0.97770 | 0.27970 | 0.97100 | 0.0880* | 0.457 (9) |
H24C | 0.77180 | 0.35110 | 0.97790 | 0.0950* | 0.457 (9) |
H24D | 0.73370 | 0.38290 | 1.04840 | 0.0950* | 0.457 (9) |
H25C | 0.92560 | 0.30610 | 1.08140 | 0.0950* | 0.457 (9) |
H25D | 0.83080 | 0.20940 | 1.05780 | 0.0950* | 0.457 (9) |
U11 | U22 | U33 | U12 | U13 | U23 | |
F1 | 0.098 (4) | 0.064 (3) | 0.048 (3) | −0.004 (3) | −0.034 (3) | −0.008 (2) |
F2 | 0.138 (6) | 0.066 (3) | 0.044 (3) | −0.011 (4) | 0.050 (3) | −0.005 (2) |
F3 | 0.083 (3) | 0.040 (2) | 0.0286 (19) | 0.005 (3) | 0.007 (2) | −0.0019 (17) |
F4 | 0.054 (3) | 0.035 (2) | 0.065 (3) | −0.011 (2) | 0.003 (2) | −0.018 (2) |
F5 | 0.057 (3) | 0.039 (2) | 0.091 (4) | 0.011 (2) | −0.003 (3) | −0.017 (3) |
F6 | 0.085 (4) | 0.056 (3) | 0.060 (3) | −0.002 (3) | 0.033 (3) | −0.027 (3) |
O1 | 0.039 (2) | 0.036 (2) | 0.028 (2) | 0.008 (2) | −0.005 (2) | 0.0023 (19) |
O2 | 0.053 (3) | 0.075 (4) | 0.044 (3) | 0.024 (3) | 0.009 (3) | 0.007 (3) |
O3 | 0.053 (3) | 0.029 (2) | 0.025 (2) | −0.001 (2) | 0.003 (2) | −0.0058 (19) |
O4 | 0.038 (3) | 0.035 (3) | 0.048 (3) | 0.003 (2) | −0.010 (2) | −0.018 (2) |
O5A | 0.074 (10) | 0.029 (5) | 0.022 (5) | 0.000 (8) | 0.006 (7) | 0.002 (4) |
O6A | 0.078 (10) | 0.082 (10) | 0.22 (2) | 0.012 (9) | 0.051 (13) | 0.056 (13) |
N1 | 0.062 (4) | 0.028 (3) | 0.026 (3) | 0.008 (3) | 0.011 (3) | 0.003 (2) |
N2 | 0.034 (3) | 0.026 (3) | 0.021 (2) | −0.003 (2) | 0.005 (2) | −0.003 (2) |
N3A | 0.030 (13) | 0.035 (6) | 0.029 (9) | 0.004 (11) | 0.016 (9) | 0.004 (5) |
C1 | 0.040 (4) | 0.035 (3) | 0.030 (3) | 0.002 (3) | 0.001 (3) | 0.001 (3) |
C2 | 0.042 (4) | 0.037 (3) | 0.022 (3) | 0.003 (3) | 0.001 (3) | 0.003 (3) |
C3 | 0.042 (4) | 0.054 (5) | 0.040 (4) | 0.003 (4) | 0.006 (3) | 0.014 (4) |
C4 | 0.036 (4) | 0.040 (4) | 0.040 (4) | 0.011 (3) | −0.005 (3) | 0.006 (3) |
C5 | 0.054 (5) | 0.073 (6) | 0.057 (5) | −0.007 (5) | −0.014 (4) | 0.018 (5) |
C6 | 0.073 (6) | 0.040 (4) | 0.068 (6) | 0.016 (4) | −0.002 (5) | 0.007 (4) |
C7 | 0.063 (5) | 0.051 (5) | 0.037 (4) | 0.007 (4) | −0.005 (4) | 0.009 (3) |
C8 | 0.029 (3) | 0.027 (3) | 0.022 (3) | −0.003 (3) | 0.001 (2) | −0.001 (2) |
C9 | 0.038 (3) | 0.025 (3) | 0.025 (3) | −0.002 (3) | 0.007 (3) | −0.003 (3) |
C14 | 0.049 (4) | 0.030 (3) | 0.022 (3) | 0.006 (3) | −0.003 (3) | 0.001 (3) |
C15 | 0.040 (4) | 0.026 (3) | 0.033 (3) | −0.003 (3) | 0.002 (3) | −0.002 (3) |
C16 | 0.039 (4) | 0.037 (4) | 0.032 (3) | 0.001 (3) | 0.004 (3) | −0.011 (3) |
C17 | 0.039 (4) | 0.034 (4) | 0.051 (4) | −0.004 (3) | 0.005 (3) | −0.014 (3) |
C18 | 0.065 (5) | 0.039 (4) | 0.028 (3) | −0.009 (4) | 0.012 (3) | −0.009 (3) |
C19 | 0.039 (4) | 0.042 (4) | 0.050 (4) | −0.006 (3) | 0.008 (4) | −0.018 (3) |
C20 | 0.051 (4) | 0.026 (3) | 0.030 (3) | 0.000 (3) | 0.002 (3) | 0.002 (3) |
C21 | 0.074 (5) | 0.051 (4) | 0.044 (4) | 0.007 (4) | 0.003 (4) | 0.013 (3) |
C22 | 0.107 (8) | 0.031 (4) | 0.038 (4) | 0.009 (5) | 0.016 (5) | 0.008 (3) |
C23A | 0.074 (5) | 0.051 (4) | 0.044 (4) | 0.007 (4) | 0.003 (4) | 0.013 (3) |
C23B | 0.074 (5) | 0.051 (4) | 0.044 (4) | 0.007 (4) | 0.003 (4) | 0.013 (3) |
C24A | 0.093 (8) | 0.038 (5) | 0.108 (8) | 0.016 (6) | 0.024 (7) | 0.034 (7) |
C25A | 0.093 (8) | 0.038 (5) | 0.108 (8) | 0.016 (6) | 0.024 (7) | 0.034 (7) |
N3B | 0.030 (13) | 0.035 (6) | 0.029 (9) | 0.004 (11) | 0.016 (9) | 0.004 (5) |
O5B | 0.080 (14) | 0.037 (9) | 0.060 (10) | 0.013 (11) | 0.029 (12) | −0.002 (7) |
O6B | 0.102 (12) | 0.043 (8) | 0.074 (9) | 0.028 (8) | 0.018 (9) | 0.019 (7) |
C24B | 0.093 (8) | 0.038 (5) | 0.108 (8) | 0.016 (6) | 0.024 (7) | 0.034 (7) |
C25B | 0.093 (8) | 0.038 (5) | 0.108 (8) | 0.016 (6) | 0.024 (7) | 0.034 (7) |
F1—C18 | 1.350 (10) | C24B—C25B | 1.50 (3) |
F2—C18 | 1.354 (10) | C2—H2 | 1.0000 |
F3—C18 | 1.349 (9) | C3—H3A | 0.9800 |
F4—C17 | 1.309 (9) | C3—H3C | 0.9800 |
F5—C17 | 1.362 (10) | C3—H3B | 0.9800 |
F6—C17 | 1.336 (10) | C5—H5B | 0.9800 |
O1—C1 | 1.341 (8) | C5—H5A | 0.9800 |
O1—C4 | 1.478 (9) | C5—H5C | 0.9800 |
O2—C1 | 1.212 (9) | C6—H6B | 0.9800 |
O3—C8 | 1.217 (8) | C6—H6A | 0.9800 |
O4—C14 | 1.244 (9) | C6—H6C | 0.9800 |
O5A—N3A | 1.48 (4) | C7—H7C | 0.9800 |
O5A—C24A | 1.47 (2) | C7—H7A | 0.9800 |
O5B—C24B | 1.36 (3) | C7—H7B | 0.9800 |
O5B—N3B | 1.45 (4) | C9—H9 | 1.0000 |
O6A—C25A | 1.47 (2) | C15—H15 | 1.0000 |
O6B—C25B | 1.43 (3) | C16—H16 | 1.0000 |
O6A—H6A1 | 0.8400 | C19—H19B | 0.9800 |
O6B—H6B1 | 0.8400 | C19—H19A | 0.9800 |
N1—C8 | 1.358 (9) | C19—H19C | 0.9800 |
N1—C2 | 1.443 (9) | C20—H20B | 0.9900 |
N2—C19 | 1.457 (9) | C20—H20A | 0.9900 |
N2—C14 | 1.342 (9) | C21—H21A | 0.9800 |
N2—C9 | 1.472 (8) | C21—H21B | 0.9800 |
N3A—C15 | 1.46 (3) | C21—H21C | 0.9800 |
N3B—C15 | 1.51 (4) | C22—H22A | 1.0000 |
N1—H1N | 0.88 (5) | C22—H22B | 1.0000 |
N3A—H3A1 | 0.8800 | C23A—H23C | 0.9800 |
N3B—H3B1 | 0.8800 | C23A—H23D | 0.3900 |
C1—C2 | 1.505 (10) | C23A—H23B | 0.9800 |
C2—C3 | 1.526 (11) | C23A—H23A | 0.9800 |
C4—C6 | 1.503 (11) | C23A—H23F | 1.3600 |
C4—C7 | 1.523 (10) | C23B—H23C | 1.0800 |
C4—C5 | 1.516 (12) | C23B—H23A | 1.0600 |
C8—C9 | 1.554 (9) | C23B—H23F | 0.9800 |
C9—C20 | 1.547 (9) | C23B—H23D | 0.9800 |
C14—C15 | 1.548 (9) | C23B—H23E | 0.9800 |
C15—C16 | 1.539 (10) | C24A—H24A | 0.9900 |
C16—C17 | 1.524 (10) | C24A—H24B | 0.9900 |
C16—C18 | 1.496 (10) | C24B—H24C | 0.9900 |
C20—C22 | 1.501 (11) | C24B—H24D | 0.9900 |
C21—C22 | 1.510 (13) | C25A—H25A | 0.9900 |
C22—C23B | 1.413 (19) | C25A—H25B | 0.9900 |
C22—C23A | 1.63 (2) | C25B—H25C | 0.9900 |
C23A—C23B | 0.73 (2) | C25B—H25D | 0.9900 |
C24A—C25A | 1.58 (3) | ||
C1—O1—C4 | 122.3 (5) | C4—C7—H7B | 109.00 |
N3A—O5A—C24A | 114.8 (18) | N2—C9—H9 | 107.00 |
N3B—O5B—C24B | 104 (3) | C8—C9—H9 | 107.00 |
C25A—O6A—H6A1 | 109.00 | C20—C9—H9 | 107.00 |
C25B—O6B—H6B1 | 109.00 | C14—C15—H15 | 113.00 |
C2—N1—C8 | 121.6 (6) | N3A—C15—H15 | 113.00 |
C9—N2—C19 | 119.8 (5) | C16—C15—H15 | 113.00 |
C9—N2—C14 | 116.7 (6) | N3B—C15—H15 | 98.00 |
C14—N2—C19 | 123.5 (6) | C15—C16—H16 | 108.00 |
O5A—N3A—C15 | 103.3 (18) | C18—C16—H16 | 109.00 |
O5B—N3B—C15 | 107 (3) | C17—C16—H16 | 109.00 |
C8—N1—H1N | 135 (4) | N2—C19—H19C | 109.00 |
C2—N1—H1N | 104 (4) | N2—C19—H19B | 109.00 |
C15—N3A—H3A1 | 128.00 | H19B—C19—H19C | 109.00 |
O5A—N3A—H3A1 | 128.00 | H19A—C19—H19B | 109.00 |
C15—N3B—H3B1 | 126.00 | H19A—C19—H19C | 110.00 |
O5B—N3B—H3B1 | 127.00 | N2—C19—H19A | 110.00 |
O1—C1—O2 | 125.6 (7) | C22—C20—H20B | 109.00 |
O1—C1—C2 | 109.7 (6) | H20A—C20—H20B | 108.00 |
O2—C1—C2 | 124.5 (6) | C9—C20—H20B | 108.00 |
C1—C2—C3 | 110.3 (6) | C22—C20—H20A | 109.00 |
N1—C2—C3 | 110.0 (5) | C9—C20—H20A | 109.00 |
N1—C2—C1 | 109.7 (6) | C22—C21—H21A | 109.00 |
C5—C4—C6 | 112.0 (7) | C22—C21—H21B | 109.00 |
O1—C4—C7 | 102.2 (6) | H21B—C21—H21C | 109.00 |
O1—C4—C6 | 109.6 (6) | H21A—C21—H21C | 110.00 |
C6—C4—C7 | 109.0 (7) | H21A—C21—H21B | 109.00 |
O1—C4—C5 | 111.1 (6) | C22—C21—H21C | 109.00 |
C5—C4—C7 | 112.5 (6) | C21—C22—H22A | 112.00 |
O3—C8—N1 | 123.4 (6) | C20—C22—H22B | 105.00 |
N1—C8—C9 | 115.6 (6) | C23A—C22—H22B | 124.00 |
O3—C8—C9 | 120.9 (6) | C21—C22—H22B | 105.00 |
C8—C9—C20 | 111.6 (5) | C23A—C22—H22A | 112.00 |
N2—C9—C8 | 112.3 (5) | H22A—C22—H22B | 13.00 |
N2—C9—C20 | 112.5 (5) | C20—C22—H22A | 112.00 |
N2—C14—C15 | 119.6 (6) | C23B—C22—H22A | 86.00 |
O4—C14—C15 | 115.0 (6) | C23B—C22—H22B | 99.00 |
O4—C14—N2 | 125.3 (6) | C22—C23A—H23A | 110.00 |
N3B—C15—C14 | 107.6 (17) | C22—C23A—H23B | 109.00 |
C14—C15—C16 | 110.3 (6) | C22—C23A—H23C | 110.00 |
N3A—C15—C14 | 106.7 (14) | C22—C23A—H23D | 147.00 |
N3A—C15—C16 | 100.8 (12) | C23B—C23A—H23C | 77.00 |
N3B—C15—C16 | 115.1 (15) | C23B—C23A—H23D | 119.00 |
C15—C16—C18 | 110.3 (6) | C23B—C23A—H23F | 44.00 |
C17—C16—C18 | 109.3 (6) | H23A—C23A—H23B | 109.00 |
C15—C16—C17 | 111.7 (6) | H23A—C23A—H23C | 109.00 |
F6—C17—C16 | 112.3 (6) | H23A—C23A—H23D | 101.00 |
F5—C17—F6 | 104.3 (6) | H23A—C23A—H23F | 33.00 |
F4—C17—C16 | 114.6 (6) | H23B—C23A—H23C | 109.00 |
F4—C17—F5 | 107.0 (6) | H23B—C23A—H23D | 70.00 |
F4—C17—F6 | 107.5 (6) | H23B—C23A—H23F | 138.00 |
F5—C17—C16 | 110.5 (6) | H23C—C23A—H23D | 47.00 |
F1—C18—F3 | 105.4 (7) | H23C—C23A—H23F | 104.00 |
F2—C18—F3 | 105.6 (6) | C22—C23A—H23F | 82.00 |
F3—C18—C16 | 112.3 (5) | C23B—C23A—H23A | 75.00 |
F2—C18—C16 | 112.3 (7) | C23B—C23A—H23B | 169.00 |
F1—C18—F2 | 107.5 (5) | H23D—C23A—H23F | 121.00 |
F1—C18—C16 | 113.2 (6) | C22—C23B—H23E | 110.00 |
C9—C20—C22 | 114.7 (6) | C22—C23B—H23F | 109.00 |
C20—C22—C23A | 104.1 (8) | C22—C23B—H23D | 109.00 |
C23A—C22—C23B | 26.5 (10) | C23A—C23B—H23C | 62.00 |
C20—C22—C21 | 109.8 (7) | C23A—C23B—H23D | 20.00 |
C21—C22—C23B | 111.8 (10) | C23A—C23B—H23A | 63.00 |
C21—C22—C23A | 107.5 (9) | C23A—C23B—H23F | 105.00 |
C20—C22—C23B | 123.2 (10) | H23A—C23B—H23C | 97.00 |
C22—C23A—C23B | 60.0 (17) | H23A—C23B—H23D | 66.00 |
C22—C23B—C23A | 94 (2) | H23A—C23B—H23E | 128.00 |
O5A—C24A—C25A | 106.5 (16) | H23A—C23B—H23F | 43.00 |
O5B—C24B—C25B | 114.9 (19) | H23C—C23B—H23D | 43.00 |
O6A—C25A—C24A | 109.9 (15) | C23A—C23B—H23E | 128.00 |
O6B—C25B—C24B | 116 (2) | H23C—C23B—H23F | 129.00 |
N1—C2—H2 | 109.00 | H23D—C23B—H23E | 109.00 |
C1—C2—H2 | 109.00 | H23D—C23B—H23F | 109.00 |
C3—C2—H2 | 109.00 | H23E—C23B—H23F | 109.00 |
C2—C3—H3A | 109.00 | H23C—C23B—H23E | 66.00 |
H3A—C3—H3C | 109.00 | C22—C23B—H23A | 121.00 |
H3B—C3—H3C | 109.00 | C22—C23B—H23C | 120.00 |
C2—C3—H3B | 109.00 | O5A—C24A—H24A | 110.00 |
C2—C3—H3C | 109.00 | O5A—C24A—H24B | 110.00 |
H3A—C3—H3B | 109.00 | C25A—C24A—H24A | 110.00 |
C4—C5—H5A | 109.00 | C25A—C24A—H24B | 110.00 |
C4—C5—H5B | 110.00 | H24A—C24A—H24B | 109.00 |
C4—C5—H5C | 109.00 | O5B—C24B—H24C | 109.00 |
H5B—C5—H5C | 109.00 | C25B—C24B—H24D | 108.00 |
H5A—C5—H5B | 110.00 | O5B—C24B—H24D | 109.00 |
H5A—C5—H5C | 109.00 | C25B—C24B—H24C | 109.00 |
C4—C6—H6A | 109.00 | H24C—C24B—H24D | 108.00 |
C4—C6—H6B | 109.00 | O6A—C25A—H25A | 110.00 |
C4—C6—H6C | 109.00 | O6A—C25A—H25B | 110.00 |
H6A—C6—H6B | 110.00 | C24A—C25A—H25B | 110.00 |
H6B—C6—H6C | 109.00 | H25A—C25A—H25B | 108.00 |
H6A—C6—H6C | 110.00 | C24A—C25A—H25A | 110.00 |
C4—C7—H7C | 109.00 | O6B—C25B—H25C | 108.00 |
H7A—C7—H7B | 109.00 | O6B—C25B—H25D | 108.00 |
H7B—C7—H7C | 109.00 | C24B—C25B—H25C | 108.00 |
C4—C7—H7A | 110.00 | C24B—C25B—H25D | 109.00 |
H7A—C7—H7C | 109.00 | H25C—C25B—H25D | 107.00 |
C4—O1—C1—O2 | −4.5 (11) | C8—C9—C20—C22 | 165.1 (6) |
C4—O1—C1—C2 | 170.9 (6) | O4—C14—C15—N3A | 57.1 (13) |
C1—O1—C4—C5 | 62.9 (8) | O4—C14—C15—C16 | −51.5 (8) |
C1—O1—C4—C6 | −61.4 (8) | N2—C14—C15—N3A | −118.8 (12) |
C1—O1—C4—C7 | −176.9 (6) | N2—C14—C15—C16 | 132.6 (6) |
C24A—O5A—N3A—C15 | 132.9 (18) | N3A—C15—C16—C17 | 55.9 (14) |
N3A—O5A—C24A—C25A | −72 (2) | N3A—C15—C16—C18 | 177.7 (13) |
C8—N1—C2—C1 | −134.2 (6) | C14—C15—C16—C17 | 168.4 (6) |
C8—N1—C2—C3 | 104.4 (7) | C14—C15—C16—C18 | −69.9 (8) |
C2—N1—C8—O3 | 2.2 (10) | C15—C16—C17—F4 | 41.6 (9) |
C2—N1—C8—C9 | 178.7 (6) | C15—C16—C17—F5 | −79.4 (8) |
C14—N2—C9—C8 | −105.0 (6) | C15—C16—C17—F6 | 164.6 (6) |
C14—N2—C9—C20 | 128.2 (6) | C18—C16—C17—F4 | −80.8 (8) |
C19—N2—C9—C8 | 74.6 (7) | C18—C16—C17—F5 | 158.3 (7) |
C19—N2—C9—C20 | −52.3 (8) | C18—C16—C17—F6 | 42.3 (9) |
C9—N2—C14—O4 | −1.8 (9) | C15—C16—C18—F1 | −76.2 (8) |
C9—N2—C14—C15 | 173.6 (5) | C15—C16—C18—F2 | 161.9 (6) |
C19—N2—C14—O4 | 178.6 (6) | C15—C16—C18—F3 | 43.0 (9) |
C19—N2—C14—C15 | −6.0 (9) | C17—C16—C18—F1 | 47.0 (9) |
O5A—N3A—C15—C14 | 55.9 (18) | C17—C16—C18—F2 | −75.0 (8) |
O5A—N3A—C15—C16 | 171.0 (14) | C17—C16—C18—F3 | 166.2 (7) |
O1—C1—C2—N1 | 169.0 (5) | C9—C20—C22—C21 | 177.4 (6) |
O1—C1—C2—C3 | −69.6 (7) | C9—C20—C22—C23A | −67.8 (9) |
O2—C1—C2—N1 | −15.5 (10) | C9—C20—C22—C23B | −47.6 (13) |
O2—C1—C2—C3 | 105.8 (8) | C20—C22—C23A—C23B | 140 (2) |
O3—C8—C9—N2 | −152.0 (6) | C21—C22—C23A—C23B | −104 (2) |
O3—C8—C9—C20 | −24.6 (8) | C20—C22—C23B—C23A | −49 (2) |
N1—C8—C9—N2 | 31.5 (8) | C21—C22—C23B—C23A | 86 (2) |
N1—C8—C9—C20 | 158.8 (6) | O5A—C24A—C25A—O6A | −60 (2) |
N2—C9—C20—C22 | −67.7 (8) |
D—H···A | D—H | H···A | D···A | D—H···A |
N3A—H3A1···F5 | 0.88 | 1.94 | 2.60 (3) | 130 |
N1—H1N···O2 | 0.88 (5) | 2.37 (7) | 2.720 (9) | 104 (5) |
N1—H1N···O5A | 0.88 (5) | 2.38 (6) | 3.245 (17) | 169 (6) |
Experimental details
Crystal data | |
Chemical formula | C21H35F6N3O6 |
Mr | 539.52 |
Crystal system, space group | Orthorhombic, P212121 |
Temperature (K) | 153 |
a, b, c (Å) | 11.1608 (7), 11.2088 (7), 21.2562 (15) |
V (Å3) | 2659.1 (3) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.12 |
Crystal size (mm) | 0.50 × 0.50 × 0.40 |
Data collection | |
Diffractometer | Stoe IPDS |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 18889, 2917, 2554 |
Rint | 0.063 |
(sin θ/λ)max (Å−1) | 0.614 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.077, 0.201, 1.14 |
No. of reflections | 2917 |
No. of parameters | 358 |
No. of restraints | 8 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.54, −0.37 |
Computer programs: EXPOSE in IPDS-I (Stoe & Cie, 2000), CELL in IPDS-I (Stoe & Cie, 2000), INTEGRATE in IPDS-I (Stoe & Cie, 2000), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), PLATON (Spek, 2009).
D—H···A | D—H | H···A | D···A | D—H···A |
N3A—H3A1···F5 | 0.88 | 1.94 | 2.60 (3) | 130 |
N1—H1N···O2 | 0.88 (5) | 2.37 (7) | 2.720 (9) | 104 (5) |
N1—H1N···O5A | 0.88 (5) | 2.38 (6) | 3.245 (17) | 169 (6) |
Acknowledgements
This work was supported financially by the Swiss National Science Foundation (project No. 20–43565.95). We thank Dr L. Tenud (Lonza, Visp AG) for the generous gift of fluorinated chemicals.
References
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This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.
Biomolecules with fluoro substituents differ in their properties compared to their congeners by a variety of properties. For example, they tend to be more lipophilic, exhibit a higher stability and may excert specific medicinal effects (Kirsch, 2004; Mikol et al., 1997). As part of our interest in fluorinated biomolecules we have prepared (R)- and (S)-4,4,4,4',4',4'-hexafluorovaline (Eberle et al., 1998; Eberle & Keese, 2009) and (S)-5,5,5,5',5,'5'-hexafluoroleucine (Zhang et al., 1998). Our interest was further stimulated when we realised that cyclosporine, an undecapeptide and an important immunosuppressant, contains (S)-valine as one of the 11 aminoacids (Mikol et al., 1997). Furthermore, earlier work had shown that the tripeptide Val-MeLeu-Ala can be chemically cut out of the undecapeptide and reintroduced eventually into the remaining octapeptide (Eberle et al., 1994).
In order to replace Val in the tripeptide Val-MeLeu-Ala by hexafluoro-valine the depsipeptide, (S)-1N-methyl-leucine-(S)-alanine-O-tert-butylester-1N-(3,3-bistrifluoromethyl-acryloylamide, was prepared and subsequently the title tripeptide containing an N-functionalized 4,4,4,4',4',4'-hexafluorovaline. The depsipeptide was obtained from (S)-N-methylleucine-(S)-alanine-O-tert-butylester by acylation with 4,4,4,4',4',4'-hexafluoro acrylic acid. Subsequent addition of 2-hydroxyethyloxyamine in α-position of the hexafluoroacrylic moiety in the depsipeptide gave two diastereomers of the title tripeptide. One of these solidified and gave crystals suitable for an X-ray structure analysis, and we describe its crystal structure herein.
Based on the known absolute configuration of MeLeu and Ala, (SS), used in the synthesis, the hexafluoro-valine moiety in the title compound has (R)-configuration (Fig. 1). The geometrical parameters are available in the archived CIF. The –NH—O—CH2—CH2OH side chain of the hexafluoro Valine is disordered over two positions [occupancies A:B = 0.6:0.4]. One methyl group (C23) of the isopropyl substituent in the central amino acid MeLeu is also disordered over two positions [occupancies A:B = 0.5:0.5]. The bond angle in the hexafluoroisopropyl group (C17—C16—C18) in hexafluoro valine is 109.3 (6)°, whereas the bond angles in the isopropyl group of MeLeu within the two orientations (C21—C22—C23A and C21—C22—C23B) are 107.5 (9)° and 111.8 (10)°, respectively. The bond angle C9—C20—C22 of the leucine side chain is 114.7 (4)°. The bond angles at the acylated N-atoms, N1 and N2, are close to 120°, the value expected for tricoordinate sp2 hybridized N-atoms. The torsional angles around the two amide groups [2.2 (10)° for C2—N1—C8—O3, 178.7 (6) ° for C2—N1—C8—C9, and -1.8 (9) ° for C9—N2—C14—O4, 173.6 (5) ° for C9—N2—C14—C15] are within the normal range and provide the evidence for almost planar arrangements (Fig. 1).
In the crystal structure there is a three-centered hydrogen bond located between N3—H3N···F5, whereas a bifurcated hydrogen bond O2—H1N—O5 leads to interactions between the N1—H and atom O5, the N-bonded O-atom of the hydroxyethyloxy side chain, and the carbonyl group of the BOC protecting group (Table 1 and Fig. 1). These intramolecular hydrogen bonds support the coiled structure of this tripeptide with the three hydrophobic substituents on the outside.