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Two crystal structures of urethane-protected derivatives of aspartic acid dimethyl ester are presented, namely dimethyl (2S)-2-[(tert-but­oxy­carbonyl)amino]­butane­dioate, C11H19NO6, and dimethyl (2S)-2-{bis­[(tert-but­oxy­carbonyl]amino}­butane­dioate, C16H27NO8. The geometry at the N atom is discussed and compared with similar structures. The analysis of singly and doubly N-substituted derivatives reveals an elongation of all bonds involving the N atom and conformational changes of the amino acid side chain due to steric inter­actions with two bulky substituents on the amino group.

Supporting information

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Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270112048846/qs3019sup1.cif
Contains datablocks I, II, global

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Structure factor file (CIF format) https://doi.org/10.1107/S0108270112048846/qs3019Isup2.hkl
Contains datablock I

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Structure factor file (CIF format) https://doi.org/10.1107/S0108270112048846/qs3019IIsup3.hkl
Contains datablock II

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Chemical Markup Language (CML) file https://doi.org/10.1107/S0108270112048846/qs3019Isup4.cml
Supplementary material

CCDC references: 925269; 925270

Comment top

Selective protection of functional groups is one of the main issues in organic chemistry (Greene & Wuts, 1999). The strategy of protection is vital in peptide synthesis, especially when peptides are used as scaffolds for complex bioconjugates (e.g. Alkhader et al., 2010). The tert-butoxycarbonyl (Boc) and bis(tert-butoxycarbonyl) (bis-Boc) groups are frequently used to protect amino groups. While Boc-protected organic structures are fairly well represented (452 hits) in the Cambridge Structural Database (CSD, Version?; Allen, 2002), to the best of our knowledge only nine organic structures with bis-Boc protection on the N atom have been deposited to date, and the structures of only two sets of compounds with Boc and bis-Boc protection are available in the CSD [CSD refcodes MUTTOK and MUTTUQ (Macleod et al., 2003), and XUDQUJ and XUDQOD (Ikonen et al., 2009)]. During the synthesis of some novel nonproteinaceous amino acids, we obtained two derivatives of aspartic acid, and their structures form a third pair of this type. We thus present here the crystal structures of dimethyl (2S)-2-[(tert-butoxycarbonyl)amino]butanedioate, (I), and dimethyl (2S)-2-{bis[(tert-butoxycarbonyl]amino}butanedioate, (II). We compare the geometry at the N atom in each structure, as well as in the other two Boc-protected pairs mentioned above and in structures protected by related groups. It is worth noting that (II) is the first chiral and second non-aromatic example of a bis-Boc compound, opening the possibility of observing the arrangement of bulky substituents.

The asymmetric units of (I) and (II) are shown in Fig. 1. The absolute configuration at atom C3 is S in both structures, as the applied synthetic procedure preserves the configuration of the substrate. All bond lengths and angles are typical, except for those in the urethane group, which will be discussed in detail (Tables 1 and 3). In (I), the orientation of the carbonyl O atom in the Boc substituent is antiperiplanar relative to atom H1N [torsion angle O5—C7—N1—H1N = -175.9 (14)°], which is stabilized by two very weak intramolecular hydrogen-bond contacts of C—H···O type (C10—H10B···O5 and C11—H11A···O5). Therefore, rotation around the C8—O6 single bond is most probably hindered. In (II), carbonyl atom O5 is synperiplanar to atom C3 and carbonyl atom O7 is antiperiplanar to atom C3. In the other two bis-Boc compounds, the carbonyl O atoms are oriented in the same direction, both antiperiplanar to the C—N bond, but these structures are much less crowded (Macleod et al., 2003; Ikonen et al., 2009). Four very weak intramolecular hydrogen-bond contacts of C—H···O type (C9—H9A···O5, C11—H11C···O5, C15—H15C···O7 and C16—H16A···O7) stabilize the conformation of both Boc groups in (II) (Fig. 3a) by hindering rotation around the C8—O6 and C13—O8 single bonds.

In (I), intermolecular hydrogen bonds, utilizing mainly the NH group and both ester groups, stabilize infinite chains running along the b axis (Fig. 2a). Two adjacent chains (related by a 21 symmetry operation) are joined to each other via C1—H1C···O5ii hydrogen bonds to form helical ribbons down the b axis (Fig. 2b and Table 2; symmetry code in Table 2). The same atom C1 and urethane atom O5 are involved in weaker C1—H1B···O5iii contacts, giving rise to layers parallel to the (001) plane (Table 2). In contrast, the crystal structure of (II) has a three-dimensional architecture, although chains of molecules (related by a direct a-axis translation), joined via C1—H1B···O1iii and C3—H3···O4iii hydrogen bonds, may be distinguished (Fig. 3a and Table 4; symmetry code in Table 4). Nonetheless, each chain interacts with five others (related by a b-axis translation and symmetries of two 21 axes), utilizing ester, tBu and urethane groups to give a three-dimensional network of hydrogen bonds, as shown in Fig. 3(b).

The limited data available on mono- and bis-Boc substituted compounds prompted us to take a closer look at the N-atom geometry. We found almost no information on the values of C—N bond lengths in such urethane-type structures in International Tables for Crystallography, Vol. C (Prince, 2004). The only available structural information is the H—N3 distance in X2—N—H = 1.01 Å (Prince, 2004) and the Csp3—Nsp3 distance in C*—NH—CO (acyclic amides) = 1.45 Å (Prince, 2004), which is the best available representation of a urethane group. We found 874 urethane-type organic structures in the CSD [tert-butoxycarbonyl-, benzyloxycarbonyl-, ethoxycarbonyl-, methoxycarbonyl-, (9H-fluoren-9-ylmethoxy)carbonyl- and others] and only 11 bis-urethane structures. The mean values of selected geometric parameters, defined in Fig. 4, are presented in Table 5 for comparison with (I) and (II), and with acetyl-substituted compounds (non-urethane derivatives).

All bonds at the N atom atom in (II) are longer than those in (I) due to the introduction of a second bulky tert-butoxycarbonyl substituent. Elongation of these bonds should be expected from resonance theory, as the introduction of a second substituent provides a decrease in the double-bond character of the N—C bonds, while the elongation of the N1—C3 bond (DIST3) from 1.4438 (16) to 1.4669 (13) Å seems to be caused by steric effects. It is worth noting that the CO and C—O bonds in the Boc substituent in (II) are shorter [CO = 1.2067 (14) and 1.2057 (13) Å, and C—O = 1.3241 (13) and 1.3312 (13) Å] than the respective bonds in (I) [CO = 1.2169 (14) Å and C—O = 1.3455 (15) Å]. The same is true for the other two sets of Boc and bis-Boc structures (Macleod et al., 2003; Ikonen et al., 2009).

The hybridization of atom N1 in both structures is sp2, with angles tending towards 120°. The urethane group in (I) is almost planar and atom N1 is out-of-plane by 0.031 (2) Å. In (II), atom N1 is out of the plane of the neighbouring atoms (C3, C7 and C12) by 0.184 (2) Å, suggesting a partial sp3 character. The shift of electron density around atoms C7 and C12 towards the O atoms in (II) may be a consequence of this change, probably related to the limited delocalization of electrons in a bis-protected amino acid derivative. It is also possible that the steric repulsion between two bulky Boc substituents also affects the N1 out-of-plane distance. In (II), the C7—N1—C3 angle (ANG1) is much smaller than the C12—N1—C3 angle (ANG2). As atoms C7 and C12 should create the same chemical environment, this is the effect of stereochemistry and resulting steric correlations with the Cα—C(O)OMe group of aspartic acid. Only a single H atom (H3) points towards atom C7 (of the Boc group), while the rest of the amino acid chain points towards atom C12 from the other Boc group and therefore decreases the value of ANG1, as the result of steric repulsion between two bulky Boc groups and the side chain. It is of interest that the side-chain ester group has dramatically changed its conformation, as shown in Fig. 5. It seems that this effect was forced by the introduction of the second Boc group and provides the best spatial location of the substituents on the N atom: two Boc groups and the ester side chain of aspartic acid.

The elongation of bonds in (II) is similar to two other Boc and bis-Boc structures (see Scheme 2), as shown in Table 5. The N atom out-of-plane value is much greater in (II) than in XUDQOD or MUTTUQ. In (II), DIST3 is longer than in the two bis-Boc aromatic structures, while the other two distances (DIST1 and DIST2) are similar. The differences in the angle values are greater in the two aromatic CSD structures than in (II), as the Boc substituents are rotated out of the plane of the aromatic ring, whereas in (II) the side chain of the aspartic acid limits the available space, even with the conformational change of the ester side chain (C2—C3—C4—C5 torsion angle).

The interatomic distances in (I) and (II) are within the range of other tert-butoxycarbonyl- and bis(tert-butoxycarbonyl) structures, and those of general urethane and bis-urethane structures. They are also close to those in acyl-substituted species. Resonance theory allows the participation of the second noncarbonyl O atom in resonance structures. Urethane groups are known for their racemization-protecting properties during peptide synthesis, as the resonance of the urethane group lowers the rate of cyclic transient product formation, which is associated with decreased acidity of urethane NH (R—O—CO—NH) compared with amide NH (R—CO—NH) (Sewald & Jakubke, 2002; Goodman, 2004). As can be estimated from the Boc and acetyl derivatives, the difference in bond length is rather insignificant, which supports the theory of acidity.

In conclusion, we have observed the elongation of all bonds formed by the N atom in bis-substituted urethane organic compounds. This is probably caused by steric repulsion of bulky substituents and is enhanced by delocalization of the electron pair of the N atom. The nature of the changes depends on the structure of the main part of the molecule and leads to the optimum spatial accommodation of the Boc substituents.

Related literature top

For related literature, see: Alkhader et al. (2010); Allen (2002); Bodanszky & Bodanszky (1994); Englund et al. (2004); Goodman (2004); Greene & Wuts (1999); Ikonen et al. (2009); Macleod et al. (2003); Prince (2004); Schröder & Lübke (1965); Sewald & Jakubke (2002).

Experimental top

Dimethyl (2S)-2-aminobutanedioate hydrochloride was obtained according to a modified procedure (Schröder & Lübke, 1965) from L-aspartic acid (Reanal) as a colourless oil. The oil was diluted with MeCN, neutralized with N,N,N-triethylamine (Ubichem Ltd) and subjected to further reaction with di-tert-butyl dicarbonate (Boc2O, GL Biochem) for 9 h, according to Bodanszky & Bodanszky (1994). The resulting oil was treated with n-hexane (oil–n-hexane, 1:6 v/v), yielding long colourless block-shaped crystals of (I) (yield 89%; m.p. 335.7–337.1 K). Spectroscopic analysis: 1H NMR (500 MHz, CD3OD, δ, p.p.m.): 4.55 (t, J1 = 6.0 Hz, 1H), 3.77 (s, 3H), 3.73 (s, 3H), 2.89 (dd, J1 = 6.0 Hz, J2 = 16.5 Hz, 1H), 2.81 (dd, J1 = 6.0 Hz, J2 = 16.5 Hz, 1H), 1.48 (s, 9H). MS (ESI), m/z, calculated for C11H20NO6 [M + H]+: 262.128; found: 262.129.

Compound (II) was obtained from (I) according to a modified method (Englund et al., 2004) by overnight reaction with Boc2O in MeCN in the presence of 4-(dimethylamino)pyridine (Fluka) at room temperature. Thin colourless needle-shaped crystals of (II) (yield 88%; 325.2–326.0 K) were obtained by slow evaporation of AcOEt. Spectroscopic analysis: 1H NMR (500 MHz, CD3OD, δ, p.p.m.): 5.44 (t, J1 = 6.5 Hz, 1H), 3.77 (s, 3H), 3.73 (s, 3H), 3.21 (dd, J1 = 6.5 Hz, J2 = 16.3 Hz, 1H), 2.83 (dd, J1 = 6.5 Hz, J2 = 16.3 Hz, 1H), 1.54 (s, 18H). MS (ESI), m/z, calculated for C16H27NNaO8 [M + Na]+: 384.163; found: 384.163.

Refinement top

All H atoms were found in difference Fourier maps. In the final refinement cycles, C-bonded H atoms were positioned geometrically and treated as riding atoms, with C—H = 0.98–1.00 Å and Uiso(H) = 1.2Ueq(CH,CH2) or 1.5Ueq(CH3). Atom H1N in (I) was refined isotropically.

Computing details top

For both compounds, data collection: CrysAlis CCD (Oxford Diffraction, 2009); cell refinement: CrysAlis RED (Oxford Diffraction, 2009); data reduction: CrysAlis RED (Oxford Diffraction, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2012); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures top
Fig. 1. The structure and atom-numbering of (a) (I) and (b) (II). Displacement ellipsoids are drawn at the 50% probability level.

Fig. 2. The arrangement of molecules of (I) in the crystal structure. (a) The chains along the b axis, with hydrogen-bond contacts shown as dashed lines (in the electronic version of the journal, intramolecular contacts are shown in orange and intermolecular in blue). (b) Layers parallel to the (001) plane, formed by adjacent chains linked via C—H···O contacts (red dashed lines). H atoms not involved in hydrogen bonding have been omitted for clarity. [Symmetry codes: (i) x, y - 1, z; (ii) -x + 1, y + 1/2, -z; (iii) x + 1, y, z; (iv) x, y + 1, z.]

Fig. 3. The arrangement of molecules of (II) in the crystal structure. (a) The chains along the aaxis, with hydrogen-bond contacts shown as dashed lines (intramolecular in orange and intermolecular in blue). (b) The three-dimensional architecture formed by C—H···O contacts (red dashed lines) linking adjacent chains. H atoms not involved in hydrogen bonding have been omitted for clarity. [Symmetry codes: (iii) x + 1, y, z; (v) x - 1/2, -y + 3/2, -z + 1; (vi) -x + 1, y + 1/2, -z + 1/2; (i) x, y - 1, z; (vii) x + 1/2, -y + 3/2, -z + 1; (viii) -x + 1, y - 1/2, -z + 1/2.]

Fig. 4. Definitions of the geometric parameters presented in Table 5.

Fig. 5. Superposition of (I) (green in the electronic version of the paper) and (II) (violet), showing the significant changes in conformation of the aspartic acid side chain. The common reference points are C2, C3 and C4.
(I) Dimethyl (2S)-2-[(tert-butoxycarbonyl)amino]butanedioate top
Crystal data top
C11H19NO6F(000) = 280
Mr = 261.27Dx = 1.339 Mg m3
Monoclinic, P21Melting point: 335.7 K
Hall symbol: P 2ybMo Kα radiation, λ = 0.71073 Å
a = 9.219 (3) ÅCell parameters from 5074 reflections
b = 5.815 (2) Åθ = 5.0–38.6°
c = 12.263 (4) ŵ = 0.11 mm1
β = 99.74 (3)°T = 100 K
V = 647.9 (4) Å3Block, colourless
Z = 20.46 × 0.16 × 0.12 mm
Data collection top
Oxford Xcalibur PX κ-geometry
diffractometer with Onyx CCD camera
2437 independent reflections
Radiation source: Enhance (Mo) X-ray Source2219 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.025
ω and ϕ scansθmax = 33.0°, θmin = 4.9°
Absorption correction: multi-scan
(CrysAlis RED; Oxford Diffraction, 2009)
h = 1313
Tmin = 0.942, Tmax = 1.000k = 68
7321 measured reflectionsl = 189
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.030H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.078 w = 1/[σ2(Fo2) + (0.0502P)2 + 0.0009P]
where P = (Fo2 + 2Fc2)/3
S = 1.07(Δ/σ)max < 0.001
2437 reflectionsΔρmax = 0.25 e Å3
172 parametersΔρmin = 0.18 e Å3
1 restraintAbsolute structure: known absolute configuration
Primary atom site location: structure-invariant direct methods
Crystal data top
C11H19NO6V = 647.9 (4) Å3
Mr = 261.27Z = 2
Monoclinic, P21Mo Kα radiation
a = 9.219 (3) ŵ = 0.11 mm1
b = 5.815 (2) ÅT = 100 K
c = 12.263 (4) Å0.46 × 0.16 × 0.12 mm
β = 99.74 (3)°
Data collection top
Oxford Xcalibur PX κ-geometry
diffractometer with Onyx CCD camera
2437 independent reflections
Absorption correction: multi-scan
(CrysAlis RED; Oxford Diffraction, 2009)
2219 reflections with I > 2σ(I)
Tmin = 0.942, Tmax = 1.000Rint = 0.025
7321 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0301 restraint
wR(F2) = 0.078H atoms treated by a mixture of independent and constrained refinement
S = 1.07Δρmax = 0.25 e Å3
2437 reflectionsΔρmin = 0.18 e Å3
172 parametersAbsolute structure: known absolute configuration
Special details top

Experimental. 1HNMR (CD3OD): δ = 4.55 (t, J1 = 6.0 Hz, 1H), 3.77 (s, 3H), 3.73 (s, 3H), 2.89 (dd, J1 = 6.0 Hz, J2 = 16.5 Hz, 1H), 2.81 (dd, J1 = 6.0 Hz, J2 = 16.5 Hz, 1H), 1.48 (s, 9H)

MS (ESI), [M+H]+obsd ([M+H]+calcd), [M+Na]+obsd ([M+Na]+calcd) Da: 262.129 (262.128), 284.110 (284.110)

Melting point range 335.7–337.1 K

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
O10.63269 (10)0.20152 (18)0.13353 (8)0.0217 (2)
O20.65256 (9)0.55942 (17)0.06905 (7)0.01841 (19)
O30.65512 (12)0.5827 (2)0.34131 (8)0.0310 (3)
O40.54946 (10)0.92255 (18)0.36528 (7)0.0212 (2)
O50.14865 (9)0.41478 (17)0.15578 (7)0.01748 (18)
O60.21240 (9)0.12764 (17)0.28274 (7)0.01610 (18)
N10.38691 (11)0.31665 (19)0.21778 (8)0.0154 (2)
H1N0.445 (2)0.220 (4)0.2574 (13)0.027 (4)*
C10.78864 (13)0.4954 (3)0.03299 (10)0.0190 (2)
H1A0.77090.36420.01770.029*
H1B0.86190.45300.09740.029*
H1C0.82530.62570.00520.029*
C20.58746 (12)0.3950 (2)0.11908 (9)0.0150 (2)
C30.44432 (12)0.4842 (2)0.14933 (9)0.0139 (2)
H30.37200.49660.07900.017*
C40.45833 (12)0.7232 (2)0.20160 (9)0.0151 (2)
H4A0.49090.83300.14900.018*
H4B0.36050.77370.21540.018*
C50.56600 (12)0.7290 (2)0.30909 (9)0.0174 (2)
C60.64810 (15)0.9499 (3)0.46926 (10)0.0273 (3)
H6A0.75010.93890.45690.041*
H6B0.62910.82860.52060.041*
H6C0.63201.10060.50090.041*
C70.23948 (12)0.2960 (2)0.21367 (9)0.0137 (2)
C80.05995 (12)0.0577 (2)0.29009 (9)0.0155 (2)
C90.08611 (15)0.1302 (3)0.37752 (11)0.0227 (3)
H9A0.14020.06630.44650.034*
H9B0.14370.25460.35180.034*
H9C0.00870.19080.39050.034*
C100.01501 (14)0.0408 (2)0.17988 (10)0.0191 (2)
H10A0.04440.16710.15810.029*
H10B0.02500.07980.12330.029*
H10C0.11270.09860.18730.029*
C110.02366 (14)0.2580 (3)0.32932 (10)0.0199 (2)
H11A0.03030.38340.27530.030*
H11B0.02830.31210.40110.030*
H11C0.12290.20770.33690.030*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0194 (4)0.0158 (5)0.0316 (4)0.0010 (3)0.0090 (4)0.0010 (4)
O20.0151 (4)0.0200 (5)0.0213 (4)0.0004 (3)0.0065 (3)0.0040 (4)
O30.0294 (5)0.0296 (6)0.0296 (4)0.0128 (5)0.0079 (4)0.0053 (5)
O40.0208 (4)0.0217 (5)0.0194 (4)0.0025 (4)0.0015 (3)0.0048 (4)
O50.0146 (4)0.0169 (4)0.0210 (4)0.0025 (3)0.0031 (3)0.0033 (3)
O60.0134 (3)0.0162 (4)0.0190 (4)0.0000 (3)0.0037 (3)0.0043 (3)
N10.0135 (4)0.0139 (5)0.0189 (4)0.0004 (4)0.0027 (3)0.0053 (4)
C10.0145 (5)0.0260 (7)0.0175 (5)0.0022 (5)0.0052 (4)0.0010 (5)
C20.0138 (4)0.0162 (5)0.0149 (4)0.0014 (4)0.0019 (4)0.0008 (4)
C30.0137 (4)0.0127 (5)0.0157 (4)0.0002 (4)0.0034 (4)0.0018 (4)
C40.0152 (4)0.0131 (5)0.0169 (4)0.0012 (4)0.0020 (4)0.0005 (4)
C50.0150 (5)0.0193 (6)0.0178 (4)0.0002 (5)0.0027 (4)0.0002 (5)
C60.0236 (6)0.0367 (9)0.0197 (5)0.0000 (6)0.0019 (4)0.0090 (6)
C70.0145 (4)0.0132 (5)0.0140 (4)0.0006 (4)0.0039 (4)0.0017 (4)
C80.0137 (4)0.0148 (6)0.0191 (5)0.0014 (4)0.0059 (4)0.0000 (4)
C90.0241 (6)0.0203 (7)0.0252 (5)0.0008 (5)0.0088 (5)0.0070 (5)
C100.0177 (5)0.0174 (6)0.0224 (5)0.0022 (4)0.0045 (4)0.0042 (5)
C110.0207 (5)0.0194 (6)0.0213 (5)0.0007 (5)0.0081 (4)0.0021 (5)
Geometric parameters (Å, º) top
O1—C21.2026 (17)C4—C51.5104 (16)
O2—C21.3324 (16)C4—H4A0.99
O2—C11.4476 (15)C4—H4B0.99
O3—C51.2021 (17)C6—H6A0.98
O4—C51.3416 (17)C6—H6B0.98
O4—C61.4443 (15)C6—H6C0.98
O5—C71.2169 (14)C8—C111.5188 (19)
O6—C71.3455 (15)C8—C91.5214 (19)
O6—C81.4804 (15)C8—C101.5220 (17)
N1—C31.4438 (16)C9—H9A0.98
N1—C71.3568 (16)C9—H9B0.98
N1—H1N0.87 (2)C9—H9C0.98
C1—H1A0.98C10—H10A0.98
C1—H1B0.98C10—H10B0.98
C1—H1C0.98C10—H10C0.98
C2—C31.5211 (17)C11—H11A0.98
C3—C41.5264 (18)C11—H11B0.98
C3—H31.00C11—H11C0.98
C2—O2—C1115.93 (11)H6A—C6—H6B109.5
C5—O4—C6115.87 (11)O4—C6—H6C109.5
C7—O6—C8121.15 (9)H6A—C6—H6C109.5
C7—N1—C3120.10 (10)H6B—C6—H6C109.5
C3—N1—H1N120.6 (12)O5—C7—O6126.69 (11)
C7—N1—H1N119.1 (13)O5—C7—N1123.90 (11)
O2—C1—H1A109.5O6—C7—N1109.41 (10)
O2—C1—H1B109.5O6—C8—C11110.29 (10)
H1A—C1—H1B109.5O6—C8—C9101.61 (10)
O2—C1—H1C109.5C11—C8—C9110.85 (11)
H1A—C1—H1C109.5O6—C8—C10110.03 (10)
H1B—C1—H1C109.5C11—C8—C10113.04 (10)
O1—C2—O2124.55 (12)C9—C8—C10110.45 (12)
O1—C2—C3125.22 (12)C8—C9—H9A109.5
O2—C2—C3110.15 (11)C8—C9—H9B109.5
N1—C3—C2109.27 (10)H9A—C9—H9B109.5
N1—C3—C4112.56 (10)C8—C9—H9C109.5
C2—C3—C4113.43 (10)H9A—C9—H9C109.5
N1—C3—H3107.1H9B—C9—H9C109.5
C2—C3—H3107.1C8—C10—H10A109.5
C4—C3—H3107.1C8—C10—H10B109.5
C5—C4—C3112.54 (10)H10A—C10—H10B109.5
C5—C4—H4A109.1C8—C10—H10C109.5
C3—C4—H4A109.1H10A—C10—H10C109.5
C5—C4—H4B109.1H10B—C10—H10C109.5
C3—C4—H4B109.1C8—C11—H11A109.5
H4A—C4—H4B107.8C8—C11—H11B109.5
O3—C5—O4123.75 (11)H11A—C11—H11B109.5
O3—C5—C4125.63 (12)C8—C11—H11C109.5
O4—C5—C4110.62 (10)H11A—C11—H11C109.5
O4—C6—H6A109.5H11B—C11—H11C109.5
O4—C6—H6B109.5
C1—O2—C2—O11.44 (16)C6—O4—C5—C4179.15 (11)
C1—O2—C2—C3178.41 (8)C3—C4—C5—O315.03 (19)
C7—N1—C3—C2149.02 (10)C3—C4—C5—O4165.07 (10)
C7—N1—C3—C484.01 (12)C8—O6—C7—O53.94 (17)
O1—C2—C3—N111.62 (15)C8—O6—C7—N1176.27 (10)
O2—C2—C3—N1171.43 (9)C3—N1—C7—O51.19 (18)
O1—C2—C3—C4138.10 (12)C3—N1—C7—O6179.01 (10)
O2—C2—C3—C444.96 (12)C7—O6—C8—C1161.77 (13)
N1—C3—C4—C562.96 (13)C7—O6—C8—C9179.37 (10)
C2—C3—C4—C561.75 (13)C7—O6—C8—C1063.61 (14)
C6—O4—C5—O30.76 (19)O5—C7—N1—H1N175.9 (14)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1N···O4i0.87 (2)2.29 (2)3.1388 (16)166.6 (17)
C1—H1C···O5ii0.982.543.4775 (19)160
C1—H1B···O5iii0.982.633.4368 (18)140
C4—H4A···O1iv0.992.533.3869 (19)144
C10—H10B···O50.982.513.0875 (19)118
C10—H10A···O5i0.982.623.5407 (19)157
C11—H11A···O50.982.393.0045 (18)120
Symmetry codes: (i) x, y1, z; (ii) x+1, y+1/2, z; (iii) x+1, y, z; (iv) x, y+1, z.
(II) Dimethyl (2S)-2-{bis[(tert-butoxycarbonyl]amino}butanedioate top
Crystal data top
C16H27NO8Dx = 1.274 Mg m3
Mr = 361.39Melting point: 325.2 K
Orthorhombic, P212121Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2abCell parameters from 9210 reflections
a = 5.922 (2) Åθ = 2.8–35.0°
b = 9.635 (2) ŵ = 0.10 mm1
c = 33.026 (8) ÅT = 100 K
V = 1884.4 (9) Å3Needle, colourless
Z = 40.58 × 0.18 × 0.13 mm
F(000) = 776
Data collection top
Oxford Xcalibur PX κ-geometry
diffractometer with Onyx CCD camera
4374 independent reflections
Radiation source: Enhance (Mo) X-ray Source3766 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.026
ω and ϕ scansθmax = 35.1°, θmin = 2.8°
Absorption correction: multi-scan
(CrysAlis RED; Oxford Diffraction, 2009)
h = 79
Tmin = 0.915, Tmax = 1.000k = 1314
19441 measured reflectionsl = 5249
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.033H-atom parameters constrained
wR(F2) = 0.084 w = 1/[σ2(Fo2) + (0.0513P)2]
where P = (Fo2 + 2Fc2)/3
S = 1.06(Δ/σ)max = 0.001
4374 reflectionsΔρmax = 0.33 e Å3
234 parametersΔρmin = 0.21 e Å3
0 restraintsAbsolute structure: known absolute configuration
Primary atom site location: structure-invariant direct methods
Crystal data top
C16H27NO8V = 1884.4 (9) Å3
Mr = 361.39Z = 4
Orthorhombic, P212121Mo Kα radiation
a = 5.922 (2) ŵ = 0.10 mm1
b = 9.635 (2) ÅT = 100 K
c = 33.026 (8) Å0.58 × 0.18 × 0.13 mm
Data collection top
Oxford Xcalibur PX κ-geometry
diffractometer with Onyx CCD camera
4374 independent reflections
Absorption correction: multi-scan
(CrysAlis RED; Oxford Diffraction, 2009)
3766 reflections with I > 2σ(I)
Tmin = 0.915, Tmax = 1.000Rint = 0.026
19441 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0330 restraints
wR(F2) = 0.084H-atom parameters constrained
S = 1.06Δρmax = 0.33 e Å3
4374 reflectionsΔρmin = 0.21 e Å3
234 parametersAbsolute structure: known absolute configuration
Special details top

Experimental. 1HNMR (CD3OD): δ = 5.44 (t, J1 = 6.5 Hz, 1H), 3.77 (s, 3H), 3.73 (s, 3H), 3.21 (dd, J1 = 6.5 Hz, J2 = 16.3 Hz, 1H), 2.83 (dd, J1 = 6.5 Hz, J2 = 16.3 Hz, 1H), 1.54 (s, 18H)

MS (ESI), [M+Na]+obsd ([M+Na]+calcd), [M+K]+obsd ([M+K]+calcd), Da: 384.163(384.163), 400.137(400.137)

Melting point range 325.2–326.0 K

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
O10.10714 (14)0.44229 (11)0.46790 (2)0.02093 (18)
O20.46447 (14)0.45633 (11)0.44508 (2)0.02078 (18)
O30.02379 (14)0.79384 (11)0.45873 (3)0.02407 (19)
O40.34966 (13)0.77487 (10)0.42441 (2)0.01899 (17)
O50.30700 (15)0.78565 (9)0.35433 (3)0.01948 (17)
O60.55821 (13)0.63292 (9)0.32733 (2)0.01469 (15)
O70.28257 (14)0.41338 (9)0.31658 (2)0.01874 (17)
O80.15137 (15)0.34646 (9)0.37807 (2)0.01785 (16)
N10.30205 (15)0.55636 (10)0.37260 (3)0.01333 (16)
C10.5351 (2)0.36784 (19)0.47807 (4)0.0337 (3)
H1A0.48740.40890.50380.051*
H1B0.69990.35860.47770.051*
H1C0.46590.27610.47500.051*
C20.24361 (18)0.48566 (13)0.44408 (3)0.0159 (2)
C30.19056 (17)0.59140 (12)0.41093 (3)0.01350 (18)
H30.25900.68100.42010.016*
C40.06274 (18)0.61855 (13)0.40689 (3)0.0157 (2)
H4A0.09890.63970.37830.019*
H4B0.14700.53390.41470.019*
C50.13714 (18)0.73779 (12)0.43324 (3)0.01488 (19)
C60.4464 (2)0.88285 (14)0.44944 (4)0.0221 (2)
H6A0.46330.84860.47720.033*
H6B0.59480.90900.43870.033*
H6C0.34680.96400.44930.033*
C70.38586 (18)0.67098 (12)0.35033 (3)0.01373 (19)
C80.63469 (18)0.72188 (13)0.29332 (3)0.0171 (2)
C90.7367 (2)0.85604 (15)0.30919 (4)0.0263 (3)
H9A0.61950.91060.32280.039*
H9B0.79880.90960.28650.039*
H9C0.85750.83440.32850.039*
C100.8129 (2)0.63109 (16)0.27350 (4)0.0245 (3)
H10A0.93300.61120.29310.037*
H10B0.87670.67960.25010.037*
H10C0.74380.54390.26460.037*
C110.4374 (2)0.74738 (16)0.26484 (4)0.0254 (3)
H11A0.36710.65860.25770.038*
H11B0.49180.79310.24020.038*
H11C0.32590.80690.27820.038*
C120.24901 (18)0.43346 (12)0.35211 (3)0.01332 (18)
C130.0502 (2)0.21508 (13)0.36310 (3)0.0196 (2)
C140.0482 (3)0.15313 (18)0.40150 (4)0.0401 (4)
H14A0.07180.14170.42170.060*
H14B0.11520.06250.39540.060*
H14C0.16480.21520.41230.060*
C150.1346 (2)0.24836 (15)0.33290 (4)0.0270 (3)
H15A0.23840.31650.34470.040*
H15B0.21780.16340.32630.040*
H15C0.06730.28670.30820.040*
C160.2339 (2)0.12174 (14)0.34624 (4)0.0250 (3)
H16A0.29600.16320.32150.037*
H16B0.17010.03040.33990.037*
H16C0.35430.11130.36640.037*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0171 (3)0.0299 (5)0.0157 (3)0.0009 (3)0.0034 (3)0.0026 (3)
O20.0141 (3)0.0311 (5)0.0172 (3)0.0045 (4)0.0009 (3)0.0094 (3)
O30.0191 (4)0.0300 (5)0.0230 (4)0.0032 (4)0.0045 (3)0.0109 (4)
O40.0139 (3)0.0206 (4)0.0225 (4)0.0038 (3)0.0018 (3)0.0067 (3)
O50.0221 (4)0.0137 (4)0.0226 (4)0.0026 (3)0.0003 (3)0.0024 (3)
O60.0141 (3)0.0146 (4)0.0154 (3)0.0006 (3)0.0017 (3)0.0042 (3)
O70.0246 (4)0.0180 (4)0.0136 (3)0.0037 (3)0.0040 (3)0.0022 (3)
O80.0260 (4)0.0135 (4)0.0141 (3)0.0059 (3)0.0042 (3)0.0004 (3)
N10.0152 (4)0.0127 (4)0.0121 (3)0.0010 (3)0.0017 (3)0.0005 (3)
C10.0215 (5)0.0537 (10)0.0259 (6)0.0102 (6)0.0022 (5)0.0215 (6)
C20.0137 (4)0.0203 (5)0.0138 (4)0.0009 (4)0.0001 (3)0.0005 (4)
C30.0125 (4)0.0156 (5)0.0124 (4)0.0012 (4)0.0002 (3)0.0014 (3)
C40.0129 (4)0.0187 (5)0.0156 (4)0.0014 (4)0.0015 (3)0.0035 (4)
C50.0134 (4)0.0170 (5)0.0142 (4)0.0014 (4)0.0009 (3)0.0004 (4)
C60.0181 (5)0.0198 (6)0.0285 (5)0.0026 (5)0.0046 (4)0.0060 (5)
C70.0131 (4)0.0138 (5)0.0143 (4)0.0015 (4)0.0022 (3)0.0014 (4)
C80.0151 (4)0.0187 (5)0.0175 (4)0.0043 (4)0.0004 (4)0.0061 (4)
C90.0252 (6)0.0201 (6)0.0335 (6)0.0089 (5)0.0001 (5)0.0042 (5)
C100.0210 (5)0.0295 (7)0.0229 (5)0.0006 (5)0.0064 (4)0.0046 (5)
C110.0205 (5)0.0351 (8)0.0206 (5)0.0029 (5)0.0027 (4)0.0111 (5)
C120.0125 (4)0.0125 (5)0.0150 (4)0.0004 (4)0.0005 (3)0.0013 (4)
C130.0240 (5)0.0136 (5)0.0211 (5)0.0065 (5)0.0053 (4)0.0014 (4)
C140.0623 (11)0.0284 (8)0.0296 (6)0.0220 (8)0.0186 (7)0.0001 (6)
C150.0183 (5)0.0242 (7)0.0384 (7)0.0037 (5)0.0019 (5)0.0062 (5)
C160.0281 (6)0.0150 (5)0.0318 (6)0.0024 (5)0.0008 (5)0.0001 (5)
Geometric parameters (Å, º) top
O1—C21.2026 (14)C6—H6C0.98
O2—C21.3385 (14)C8—C101.5188 (18)
O2—C11.4453 (15)C8—C91.5201 (18)
O3—C51.2045 (13)C8—C111.5202 (17)
O4—C51.3404 (14)C9—H9A0.98
O4—C61.4471 (14)C9—H9B0.98
O5—C71.2067 (14)C9—H9C0.98
O6—C71.3241 (13)C10—H10A0.98
O6—C81.4836 (13)C10—H10B0.98
O7—C121.2057 (13)C10—H10C0.98
O8—C121.3312 (13)C11—H11A0.9800
O8—C131.4851 (14)C11—H11B0.9800
N1—C31.4669 (13)C11—H11C0.9800
N1—C71.4168 (14)C13—C151.5154 (19)
N1—C121.3996 (14)C13—C161.5174 (18)
C1—H1A0.98C13—C141.5180 (17)
C1—H1B0.98C14—H14A0.98
C1—H1C0.98C14—H14B0.98
C2—C31.5283 (16)C14—H14C0.98
C3—C41.5285 (15)C15—H15A0.98
C3—H31.0000C15—H15B0.98
C4—C51.5071 (16)C15—H15C0.98
C4—H4A0.99C16—H16A0.98
C4—H4B0.99C16—H16B0.98
C6—H6A0.98C16—H16C0.98
C6—H6B0.98
C2—O2—C1115.20 (10)C8—C9—H9A109.5
C5—O4—C6116.05 (9)C8—C9—H9B109.5
C7—O6—C8120.64 (9)H9A—C9—H9B109.5
C12—O8—C13119.84 (8)C8—C9—H9C109.5
C7—N1—C3115.23 (9)H9A—C9—H9C109.5
C12—N1—C3120.73 (9)H9B—C9—H9C109.5
C12—N1—C7119.14 (8)C8—C10—H10A109.5
O2—C1—H1A109.5C8—C10—H10B109.5
O2—C1—H1B109.5H10A—C10—H10B109.5
H1A—C1—H1B109.5C8—C10—H10C109.5
O2—C1—H1C109.5H10A—C10—H10C109.5
H1A—C1—H1C109.5H10B—C10—H10C109.5
H1B—C1—H1C109.5C8—C11—H11A109.5
O1—C2—O2124.56 (11)C8—C11—H11B109.5
O1—C2—C3124.20 (10)H11A—C11—H11B109.5
O2—C2—C3111.05 (9)C8—C11—H11C109.5
N1—C3—C2111.85 (9)H11A—C11—H11C109.5
N1—C3—C4113.94 (8)H11B—C11—H11C109.5
C2—C3—C4112.23 (9)O7—C12—O8126.68 (11)
N1—C3—H3106.0O7—C12—N1124.71 (10)
C2—C3—H3106.0O8—C12—N1108.59 (9)
C4—C3—H3106.0O8—C13—C15109.28 (10)
C5—C4—C3111.53 (9)O8—C13—C16109.76 (10)
C5—C4—H4A109.3C15—C13—C16113.69 (10)
C3—C4—H4A109.3O8—C13—C14102.24 (10)
C5—C4—H4B109.3C15—C13—C14110.84 (12)
C3—C4—H4B109.3C16—C13—C14110.42 (12)
H4A—C4—H4B108.0C13—C14—H14A109.5
O3—C5—O4123.76 (11)C13—C14—H14B109.5
O3—C5—C4125.62 (10)H14A—C14—H14B109.5
O4—C5—C4110.62 (9)C13—C14—H14C109.5
O4—C6—H6A109.5H14A—C14—H14C109.5
O4—C6—H6B109.5H14B—C14—H14C109.5
H6A—C6—H6B109.5C13—C15—H15A109.5
O4—C6—H6C109.5C13—C15—H15B109.5
H6A—C6—H6C109.5H15A—C15—H15B109.5
H6B—C6—H6C109.5C13—C15—H15C109.5
O5—C7—O6127.93 (10)H15A—C15—H15C109.5
O5—C7—N1121.41 (10)H15B—C15—H15C109.5
O6—C7—N1110.61 (9)C13—C16—H16A109.5
O6—C8—C10101.86 (10)C13—C16—H16B109.5
O6—C8—C9110.58 (9)H16A—C16—H16B109.5
C10—C8—C9111.24 (10)C13—C16—H16C109.5
O6—C8—C11109.09 (9)H16A—C16—H16C109.5
C10—C8—C11111.13 (10)H16B—C16—H16C109.5
C9—C8—C11112.42 (11)
C1—O2—C2—O11.06 (19)C8—O6—C7—N1163.20 (8)
C1—O2—C2—C3174.06 (11)C3—N1—C7—O524.65 (14)
C7—N1—C3—C2141.94 (9)C12—N1—C7—O5130.78 (11)
C12—N1—C3—C263.05 (12)C12—N1—C7—O651.38 (12)
C7—N1—C3—C489.45 (12)C3—N1—C7—O6153.18 (8)
C12—N1—C3—C465.56 (13)C7—O6—C8—C10174.02 (9)
O1—C2—C3—N1138.79 (12)C7—O6—C8—C967.66 (12)
O2—C2—C3—N146.07 (13)C7—O6—C8—C1156.47 (13)
O1—C2—C3—C49.28 (16)C13—O8—C12—O76.33 (18)
O2—C2—C3—C4175.58 (10)C13—O8—C12—N1171.91 (9)
N1—C3—C4—C5140.53 (10)C3—N1—C12—O7159.03 (11)
C2—C3—C4—C591.04 (12)C7—N1—C12—O74.97 (16)
C6—O4—C5—O34.08 (17)C3—N1—C12—O819.26 (13)
C6—O4—C5—C4176.22 (10)C7—N1—C12—O8173.32 (9)
C3—C4—C5—O39.91 (16)C12—O8—C13—C1560.14 (13)
C3—C4—C5—O4169.78 (9)C12—O8—C13—C1665.16 (13)
C8—O6—C7—O519.14 (16)C12—O8—C13—C14177.62 (12)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C1—H1B···O1i0.982.563.479 (2)156
C3—H3···O31.002.372.8121 (15)106
C3—H3···O4i1.002.493.2767 (16)135
C6—H6A···O3ii0.982.553.5079 (18)167
C9—H9A···O50.982.443.0261 (17)118
C11—H11C···O50.982.523.0769 (17)116
C11—H11B···O7iii0.982.583.5412 (16)168
C15—H15C···O70.982.422.9871 (17)116
C16—H16A···O70.982.422.9897 (17)117
C16—H16B···O5iv0.982.543.2780 (17)132
Symmetry codes: (i) x+1, y, z; (ii) x1/2, y+3/2, z+1; (iii) x+1, y+1/2, z+1/2; (iv) x, y1, z.

Experimental details

(I)(II)
Crystal data
Chemical formulaC11H19NO6C16H27NO8
Mr261.27361.39
Crystal system, space groupMonoclinic, P21Orthorhombic, P212121
Temperature (K)100100
a, b, c (Å)9.219 (3), 5.815 (2), 12.263 (4)5.922 (2), 9.635 (2), 33.026 (8)
α, β, γ (°)90, 99.74 (3), 9090, 90, 90
V3)647.9 (4)1884.4 (9)
Z24
Radiation typeMo KαMo Kα
µ (mm1)0.110.10
Crystal size (mm)0.46 × 0.16 × 0.120.58 × 0.18 × 0.13
Data collection
DiffractometerOxford Xcalibur PX κ-geometry
diffractometer with Onyx CCD camera
Oxford Xcalibur PX κ-geometry
diffractometer with Onyx CCD camera
Absorption correctionMulti-scan
(CrysAlis RED; Oxford Diffraction, 2009)
Multi-scan
(CrysAlis RED; Oxford Diffraction, 2009)
Tmin, Tmax0.942, 1.0000.915, 1.000
No. of measured, independent and
observed [I > 2σ(I)] reflections
7321, 2437, 2219 19441, 4374, 3766
Rint0.0250.026
(sin θ/λ)max1)0.7660.809
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.030, 0.078, 1.07 0.033, 0.084, 1.06
No. of reflections24374374
No. of parameters172234
No. of restraints10
H-atom treatmentH atoms treated by a mixture of independent and constrained refinementH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.25, 0.180.33, 0.21
Absolute structureKnown absolute configurationKnown absolute configuration

Computer programs: CrysAlis CCD (Oxford Diffraction, 2009), CrysAlis RED (Oxford Diffraction, 2009), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), DIAMOND (Brandenburg, 2012).

Selected geometric parameters (Å, º) for (I) top
N1—C31.4438 (16)N1—H1N0.87 (2)
N1—C71.3568 (16)
C7—N1—C3120.10 (10)C7—N1—H1N119.1 (13)
C3—N1—H1N120.6 (12)
C7—N1—C3—C2149.02 (10)C3—N1—C7—O51.19 (18)
C7—N1—C3—C484.01 (12)C3—N1—C7—O6179.01 (10)
C2—C3—C4—C561.75 (13)O5—C7—N1—H1N175.9 (14)
Hydrogen-bond geometry (Å, º) for (I) top
D—H···AD—HH···AD···AD—H···A
N1—H1N···O4i0.87 (2)2.29 (2)3.1388 (16)166.6 (17)
C1—H1C···O5ii0.982.543.4775 (19)160
C1—H1B···O5iii0.982.633.4368 (18)140
C4—H4A···O1iv0.992.533.3869 (19)144
C10—H10B···O50.982.513.0875 (19)118
C10—H10A···O5i0.982.623.5407 (19)157
C11—H11A···O50.982.393.0045 (18)120
Symmetry codes: (i) x, y1, z; (ii) x+1, y+1/2, z; (iii) x+1, y, z; (iv) x, y+1, z.
Selected geometric parameters (Å, º) for (II) top
N1—C31.4669 (13)N1—C121.3996 (14)
N1—C71.4168 (14)
C7—N1—C3115.23 (9)C12—N1—C7119.14 (8)
C12—N1—C3120.73 (9)
C7—N1—C3—C2141.94 (9)C12—N1—C7—O651.38 (12)
C12—N1—C3—C263.05 (12)C3—N1—C7—O6153.18 (8)
C7—N1—C3—C489.45 (12)C3—N1—C12—O7159.03 (11)
C12—N1—C3—C465.56 (13)C7—N1—C12—O74.97 (16)
C2—C3—C4—C591.04 (12)C3—N1—C12—O819.26 (13)
C3—N1—C7—O524.65 (14)C7—N1—C12—O8173.32 (9)
C12—N1—C7—O5130.78 (11)
Hydrogen-bond geometry (Å, º) for (II) top
D—H···AD—HH···AD···AD—H···A
C1—H1B···O1i0.982.563.479 (2)156
C3—H3···O31.002.372.8121 (15)106
C3—H3···O4i1.002.493.2767 (16)135
C6—H6A···O3ii0.982.553.5079 (18)167
C9—H9A···O50.982.443.0261 (17)118
C11—H11C···O50.982.523.0769 (17)116
C11—H11B···O7iii0.982.583.5412 (16)168
C15—H15C···O70.982.422.9871 (17)116
C16—H16A···O70.982.422.9897 (17)117
C16—H16B···O5iv0.982.543.2780 (17)132
Symmetry codes: (i) x+1, y, z; (ii) x1/2, y+3/2, z+1; (iii) x+1, y+1/2, z+1/2; (iv) x, y1, z.
Selected bond lengths and angles (Å, °) for structures (I) and (II) compared with average values obtained from the CSD (Allen, 2002). top
Boc/bis-Boc pairsDIST1DIST2DIST3ANG1ANG2ANG3DIST4a
(I)1.357 (2)0.87 (2)1.444 (2)120.10 (10)121 (2)119 (2)0.031 (2)
(II)1.417 (2)1.400 (2)1.467 (2)115.23 (9)120.73 (9)119.14 (8)0.184 (2)
MUTTOK1.366 (3)b1.419 (3)125.0 (2)118 (2)117 (2)0.005 (2)
MUTTUQ, fragment 11.406 (2)1.413 (2)1.451 (2)120.5 (1)119.6 (1)119.9 (1)0.013 (1)
MUTTUQ, fragment 21.408 (2)1.408 (2)1.448 (2)119.5 (1)119.9 (1)120.6 (1)0.012 (1)
XUDQUJ, fragment 11.373 (3)b1.390 (2)125.9 (2)115 (2)117 (2)0.090 (2)
XUDQUJ, fragment 21.372 (2)b1.386 (3)127.2 (2)115 (2)118 (2)0.015 (2)
XUDQOD1.420 (2)1.405 (2)1.431 (2)118.5 (1)120.8 (1)120.6 (1)0.037 (2)
Protecting groups
Boc1.35b1.451221191190.04
Bis-Boc1.411.411.441181191230.04
Urethane1.35b1.441231181180.04
Bis-urethane1.411.411.441191181220.05
Acetyl1.35b1.431251171180.03
Bis-acetyl1.411.411.451191171250.03
Notes: (a) DIST4 is the distance between the N atom and the plane defined by the neighbouring atoms; other definitions are given in Fig. 4; (b) DIST2 in monosubstituted species is not given, as the H atoms were treated in different ways.
 

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