In the title compound, C16H17NO4, the benzyloxycarbonyl group is anti to the pyrrolic N atom. The molecules are joined into head-to-head dimers by hydrogen bonds involving the carboxylic acid groups. There is orientational disorder of these groups over two positions with approximately equal occupancy. A weaker hydrogen bond between the pyrrolic N atom and the carbonyl O atom of the benzyloxycarbonyl group joins the dimers into chains running parallel to the [110] direction.
Supporting information
CCDC reference: 152629
The title compound was prepared according to Archibald et al. (1966) from the parent 2,4-dimethyl-3-ethyl-5-carbobinzoxypyrrole by methyl chlorination with sulfuryl chloride followed by hydrolysis, giving the title compound in 60% yield. The compound was crystallized by slow evaporation from dichloromethane/methanol (1:1) giving small translucent plate-shaped crystals. A large number of crystals were examined by photographic methods until a specimen suitable for data collection was found. The crystal was still weakly diffracting (only ~50% of the measured reflections up to θ = 25° have I > 2σ). M.p. 437–438 K [literature 439 K (Archibald et al., 1966)]; elemental analysis: calculated for C16H17NO4: C 66.8, H 5.9, N 4.8%; found: C 65.9, H 6.0, N 4.1%.
The H atoms were placed at calculated positions and refined as riding using SHELX97 defaults (N—H 0.86 Å and C—H 0.93–0.97 Å), except for the carboxylic acid H atom. Inspection of a Fourier difference map showed the carboxylic acid H atom to be disordered. Refinement of the occupancy gave a 53 (8):47 (8)% occupancy ratio of the two alternate positions (attached to O1 or O2). Examination of the crystal structure with PLATON (Spek, 1995) showed that there are no solvent-accessible voids in the crystal lattice.
Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software; data reduction: HELENA (Spek, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: SHELXL97.
benzyl 2-carboxy-3-ethyl-4-methylpyrrole-5-carboxylate
top
Crystal data top
C16H17NO4 | F(000) = 1216 |
Mr = 287.31 | Dx = 1.302 Mg m−3 |
Monoclinic, C2/c | Mo Kα radiation, λ = 0.71073 Å |
a = 22.195 (6) Å | Cell parameters from 25 reflections |
b = 5.2607 (13) Å | θ = 6.0–13.1° |
c = 25.413 (3) Å | µ = 0.09 mm−1 |
β = 98.938 (15)° | T = 293 K |
V = 2931.3 (11) Å3 | Plate, colourless translucent |
Z = 8 | 0.37 × 0.37 × 0.10 mm |
Data collection top
Enraf-Nonius CAD-4 diffractometer | Rint = 0.045 |
Radiation source: fine-focus sealed tube | θmax = 25.0°, θmin = 3.3° |
Graphite monochromator | h = 0→26 |
ω–2θ scans | k = 0→6 |
2638 measured reflections | l = −30→29 |
2568 independent reflections | 3 standard reflections every 180 min |
1253 reflections with I > 2σ(I) | intensity decay: 1% |
Refinement top
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.041 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.129 | H atoms treated by a mixture of independent and constrained refinement |
S = 0.96 | w = 1/[σ2(Fo2) + (0.0669P)2 + 0.6191P] where P = (Fo2 + 2Fc2)/3 |
2568 reflections | (Δ/σ)max < 0.001 |
199 parameters | Δρmax = 0.16 e Å−3 |
0 restraints | Δρmin = −0.17 e Å−3 |
Crystal data top
C16H17NO4 | V = 2931.3 (11) Å3 |
Mr = 287.31 | Z = 8 |
Monoclinic, C2/c | Mo Kα radiation |
a = 22.195 (6) Å | µ = 0.09 mm−1 |
b = 5.2607 (13) Å | T = 293 K |
c = 25.413 (3) Å | 0.37 × 0.37 × 0.10 mm |
β = 98.938 (15)° | |
Data collection top
Enraf-Nonius CAD-4 diffractometer | Rint = 0.045 |
2638 measured reflections | 3 standard reflections every 180 min |
2568 independent reflections | intensity decay: 1% |
1253 reflections with I > 2σ(I) | |
Refinement top
R[F2 > 2σ(F2)] = 0.041 | 0 restraints |
wR(F2) = 0.129 | H atoms treated by a mixture of independent and constrained refinement |
S = 0.96 | Δρmax = 0.16 e Å−3 |
2568 reflections | Δρmin = −0.17 e Å−3 |
199 parameters | |
Special details top
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 | x | y | z | Uiso*/Ueq | Occ. (<1) |
N1 | 0.15075 (8) | 0.4042 (4) | 0.46155 (7) | 0.0524 (6) | |
H1 | 0.1701 | 0.3000 | 0.4842 | 0.063* | |
O1 | 0.07475 (8) | 0.0965 (5) | 0.50807 (8) | 0.0695 (7) | |
H1A | 0.048 (4) | −0.01 (2) | 0.517 (3) | 0.104* | 0.53 (8) |
O2 | −0.00716 (8) | 0.2519 (4) | 0.45602 (8) | 0.0662 (6) | |
H2 | −0.030 (4) | 0.16 (2) | 0.472 (3) | 0.099* | 0.47 (8) |
O3 | 0.27747 (9) | 0.4599 (5) | 0.46634 (9) | 0.0950 (8) | |
O4 | 0.26078 (8) | 0.7786 (5) | 0.40986 (9) | 0.0898 (8) | |
C2 | 0.08877 (10) | 0.4190 (5) | 0.44821 (9) | 0.0483 (6) | |
C3 | 0.07518 (11) | 0.6099 (5) | 0.41066 (9) | 0.0496 (6) | |
C5 | 0.17672 (10) | 0.5810 (6) | 0.43316 (9) | 0.0511 (7) | |
C6 | 0.04998 (11) | 0.2466 (6) | 0.47229 (10) | 0.0516 (7) | |
C7 | 0.01351 (11) | 0.6876 (6) | 0.38249 (11) | 0.0635 (8) | |
H7A | 0.0120 | 0.8713 | 0.3792 | 0.076* | |
H7B | −0.0173 | 0.6361 | 0.4036 | 0.076* | |
C8 | −0.00078 (13) | 0.5699 (8) | 0.32772 (13) | 0.0949 (11) | |
H8A | 0.0300 | 0.6179 | 0.3069 | 0.142* | |
H8B | −0.0398 | 0.6290 | 0.3105 | 0.142* | |
H8C | −0.0016 | 0.3882 | 0.3309 | 0.142* | |
C9 | 0.13762 (12) | 0.9259 (6) | 0.36351 (11) | 0.0662 (8) | |
H9A | 0.1635 | 1.0546 | 0.3818 | 0.099* | |
H9B | 0.0983 | 0.9973 | 0.3507 | 0.099* | |
H9C | 0.1554 | 0.8627 | 0.3340 | 0.099* | |
C10 | 0.24292 (11) | 0.5948 (6) | 0.43876 (10) | 0.0578 (7) | |
C11 | 0.32562 (12) | 0.8112 (8) | 0.40807 (12) | 0.0863 (11) | |
H11A | 0.3484 | 0.6684 | 0.4252 | 0.104* | |
H11B | 0.3404 | 0.9655 | 0.4266 | 0.104* | |
C12 | 0.33374 (11) | 0.8269 (6) | 0.35103 (11) | 0.0594 (8) | |
C13 | 0.36806 (14) | 0.6519 (6) | 0.32857 (14) | 0.0792 (10) | |
H13 | 0.3869 | 0.5202 | 0.3493 | 0.095* | |
C14 | 0.37483 (16) | 0.6693 (7) | 0.27582 (16) | 0.0903 (11) | |
H14 | 0.3987 | 0.5510 | 0.2614 | 0.108* | |
C15 | 0.34672 (14) | 0.8590 (7) | 0.24453 (13) | 0.0764 (9) | |
H15 | 0.3512 | 0.8693 | 0.2088 | 0.092* | |
C16 | 0.31222 (13) | 1.0324 (7) | 0.26582 (12) | 0.0739 (9) | |
H16 | 0.2928 | 1.1613 | 0.2446 | 0.089* | |
C17 | 0.30587 (13) | 1.0183 (6) | 0.31852 (13) | 0.0685 (8) | |
H17 | 0.2824 | 1.1394 | 0.3327 | 0.082* | |
C4 | 0.13078 (10) | 0.7118 (5) | 0.40117 (9) | 0.0504 (7) | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
N1 | 0.0452 (11) | 0.0716 (16) | 0.0405 (11) | −0.0103 (11) | 0.0069 (8) | 0.0088 (12) |
O1 | 0.0484 (10) | 0.0903 (18) | 0.0703 (13) | −0.0121 (11) | 0.0102 (9) | 0.0268 (13) |
O2 | 0.0444 (11) | 0.0855 (16) | 0.0678 (12) | −0.0143 (10) | 0.0054 (8) | 0.0152 (11) |
O3 | 0.0508 (11) | 0.123 (2) | 0.1076 (18) | −0.0135 (12) | 0.0003 (11) | 0.0603 (16) |
O4 | 0.0499 (11) | 0.123 (2) | 0.0990 (15) | −0.0135 (12) | 0.0185 (10) | 0.0503 (15) |
C2 | 0.0435 (13) | 0.0627 (18) | 0.0401 (12) | −0.0079 (13) | 0.0112 (10) | −0.0015 (14) |
C3 | 0.0510 (14) | 0.0562 (18) | 0.0436 (13) | −0.0010 (13) | 0.0137 (10) | −0.0007 (13) |
C5 | 0.0480 (14) | 0.0652 (18) | 0.0418 (13) | −0.0147 (13) | 0.0121 (11) | 0.0015 (14) |
C6 | 0.0462 (15) | 0.0657 (19) | 0.0432 (14) | −0.0084 (14) | 0.0074 (11) | 0.0028 (14) |
C7 | 0.0526 (15) | 0.071 (2) | 0.0686 (18) | 0.0039 (14) | 0.0137 (13) | 0.0108 (16) |
C8 | 0.0676 (19) | 0.123 (3) | 0.085 (2) | 0.005 (2) | −0.0168 (16) | −0.006 (2) |
C9 | 0.0673 (17) | 0.065 (2) | 0.0698 (18) | −0.0048 (16) | 0.0206 (14) | 0.0148 (17) |
C10 | 0.0525 (16) | 0.077 (2) | 0.0443 (14) | −0.0155 (16) | 0.0087 (12) | 0.0055 (15) |
C11 | 0.0501 (16) | 0.131 (3) | 0.078 (2) | −0.0308 (18) | 0.0109 (14) | 0.028 (2) |
C12 | 0.0438 (13) | 0.065 (2) | 0.0683 (18) | −0.0197 (15) | 0.0061 (13) | 0.0088 (16) |
C13 | 0.0704 (19) | 0.062 (2) | 0.101 (3) | −0.0020 (17) | −0.0014 (18) | 0.011 (2) |
C14 | 0.095 (2) | 0.086 (3) | 0.090 (3) | 0.008 (2) | 0.014 (2) | −0.023 (2) |
C15 | 0.082 (2) | 0.085 (3) | 0.0624 (18) | −0.0137 (19) | 0.0122 (16) | −0.0132 (19) |
C16 | 0.080 (2) | 0.072 (2) | 0.072 (2) | −0.0001 (17) | 0.0202 (16) | 0.0138 (18) |
C17 | 0.0641 (17) | 0.064 (2) | 0.083 (2) | 0.0001 (15) | 0.0282 (15) | 0.0059 (17) |
C4 | 0.0546 (14) | 0.0570 (18) | 0.0419 (13) | −0.0030 (13) | 0.0146 (11) | 0.0018 (13) |
Geometric parameters (Å, º) top
N1—C5 | 1.359 (3) | C8—H8B | 0.9600 |
N1—C2 | 1.367 (3) | C8—H8C | 0.9600 |
N1—H1 | 0.8600 | C9—C4 | 1.501 (3) |
O1—C6 | 1.264 (3) | C9—H9A | 0.9600 |
O1—H1A | 0.87 (12) | C9—H9B | 0.9600 |
O2—C6 | 1.272 (3) | C9—H9C | 0.9600 |
O2—H2 | 0.86 (13) | C11—C12 | 1.491 (4) |
O3—C10 | 1.190 (3) | C11—H11A | 0.9700 |
O4—C10 | 1.312 (3) | C11—H11B | 0.9700 |
O4—C11 | 1.457 (3) | C12—C13 | 1.374 (4) |
C2—C3 | 1.386 (3) | C12—C17 | 1.386 (4) |
C2—C6 | 1.450 (3) | C13—C14 | 1.375 (5) |
C3—C4 | 1.400 (3) | C13—H13 | 0.9300 |
C3—C7 | 1.499 (3) | C14—C15 | 1.365 (5) |
C5—C4 | 1.385 (3) | C14—H14 | 0.9300 |
C5—C10 | 1.456 (3) | C15—C16 | 1.357 (4) |
C7—C8 | 1.511 (4) | C15—H15 | 0.9300 |
C7—H7A | 0.9700 | C16—C17 | 1.370 (4) |
C7—H7B | 0.9700 | C16—H16 | 0.9300 |
C8—H8A | 0.9600 | C17—H17 | 0.9300 |
| | | |
C5—N1—C2 | 108.8 (2) | C4—C9—H9C | 109.5 |
C5—N1—H1 | 125.6 | H9A—C9—H9C | 109.5 |
C2—N1—H1 | 125.6 | H9B—C9—H9C | 109.5 |
C6—O1—H1A | 111 (5) | O3—C10—O4 | 123.1 (2) |
C6—O2—H2 | 117 (5) | O3—C10—C5 | 125.2 (3) |
C10—O4—C11 | 119.3 (2) | O4—C10—C5 | 111.7 (3) |
N1—C2—C3 | 108.3 (2) | O4—C11—C12 | 107.8 (2) |
N1—C2—C6 | 120.0 (2) | O4—C11—H11A | 110.1 |
C3—C2—C6 | 131.6 (2) | C12—C11—H11A | 110.1 |
C2—C3—C4 | 107.0 (2) | O4—C11—H11B | 110.1 |
C2—C3—C7 | 127.6 (2) | C12—C11—H11B | 110.1 |
C4—C3—C7 | 125.2 (2) | H11A—C11—H11B | 108.5 |
N1—C5—C4 | 108.5 (2) | C13—C12—C17 | 117.7 (3) |
N1—C5—C10 | 119.2 (2) | C13—C12—C11 | 121.7 (3) |
C4—C5—C10 | 132.3 (2) | C17—C12—C11 | 120.6 (3) |
O1—C6—O2 | 123.2 (2) | C12—C13—C14 | 120.8 (3) |
O1—C6—C2 | 118.3 (2) | C12—C13—H13 | 119.6 |
O2—C6—C2 | 118.5 (2) | C14—C13—H13 | 119.6 |
C3—C7—C8 | 111.9 (2) | C15—C14—C13 | 120.5 (3) |
C3—C7—H7A | 109.2 | C15—C14—H14 | 119.8 |
C8—C7—H7A | 109.2 | C13—C14—H14 | 119.8 |
C3—C7—H7B | 109.2 | C16—C15—C14 | 119.6 (3) |
C8—C7—H7B | 109.2 | C16—C15—H15 | 120.2 |
H7A—C7—H7B | 107.9 | C14—C15—H15 | 120.2 |
C7—C8—H8A | 109.5 | C15—C16—C17 | 120.2 (3) |
C7—C8—H8B | 109.5 | C15—C16—H16 | 119.9 |
H8A—C8—H8B | 109.5 | C17—C16—H16 | 119.9 |
C7—C8—H8C | 109.5 | C16—C17—C12 | 121.2 (3) |
H8A—C8—H8C | 109.5 | C16—C17—H17 | 119.4 |
H8B—C8—H8C | 109.5 | C12—C17—H17 | 119.4 |
C4—C9—H9A | 109.5 | C5—C4—C3 | 107.3 (2) |
C4—C9—H9B | 109.5 | C5—C4—C9 | 127.5 (2) |
H9A—C9—H9B | 109.5 | C3—C4—C9 | 125.2 (2) |
| | | |
C5—N1—C2—C3 | −0.2 (3) | C10—O4—C11—C12 | 129.5 (3) |
C5—N1—C2—C6 | 178.9 (2) | O4—C11—C12—C13 | −118.6 (3) |
N1—C2—C3—C4 | 0.2 (3) | O4—C11—C12—C17 | 60.5 (4) |
C6—C2—C3—C4 | −178.7 (3) | C17—C12—C13—C14 | 0.7 (4) |
N1—C2—C3—C7 | 177.0 (2) | C11—C12—C13—C14 | 179.8 (3) |
C6—C2—C3—C7 | −1.9 (4) | C12—C13—C14—C15 | −1.0 (5) |
C2—N1—C5—C4 | 0.1 (3) | C13—C14—C15—C16 | 0.5 (5) |
C2—N1—C5—C10 | −177.3 (2) | C14—C15—C16—C17 | 0.4 (5) |
N1—C2—C6—O1 | 4.7 (4) | C15—C16—C17—C12 | −0.7 (5) |
C3—C2—C6—O1 | −176.5 (3) | C13—C12—C17—C16 | 0.1 (4) |
N1—C2—C6—O2 | −174.6 (2) | C11—C12—C17—C16 | −179.0 (3) |
C3—C2—C6—O2 | 4.2 (4) | N1—C5—C4—C3 | 0.0 (3) |
C2—C3—C7—C8 | −97.9 (3) | C10—C5—C4—C3 | 177.0 (3) |
C4—C3—C7—C8 | 78.4 (4) | N1—C5—C4—C9 | 179.2 (2) |
C11—O4—C10—O3 | 4.3 (5) | C10—C5—C4—C9 | −3.8 (5) |
C11—O4—C10—C5 | −176.4 (3) | C2—C3—C4—C5 | −0.1 (3) |
N1—C5—C10—O3 | 0.8 (4) | C7—C3—C4—C5 | −177.0 (2) |
C4—C5—C10—O3 | −175.9 (3) | C2—C3—C4—C9 | −179.3 (2) |
N1—C5—C10—O4 | −178.4 (2) | C7—C3—C4—C9 | 3.7 (4) |
C4—C5—C10—O4 | 4.8 (4) | | |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···O3i | 0.86 | 2.09 | 2.942 (3) | 175 |
O1—H1A···O2ii | 0.87 (12) | 1.77 (13) | 2.621 (3) | 168 (8) |
Symmetry codes: (i) −x+1/2, −y+1/2, −z+1; (ii) −x, −y, −z+1. |
Experimental details
Crystal data |
Chemical formula | C16H17NO4 |
Mr | 287.31 |
Crystal system, space group | Monoclinic, C2/c |
Temperature (K) | 293 |
a, b, c (Å) | 22.195 (6), 5.2607 (13), 25.413 (3) |
β (°) | 98.938 (15) |
V (Å3) | 2931.3 (11) |
Z | 8 |
Radiation type | Mo Kα |
µ (mm−1) | 0.09 |
Crystal size (mm) | 0.37 × 0.37 × 0.10 |
|
Data collection |
Diffractometer | Enraf-Nonius CAD-4 diffractometer |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 2638, 2568, 1253 |
Rint | 0.045 |
(sin θ/λ)max (Å−1) | 0.594 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.041, 0.129, 0.96 |
No. of reflections | 2568 |
No. of parameters | 199 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.16, −0.17 |
Selected geometric parameters (Å, º) topN1—C5 | 1.359 (3) | O4—C11 | 1.457 (3) |
N1—C2 | 1.367 (3) | C2—C3 | 1.386 (3) |
O3—C10 | 1.190 (3) | C3—C4 | 1.400 (3) |
O4—C10 | 1.312 (3) | C5—C4 | 1.385 (3) |
| | | |
C10—O4—C11 | 119.3 (2) | O4—C10—C5 | 111.7 (3) |
O3—C10—O4 | 123.1 (2) | O4—C11—C12 | 107.8 (2) |
O3—C10—C5 | 125.2 (3) | | |
| | | |
C11—O4—C10—C5 | −176.4 (3) | C10—C5—C4—C9 | −3.8 (5) |
N1—C5—C10—O3 | 0.8 (4) | C7—C3—C4—C9 | 3.7 (4) |
C10—O4—C11—C12 | 129.5 (3) | | |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···O3i | 0.86 | 2.09 | 2.942 (3) | 175 |
O1—H1A···O2ii | 0.87 (12) | 1.77 (13) | 2.621 (3) | 168 (8) |
Symmetry codes: (i) −x+1/2, −y+1/2, −z+1; (ii) −x, −y, −z+1. |
The class of pyrrole derivatives has many members and includes naturally occurring compounds with important biological functions (Battersby & McDonald, 1976). Synthesized pyrroles have been used widely in the pharmaceutical industry and are precursors for the synthesis of porphyrins and other macrocycles which are of increasing use in the medical (Bonnet, 1995) and material sciences (Hudson et al., 1993; Grieve et al., 1994a,b). The incorporation of one or several fused-pyrrole rings the at β-pyrrolic positions of porphyrins is considered to afford an efficient pathway to a molecular architecture based on fused porphyrins. With this objective in mind, the title compound, (I), was synthesized and an X-ray diffraction study was undertaken to clarify the conformation of the molecule.
The endocyclic angles of the pyrrole ring add up to exactly 540°, indicating that the heterocycle is almost perfectly planar; in fact, no atom deviates by more than 0.0010 (15) Å from the least-squares plane. The two Nsp2—C bonds are consistent with the tabulated average value [1.372 (16) Å; Allen et al., 1987]. The largest bond distance within the heterocyclic ring is that opposite the N atom [1.400 (3) Å]. Whereas the methyl C9 atom is practically within the ring plane, with a deviation from the least-squares plane of just 0.015 (5) Å, the C6, C7 and C10 atoms have small but significant deviations from the plane of the ring [C6 − 0.025 (5), C7 − 0.063 (5) and C10 − 0.058 (5) Å].
The benzyloxycarbonyl group bonds to the pyrrole ring adopting an anti conformation with respect to N atom, as shown by the torsion angle N1—C5—C10—O4 of −178.4 (2)°. The phenyl ring is planar and makes an angle of 60.89 (11)° with the carboxylate group.
The carboxylic acid group exhibits disorder around the C2—C6 single bond, as shown by the similar C6—O1 [1.264 (3) Å] and C6—O2 [1.272 (3) Å] bond lengths. This group is twisted around the C2—C6 bond by an angle of 8.2 (2)°.
The plane formed by the ethyl group and the C3 atom is almost orthogonal to the pyrrole ring, a conformation that minimizes the steric interaction between the ethyl group and the adjacent methyl and carboxylic acid groups. The observed deviation of the C2—C3—C7—C8 torsion angle [−97.9 (3)°] from orthogonality and the small observed asymmetry between the exocyclic angles at C2 have the correct sign as expected from a stronger interaction with the carboxylic acid group.
The molecules are joined into head-to-head dimers by strong hydrogen bonds involving two carboxylic acid groups [O1···O2 2.621 (3) Å]. Weaker hydrogen bonds exist between the N1 atom and the carbonyl O3 atom of the benzyloxycarbonyl group of a neighbouring molecule. This hydrogen-bond pattern joins the molecules into infinite chains running parallel to the [110] direction. C—H···O interactions have been recognized as important secondary interactions and, in many cases, play a dominant role in the molecular conformation (Steiner, 1997). Two such intramolecular interactions can be identified in the present structure, i.e. a weak C7···O2 [3.037 (4) Å] interaction and a strong C11···O3 [2.691 (4) Å] interaction.