Reactive intermediates in peptide synthesis. ortho-Nitrophenyl N^[alpha]-para-toluenesulfonyl-[alpha]-aminoisobutyrate

The preparation, characterization, and molecular and crystal structures of the title compound [IUPAC name: 2-nitro­phenyl 2-methyl-2-(para-toluene­sulfonyl­amino)­propanoate], C₁₇H₁₈­N₂O₆S, are reported. The phenyl group is almost perpendicular to the plane of the adjacent ester moiety. One O atom of the nitro group is wedged between the two ester O atoms. The implications of this peculiar conformation for the chemistry of ortho-nitro­phenyl esters in peptide synthesis are discussed.

Computing details

Data collection: FEBO (Belletti, 1993); cell refinement: FEBO; data reduction: FEBO; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: PARST96 (Nardelli, 1995).

2-nitrophenyl 2-methyl-2-(para-toluenesulfonylamino)propanoate

Crystal data

C17H18N2O6S	F(000) = 1584
Mr = 378.39	Dx = 1.358 Mg m^−3
Monoclinic, C2/c	Melting point = 413–414 K
Hall symbol: -C 2yc	Mo Kα radiation, λ = 0.71073 Å
a = 36.449 (3) Å	Cell parameters from 48 reflections
b = 9.082 (2) Å	θ = 7–12°
c = 11.636 (2) Å	µ = 0.21 mm^−1
β = 106.10 (7)°	T = 293 K
V = 3700.8 (17) Å^3	Prism, colourless
Z = 8	0.5 × 0.3 × 0.3 mm

Data collection

Philips PW1100 diffractometer	Rint = 0.021
Radiation source: fine-focus sealed tube	θmax = 26.4°, θmin = 2.8°
Graphite monochromator	h = −45→43
θ/2θ scans	k = 0→11
3981 measured reflections	l = 0→14
3785 independent reflections	3 standard reflections every 50 reflections
2144 reflections with I > 2σ(I)	intensity decay: none

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.047	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.144	H-atom parameters constrained
S = 0.92	w = 1/[σ^2(Fo^2) + (0.0825P)^2] where P = (Fo^2 + 2Fc^2)/3
3785 reflections	(Δ/σ)max = 0.001
237 parameters	Δρmax = 0.32 e Å^−3
0 restraints	Δρmin = −0.33 e Å^−3

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
S1	0.159604 (19)	0.06512 (7)	0.85370 (5)	0.0460 (2)
O4	0.08239 (5)	0.25421 (18)	0.65733 (13)	0.0464 (4)
O1	0.16466 (5)	0.1328 (2)	0.74772 (16)	0.0602 (5)
O2	0.17315 (6)	0.1374 (2)	0.96724 (16)	0.0620 (6)
O3	0.09049 (6)	0.0876 (2)	0.52594 (15)	0.0667 (6)
O5	0.01270 (7)	0.2280 (4)	0.5083 (3)	0.1359 (14)
O6	−0.00882 (9)	0.3861 (4)	0.3773 (3)	0.1406 (14)
N1	0.11416 (6)	0.0471 (2)	0.83265 (16)	0.0443 (5)
H1	0.1053	0.0653	0.8923	0.053*
N2	0.01754 (8)	0.3320 (3)	0.4525 (2)	0.0755 (8)
C1	0.22880 (11)	−0.5468 (4)	0.8990 (4)	0.1073 (15)
H1A	0.2279	−0.5880	0.9742	0.161*	0.50
H1B	0.2548	−0.5437	0.8955	0.161*	0.50
H1C	0.2140	−0.6067	0.8349	0.161*	0.50
H1D	0.2365	−0.5709	0.8289	0.161*	0.50
H1E	0.2096	−0.6152	0.9075	0.161*	0.50
H1F	0.2505	−0.5522	0.9682	0.161*	0.50
C2	0.21266 (8)	−0.3926 (3)	0.8873 (3)	0.0692 (9)
C3	0.21036 (9)	−0.3058 (4)	0.7880 (3)	0.0734 (9)
H3	0.2195	−0.3428	0.7268	0.088*
C4	0.19487 (8)	−0.1660 (4)	0.7766 (3)	0.0627 (8)
H4	0.1936	−0.1101	0.7086	0.075*
C5	0.18121 (7)	−0.1099 (3)	0.8676 (2)	0.0453 (6)
C6	0.18382 (8)	−0.1932 (3)	0.9692 (2)	0.0575 (7)
H6	0.1751	−0.1557	1.0312	0.069*
C7	0.19947 (9)	−0.3322 (3)	0.9776 (3)	0.0689 (9)
H7	0.2012	−0.3873	1.0463	0.083*
C8	0.08643 (7)	0.0016 (3)	0.7187 (2)	0.0443 (6)
C9	0.04642 (8)	0.0087 (4)	0.7398 (3)	0.0630 (8)
H9A	0.0445	−0.0655	0.7966	0.094*
H9B	0.0273	−0.0082	0.6656	0.094*
H9C	0.0427	0.1040	0.7703	0.094*
C10	0.09383 (9)	−0.1514 (3)	0.6765 (3)	0.0663 (8)
H10A	0.1172	−0.1507	0.6538	0.099*
H10B	0.0731	−0.1791	0.6091	0.099*
H10C	0.0958	−0.2208	0.7402	0.099*
C11	0.08728 (7)	0.1153 (3)	0.6234 (2)	0.0421 (6)
C12	0.08504 (8)	0.3656 (3)	0.5769 (2)	0.0450 (6)
C13	0.11873 (8)	0.4419 (3)	0.6004 (2)	0.0560 (7)
H13	0.1387	0.4177	0.6669	0.067*
C14	0.12326 (9)	0.5552 (3)	0.5254 (3)	0.0658 (8)
H14	0.1462	0.6068	0.5417	0.079*
C15	0.09371 (11)	0.5906 (4)	0.4271 (3)	0.0717 (9)
H15	0.0969	0.6651	0.3758	0.086*
C16	0.05983 (11)	0.5173 (4)	0.4043 (3)	0.0733 (9)
H16	0.0399	0.5429	0.3380	0.088*
C17	0.05484 (8)	0.4043 (3)	0.4793 (2)	0.0551 (7)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
S1	0.0514 (4)	0.0496 (4)	0.0368 (3)	−0.0020 (3)	0.0119 (3)	0.0042 (3)
O4	0.0665 (12)	0.0432 (10)	0.0323 (9)	0.0020 (9)	0.0186 (8)	−0.0006 (7)
O1	0.0591 (12)	0.0714 (13)	0.0538 (11)	−0.0032 (10)	0.0220 (9)	0.0221 (10)
O2	0.0692 (13)	0.0618 (13)	0.0457 (10)	0.0005 (10)	0.0004 (9)	−0.0092 (9)
O3	0.1056 (17)	0.0647 (13)	0.0366 (10)	0.0067 (12)	0.0311 (10)	−0.0055 (9)
O5	0.0758 (18)	0.124 (2)	0.177 (3)	−0.0286 (17)	−0.0166 (19)	0.078 (2)
O6	0.091 (2)	0.190 (3)	0.104 (2)	−0.027 (2)	−0.0328 (17)	0.053 (2)
N1	0.0517 (12)	0.0549 (13)	0.0291 (10)	0.0022 (10)	0.0158 (9)	0.0020 (9)
N2	0.0690 (18)	0.080 (2)	0.0648 (17)	−0.0004 (16)	−0.0031 (14)	0.0096 (15)
C1	0.077 (3)	0.063 (2)	0.170 (4)	0.0108 (19)	0.016 (3)	−0.018 (3)
C2	0.0454 (17)	0.0568 (19)	0.100 (3)	0.0000 (14)	0.0115 (17)	−0.0140 (19)
C3	0.064 (2)	0.085 (2)	0.072 (2)	0.0101 (18)	0.0216 (17)	−0.023 (2)
C4	0.0596 (18)	0.083 (2)	0.0482 (16)	0.0054 (16)	0.0202 (14)	−0.0010 (15)
C5	0.0431 (14)	0.0548 (16)	0.0378 (13)	−0.0001 (12)	0.0108 (11)	−0.0004 (12)
C6	0.0673 (19)	0.0578 (17)	0.0509 (16)	0.0040 (15)	0.0224 (14)	0.0090 (14)
C7	0.068 (2)	0.0587 (19)	0.080 (2)	0.0045 (16)	0.0200 (17)	0.0188 (17)
C8	0.0468 (14)	0.0466 (14)	0.0392 (13)	−0.0035 (12)	0.0116 (11)	−0.0014 (11)
C9	0.0533 (17)	0.078 (2)	0.0606 (18)	−0.0101 (16)	0.0213 (14)	0.0106 (16)
C10	0.078 (2)	0.0474 (17)	0.0668 (19)	−0.0073 (15)	0.0087 (16)	−0.0062 (15)
C11	0.0453 (14)	0.0492 (15)	0.0324 (12)	0.0006 (12)	0.0116 (10)	−0.0059 (11)
C12	0.0598 (16)	0.0421 (14)	0.0347 (13)	0.0012 (13)	0.0158 (11)	0.0017 (11)
C13	0.0608 (18)	0.0544 (17)	0.0511 (16)	0.0005 (14)	0.0126 (13)	0.0082 (14)
C14	0.079 (2)	0.0556 (18)	0.0657 (19)	−0.0081 (16)	0.0242 (17)	0.0080 (15)
C15	0.107 (3)	0.0558 (19)	0.0533 (18)	−0.0030 (19)	0.0237 (18)	0.0139 (15)
C16	0.096 (3)	0.067 (2)	0.0459 (17)	0.0031 (19)	0.0010 (16)	0.0139 (15)
C17	0.0639 (18)	0.0544 (17)	0.0427 (14)	0.0021 (14)	0.0077 (13)	0.0018 (13)

Geometric parameters (Å, º)

S1—O2	1.4348 (19)	C4—H4	0.9300
S1—O1	1.4347 (18)	C5—C6	1.385 (3)
S1—N1	1.614 (2)	C6—C7	1.377 (4)
S1—C5	1.761 (3)	C6—H6	0.9300
O4—C11	1.348 (3)	C7—H7	0.9300
O4—C12	1.399 (3)	C8—C11	1.521 (3)
O3—C11	1.199 (3)	C8—C10	1.522 (4)
O5—N2	1.186 (3)	C8—C9	1.546 (3)
O6—N2	1.210 (4)	C9—H9A	0.9600
N1—C8	1.485 (3)	C9—H9B	0.9600
N1—H1	0.8600	C9—H9C	0.9600
N2—C17	1.463 (4)	C10—H10A	0.9600
C1—C2	1.511 (4)	C10—H10B	0.9600
C1—H1A	0.9600	C10—H10C	0.9600
C1—H1B	0.9600	C12—C13	1.370 (4)
C1—H1C	0.9600	C12—C17	1.390 (4)
C1—H1D	0.9600	C13—C14	1.388 (4)
C1—H1E	0.9600	C13—H13	0.9300
C1—H1F	0.9600	C14—C15	1.375 (4)
C2—C3	1.382 (5)	C14—H14	0.9300
C2—C7	1.385 (4)	C15—C16	1.362 (5)
C3—C4	1.382 (5)	C15—H15	0.9300
C3—H3	0.9300	C16—C17	1.392 (4)
C4—C5	1.386 (4)	C16—H16	0.9300
O2—S1—O1	120.14 (13)	C7—C6—C5	119.4 (3)
O2—S1—N1	105.23 (13)	C7—C6—H6	120.3
O1—S1—N1	106.51 (12)	C5—C6—H6	120.3
O2—S1—C5	107.31 (12)	C6—C7—C2	122.2 (3)
O1—S1—C5	107.74 (12)	C6—C7—H7	118.9
N1—S1—C5	109.65 (12)	C2—C7—H7	118.9
C11—O4—C12	116.22 (18)	N1—C8—C11	108.4 (2)
C8—N1—S1	125.39 (16)	N1—C8—C10	113.8 (2)
C8—N1—H1	117.3	C11—C8—C10	110.1 (2)
S1—N1—H1	117.3	N1—C8—C9	106.6 (2)
O5—N2—O6	120.7 (3)	C11—C8—C9	107.4 (2)
O5—N2—C17	120.7 (3)	C10—C8—C9	110.4 (2)
O6—N2—C17	118.4 (3)	C8—C9—H9A	109.5
C2—C1—H1A	109.5	C8—C9—H9B	109.5
C2—C1—H1B	109.5	H9A—C9—H9B	109.5
H1A—C1—H1B	109.5	C8—C9—H9C	109.5
C2—C1—H1C	109.5	H9A—C9—H9C	109.5
H1A—C1—H1C	109.5	H9B—C9—H9C	109.5
H1B—C1—H1C	109.5	C8—C10—H10A	109.5
C2—C1—H1D	109.5	C8—C10—H10B	109.5
H1A—C1—H1D	141.1	H10A—C10—H10B	109.5
H1B—C1—H1D	56.3	C8—C10—H10C	109.5
H1C—C1—H1D	56.3	H10A—C10—H10C	109.5
C2—C1—H1E	109.5	H10B—C10—H10C	109.5
H1A—C1—H1E	56.3	O3—C11—O4	121.9 (2)
H1B—C1—H1E	141.1	O3—C11—C8	125.0 (2)
H1C—C1—H1E	56.3	O4—C11—C8	113.00 (19)
H1D—C1—H1E	109.5	C13—C12—C17	119.9 (2)
C2—C1—H1F	109.5	C13—C12—O4	117.2 (2)
H1A—C1—H1F	56.3	C17—C12—O4	122.9 (2)
H1B—C1—H1F	56.3	C12—C13—C14	120.4 (3)
H1C—C1—H1F	141.1	C12—C13—H13	119.8
H1D—C1—H1F	109.5	C14—C13—H13	119.8
H1E—C1—H1F	109.5	C15—C14—C13	119.6 (3)
C3—C2—C7	117.1 (3)	C15—C14—H14	120.2
C3—C2—C1	122.4 (4)	C13—C14—H14	120.2
C7—C2—C1	120.5 (4)	C16—C15—C14	120.4 (3)
C2—C3—C4	122.2 (3)	C16—C15—H15	119.8
C2—C3—H3	118.9	C14—C15—H15	119.8
C4—C3—H3	118.9	C15—C16—C17	120.5 (3)
C3—C4—C5	119.2 (3)	C15—C16—H16	119.8
C3—C4—H4	120.4	C17—C16—H16	119.8
C5—C4—H4	120.4	C12—C17—C16	119.2 (3)
C6—C5—C4	119.8 (3)	C12—C17—N2	122.6 (3)
C6—C5—S1	119.7 (2)	C16—C17—N2	118.2 (3)
C4—C5—S1	120.5 (2)
O2—S1—N1—C8	168.99 (19)	N1—C8—C11—O3	130.1 (3)
O1—S1—N1—C8	40.4 (2)	C10—C8—C11—O3	5.1 (4)
C5—S1—N1—C8	−75.9 (2)	C9—C8—C11—O3	−115.1 (3)
C7—C2—C3—C4	−1.4 (5)	N1—C8—C11—O4	−52.5 (3)
C1—C2—C3—C4	178.7 (3)	C10—C8—C11—O4	−177.5 (2)
C2—C3—C4—C5	0.2 (5)	C9—C8—C11—O4	62.3 (3)
C3—C4—C5—C6	1.1 (4)	C11—O4—C12—C13	−100.6 (3)
C3—C4—C5—S1	−177.5 (2)	C11—O4—C12—C17	82.1 (3)
O2—S1—C5—C6	42.9 (2)	C17—C12—C13—C14	−1.7 (4)
O1—S1—C5—C6	173.6 (2)	O4—C12—C13—C14	−179.2 (2)
N1—S1—C5—C6	−70.9 (2)	C12—C13—C14—C15	−0.1 (4)
O2—S1—C5—C4	−138.5 (2)	C13—C14—C15—C16	1.3 (5)
O1—S1—C5—C4	−7.8 (3)	C14—C15—C16—C17	−0.8 (5)
N1—S1—C5—C4	107.7 (2)	C13—C12—C17—C16	2.2 (4)
C4—C5—C6—C7	−1.0 (4)	O4—C12—C17—C16	179.5 (3)
S1—C5—C6—C7	177.6 (2)	C13—C12—C17—N2	−177.0 (3)
C5—C6—C7—C2	−0.3 (5)	O4—C12—C17—N2	0.3 (4)
C3—C2—C7—C6	1.5 (5)	C15—C16—C17—C12	−1.0 (5)
C1—C2—C7—C6	−178.6 (3)	C15—C16—C17—N2	178.3 (3)
S1—N1—C8—C11	−61.5 (3)	O5—N2—C17—C12	−6.5 (5)
S1—N1—C8—C10	61.3 (3)	O6—N2—C17—C12	169.0 (3)
S1—N1—C8—C9	−176.83 (18)	O5—N2—C17—C16	174.3 (4)
C12—O4—C11—O3	−6.1 (3)	O6—N2—C17—C16	−10.2 (5)
C12—O4—C11—C8	176.4 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O3^i	0.86	2.26	2.894 (3)	131

Symmetry code: (i) x, −y, z+1/2.