tert-Butoxy­carbonyl-L-leucyl-L-alanine trichloro­ethyl ester (Boc-L-Leu-L-Ala-OTce)

The title compound, C₁₆H₂₇Cl₃N₂O₅, which is an enantiopure dipeptide trichloro­ethyl ester, adopts an extended conformation. The mol­ecules are linked via –NH...O=C hydrogen bonds into a unique β-spiral assembly along the c axis.

Key indicators

• Single-crystal X-ray study
• T = 173 K
• Mean [sigma](C-C) = 0.009 Å
• R factor = 0.043
• wR factor = 0.079
• Data-to-parameter ratio = 15.7

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT026_ALERT_3_B Ratio Observed / Unique Reflections too Low ....         32 Perc.

Author Response: Diffractions from the crystal of (I) were too weak to collect enough numbers, even we have used many techniques to increase the number data available (low temperature, Cu-K(alpha) radiationan, area detector).

PLAT220_ALERT_2_B Large Non-Solvent    C     Ueq(max)/Ueq(min) ...       4.47 Ratio

Author Response: It is due to the difference of thermal mobility. The atoms located at chain-ends and amino-acid side chains often show higer U(eq) compared with the atoms located inside of the molecule.

PLAT242_ALERT_2_B Check Low       Ueq as Compared to Neighbors for       C101

Author Response: It is due to the difference of thermal mobility. The atoms (C102, C103, and C104) often show higer U(eq) compared with the atoms (C101 and C105) located inside of the Boc group.

Alert level C
PLAT222_ALERT_3_C Large Non-Solvent    H     Ueq(max)/Ueq(min) ...       3.75 Ratio

Author Response: It is due to the difference of thermal mobility. The atoms located at chain-ends (Boc- and -OEt) and amino-acid side chains often show higer U(eq) compared with the atoms located inside of the molecule.

PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for       C105

Author Response: It is due to the difference of thermal mobility. The atoms (C102, C103, and C104) often show higer U(eq) compared with the atoms (C101 and C105) located inside of the Boc group.

PLAT340_ALERT_3_C Low Bond Precision on C-C bonds (x 1000) Ang ...          9

Author Response: The chain end atoms (such as Boc- and -OEt) often show lower bond precision due to their higher thermal mobility compared with the atoms located inside of the chain.

PLAT431_ALERT_2_C Short Inter HL..A Contact  Cl43   ..  O301    ..       3.02 Ang.

Alert level G
REFLT03_ALERT_4_G Please check that the estimate of the number of Friedel pairs is
            correct. If it is not, please give the correct count in the
            _publ_section_exptl_refinement section of the submitted CIF.
           From the CIF: _diffrn_reflns_theta_max           68.19
           From the CIF: _reflns_number_total               4134
           Count of symmetry unique reflns         2145
           Completeness (_total/calc)            192.73%
           TEST3: Check Friedels for noncentro structure
           Estimate of Friedel pairs measured      1989
           Fraction of Friedel pairs measured     0.927
           Are heavy atom types Z>Si present        yes

Author Response: We have checked the number of Friedel pairs is correct.

   0 ALERT level A = In general: serious problem
   3 ALERT level B = Potentially serious problem
   4 ALERT level C = Check and explain
   1 ALERT level G = General alerts; check

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   4 ALERT type 2 Indicator that the structure model may be wrong or deficient
   3 ALERT type 3 Indicator that the structure quality may be low
   1 ALERT type 4 Improvement, methodology, query or suggestion

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Computing details

Data collection: RAPID-AUTO (Rigaku, 2003); cell refinement: RAPID-AUTO; data reduction: CrystalStructure (Rigaku, 2003); program(s) used to solve structure: SIR2002 (Burla et al., 2003); program(s) used to refine structure: CRYSTALS (Betteridge et al., 2003); molecular graphics: ORTEP (Johnson, 1965); software used to prepare material for publication: CrystalStructure.

tert-Butoxycarbonyl-L-leucyl-L-alanine trichloroethyl ester

Crystal data

C16H27Cl3N2O5	Dx = 1.264 Mg m^−3
Mr = 433.75	Melting point = 415–417 K
Hexagonal, P65	Cu Kα radiation, λ = 1.5418 Å
Hall symbol: P 65	Cell parameters from 21563 reflections
a = 12.1055 (14) Å	θ = 3.3–68.2°
c = 26.939 (5) Å	µ = 3.85 mm^−1
V = 3418.8 (8) Å^3	T = 173 K
Z = 6	Needle, colorless
F(000) = 1368.00	0.30 × 0.01 × 0.01 mm
? # Insert any comments here.

Data collection

Rigaku R-AXIS RAPID diffractometer	Rint = 0.097
Detector resolution: 10.00 pixels mm^-1	θmax = 68.2°
ω scans	h = −14→14
29240 measured reflections	k = −14→14
4134 independent reflections	l = −31→32
1326 reflections with F^2 > 2σ(F^2)

Refinement

Refinement on F^2	w = 1/[0.1σ(Fo^2) + 2.0]/(4Fo^2)
R[F^2 > 2σ(F^2)] = 0.043	(Δ/σ)max < 0.001
wR(F^2) = 0.079	Δρmax = 1.14 e Å^−3
S = 1.06	Δρmin = −0.65 e Å^−3
4134 reflections	Absolute structure: Flack (1983), 1992 Friedel pairs
263 parameters	Absolute structure parameter: 0.05 (2)
H-atom parameters constrained

Special details

Refinement. Refinement using all reflections. The weighted R-factor (wR) and goodness of fit (S) are based on F². R-factor (gt) are based on F. The threshold expression of F² > 2.0 σ(F²) is used only for calculating R-factor (gt).

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Cl41	0.70249 (14)	0.13892 (18)	0.55437 (6)	0.0759 (5)
Cl42	0.78694 (16)	0.3511 (2)	0.62183 (6)	0.0851 (6)
Cl43	0.53865 (16)	0.12709 (19)	0.63264 (6)	0.0765 (5)
O101	−0.2252 (4)	−0.1300 (3)	0.61682 (12)	0.0587 (10)
O102	−0.1765 (5)	−0.0711 (3)	0.53796 (13)	0.0844 (14)
O201	0.1976 (3)	0.1218 (3)	0.59163 (12)	0.0499 (11)
O301	0.4220 (3)	0.3423 (4)	0.53180 (16)	0.0664 (13)
O401	0.4902 (3)	0.2020 (4)	0.53375 (12)	0.0581 (11)
N201	−0.0625 (3)	0.0564 (4)	0.59947 (12)	0.0448 (12)
N301	0.1778 (3)	0.1437 (4)	0.51002 (14)	0.0439 (12)
C101	−0.3418 (6)	−0.2494 (5)	0.6070 (2)	0.0737 (19)
C102	−0.3883 (7)	−0.3026 (7)	0.6566 (2)	0.098 (2)
C103	−0.4377 (7)	−0.2222 (10)	0.5836 (3)	0.143 (3)
C104	−0.3139 (13)	−0.3318 (8)	0.5771 (4)	0.162 (4)
C105	−0.1566 (5)	−0.0495 (5)	0.58122 (17)	0.0464 (16)
C201	0.0292 (4)	0.1567 (5)	0.56708 (14)	0.0380 (13)
C202	0.1402 (4)	0.1392 (4)	0.55772 (18)	0.0362 (13)
C203	0.0738 (4)	0.2865 (4)	0.59201 (19)	0.0393 (13)
C204	0.1523 (5)	0.4006 (5)	0.5584 (2)	0.0568 (17)
C205	0.2060 (7)	0.5224 (5)	0.5901 (2)	0.087 (2)
C206	0.0732 (6)	0.4062 (6)	0.5164 (2)	0.070 (2)
C301	0.2858 (4)	0.1316 (5)	0.49924 (18)	0.0468 (16)
C302	0.4038 (4)	0.2403 (6)	0.52338 (18)	0.0470 (16)
C303	0.3090 (6)	0.1349 (8)	0.4433 (2)	0.085 (2)
C401	0.6029 (5)	0.2933 (6)	0.5578 (2)	0.066 (2)
C402	0.6567 (5)	0.2319 (7)	0.5900 (2)	0.0630 (19)
H1	−0.4028	−0.2466	0.6767	0.100*
H2	−0.4650	−0.3823	0.6538	0.100*
H3	−0.3240	−0.3151	0.6713	0.100*
H4	−0.4557	−0.1679	0.6032	0.141*
H5	−0.4026	−0.1822	0.5527	0.141*
H6	−0.5142	−0.3006	0.5779	0.141*
H7	−0.3923	−0.4083	0.5714	0.180*
H8	−0.2801	−0.2902	0.5463	0.180*
H9	−0.2552	−0.3515	0.5924	0.180*
H10	−0.0582	0.0700	0.6343	0.053*
H11	−0.0122	0.1546	0.5368	0.048*
H12	0.0028	0.2917	0.6040	0.048*
H13	0.1259	0.2907	0.6191	0.048*
H14	0.2219	0.3948	0.5451	0.068*
H15	0.2561	0.5187	0.6165	0.099*
H16	0.2568	0.5955	0.5703	0.099*
H17	0.1359	0.5275	0.6034	0.099*
H18	0.0039	0.4121	0.5300	0.083*
H19	0.1223	0.4776	0.4955	0.083*
H20	0.0413	0.3299	0.4976	0.082*
H21	0.1368	0.1622	0.4839	0.056*
H22	0.2718	0.0525	0.5122	0.059*
H23	0.3817	0.1275	0.4358	0.111*
H24	0.2364	0.0691	0.4268	0.110*
H25	0.3231	0.2156	0.4324	0.111*
H26	0.6636	0.3410	0.5328	0.084*
H27	0.5857	0.3487	0.5770	0.084*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cl41	0.0749 (11)	0.1125 (13)	0.0685 (9)	0.0680 (10)	0.0112 (8)	0.0066 (8)
Cl42	0.0596 (9)	0.1154 (15)	0.0830 (11)	0.0457 (10)	−0.0121 (8)	−0.0095 (10)
Cl43	0.0700 (10)	0.1015 (12)	0.0605 (8)	0.0447 (9)	0.0191 (7)	0.0151 (8)
O101	0.065 (2)	0.046 (2)	0.041 (2)	0.0104 (18)	0.0005 (18)	0.0047 (17)
O102	0.111 (3)	0.064 (2)	0.037 (2)	0.012 (2)	0.006 (2)	−0.0059 (19)
O201	0.062 (2)	0.068 (2)	0.0360 (18)	0.046 (2)	0.0037 (17)	0.0142 (17)
O301	0.058 (2)	0.059 (2)	0.087 (3)	0.033 (2)	0.002 (2)	0.009 (2)
O401	0.045 (2)	0.079 (2)	0.065 (2)	0.042 (2)	−0.0083 (17)	−0.008 (2)
N201	0.046 (2)	0.057 (2)	0.029 (2)	0.023 (2)	0.0026 (19)	0.0044 (19)
N301	0.038 (2)	0.068 (2)	0.033 (2)	0.032 (2)	−0.0010 (17)	0.0028 (18)
C101	0.067 (4)	0.041 (3)	0.078 (4)	0.000 (3)	0.011 (3)	0.003 (3)
C102	0.083 (5)	0.066 (4)	0.100 (5)	0.005 (3)	0.013 (4)	0.021 (4)
C103	0.041 (4)	0.132 (8)	0.180 (10)	−0.012 (4)	−0.030 (5)	0.025 (7)
C104	0.166 (11)	0.055 (4)	0.229 (11)	0.028 (5)	0.062 (8)	−0.022 (6)
C105	0.047 (3)	0.048 (3)	0.031 (3)	0.014 (2)	0.016 (2)	0.007 (2)
C201	0.039 (2)	0.057 (3)	0.024 (2)	0.028 (2)	−0.0022 (19)	0.005 (2)
C202	0.045 (2)	0.040 (2)	0.030 (2)	0.026 (2)	0.003 (2)	0.007 (2)
C203	0.036 (2)	0.040 (2)	0.044 (2)	0.021 (2)	0.007 (2)	0.004 (2)
C204	0.060 (3)	0.051 (3)	0.059 (3)	0.028 (2)	0.010 (2)	0.021 (2)
C205	0.104 (5)	0.047 (3)	0.097 (5)	0.028 (3)	0.035 (4)	0.017 (3)
C206	0.066 (3)	0.066 (3)	0.074 (4)	0.030 (3)	−0.003 (3)	0.015 (3)
C301	0.030 (2)	0.081 (4)	0.037 (2)	0.033 (2)	−0.001 (2)	0.003 (2)
C302	0.043 (3)	0.069 (3)	0.038 (2)	0.035 (2)	0.010 (2)	0.011 (2)
C303	0.070 (4)	0.151 (7)	0.056 (3)	0.071 (5)	0.006 (3)	−0.010 (3)
C401	0.045 (3)	0.092 (4)	0.074 (4)	0.043 (3)	−0.009 (3)	0.001 (3)
C402	0.062 (3)	0.088 (4)	0.050 (3)	0.045 (3)	−0.001 (3)	0.006 (3)

Geometric parameters (Å, º)

Cl41—C402	1.766 (9)	N301—H21	0.950
Cl42—C402	1.740 (5)	C102—H1	0.950
Cl43—C402	1.777 (5)	C102—H2	0.950
O101—C101	1.453 (6)	C102—H3	0.950
O101—C105	1.323 (5)	C103—H4	0.950
O102—C105	1.192 (5)	C103—H5	0.950
O201—C202	1.228 (7)	C103—H6	0.950
O301—C302	1.163 (9)	C104—H7	0.950
O401—C302	1.368 (9)	C104—H8	0.950
O401—C401	1.412 (6)	C104—H9	0.950
N201—C105	1.312 (5)	C201—H11	0.950
N201—C201	1.456 (5)	C203—H12	0.950
N301—C202	1.355 (6)	C203—H13	0.950
N301—C301	1.418 (8)	C204—H14	0.950
C101—C102	1.467 (9)	C205—H15	0.950
C101—C103	1.495 (14)	C205—H16	0.950
C101—C104	1.448 (16)	C205—H17	0.950
C201—C202	1.482 (9)	C206—H18	0.950
C201—C203	1.537 (7)	C206—H19	0.950
C203—C204	1.523 (6)	C206—H20	0.950
C204—C205	1.538 (8)	C301—H22	0.950
C204—C206	1.505 (9)	C303—H23	0.950
C301—C302	1.522 (6)	C303—H24	0.950
C301—C303	1.530 (7)	C303—H25	0.950
C401—C402	1.488 (12)	C401—H26	0.950
N201—H10	0.950	C401—H27	0.950
C101—O101—C105	122.7 (4)	C101—C103—H6	108.9
C302—O401—C401	115.6 (5)	H4—C103—H5	109.5
C105—N201—C201	121.2 (3)	H4—C103—H6	109.5
C202—N301—C301	119.9 (4)	H5—C103—H6	109.4
O101—C101—C102	103.8 (4)	C101—C104—H7	107.3
O101—C101—C103	109.4 (6)	C101—C104—H8	107.9
O101—C101—C104	110.0 (7)	C101—C104—H9	113.1
C102—C101—C103	108.1 (7)	H7—C104—H8	109.5
C102—C101—C104	112.0 (7)	H7—C104—H9	109.5
C103—C101—C104	113.0 (8)	H8—C104—H9	109.5
O101—C105—O102	124.3 (4)	N201—C201—H11	108.6
O101—C105—N201	111.5 (3)	C202—C201—H11	110.7
O102—C105—N201	124.2 (4)	C203—C201—H11	108.3
N201—C201—C202	110.5 (5)	C201—C203—H12	110.5
N201—C201—C203	108.8 (3)	C201—C203—H13	106.0
C202—C201—C203	109.9 (3)	C204—C203—H12	108.5
O201—C202—N301	120.3 (5)	C204—C203—H13	108.2
O201—C202—C201	121.9 (4)	H12—C203—H13	109.5
N301—C202—C201	117.7 (4)	C203—C204—H14	109.3
C201—C203—C204	114.1 (4)	C205—C204—H14	108.4
C203—C204—C205	108.2 (4)	C206—C204—H14	109.1
C203—C204—C206	111.4 (4)	C204—C205—H15	110.1
C205—C204—C206	110.4 (6)	C204—C205—H16	110.3
N301—C301—C302	109.8 (5)	C204—C205—H17	107.9
N301—C301—C303	111.4 (5)	H15—C205—H16	109.5
C302—C301—C303	108.5 (4)	H15—C205—H17	109.5
O301—C302—O401	123.3 (4)	H16—C205—H17	109.5
O301—C302—C301	126.8 (6)	C204—C206—H18	108.7
O401—C302—C301	109.9 (6)	C204—C206—H19	111.2
O401—C401—C402	111.7 (5)	C204—C206—H20	108.5
Cl41—C402—Cl42	110.7 (4)	H18—C206—H19	109.5
Cl41—C402—Cl43	107.0 (4)	H18—C206—H20	109.5
Cl41—C402—C401	110.9 (4)	H19—C206—H20	109.5
Cl42—C402—Cl43	110.2 (3)	N301—C301—H22	108.7
Cl42—C402—C401	108.4 (5)	C302—C301—H22	109.4
Cl43—C402—C401	109.7 (4)	C303—C301—H22	109.0
C105—N201—H10	119.0	C301—C303—H23	111.9
C201—N201—H10	119.6	C301—C303—H24	110.9
C202—N301—H21	120.5	C301—C303—H25	105.5
C301—N301—H21	119.4	H23—C303—H24	109.5
C101—C102—H1	111.9	H23—C303—H25	109.5
C101—C102—H2	109.9	H24—C303—H25	109.5
C101—C102—H3	106.6	O401—C401—H26	107.6
H1—C102—H2	109.5	O401—C401—H27	109.6
H1—C102—H3	109.5	C402—C401—H26	108.5
H2—C102—H3	109.5	C402—C401—H27	109.8
C101—C103—H4	113.0	H26—C401—H27	109.5
C101—C103—H5	106.4
C101—O101—C105—O102	−6.9 (12)	N201—C201—C202—O201	−49.8 (5)
C101—O101—C105—N201	174.3 (6)	N201—C201—C202—N301	130.6 (4)
C105—O101—C101—C102	−176.9 (7)	N201—C201—C203—C204	−170.0 (5)
C105—O101—C101—C103	−61.6 (9)	C202—C201—C203—C204	68.9 (6)
C105—O101—C101—C104	63.1 (10)	C203—C201—C202—O201	70.3 (5)
C302—O401—C401—C402	150.4 (5)	C203—C201—C202—N301	−109.3 (4)
C401—O401—C302—O301	2.8 (7)	C201—C203—C204—C205	−171.9 (6)
C401—O401—C302—C301	−178.1 (4)	C201—C203—C204—C206	66.5 (7)
C105—N201—C201—C202	−91.6 (6)	N301—C301—C302—O301	−29.1 (7)
C105—N201—C201—C203	147.7 (6)	N301—C301—C302—O401	151.8 (4)
C201—N201—C105—O101	177.2 (6)	C303—C301—C302—O301	92.9 (8)
C201—N201—C105—O102	−1.6 (11)	C303—C301—C302—O401	−86.2 (6)
C202—N301—C301—C302	−61.6 (6)	O401—C401—C402—Cl41	63.2 (5)
C202—N301—C301—C303	178.2 (4)	O401—C401—C402—Cl42	−175.1 (4)
C301—N301—C202—O201	−1.6 (6)	O401—C401—C402—Cl43	−54.8 (6)
C301—N301—C202—C201	178.0 (4)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N201—H10···O102^i	0.95	1.97	2.907 (5)	171
N301—H21···O201^ii	0.95	1.89	2.829 (6)	170

Symmetry codes: (i) y, −x+y, z+1/6; (ii) x−y, x, z−1/6.