(S)-(+)-2-Formamido-4-methyl­penta­noic acid

The title compound, C₇H₁₃NO₃, was synthesized from (S)-(+)-leucine. The stereochemistry is assumed to be unchanged by the reaction and only a single enanti­omer is present in the structure. The asymmetric unit consists of a single mol­ecule. The crystal structure displays N—H...O and O—H...O inter­molecular hydrogen bonding.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.031
• wR factor = 0.086
• Data-to-parameter ratio = 10.0

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for         C4

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           25.99
           From the CIF: _reflns_number_total               1044
           Count of symmetry unique reflns         1044
           Completeness (_total/calc)            100.00%
           TEST3: Check Friedels for noncentro structure
           Estimate of Friedel pairs measured         0
           Fraction of Friedel pairs measured     0.000
           Are heavy atom types Z>Si present         no
PLAT199_ALERT_1_G Check the Reported _cell_measurement_temperature        293 K
PLAT200_ALERT_1_G Check the Reported _diffrn_ambient_temperature .        293 K
PLAT791_ALERT_1_G Confirm the Absolute Configuration of C2     = .          S

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

   3 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   1 ALERT type 2 Indicator that the structure model may be wrong or deficient
   0 ALERT type 3 Indicator that the structure quality may be low
   1 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

The title compound (I) was synthesized as an intermediate in the synthesis of a chiral secondary alcohol. This chiral alcohol was in turn used as a chiral source in ligands used for the asymmetric addition of diethylzinc to benzaldehyde (Boyle et al., 2004).

The title compound was synthesized from commercial (S)-(+)-leucine and the stereochemistry is retained during the reaction. The structure therefore contains only a single enantiomer. The unit cell contains a single molecule. C6 and N1 are equatorial to the plane through C1 and C5 along the backbone of the molecule. Fig. 1 illustrates the geometry of the molecule and the labelling scheme employed. Each molecule exhibits intermolecular hydrogen bonding (N1—H1···O2ⁱ and O1—H1A···O3ⁱⁱ), resulting in a layered structure with O—H···O hydrogen bonding interactions between molecules within the layer and N—H···O interactions between layers. The molecular packing and hydrogen bonding interactions are shown in Fig. 2.

Related literature

For related literature, see: Boyle et al. (2004).

S2. Experimental

Acetic anhydride (30 mol equivalents) was added dropwise to a stirred solution of (S)-(+)-Leucine (1 mol equivalent) in formic acid (approximately 30 ml per 1.0 g of amino acid) at 0°C. After addition of the acetic anhydride, the external ice bath was removed and the solution stirred at room temperature for 24 h. The solution was treated with water (60 ml) and stirred for 1 hr. The solvent was removed under reduced pressure to yield a white residue. This residue was recrystallized from water to yield the pure product (I) (Boyle et al., 2004). Yield 72%. Colorless crystals suitable for X-ray diffraction were obtained by evaporation of water at room temperature in a fume hood over a period of 2 days.

S3. Refinement

Hydrogen atoms were first located in the difference map then positioned geometrically and allowed to ride on their respective parent atoms, with C—H = 0.93 or 0.97 Å, N—H = 0.86 Å and O—H = 0.82 Å. U_iso(H) values were set equal to 1.5U_eq for methyl C and O and 1.2U_eq for the remainder.

Computing details

Figures

	Fig. 1. The asymmetric unit of (I) showing atomic numbering scheme and ellipsoids at the 50% probability level.
	Fig. 2. The molecular packing, viewed down the a axis, showing layered structure and hydrogen bonding (dashed lines). H atoms have been omitted.