Valyl benzyl ester chloride

In the title compound (systematic name: 1-benzyloxy-3-methyl-1-oxobutan-2-aminium chloride), C12H18NO2 +·Cl−, the ester group is approximately planar, with a maximum deviation of 0.040 (2) Å from the least-squares plane, and makes a dihedral angle of 28.92 (16)° with the phenyl ring. The crystal structure is organized by N—H⋯Cl hydrogen bonds which join the two components into a chain along the b axis. Pairs of chains arranged antiparallel are interconnected by further N—H⋯Cl hydrogen bonds, forming eight-membered rings. Similar packing modes have been observed in a number of amino acid ester halides with a short unit-cell parameter of ca 5.5 Å along the direction in which the chains run.

In the title compound (systematic name: 1-benzyloxy-3methyl-1-oxobutan-2-aminium chloride), C 12 H 18 NO 2 + ÁCl À , the ester group is approximately planar, with a maximum deviation of 0.040 (2) Å from the least-squares plane, and makes a dihedral angle of 28.92 (16) with the phenyl ring. The crystal structure is organized by N-HÁ Á ÁCl hydrogen bonds which join the two components into a chain along the b axis. Pairs of chains arranged antiparallel are interconnected by further N-HÁ Á ÁCl hydrogen bonds, forming eight-membered rings. Similar packing modes have been observed in a number of amino acid ester halides with a short unit-cell parameter of ca 5.5 Å along the direction in which the chains run.
BPS thanks Cipla, Bangalore for the gift of a sample of the title compound Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: IS2507).  The title compound (I, Scheme 1), valyl benzyl ester chloride [1-(benzyloxy)-3-methyl-1-oxobutan-2-aminium chloride], is a reactant (Buhlmayer et al., 1994) for the synthesis of valsartan, which belongs to the class of angiotensin II receptor antagonists (Black et al., 1997).

Structure Reports Online
The ester fragment C2/C1/O1/O11/C12 ( Fig. 1) is in a good approximation planar, maximum deviation from the least squares plane being 0.040 (2) Å, and it makes a dihedral angle of 28.92 (16) In the crystal structure, the N-H···Cl hydrogen bonds between the cations and chloride anions join the ionic components into the chains along the b direction ( Fig. 2 and Table 1). Within these chains there are additional relatively short and linear C-H···O hydrogen bonds involving the C=O oxygen atom. Using graph-set notation (Bernstein et al., 1995), there are two second-order antiparallel C 2 1 (4) chains which are interconnected by another hydrogen bonds into two different kinds of third-order hydrogen bonded R 4 2 (8) rings. Similar packing was observed in a number of the amino acid ester halides, and it always was connected with the unit-cell parameter of ca 5.5 Å. In the Cambridge Structural Database (Allen, 2002), there are 25 organic structures of the amino acid ester halides, and 10 of them display similar crystal packing and appropriate unit-cell parameter. For instance, L-tyrosyl methyl ester chloride (Bryndal et al., 2006) crystallizes in P2 1 2 1 2 1 space group with one of the unit-cell parameters 5.424 (2) Å, valyl methyl ester chloride (Jaeger et al., 2003) -also P2 1 2 1 2 1 , with 5.894 (2) Å, and (S-benzyl-L-cysteine methyl ester hydrochloride (Nastopoulos et al., 1987) -in P2 1 with c = 5.211 (2) Å.
The coordination of Cl ion by three hydrogen bonded N-H groups might be described as a trigonal pyramid with N-H groups at the base and Cl ion in the apex. The H···Cl···H angles are in the range 77-118°, and the sum of these angles is 277°.
It might be noted that if these coordination is described as tetragonal, the empty coordination place is taken by relatively strong C-H(methyl)···Cl hydrogen bond (Table 1).

Experimental
The title compound was obtained as a gift sample from Cipla, Bangalore, India. X-ray quality crystals were obtained from slow evaporation of an aqueous solution (m.p. 409-412 K).

Refinement
Positional and isotropic thermal parameters of the H atoms from the NH 3 group were freely refined. All other H atoms were put in the calculated idealized positions (C-H = 0.93-0.97 Å) and refined as riding, with U iso 's set at 1.2 (1.4 for methyl groups) times the U eq 's of appropriate carrier atoms. Fig. 1. Anisotropic ellipsoid representation of the title compound together with atom labelling scheme. The ellipsoids are drawn at 50% probability level, hydrogen atoms are depicted as spheres with arbitrary radii. Hydrogen bond is shown as dashed line. Fig. 2. The hydrogen-bonded structure of the title compound. Hydrogen bonds are shown as dashed lines. [Symmetry codes: (i) 1 -x, 1/2 + y, -z; (ii) x, 1 + y, z; (iii) 1 -x, -1/2 + y, -z; (iv) x, -1 + y, z; (v) 1 -x, -3/2 + y, -z.] Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.