Total synthesis of (+)-conagenin

tert-Butyl N-((1S)-2-hy-droxy-1-{N'-[(E)-2-hy-droxy-4-meth-oxy-benzyl-idene]hydrazinecarbon-yl}eth-yl)carbamate

The mol-ecule of the title compound, C(16)H(23)N(3)O(6), is twisted about the chiral C atom with the dihedral angle formed between the amide residues being 76.9 (3)°. Overall, the mol-ecule is curved with the terminal organic groups lying to the same side. The conformation about the imine bond [1.291 (5) Å] is E and an intra-molecular O-H⋯N hydrogen bond generates an S(6) ring. In the crystal, O-H⋯O and N-H⋯O hydrogen bonds involving the hy-droxy, amine and carbonyl groups lead to the formation of supra-molecular layers, which stack along the c-axis direction.

Benzyl N-(1-{N'-[(E)-2,3-dihy-droxy-benzyl-idene]hydrazinecarbon-yl}-2-hy-droxy-eth-yl)carbamate dihydrate

The organic mol­ecule in the title dihydrate, C₁₈H₁₉N₃O₆·2H₂O, adopts a twisted U-shape with the major twists evident about the chiral C atom [the C—N—C—C torsion angle is −88.2 (4) °] and about the oxygen–benzyl bond [C—O—C—C = 74.2 (4) °]. The conformation about the imine bond [1.290 (4) Å] is E and an intra­molecular O—H⋯N hydrogen bond helps to establish the near coplanarity of the hy­droxy­benzene and hydrazine groups. The crystal packing features O—H⋯O and N—H⋯O hydrogen bonds, leading to two-dimensional supra­molecular arrays in the ab plane with weak C—H⋯π connections between the arrays.

Benzyl N-(2-hy-droxy-1-{N'-[(1E)-2-hy-droxy-benzyl-idene]hydrazinecarbon-yl}eth-yl)carbamate

The mol-ecule of the title compound, C(18)H(19)N(3)O(5), adopts a curved arrangement with the terminal benzene rings lying to the same side. The hydroxyl-benzene ring is close to coplanar with the adjacent hydrazine residue [dihedral angle = 11.14 (12)°], an observation which correlates with the presence of an intra-molecular O-H⋯N hydrogen bond. The benzyl ring forms a dihedral angle of 50.84 (13)° with the adjacent carbamate group. A twist in the mol-ecule, at the chiral C atom, is reflected in the dihedral angle of 80.21 (12)° formed between the amide residues. In the crystal, two-dimensional arrays in the ac plane are mediated by O-H⋯O and N-H⋯O hydrogen bonds.

tert-Butyl N-((1S)-2-hy-droxy-1-{N'-[(1E)-4-meth-oxy-benzyl-idene]hydrazinecarbon-yl}eth-yl)carbamate

The mol-ecule of the title compound, C(16)H(23)N(3)O(5), is twisted about the chiral C atom, the dihedral angle formed between the amide residues being 79.6 (3)°. The conformation about the imine bond [1.278 (5) Å] is E. In the crystal, O-H⋯O and N-H⋯O hydrogen bonding between the hy-droxy, amine and carbonyl groups leads to the formation of supra-molecular layers, which stack along the c-axis direction.

Benzyl N-(1-{N'-[(E)-2-chloro-benzyl-idene]hydrazinecarbon-yl}-2-hy-droxy-eth-yl)carbamate

The mol­ecule of the title compound, C₁₈H₁₈ClN₃O₄, is twisted about the chiral C atom with the dihedral angle between the two amide residues being 87.8 (5)°, but, overall, it can be described as curved, with the benzene rings lying on the same side of the mol­ecule [dihedral angle = 62.8 (4)°]. The conformation about the imine bond [1.294 (7) Å] is E. In the crystal, a two-dimensional array in the ab plane is mediated by O—H⋯O and N—H⋯O hydrogen bonds as well as C—H⋯Cl inter­actions. The layers stack along the c-axis direction, being connected by C—H⋯.π contacts.

tert-Butyl N-{(1S)-1-[(2,4-dihy-droxy-benzyl-idene)hydrazinecarbon-yl]-2-hy-droxy-eth-yl}carbamate ethanol monosolvate

The mol-ecule of the title ethanol solvate, C(15)H(21)N(3)O(6)·C(2)H(6)O, adopts a curved shape; the conformation about the imine bond [N=N = 1.287 (3) Å] is E. The amide residues occupy positions almost orthogonal to each other [dihedral angle = 85.7 (2)°]. In the crystal, a network of O-H⋯O, O-H⋯N and N-H⋯O hydrogen bonds leads to the formation of supra-molecular arrays in the ab plane with the ethanol mol-ecules lying to the periphery on either side. Disorder in the solvent ethanol mol-ecule was evident with two positions being resolved for the C atoms [site occupancy of the major component = 0.612 (10)].

Benzyl N-[(S)-2-hy-droxy-1-({[(E)-2-hy-droxy-4-meth-oxy-benzyl-idene]hydrazin-yl}carbon-yl)eth-yl]carbamate

The shape of the title compound, C(19)H(21)N(3)O(6), is curved with the conformation about the imine bond [1.291 (3) Å] being E. While the hy-droxy-substituted benzene ring is almost coplanar with the hydrazinyl residue [N-N-C-C = 177.31 (18)°], an observation correlated with an intra-molecular O-H⋯N hydrogen bond leading to an S(6) ring, the remaining residues exhibit significant twists. The carbonyl residues are directed away from each other as are the amines. This allows for the formation of O-H⋯O and N-H⋯O hydrogen bonds in the crystal, which lead to two-dimensional supra-molecular arrays in the ac plane. Additional stabilization to the layers is afforded by C-H⋯π inter-actions.

Benzyl N-{(1S)-2-hy-droxy-1-[N'-(2-nitro-benzyl-idene)hydrazinylcarbon-yl]eth-yl}carbamate

The carbamate and hydrazone groups in the title compound, C(18)H(18)N(4)O(6), are approximately orthogonal [dihedral angle = 83.3 (4)°], and the carbonyl groups are effectively anti [O=C⋯C=O torsion angle = -116.2 (7)°]. The conformation about the imine bond [1.295 (11) Å] is E. The crystal packing is dominated by O-H⋯O and N-H⋯O hydrogen bonding, which leads to two-dimensional arrays in the ab plane.