1. Phenyl 3,5-di-tert-butyl-2-hy-droxy-benzoate
Alexander Carreño, Marcelo Preite, Juan Manuel Manriquez, Andrés Vega, Ivonne Chavez Acta Crystallogr Sect E Struct Rep Online. 2010 Nov 24;66(Pt 12):o3290. doi: 10.1107/S1600536810044028.
The title mol-ecule, C(21)H(26)O(3), has a six-membered planar carbon ring as the central core, substituted at position 1 with phen-oxy-carbonyl, at position 2 with hy-droxy and at positions 3 and 5 with tert-butyl groups. The structure shows two independent but very similar mol-ecules within the asymmetric unit. For both independent mol-ecules, the ester carboxyl-ate group is coplanar with the central core, as reflected by the small C-C-O-C torsion angles [179.95 (17) and 173.70 (17)°]. In contrast, the phenyl substituent is almost perpendicular to the carboxyl-ate -CO(2) fragment, as reflected by C-O-C-C torsion angles, ranging from 74 to 80°. The coplanarity between the central aromatic ring and the ester carboxyl-ate -CO(2)- group allows the formation of an intra-molecular hydrogen bond, with O⋯O distances of 2.563 (2) and 2.604 (2) Å.
2. Di-tert-butyl (2R,3R)-2-{[(2E)-3-(4-acet-yloxy-3-meth-oxy-phen-yl)prop-2-eno-yl]-oxy}-3-hy-droxy-butane-dioate
Josh L Hixson, Dennis K Taylor, Seik Weng Ng, Edward R T Tiekink Acta Crystallogr Sect E Struct Rep Online. 2012 Mar 1;68(Pt 3):o568-9. doi: 10.1107/S1600536812002784. Epub 2012 Feb 4.
In the title mol-ecule, C(24)H(32)O(10), one tert-butyl ester group is folded towards the central benzene ring while the other is directed away. The acetyl group is almost perpendicular to the benzene ring to which it is connected [C-C-O-C torsion angle = 90.4 (12)°]. The conformation about the ethene bond [1.313 (7) Å] is E. The atoms of the benzene ring and its attached ester group and part of the hy-droxy tert-butyl ester side chain are disordered over two sets of sites in a 50:50 ratio. Linear supra-molecular chains along the a axis mediated by hy-droxy-carbonyl O-H⋯O hydrogen bonds feature in the crystal packing. The same H atom also partakes in an intra-molecular O-H⋯O inter-action.
3. The peptide Z-Aib-Aib-Aib-L-Ala-OtBu
Renate Gessmann, Hans Brückner, Kyriacos Petratos Acta Crystallogr C Struct Chem. 2014 Apr;70(Pt 4):405-7. doi: 10.1107/S2053229614005567. Epub 2014 Mar 21.
The title peptide, N-benzyloxycarbonyl-α-aminoisobutyryl-α-aminoisobutyryl-α-aminoisobutyryl-L-alanine tert-butyl ester or Z-Aib-Aib-Aib-L-Ala-OtBu (Aib is α-aminoisobutyric acid, Z is benzyloxycarbonyl and OtBu indicates the tert-butyl ester), C27H42N4O7, is a left-handed helix with a right-handed conformation in the fourth residue, which is the only chiral residue. There are two 4→1 intramolecular hydrogen bonds in the structure. In the lattice, molecules are hydrogen bonded to form columns along the c axis.
