ABSTRACT
A series of macrocyclic receptors has been prepared containing bipyridine groups linked to two amino acids. Variations in both the amino acid and the linking spacer have been made. The structure of the resulting macrocycles has been investigated using 1H NMR spectroscopy and X-ray crystallography. The use of L-valine leads to an open conformation for the macrocycle in which the 2-propyl substituents are directed perpendicular to the plane of the ring leaving the bipyridine and amide groups accessible for binding to a metal or complementary substrate. Proline-based macrocycles take up a twisted arrangement with the linking chain stretched across the face of the bipyridine which takes up a trans conformation. The metal ion binding properties of these derivatives have been investigated and shown to occur only to the valine macrocyles which have the two pyridine rings preorganized for complexation. These macrocycles have also been shown to bind to phenolic hydroxyl groups by using hydrogen-bond donors and acceptors from the amide groups in the linking chain.
Subject(s)
2,2'-Dipyridyl/chemical synthesis , 2,2'-Dipyridyl/chemistry , Crystallography, X-Ray , Magnetic Resonance Spectroscopy , Models, MolecularABSTRACT
3 beta-Tetrahydropyranyloxy-5 alpha-cholesta-20(21),24-diene: C32H52O2, Mr = 468.77, orthorhombic, P2(1)2(1)2(1), a = 6.710 (4), b = 11.361 (4), c = 37.812 (11) A, V = 2882 (2) A3, Z = 4, Dx = 1.08 g cm-3, lambda(Cu K alpha) = 1.54178 A, mu = 4.60 cm-1, F(000) = 1040, T = 224 K, final R = 0.088 for 1729 unique observed reflections. 3 beta-Tetrahydropyranyloxy-21-nor-5 alpha-ergost- 24-en-20-one: C32H52O3, Mr = 484.77, triclinic, P1, a = 6.640 (2), b = 9.589 (2), c = 12.202 (3) A, alpha = 111.33 (2), beta = 101.22, gamma = 90.27 (2) degrees, V = 707.4 (3) A3, Z = 1, Dx = 1.14 g cm-3, lambda(Mo K alpha) = 0.71069 A, mu = 0.8 cm-1, F(000) = 268, T = 225 K, final R = 0.058 for 2208 unique observed reflections. The configuration at C(17) of these synthetic sterol derivatives, which had been uncertain, is unambiguously established to be 'normal' (possessing a 17 alpha-H).
Subject(s)
Cholestadienes/chemistry , Ergosterol/analogs & derivatives , Ergosterol/chemistry , Models, Molecular , Molecular Structure , X-Ray DiffractionABSTRACT
Two straight-chain C(15) fish antifeedants have been isolated from the sea hare Aplysia brasiliana. Chemical, spectral, and x-ray diffraction studies led to the characterization of these medium-ring ethers as brasilenyne (2) and cis-dihydrorhodophytin (3). The oxonin ring system of 2 is novel in nature. Biosynthetic considerations permit the postulation that a third compound, a noncrystalline congener of these compounds, is cis-isodihydrohodophytin (4).
