7-Lactone ring, conformational

P2j Z = 2 Dx = 1.363 R = 0.051 for 982 intensities. The lactone has the3T4 conformation, withQ = 13 pm, (p = 337°, andaC-2-C-3-C-4-O torsion-angle of — 120. Both the equatorial and the axial acetoxyl groups have their planes approximately normal to that of the lactone ring. 

P2j Z = 2 D, = 1.24 R = 0.05 for 2,421 intensities. This molecule is a cardenolide / -D-glucopyranoside. The pyranoside conformation is 4C4, with Q = 58 pm, 0 = 6°. The terminal lactone ring is planar. The conformation was compared with that of digitoxigenin by means of molecular-mechanics calculations. 

P2j Z = 4 Dx = 1.357 R = 0.048 for 1,989 intensities. The crystal structure contains two symmetry-independent molecules having almost the same conformation. The lactone rings are planar the conformation of the dioxolane ring in one is close to an envelope, and that in the other has a twist conformation. The linkage between the rings, as defined by 0-4-C-4-C-5-0-5, is -65 and —75°. The two independent molecules are hydrogen-bonded into dimers by the two N—... 

After opening the lactone ring with NaOMe, rings and substituents take up the original conformations. Esterification of the free OH group gives finally reserpine (9). 

A detailed examination of OSO4 reactions with A -steroids has been reported." The A-ring conformation of the reactant or derived complex is important in determining the stereoselectivity of these reactions, and the major role of the proximate substituents is to anchor the appropriate conformation favouring a- or /3-attack. Studies on the stereochemistry of electrophilic attack on cholest-5-en-3-one continue." As with bromine chloride," appreciable /3-attack occurs and the 5/3,6j8-epoxide was isolated along with the previously reported 5a,6a-epoxide and the Baeyer-Villiger product, the A-homo-enol lactone (58). Base-catalysed... 

Lysozyme catalyzes the hydrolysis of the polysaccharide component of plant cell walls and synthetic polymers of j8(l — 4)-linked units of A-acetylglucosamine (NAG) (Chapter 1). It is expected from studies on nonenzymatic reactions that one of the intermediates in the hydrolytic reaction is a oxocarbenium ion in which the conformation of the glucopyranose ring changes from a full-chair to a sofa (half-chair) conformation (Chapter 1). The transition state analogue I, in which the lactone ring mimics the carbonium ion-like transition state n, binds tightly to lysozyme = 8.3 X 10 8M.10... 

P2i2j2i Z = 4 Dx = 1.451 R = 0.045 for 832 intensities. The lactone ring is planar. The acetamido group makes an angle of +10° with the ring, as defined by the C-7-N-C-2-C-3 torsion-angle. The side chain has a bent conformation, as defined by the C-3-C-4-C-5-C-6 and C-4-C-5-C-6-0-6 torsion-angles of +54 and -68°, respectively. 

The macrolide antibiotics provide us with excellent examples of natural products conforming to the acetate pathway, but composed principally of propionate units, or mixtures of propionate and acetate units. The macrolides are a large family of compounds, many with antibiotic activity, characterized by a macrocyclic lactone ring, typically 12, 14, or 16 membered, reflecting the number of units utilized. Zear-alenone (Figure 3.59), a toxin produced by the... 

An improved lanthanide-induced shift analysis technique that employs Yb(fod)3 was used to investigate the conformation of a number of lactones including 3,4-dihydrocoumarin (fod = 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octadione). These studies indicate that both C-2 and C-3 are displaced from planarity to give a puckered conformation to the lactone ring <1997J(P2)1279>. 

The tubulin-bound conformation of DDM in solution has been determined from tr-NOE data [112], Sample conditions were similar to those used previously to determine the bioactive conformation of EpoA. Distance restraints were obtained from a series of tr-NOE spectra recorded at several mixing times and were used in the structure calculation based on the complete relaxation matrix methodology [37], The NMR-derived bioactive conformation is quite similar to the crystal structure except for the conformation of the 8 lactone ring, that is close to a flattened chair in solution but a twisted boat in the crystal (Fig. 18). 

Basler, B., Schuster, O., and Bach, T. (2005) Conformationally constrained p-amino acid derivatives by intramolecular [2 + 2]-photocycloaddition of a tetronic acid amide and subsequent lactone ring opening. Journal of Organic Chemistry, 70, 9798-9808. 

Finally, mention must be made of the preparation of the perhydro-furo[2,3-c]pyridin-2-ones 71 and 72. These compounds are conformation-ally restricted analogs of pilocarpine in which the imidazole ring has been replaced by a simple alkylamine moiety fused to the lactone ring (725). 

---