Tetracyclines. 10. Chemical-structural properties of tetracycline derivatives. 5. A total synthesis and structural aspects of racemic 8-oxygenated tetracyclines

Tetracycline hydrochloride: a synchrotron microcrystal study

“…Even with re®ned H atoms, the same distribution of H atoms and very similar molecular geometry have been interpreted in terms of different tautomers (Stezowski, 1977;Bordner, 1979). Our results clearly support the conclusions of Bordner (1979) and of Glatz et al (1979) regarding the major contribution of the tautomeric form shown as A in the Scheme above, and the nature of the hydrogen bonding between the amide group in its enol form and the adjacent keto group.…”

Approaches to the synthesis of cytochalasans. Part 5. Studies on the selectivity of the Diels‐Alder reaction leading to the tetrahydroiso‐indolinone sub‐unit

“…Oxidation of 2 by pyridinium dichromate [4] afforded 4-methyl-2,4-hexadien-1-a1 (12), a sensitive aldehyde which was characterized by its 2,4-dinitrophenylhydrazone 13. The acetals 14 and 15 were obtained with trimethylorthoformate and 2-methoxy-1,3-dioxolane, respectively, in the presence of anhydrous copper (11) sulfate [5] (cf: Scheme 2). …”

“…The stereochemistry of the adducts 16, 17, 18, 19, 21, 22, and 23 was derived from the values of J (4,5), which fall in the range 2 to 9 Hz as expected for the ty-endo-adducts. The cis-relationship of H-C (4) and H-C (9, and the configuration at C(3) and C ( 8 ) in the structures of type 7, were demonstrated independently by the chemical transformation of the ester 18 to the known lactam 246) by alkaline…”

Highly enantioselective catalytic hydrogenation of a 5-amino-3,5-dioxopentanoic ester

“…For example, Togni et al reported the highly enantioselective reduction of b-keto esters (up to 97% ee) catalyzed by a rhodium complex based on Josiphos as a chiral ligand under mild conditions (rt, 20 bar, 15 h). 12 Therefore, we screened also a set of analogous Rh-complexes with several commercially available chiral diphosphines (see Table 1, entries [6][7][8][9][10][11][12]. The activity of all tested Rh-complexes was nearly similar to that noted with Ru-complexes.…”

“…c o m / l o c a t e / t e t l e t procedure (Scheme 2). 8 The reaction was performed by addition of tert-butylamine to the boiling mixture of 5 in dioxane in the presence of a catalytic amount of p-toluenesulfonic acid. Slow addition of tert-butylamine is essential for the success of the reaction.…”