RESUMO
In this contribution, we describe two simple and efficient routes for the preparation of keto-aldehyde 1, a key intermediate for the synthesis of 13C3-androstanes and 13C3-estranes. In the first route, the targeted aldehyde 1 was obtained in 40% overall yield from 1,4-androstadien-3,17-dione (3 mmol scale) via a two-step sequence involving a one-pot, abnormal ozonolysis/sulfur oxidation/retro-Michael/ozonolysis process. Alternatively, a second route from 4-androsten-3,17-dione, using a six-step sequence, was optimized to produce 40 mmol batches of the key intermediate 1 in 42% overall yield. At the final stage, the A-ring was reconstructed through a Wittig reaction with the 1-triphenylphosphoranylidene-13C3-2-propanone 2, followed by an intramolecular condensation assisted by thioacetic acid via a Michael addition/retro-Michael reaction sequence to provide 2,3,4-13C3-1,4-androstadien-3,17-dione.
RESUMO
The design, synthesis, structure, and binding affinity of two dioptic receptors for the selective molecular recognition of the cis,syn cyclobutane pyrimidine dimer are reported. The design is based on two 2,6-di(acetamino)pyridine recognition units that are covalently linked via triple bonds to an anthraquinone functional spacer unit. The convergent synthesis uses a modified Sonogashira reaction involving a zinc transmetalation as the key step. The crystal structure of one of the receptors reveals a supramolecular 1D polymer with strong interactions mediated by shape self-complementarity, pi-stacking, and hydrogen bonding between adjacent molecules. Hydrogen bonding between adjacent strands enforces a parallel orientation, which leads to a noncentrosymmetric crystal structure of the highly polar compound. The receptor has an association constant of K(a) = 1.0 x 10(3) M(-1) with the cis,syn pyrimidine dimer, whereas binding of the trans,syn isomer is approximately 1 order of magnitude weaker.
