The unique behavior of the active pharmaceutical ingredient Venlafaxine free base, used as an antidepressant, with respect to polymorphism and chiral resolution is reported. Using several complementary techniques, three crystal structures of Venlafaxine were identified and isolated. All three structures are composed of virtually identical enantiomeric pure layers with different stacking modes. In the crystal structure with the highest melting point, the enantiomeric separation is complete, leading to a racemic conglomerate. The conglomerate can be grown from solution or via a solid-solid phase transition of the lowest melting racemic compound. Remarkably, the crystal shape is conserved during the transition. The corresponding chiral resolution is achieved via a local melting process, allowing for a long-range migration of the molecules between layers.
A series of analogues derived from (+)-strigol, which is a germination stimulant for seeds of the parasitic weeds Striga and Orobanche, has been prepared. For the isolation and characterization of the strigol receptor, labelled analogues are required in which a photoreactive function may be incorporated. The synthetic strategy allows for the synthesis of a range of A-ring substituted analogues of GR24 (which is a strigol analogue), including fluorescent dansyl GR24 10. Bioassays reveal that the stimulatory activity of these analogues in the seed germination of Striga hermonthica is retained.
We describe the allylation and propargylation of 3-formylcephalosporins under zinc-mediated, aqueous Barbier conditions, from which the corresponding homoallylic alcohols are produced in good yields and with good-to-excellent diastereoselectivity.
New convenient syntheses of 3‐carboxycephems starting from 7‐ACA are reported. All three possible cephem derivatives with respect to the position of the double bond in the six‐membered ring and oxidation state of the sulfur atom have been synthesized in high overall yield.
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