Collin Chan

Synthesis and cytotoxic evaluation of some cribrostatin-ecteinascidin analogues.

Analogues of cribrostatin IV ( 1) and the potent antineoplastic agent ecteinascidin 743 ( 2) have been synthesized. The cytotoxic activity of these compounds ( 5, 14, 20) has been determined, and the cyanoamine-cribrostatin analogue ( 14) exhibits a 20-fold improvement with regard to the natural product 1.

Lessons from the Total Synthesis of (±) Phalarine: Insights Into the Mechanism of the Pictet-Spengler Reaction.

The furanobisindole alkaloid, phalarine, possesses a unique structural framework within the alkaloid family of natural products. Our laboratory recently disclosed the racemic total synthesis of phalarine, featuring an efficient azaspiroindolenine rearrangement; this achievement is revisited in detail. Upon completion of the first-generation total synthesis, we explored some interesting mechanism-level issues with regard to the key azaspiroindolenine rearrangement. These investigations provided valuable insights into the mechanism of racemization during the azaspiroindolenine rearrangement en route to synthetic phalarine. In addition, in the course of these studies, we demonstrated the Pictet–Spengler capture reaction for C2-aryl indoles, and successfully isolated the elusive azaspiroindolenine intermediate of the Pictet–Spengler reaction. Key insights into the remarkably subtle stereoelectronics that govern this rearrangement for C2-arylated indoles are discussed.

Synthetic studies toward cribrostatin IV: An intriguing epimerization

Surprising effects of remote substituents on the relative rates of vinylogous Pictet-Spengler reaction versus epimerization through a Grigg like progression have been encountered (contrast cyclizations of 3 and 7). Deuterium labeling experiments have been used to clarify mechanisms of epimerization, thereby allowing for the assignment of absolute configuration.