Cascade N-Alkylation/Hemiacetalization for Facile Construction of the Spiroketal Skeleton of Acortatarin Alkaloids with Therapeutic Potentiality in Diabetic Nephropathy

Cooperation of the Neutral and the Cationic Leaving Group Pathways in Acid-Catalyzed O-Benzylation of TriBOT

The reaction profile of acid-catalyzed O-benzylation with 2,4,6-tris(benzyloxy)-1,3,5-triazine (TriBOT) was analyzed to study the reaction kinetics. The first-order kinetic constant for the formation of benzyl cation species from N-protonated TriBOT (neutral leaving group pathway) was estimated and compared with that of the model compound for TriBOT. Since rapid consumption of TriBOT in the late stage could not be explained solely by this pathway, cooperation of another reaction mechanism, the cationic leaving group pathway, was proposed to rationalize the rate acceleration.

Efficient and regioselective synthesis of γ-lactone glycosides through a novel debenzylative cyclization reaction

An efficient and regioselective approach for the construction of synthetically important γ-lactone glycosides is reported from unprotected aldoses through a new debenzylative lactonization (DBL) reaction. The scope and limitations of this DBL reaction are described starting from a series of commercially available hexoses (l-fucose, d-galactose, d-glucose) and pentoses (d-arabinose, d-ribose, d-lyxose, d-xylose) to afford the corresponding γ-lactones in good yields and without concomitant δ-lactone formation.

Synthetic approaches to access acortatarins, shensongines and pollenopyrroside; potent antioxidative spiro-alkaloids with a naturally rare morpholine moiety

Pyrrole spiroketal alkaloids (PSAs) are a class of novel natural products that have been recently disclosed. Acortatarin A and acortatarin B, two potent antioxidative spiroalkaloids with a naturally rare morpholine moiety, are important members of this class. These spiroalkaloids are isolated from Acorus tatarinowii, Brassica campestris, Capparis spinose, bread crust, Xylaria nigripes and medicine Shensong Yangxin and could inhibit significantly the reactive oxygen species (ROS) production in high-glucose-induced mesangial cells in a time- and dose-dependent manner. Hence, these natural products are promising starting points for the formation of new therapeutics to medicate cardiovascular diseases, cancer, diabetic complications, and other diseases in which ROS are implicated. The impressive structure combined with an interesting pharmacological activity prompted synthetic chemists to construct an asymmetric synthetic strategy that could be used to access structural derivatives in addition to the larger quantities of natural products required for further biological investigations. This review summarizes the current state of the literature regarding with the synthesis of acortatarin A and B and its other family members viz. shensongine A, B and C, and pollenopyrroside A. The present review discusses the pros and cons of synthetic methodologies, which would be beneficial for further developments in the synthetic methodologies. Hopefully, this struggle pushes the reader's mind to consider new perspectives, think differently and forge new connections.

Stereocontrolled Synthesis of Spiroketals: An Engine for Chemical and Biological Discovery

Spiroketals are key structural motifs found in diverse natural products with compelling biological activities. However, stereocontrolled synthetic access to spiroketals, independent of their inherent thermodynamic preferences, is a classical challenge in organic synthesis that has limited in-depth biological exploration of this intriguing class. Herein, we review our laboratory's efforts to advance the glycal epoxide approach to the stereocontrolled synthesis of spiroketals via kinetically controlled spirocyclization reactions. This work has provided new synthetic methodologies with applications in both diversity- and target-oriented synthesis, fundamental insights into structure and reactivity, and efficient access to spiroketal libraries and natural products for biological evaluation.

Family-level stereoselective synthesis and biological evaluation of pyrrolomorpholine spiroketal natural product antioxidants

The pyranose spiroketal natural products pollenopyrroside A and shensongine A (also known as xylapyrroside A, ent-capparisine B) have been synthesized by stereoselective spirocyclizations of a common C1-functionalized glycal precursor. In conjunction with our previously reported syntheses of the corresponding furanose isomers, this provides a versatile family-level synthesis of the pyrrolomorpholine spiroketal natural products and analogues. In rat mesangial cells, hyperglycemia-induced production of reactive oxygen species, which is implicated in diabetic nephropathy, was inhibited by pollenopyrroside A and shensongine A with mid-μM IC50 values, while unnatural C2-hydroxy analogues exhibited more potent, sub-μM activity.

Study of O-Allylation Using Triazine-Based Reagents

Acid-catalyzed allylating reagent 2,4,6-tris(allyloxy)-1,3,5-triazine (TriAT-allyl) and its substituted derivatives have been developed. The reaction of acid-, and alkali-labile alcohols with these reagents in the presence of a catalytic amount of trifluoromethanesulfonic acid (TfOH) afforded the corresponding allyl ethers in good yields. Reactions using these reagents with an unsymmetrically-substituted regioisometric allyl group suggested that a single isometric allylic cation species would be involved.