Complete Structure Assignment of Azathioprine as a Proton-Deficient Nucleic Acid Analogue Using 1H-13C Long-Range Heteronuclear Single Quantum Multiple Bond Correlation.

In this Note, the successful structural assignment of a proton-deficient nucleic acid analogue using the 1H-13C long-range heteronuclear single quantum multiple bond correlation (LR-HSQMBC) technique is described. LR-HSQMBC is a 2D NMR technique for the sensitive detection of weak C-H spin couplings. The immunosuppressant drug, azathioprine, served as the target compound. The LR-HSQMBC measurements revealed the existence of covalent bonds between the purine and imidazole rings based on observations of 5JCH and 6JCH with good sensitivity.

Enantioselective total synthesis of pinnaic acid and halichlorine.

The enantioselective total synthesis of the bioactive marine natural products pinnaic acid and halichlorine is reported in detail. Our total synthesis features the construction of the five-membered ring and C9 and C13 stereogenic centers through a palladium-catalyzed trimethylenemethane [3+2] cyclization; the installation of the nitrogen atom through a regioselective Beckmann rearrangement of a poorly reactive ketone; the stereoselective cyclization of the spiro ring through a four-step, one-pot hydrogenation-cyclization; and efficient connection of the sterically hindered lower chain through a reduced-pressure cross olefin metathesis reaction.