Mechanistic Study of Diketopiperazine Formation during Solid-Phase Peptide Synthesis of Tirzepatide.

This study focused on investigating diketopiperazine (DKP) and the formation of associated double-amino-acid deletion impurities during linear solid-phase peptide synthesis (SPPS) of tirzepatide (TZP). We identified that the DKP formation primarily occurred during the Fmoc-deprotection reaction and post-coupling aging of the unstable Fmoc-Pro-Pro-Ser-resin active pharmaceutical ingredient (API) intermediate. Similar phenomena have also been observed for other TZP active pharmaceutical ingredient (API) intermediates that contain a penultimate proline amino acid, such as Fmoc-Ala-Pro-Pro-Pro-Ser-resin, Fmoc-Pro-Pro-Pro-Ser-resin, and Fmoc-Gly-Pro-Ser-Ser-Gly-Ala-Pro-Pro-Pro-Ser-resin, which are intermediates for both hybrid and linear synthesis approaches.

Liquid Phase Peptide Synthesis via One-Pot Nanostar Sieving (PEPSTAR).

Herein, a one-pot liquid phase peptide synthesis featuring iterative addition of amino acids to a "nanostar" support, with organic solvent nanofiltration (OSN) for isolation of the growing peptide after each synthesis cycle is reported. A cycle consists of coupling, Fmoc removal, then sieving out of the reaction by-products via nanofiltration in a reactor-separator, or synthesizer apparatus where no phase or material transfers are required between cycles. The three-armed and monodisperse nanostar facilitates both efficient nanofiltration and real-time reaction monitoring of each process cycle.

Isolation and Rationale for the Formation of Isomeric Decarbamoylmitomycin C- N-deoxyadenosine Adducts in DNA.

Mitomycin C (MC) is an anticancer agent that alkylates DNA to form monoadducts and interstrand cross-links. Decarbamoylmitomycin C (DMC) is an analogue of MC lacking the carbamate on C10. The major DNA adducts isolated from treatment of culture cells with MC and DMC are N-deoxyguanosine (dG) adducts and adopt an opposite stereochemical configuration at the dG-mitosene bond.

Studies toward the Synthesis of Lepadiformine A.

Herein is described an original approach to access a tricyclic framework of the lepadiformine-type alkaloids. A Grignard/N-acylpyridinium salt reaction of a 4-methoxytetrahydroquinoline is the key carbon-carbon bond-forming step that was used to establish the desired absolute stereochemistry at the C2 position of the target alkaloid. The synthesis features an allylation reaction with an N-acyliminium ion to set the C10 quaternary stereocenter, a mild dissolving-metal cleavage of hindered phenyl carbamates, and an aminoiodocyclization to form the pyrrolidine ring.

Development of an Intermittent-Flow Enantioselective Aza-Henry Reaction Using an Arylnitromethane and Homogeneous Brønsted Acid-Base Catalyst with Recycle.

A stereoselective aza-Henry reaction between an arylnitromethane and Boc-protected aryl aldimine using a homogeneous Brønsted acid-base catalyst was translated from batch format to an automated intermittent-flow process. This work demonstrates the advantages of a novel intermittent-flow setup with product crystallization and slow reagent addition which is not amenable to the standard continuous equipment: plug flow tube reactor (PFR) or continuous stirred tank reactor (CSTR). A significant benefit of this strategy was the integration of an organocatalytic enantioselective reaction with straightforward product separation, including recycle of the catalyst, resulting in increased intensity of the process by maintaining high catalyst concentration in the reactor.

Total synthesis of alkaloid 205B.

Concise and highly stereocontrolled total syntheses of racemic and enantiopure frog alkaloid 205B (1) were accomplished in 11 steps from 4-methoxypyridines 6 and 7 in overall yields of 8 and 8%, respectively. The assembly of the core of the natural product relies on a stereoselective Tsuji-Trost allylic amination reaction and a ring-closing metathesis. The synthesis features the use of an N-acylpyridinium salt reaction to introduce the first stereocenter and an unprecedented trifluoroacetic anhydride-mediated addition of an allylstannane to a vinylogous amide with complete facial selectivity.