This and the accompanying report (DOI: 10.1021/jm201467r ) describe the design, synthesis, and evaluation of a new generation of tetracycline antibacterial agents, 7-fluoro-9-substituted-6-demethyl-6-deoxytetracyclines ("fluorocyclines"), accessible through a recently developed total synthesis approach. These fluorocyclines possess potent antibacterial activities against multidrug resistant (MDR) Gram-positive and Gram-negative pathogens. One of the fluorocyclines, 7-fluoro-9-pyrrolidinoacetamido-6-demethyl-6-deoxytetracycline (17j, also known as TP-434, 50th Interscience Conference on Antimicrobial Agents and Chemotherapy Conference , Boston, MA , September 12-15, 2010 , poster F1 - 2157 ), is currently undergoing phase 2 clinical trials in patients with complicated intra-abdominal infections (cIAI).

We describe the total synthesis of (+)- and (-)-galbulimima alkaloid 13. The absolute stereochemistry of natural (-)-galbulimima alkaloid 13 is revised to 2S. Sequential use of catalytic cross-coupling and cross-metathesis reactions followed by an intramolecular Diels-Alder reaction provided the required trans-decalin AB-ring system and masked the C16 carbonyl as an N-vinyl carbamate for late-stage unveiling in the form of the necessary C16 enone. A vinyl radical cyclization secured the C-ring, while successful execution of our strategy for introduction of the CDE-ring system in complex galbulimima alkaloids provided the target pentacycle with complete diastereoselection.

Process research and development of the first fully synthetic broad spectrum 7-fluorotetracycline in clinical development is described. The process utilizes two key intermediates in a convergent approach. The key transformation is a Michael–Dieckmann reaction between a suitable substituted aromatic moiety and a key cyclohexenone derivative. Subsequent deprotection and acylation provide the desired active pharmaceutical ingredient in good overall yield.

Employing a highly efficient total synthesis approach, we synthesized and evaluated for antibacterial activity diverse and novel pentacycline analogs with systematic variations at C7, C8, C9, and C10. Certain substitution groups, as well as substitution patterns at various positions, were found to be preferred for increased antibacterial activity. A number of pentacycline analogs displayed potent activity in vitro and in vivo, especially against Gram-positive organisms. Several analogs have also shown promising oral bioavailability in rats and cynomolgus monkey.

Utilizing a fully synthetic route to tetracycline analogues, the C-9 side-chain of the fluorocyclines was optimized for both antibacterial activity and oral efficacy. Compounds were identified that overcome both efflux (tet(K), tet(A)) and ribosomal protection (tet(M)) tetracycline-resistance mechanisms and are active against Gram-positive and Gram-negative organisms. A murine systemic infection model was used as an oral efficacy screen to rapidly identify compounds with oral bioavailability. Two compounds were identified that exhibit both oral bioavailability in rat and clinically relevant bacterial susceptibility profiles against major respiratory pathogens. One compound demonstrated oral efficacy in rodent lung infection models that was comparable to marketed antibacterial agents.