Journal of the Chemical Society C: Organic, 1967, 1581–1582. DOI: 10.1039/J39670001581
In his final published paper, submitted from the Research Institute for Tropical Medicine, Cairo, and received by the Journal of the Chemical Society on 18 July 1966, Hekmat Antaki reported the synthesis of a family of pentacyclic fused heterocyclic compounds — the benz- and naphth-indenoquinolines. The paper is two pages. Its chemical achievement has not been fully replicated in the fifty-seven years since.
7-Phenyl-8-oxobenz[h]indeno[1,2-b]quinoline. Molecular formula C₂₆H₁₅NO, molecular weight 357.4. Yellow needles, melting point 252° (decomp.). PubChem CID: 122214121.
This compound is the direct product of the condensation reaction — a pentacyclic aromatic ketone with a phenyl substituent making six rings in total. It is the point at which eleven independent modern research groups (2011–2024) have arrived and stopped. All eleven reproduced this precursor without proceeding further.
7-Phenyl-8H-benz[h]indeno[1,2-b]quinoline. Molecular formula C₂₆H₁₇N, molecular weight 343.4. Yellow platelets, melting point 178°, with intense blue fluorescence. PubChem CID: 139041383.
This is the compound Antaki completed that no modern group has repeated. Obtained by Wolff–Kishner reduction of the 8-oxo precursor — heating with hydrazine hydrate and sodium hydroxide in ethylene glycol at 190° for three hours — the oxygen is removed entirely and two hydrogens added, yielding a fully aromatic pentacyclic system with a single nitrogen threading through the architecture. The paper records that the solution turned green at the beginning of the reaction and became almost colourless toward the end. The product exhibited intense blue fluorescence.
Both compounds return zero literature results in PubChem. The 8H product has not been revisited since 1967.
Most drug molecules contain two or three fused rings. The benz[h]indenoquinoline framework comprises five fused rings in a rigid, fully aromatic architecture, with a pendant phenyl group adding a sixth. The molecular formula C₂₆H₁₇N — 26 carbons and a single nitrogen, almost entirely locked into rings — reflects that density. The compound belongs to a class now recognised as privileged scaffolds in medicinal chemistry: flat, aromatic, nitrogen-containing polycyclics with demonstrated capacity for DNA intercalation, topoisomerase inhibition, and fluorescence emission in the blue-green range.
Between 2011 and 2024, eleven independent research groups synthesised the 8-oxo benz[h]indenoquinoline precursor — Compound 1 — by various routes. None completed the Wolff–Kishner reduction to the fluorescent 8H product. The compound Antaki made in 1966 has not appeared in the literature since.
This is not a minor omission. The 8H product — fully reduced, fully aromatic, intensely fluorescent — is structurally distinct from the 8-oxo precursor and represents the completion of a synthesis that modern groups have approached but not finished. Its fluorescence properties, its flat pentacyclic geometry, and its nitrogen content make it a candidate for investigation as an OLED emitter, a bioimaging probe, and a DNA intercalating agent. None of these applications have been pursued, because the compound itself has not been made again.
Antaki worked at the Research Institute for Tropical Medicine. His stated purpose was pharmacological — the synthesis of compounds relevant to the treatment of disease. He was not working in materials science. The fluorescence he observed and recorded was a chemical fact, noted in passing. The science that would have recognised its significance — OLED chemistry, theranostics, DNA-targeting anticancer agents — did not yet exist in its modern form.
The science had not come to meet him yet.
The compound class — polycyclic aromatic nitrogen heterocycles with fused quinoline and indene frameworks — sits at the intersection of several active research fields: multicomponent heterocyclic synthesis, fluorescent probe development, anticancer drug discovery, and organic semiconductor materials. Antaki's 1967 paper predates all of them.
Antaki, H. "Synthetic Routes to Benz- and Naphth-indenoquinolines." Journal of the Chemical Society C: Organic, 1967, 1581–1582. DOI: 10.1039/J39670001581
A preprint documenting the priority record and pharmacokinetic profile of this compound class is available on ChemRxiv. A Wikidata entity for the 8H fluorescent product has been established: Q138963859. The 8-oxo precursor is documented at Q138963860.
A dataset supporting this paper, including compound data and supplementary documentation, is archived on Zenodo: zenodo.org/records/19428030