Pathogenic fungi are a major causative group for opportunistic infections (OIs). AIDS patients and other immunocompromised individuals are at risk for OIs, which if not treated appropriately, contribute to the mortality associated with their conditions. Several studies have indicated that the majority of HIV-positive patients contract fungal infections throughout the course of their disease. Similar observations have been made regarding the increased frequency of bone marrow and organ transplants, the use of antineoplastic agents, the excessive use of antibiotics, and the prolonged use of corticosteroids among others. In addition, several pathogenic fungi have developed resistance to current drugs. Together these have conspired to spur a need for developing new treatment options for OIs. To aid this effort, this article reviews the biological targets of current and emerging drugs and agents that act through these targets for the treatment of opportunistic fungal infections.

The tetracyclic indolo[3,2-b]quinoline ring system constitutes an important structural moiety in natural products exhibiting numerous biological activities. In particular, indolo [3, 2-b]quinoline, commonly known as linear quindoline is of particular interest, because of its rigid structure and scope of derivatization. Although the core linear quindoline skeleton shows little or no activity in several biological systems, introduction of a methyl group on the N-5 atom leading to cryptolepine induces remarkable activity against a broad spectrum of biological targets. A number of analogs of quindoline and cryptolepine have been synthesized, incorporating various functional groups on the core quindoline skeleton leading to improved biological activities. In this review, we describe various synthetic methodologies leading to the quindoline scaffold, the biological activities and the structure activity relationships (SAR) of quindoline derivatives toward different disease states to give a better picture of the importance of this moiety in medicinal chemistry.