Khellin is a naturally occurring chromone extracted from the medicinal plant Amni visnaga long used in Egypt and the Eastern Mediterranean countries for the treatment of respiratory disorders. It however has many side effects making it unsuitable.
Roger Altounyan studied chromones and eventually found disodium cromoglycate.1 This drug was found to inhibit antigen challenge as well as stress induced symptoms. Comparatively free of side-effects, unfortunately the short half-life limited its value.
Nedocromil sodium was found to have a somewhat longer half-life.
References
^ HOWELL, J.B. & ALTOUNYAN, R.E. (1967). A double-blind trial of disodium cromoglycate in the treatment of allergic bronchial asthma. Lancet, 2, 539–542. Abstract