D-Glucurono-6,3-lactone belongs to the class of organic compounds known as isosorbides. These are organic polycyclic compounds containing an isosorbide(1,4-Dianhydrosorbitol) moiety, which consists of two -oxolan-3-ol rings. D-Glucurono-6,3-lactone is a very mild and mentholic tasting compound. Glucuronolactone is a naturally occurring substance that is an important structural component of nearly all connective tissues. It is frequently used in energy drinks to increase energy levels and improve alertness, and can also be used to reduce "brain fog" caused by various medical conditions. Glucuronolactone is also found in many plant gums. Glucuronolactone is a white solid odorless compound, soluble in hot and cold water. Its melting point ranges from 176 to 178 °C. The compound can exist in a monocyclic aldehyde form or in a bicyclic hemiacetal (lactol) form. Glucuronolactone is a popular ingredient in energy drinks because it has been shown to be effective at increasing energy levels and improving alertness. Glucuronolactone supplementation also significantly reduces "brain fog" cause by various medical conditions. Although levels of glucuronolactone in energy drinks can far exceed those found in the rest of the diet, glucuronolactone is extremely safe and well tolerated. The European Food Safety Authority (EFSA) has concluded that exposure to glucuronolactone from regular consumption of energy drinks is not a safety concern.[2] The no-observed-adverse-effect level of glucuronolactone is 1000 mg/kg/day. Additionally, according to The Merck Index, glucuronolactone is used as a detoxicant. The liver uses glucose to create glucuronolactone, which inhibits the enzyme B-glucuronidase (metabolizes glucuronides), which should cause blood-glucuronide levels to rise. Glucuronides combines with toxic substances, such as morphine and depot medroxyprogesterone acetate, by converting them to water-soluble glucuronide-conjugates which are excreted in the urine. Higher blood-glucuronides help remove toxins from the body, leading to the claim that energy drinks are detoxifying. Free glucuronic acid (or its self-ester glucuronolactone) has less effect on detoxification than glucose, because the body synthesizes UDP-glucuronic acid from glucose. Therefore, sufficient carbohydrate intake provides enough UDP-glucuronic acid for detoxication, and foods rich in glucose are usually abundant in developed nations. Glucuronolactone is also metabolized to glucaric acid, xylitol, and L-xylulose, and humans may also be able to use glucuronolactone as a precursor for ascorbic acid synthesis.