Discovery and development of direct Xa inhibitors Xa was identified as a promising target for the development of new anticoagulants in the early 1980s. In 1987 the first factor Xa inhibitor, the naturally occurring compound antistasin, was isolated from the salivary glands of the Mexican leech "Haementeria officinalis". Antistasin is a polypeptide and a potent Xa inhibitor. In 1990 another naturally occurring Xa inhibitor was isolated, tick anticoagulant peptide (TAP) from extracts of the tick "Ornithodoros moubata". TAP and antistasin were used to estimate factor Xa as a drug target. Blood coagulation is a complex process by which the blood forms clots. It is an essential part
DNA damage (naturally occurring) as documented below. Oxidative DNA damage can produce more than 20 types of altered bases as well as single strand breaks. Other types of endogeneous DNA damages, given below with their frequencies of occurrence, include depurinations, depyrimidinations, double-strand breaks, O6-methylguanines and cytosine deamination. DNA can be damaged via environmental factors as well. Environmental agents such as UV light, ionizing radiation, and genotoxic chemicals. Replication forks can be stalled due to damaged DNA and double strand breaks are also a form of DNA damage. The list below, from reference, shows some frequencies with which new naturally occurring DNA damages arise per