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
Beta-peptide of peptide-based drugs. β-Peptides have been used to mimic natural peptide-based antibiotics such as magainins, which are highly potent but difficult to use as drugs because they are degraded by proteolytic enzymes in the body. 8 beta forms exist: alanine, leucine, lysine, arginine, glutamate, glutamine, phenylalanine, tyrosine forms. Aspartic acid is regarded as both beta and alpha forms, although the beta form is found in microcystins. Beta-peptide β-peptides consist of β amino acids, which have their amino group bonded to the β carbon rather than the α carbon as in the 20 standard biological amino acids. The only common naturally