Chemical element named mendelevium in honor of D.I. Mendeleev, the first to arrange the elements in a periodic manner. Most recently, the synthesis of element 118 (since named oganesson) was reported in October 2006, and the synthesis of element 117 (tennessine) was reported in April 2010. Ten materials familiar to various prehistoric cultures are now known to be chemical elements: Carbon, copper, gold, iron, lead, mercury, silver, sulfur, tin, and zinc. Three additional materials now accepted as elements, arsenic, antimony, and bismuth, were recognized as distinct substances prior to 1500 AD. Phosphorus, cobalt, and platinum were isolated before 1750. Most of the
Chemical ligation with an N-terminal Ser or Thr residue. The chemoselective reaction between the peptide SAL ester and 1,2-hydroxylamine group of Ser or Thr leads to the formation of an N,O-benzylidene acetal linked intermediate, which undergoes acidolysis to afford a natural peptidic Xaa-Ser/Thr linkage. This method does not involve the use of unnatural amino acids, and it is simple to operate. Ser/Thr ligation provides a complementary method for protein chemical synthesis and semisynthesis. Schnölzer M, Kent SB. 1992, "Constructing proteins by dovetailing unprotected synthetic peptides: backbone-engineered HIV protease." "Science". 256:221-5 Dawson PE, Muir TW, Clark-Lewis I, Kent SB. 1994, "Synthesis of proteins