2- aminoethyl-2 ,4-bithiazole-4’carboxylic acid

A superb example of this approach is the total synthesis of bleomycin A2 (252) reported by Hecht. Bleomycin was isolated by Umezawa and co-workers Q nd shown to be a potent anticancer agent.l69 While determining the structure, it was shown that hydrolyses and other chemical manipulations of 252 gave nine identifiable fragments (a) aminopropyldimethyl sulfonium (253) (b) 2-aminoethyl-2, 4-bithiazole-4 -carboxylic acid (254) (c) L-threonine (255) (d) (2f ,3S,4R)-4-amino-3-hydroxy-2-methylpentanoic acid (256) (e) L-eryr/zro-(3-hydroxyhistidine (258) (f) (3-amino-P-(4-amino-6-carboxy-5-methylpyrimidin-2-yl)propionic acid (259) (g) a rearrangement product, L- 3-aminoalanine (257) (h) gulose (260) and, (j) carbamoyl mannose (261). 

The structure elucidation of BLM was not straightforward because of the noncrystalline nature of the molecule [36]. An extensive degradation study indicated that BLM contains novel amino acid constituents and an unusual disaccharide, i.e., pyrimidoblamic acid (1), rytfcro-P-hydroxy-L-histidine (2), (2S, 35,4/ )-4-amino-3-hydroxy-2-methylpentanoic acid (3), 2 -(2-aminoethyl)-2,4 -bithiazole-4-carboxylic acid (4), and 2-0-(3-0-carbamoyl-a-D-mannopyranosyl)-a-L- u/opyranose (5) (Fig. 9). The sequence of the peptide bonding and the glycoside linkage was established by selective partial hydrolysis and, in 1978, the total structure was eventually determined by Takita et al. on the basis of further direct and indirect evidence (Fig. 1) [2]. 

---