84111-39-7Relevant academic research and scientific papers
Total synthesis of the antimitotic bicyclic peptide celogentin C
Ma, Bing,Banerjee, Biplab,Litvinov, Dmitry N.,He, Liwen,Castle, Steven L.
supporting information; experimental part, p. 1159 - 1171 (2010/04/01)
An account of the total synthesis of celogentin C is presented. A right-to-left synthetic approach to this bicyclic octapeptide was unsuccessful due to an inability to elaborate derivatives of the right-hand ring. In the course of these efforts, it was discovered that the mild Braslau modification of the McFadyen-Stevens reaction offers a useful method of reducing recalcitrant esters to aldehydes. A leftto-right synthetic strategy was then examined. The unusual Leu-Trp side-chain cross-link present in the left-hand macrocycle was fashioned via a three-step sequence comprised of an intermolecular Knoevenagel condensation, a radical conjugate addition, and a SmI2-mediated nitro reduction. A subsequent macrolactamization provided the desired ring system. The high yield and concise nature of the left-hand ring synthesis offset the modest diastereoselectivity of the radical conjugate addition. Formation of the Trp-His sidechain linkage characteristic of the right-hand ring was then accomplished by means of an indole-imidazole oxidative coupling. Notably, Pro-OBn was required as an additive in this reaction. Detailed mechanistic investigations indicated that Pro-OBn moderates the concentration of NCS in the reaction mixture, thereby minimizing the production of an undesired dichlorinated byproduct. The natural product was obtained after macrolactamization and deprotection. The chemical shifts of the imidazole hydrogen atoms exhibited significant dependence on temperature, concentration, and pH. Antitumor screening indicated that celogentin C inhibits the growth of some cancer cell lines.
The Steric Hindrance of the Stepwise Reaction of N-Carboxy α-Amino Acid Anhydride with the α-Amino Acid Ester
Oya, Masanao,Takahashi, Tomoko
, p. 2705 - 2707 (2007/10/02)
The mechanisms of the reactions of 4-alkyloxazolidinediones (1) (N-carboxy α-amino acid anhydrides(NCAs)) with α-amino acid benzyl ester p-toluenesulfonates (2) were investigated in acetonitrile containing triethylamine at low and room temperatures.Two types of reactions were observed: (1) the polymerization of NCAs was initiated with a small amount of 2 to produce polypeptides (6), and (2) the dipeptide benzyl esters (4) were produced by the stepwise reaction of NCAs with the esters.Both the polymerization and the dipeptide formation (1+2) seemed to be initiated by the nucleophilic attack of the amino group of the ester on the C-5 carbon of NCAs.The polymerization proceeded when the side chains of the amino acid esters (R2) were more bulky than those of the NCAs (R1).On the contrary, dipeptide esters were produced when the side chains of the NCAs (R1) were more bulky than those of the esters (R2).
