Total synthesis

About: Total synthesis is a research topic. Over the lifetime, 25578 publications have been published within this topic receiving 489319 citations.

Total synthesis and revision of stereochemistry of the marine metabolite trunkamide A.

Abstract: The isolation of the cytotoxic Lissoclinum sp. metabolite trunkamide A was reported in 1996. After completion of a total synthesis in 1999, it became clear that the structure of this marine natural product had to be revised. We now report the first preparation of actual trunkamide A in a total synthesis that serves as an unambiguous structural and stereochemical proof. Highlights of our synthetic strategy are a Lewis acid assisted aziridine opening that was used for the preparation of the novel reverse-prenylated serine and threonine side chains as well as an efficient oxazoline-thiazoline interconversion on the macrocyclic skeleton. In addition, several stereoisomers prepared by complementary synthetic protocols serve to illustrate the general scope of our methodology and confirm the configurational assignment.

A New Magnesium-Catalyzed Doubly Diastereoselective anti-Aldol Reaction Leads to a Highly Efficient Process for the Total Synthesis of Lactacystin in Quantity

Abstract: A new process is described for metal-catalyzed doubly diastereoselective Mukaiyama aldol coupling of a chiral tertiary α-amino aldehyde and an achiral silyl enol ether to form selectively an anti-aldol product. The metal requirement is strict, since of several salts tested only MgI2 functions as an effective catalyst. The MgI2-catalyzed aldol greatly facilitates the total synthesis of lactacystin (1) and the corresponding β-lactone (2), microbial products which are potent and selective inhibitors of proteasome function, cell cycle progression, and gene regulation. The method also allows the synthesis of analogues of 1 in which the 7β-methyl group of lactacystin is replaced by higher alkyl or aralkyl groups. Detailed experimental procedures are presented for the optimized synthesis of lactacystin on the scale required to meet the current needs of many hundreds of biological laboratories.

Chemistry of Cyclic Tautomers of Tryptophan: Formation of a Quaternary Center at C3a and Total Synthesis of the Marine Alkaloid (+)-ent-Debromoflustramine B

Abstract: A diastereoselective synthesis of the unnatural (+)-enantiomer of the marine alkaloid (-)-debromoflustramine B (1) from a cyclic tautomer (9) of L-tryptophan is described. The optical rotation of the synthetic 1 is opposite to that of the natural material enabling the configuration of the natural product to be established as 3aS,8R. As natural flustramine B has been converted to (-)-debromoflustramine B its absolute configuration may also be set as 3aS,8aR. The synthetic scheme involves radical bromination of 9 at C3a followed by allylation, at C3a, with allyltributyltin to give 21. The allyl group is then converted to the C3a prenyl derivative 23 by oxidative cleavage and Wittig reaction. The remainder of the synthesis involves removal of the now extraneous carbomethoxy group from C2 and selective removal of the two nitrogen protecting groups and alkylation of the resulting amines. Oxidation of 9 with ceric ammonium nitrate to give mixtures of the C3a nitrato- and hydroxy-derivatives 18 and 19 is also described

Total synthesis of (+)-4,5-deoxyneodolabelline.

Abstract: The first total synthesis of the marine dolabellane diterpene (+)-4,5-deoxyneodolabelline (1) has been accomplished. The highly efficient approach is characterized by the convergent assembly of dihydropyrans 2ab and cyclopentylsilanes 3ab. Allylic silane 3a was prepared from 2-methyl-2-cyclopentenone via a copper-catalyzed 1,4-addition followed by diastereoselective alkylation of the resulting enolate. A chemical resolution of racemic cyclopentanone 8 was effected by (S)-CBS-catalyzed borohydride reduction. Direct hydroxymethylation of the enantioenriched ketone 8 to form allylic alcohol 14 was achieved by a Stille palladium-catalyzed cross-coupling from the cyclopentenyl triflate 13. Treatment of the corresponding allylic phosphate 15 with trimethylsilylcopper reagent provided for displacement with allylic transposition yielding the exocyclic allylsilane 3a with excellent diastereoselectivity. Dihydropyrans 2a and 2b were prepared from optically pure acyclic acetals via ring-closing metathesis. Coupling of 3a and 2a or 2b via the carbon-Ferrier protocol gave trans-2,6-disubstituted dihydropyrans 30 and 35 with complete stereoselectivity. Vanadium-based pinacol coupling reactions were explored for closure of the medium-sized carbocycle to yield syn-diol 33. X-ray diffraction studies of the monobenzoate 34 have provided unambiguous stereochemical assignments. Substantial ring strain accounted for the lack of alkene products typical of reductive elimination using TiCl(3) and zinc-copper couple (McMurry) conditions leading to 37. Finally, the natural product 1 was obtained via Swern oxidation of the diol 37.