Synthetic studies on thiostrepton family of peptide antibiotics: synthesis of the dihydroquinoline portion of thiostrepton, the siomycins, and the thiopeptins

Synthesis of the dihydroquinoline portion of thiostrepton, the siomycins, and the thiopeptins, members of the thiostrepton family of peptide antibiotics, has been achieved featuring the one-pot olefination via the Matsumura-Boekelheide rearrangement “using trifluoromethanesulfonic anhydride and triethylamine” and the stereoselective addition reaction controlled by the stereocenter of the peri-position.     

Synthetic studies on thiostrepton family of peptide antibiotics: synthesis of the cyclic core portion containing the dehydropiperidine, dihydroquinoline, l-valine, and masked dehydroalanine segments

The cyclic core portion containing the dehydropiperidine, dihydroquinoline, l-valine, and masked dehydroalanine (i.e., β-phenylselenoalanine) segments of the thiostrepton family of peptide antibiotics was synthesized via the consecutive coupling of these four segments followed by cyclization at the amide bond between the dehydropiperidine and masked dehydroalanine segments.     

Synthetic studies towards cyclic peptides. Concise synthesis of thiazoline and thiazole containing amino acids

Concise and efficient syntheses of optically pure thiazoline and thiazole containing amino acids of the constitution (26) and (27), based on simple condensation reactions between cysteine esters and N-protected imino ethers (22) and (25) derived from chiral amino acids, are described. The synthetic procedures are compatible with a range of amino acid side chains and protecting groups, and allow the preparation of a variety of small optically pure peptides i.e. (32) and (34) suitable for elaboration to naturally occurring cyclic peptides e.g. the lissoclinamides (3) and (4).     

Synthetic studies of incednine: synthesis of C1-C13 pentaenoic acid segment

Stereoselective synthesis of the C1-C13 pentaenoic acid segment (4) of the novel antibiotic incednine (1) is described.     

Supported 12-tungstophosphoric acid as heterogeneous and recoverable catalysts for the synthesis of oxazolines,imidazolines and thiazolines under solvent-free conditions

12-Tungstophosphoric acid (TPA) supported on silica, activated carbon and poly(4-styrylmethyl)pyridinium chloride (PMP) were found to be highly efficient catalysts for the synthesis of oxazolines, imidazolines and thiazolines from the condensation of various nitriles with aminoalcohols, ethylenediamine and cisteamine, respectively. In the case of oxazolines, dicyanobenzenes were selectively converted to mono- and bis-oxazolines in the presence of these catalysts. In the reaction of dicyanobenzenes with ethylenediamine, only mono-imidazolines were produced and the remaining cyano group did not react even with long reaction times. In the case of thiazolines, only bis-thiazolines were produced in the reaction of dicyanobenzenes with cysteamine. Furthermore, these catalysts could be recovered and reused without significant loss of their activities.     

Synthetic studies on ecteinascidin 743: asymmetric synthesis of the versatile amino acid component

The asymmetric synthesis of the modified tyrosine derivative as a basic building block for the ecteinascidin and safracin family of antitumor alkaloids has been achieved in nine steps and 39% overall yield.     

Synthetic studies on amphidinolides C and F: synthesis of the C18-C29 segment of amphidinolide F

The C18-C29 segment of amphidinolide F is synthesised in 12 steps from 1,4-butanediol. Key steps include a mono-Sharpless dihydroxylation of a dienoate, iodocyclisation to construct the trans-THF ring and an E-selective Wittig reaction to introduce the C25-C26 olefin.     

Synthetic studies on palytoxin. Stereocontrolled,practical synthesis of the C.101–C.115 segment

A stereocontrolled and practical synthetic route to the acetal $\text{2a}$, a degradation product of palytoxin, in optically active form is described.     

Synthetic studies on jadomycins: synthesis of dimethyljadomycin A

Dimethyljadomycin A was synthesized as the first example for the construction of 8H-benzo[b]oxazolo[3,2-f]phenanthridine skeleton.     

Synthetic studies on dragmacidin D: synthesis of the left-hand fragment

We report a synthesis of a left-hand fragment of bis(indole)-class marine alkaloid, dragmacidin D. The synthesis features Suzuki-Miyaura reaction for the coupling of imidazolyl boronic acid and (4-indolyl)vinyl bromide.     

Synthetic studies on lytophilippine A: synthesis of the proposed structure

Synthesis of the proposed structure of lytophilippine A was accomplished employing SmI(2)-mediated 5-exo cyclization of an aldehydo β-alkoxyvinyl sulfoxide and ring-closing metathesis reaction.     

New strategies for the synthesis of heteroannulated 2-pyridinones, substituted 2-quinolinones and coumarins from dehydroamino acid derivatives

Several heteroannulated pyridinones were prepared from the methyl esters of N-Boc-β,β-diheteroaryldehydroalanines by treatment with acetic acid. The latter were obtained by a bis-Suzuki coupling of a β,β-dibromodehydroalanine with heteroarylboronate compounds. The products were obtained in good yields and the cyclization reaction involves the nucleophilic attack of one of the heteroaromatic rings on the carbonyl of the Boc group. The scope of this reaction was extended to the Z-isomer of N-Boc-β-heteroaryldehydrophenylalanines to give 4-phenylpyridinones. A tandem Suzuki coupling-cyclization protocol was developed for the synthesis of 2-quinolinones and coumarins. Thus, β-brominated dehydroamino acids were reacted with 2-(pinacolboronate)aniline or phenol in a one-pot Suzuki coupling followed by lactamization or lactonization to give the corresponding 3-amino-2-quinolinones or 3-aminocoumarins in good to high yields. This type of strategy was also applied to the synthesis of 2-quinolinones and coumarins linked in position-3 to amino acids, using as starting materials brominated dehydropeptides.     

Stereoselective addition of Grignard reagents to sulfinimines derived from tartrate diol (threitol): Generation of chiral building blocks for the collective total synthesis of lentiginosine,conhydrine and methyldihydropalustramate

A systematic investigation of the addition of Grignard reagents to sulfinimines derived from tartaric acid diol was undertaken. It was observed that the chirality of the inherent tartrate moiety influences the diastereoselectivity of the resultant sulfinamides formed in the reaction. The formed products serve as excellent building blocks for the synthesis of natural products. This has been demonstrated in the collective total synthesis of lentiginosine, (+)-α-conhydrine and methyldihydropalustramate.     

Synthetic studies of rifamycins. VI. Preparation and elaboration of the aromatic segment for the synthesis of rifamycin W

A convenient preparation of the aromatic segment 3 starting from 3,5-dibromo-2,6-dimethoxytoluene 5 and furan was described along with the elaboration of 3 by the aldol coupling with the aliphatic segment 2 to the synthetic precursor 4 of rifamycin W.     

Synthetic studies on terpenic compounds—XI : Stereospecific total synthesis of portulal,

A stereospecific total synthesis of portulal 1 has been accomplished starting from the Diels-Alder adduct 2 from chloromethylmaleic anhydride and 1-vinylcyclohexene. Firstly 2 was converted by an efficient sequence of reactions to perhydroazulenoid lactone 5, which possesses the correct relative configuration with respect to three chiral centers out of the four present in 1. The fourth chiral center at C-6 was introduced stereospecifically together with the one-carbon substituent at C-4 by the ring formation between C-4 and C-6, and its cleavage to give an exomethylene lactone 35. At this stage the stereochemical validity of the crucial intermediate 35 was confirmed by chemical correlation with the hydroxy lactone 37 which was derived from natural 1 through a systematic degradation. Then 35 was transformed to 37 and the synthesis continued further by using 37 as a relay compound to afford 1.