Synthesis of chlorine-containing angucycline BE-23254 and its analogs

The total synthesis of BE-23254, an unusual angucycline antibiotic is reported. This is achieved by adopting a Hauser annulation and a DDQ-promoted aromatization as the key steps. The strategy has been generalized for the synthesis of several analogs of the target molecule. A regioselective preparation of chlorine-containing phenols is also described.     

Total synthesis of BE-43547A2

An asymmetric total synthesis of BE-43547A₂ has been achieved in 16 steps (longest linear) on a 3.2 gram scale. The details of our efforts that led to the total synthesis of BE-43547A₂ were reported, the final 6 steps were optimized, and the overall yield was improved from 4.5% to 9.7%. The procedure utilized in the final 2 steps may serve as a better method for separating unstable APD compounds.     

Total synthesis of landomycin A, a potent antitumor angucycline antibiotic

The first total synthesis of landomycin A, the longest and most potent antitumor angucycline antibiotic, has been achieved in 63 steps and 0.34% overall yield starting from 2,5-dihydroxybenzoic acid, 3,5-dimethylphenol, triacetyl d-glucal, and d-xylose, with a convergent linear sequence of 21 steps.     

A hetero Diels-Alder approach to the synthesis of the first angucyclinone and angucycline 5-aza-analogues

The synthesis of two new heterodienes and their regioselective [4+2]cycloaddition reactions with several bromo-naphthoquinones allowed us to prepare the first angucyclinone and angucycline 5-aza-analogues.     

The first total synthesis of lactonamycin, a hexacyclic antitumor antibiotic

The total synthesis of lactonamycin has been achieved. The synthesis includes sequential intramolecular conjugate addition of alcohols to the acetylenic ester, stereoselective glycosylation of the tertiary alcohol, and Michael-Dieckmann type cyclization with the thioester, by which the highly convergent route has been established.     

Total synthesis of antibiotic althiomycin

Antibiotic althiomycin was totally synthesized from d-cysteine via the procedures of the coupling with sodium salt of pyrrolinone, hydroxymethylation, and the coupling with the thiazole part, successively.     

Total synthesis of aspidophytine

A total synthesis of aspidophytine was accomplished by employing a newly developed strategy for the enantiospecific syntheses of aspidosperma alkaloids. The key steps involve a novel ketene-lactonization reaction of a chiral vinyl sulfoxide (Marino annulation reaction) to set up the chiral quaternary carbon center, and a tandem Michael addition-alkylation reaction sequence to form the polycyclic core structure.     

Total synthesis of antibiotic streptothricin F

The first total synthesis of streptothricin F was achieved and its structure was unequivocally confirmed.     

Total synthesis of peptide antibiotic nisin

Total synthesis of a lanthionine peptide nisin was successfully achieved for the first time by application of new methods for preparations of dehydroalanine and lanthionine moieties, resulting in a confirmation of the proposed structure.     

Syntheses and biological evaluation of BE-43547A2 analogues modified at O35 ester and C15-OH sites

Total syntheses of 6 BE-43547A₂ analogues modified at O35 and C15 sites are reported. Late stage oxidation of 15-deoxy-BE-43547A₂ delivered 15-epi-BE-43547A₂, which verified the proposition that the C15 is an active site for late stage oxidation. The N35 and C15-F of analogues 1b and 1d were synthesized. Cellular level tests indicated O35 is a prohibitive site for modification and substitution of the OH at C15 with F or trim of the OH both led to a dramatic loss of activity. Compound 1e showed comparable inhibitory level towards Panc-1?cells, which indicated that the OH at C15 are permissive site for further modifications.     

Total synthesis of rutamycin B, a macrolide antibiotic from Streptomyces aureofaciens.

Rutamycin B (2) was synthesized from three principal subunits, spiroketal 75, keto aldehyde 83, and aldehyde 108. First, triol 62 was assembled by Julia coupling of sulfone 56 with aldehyde 58 followed by an acid-catalyzed spiroketalization. The three hydroxyl functions of 62 were successfully differentiated, leading to phosphonate 75. The latter was condensed in a Wadsworth-Emmons reaction with 83, prepared in six steps from (R)-aldehyde 76, to give 92. Coupling of the titanium enolate of 92 with 108 afforded Felkin product 109 with high stereoselectivity in a process that is critically dependent on the presence of the p-methoxybenzyl ether in the aldehyde. Transformation of 109 via aldehyde 116 to vinylboronate 122 was followed by macrocyclization under Suzuki conditions to yield 123. Exhaustive desilylation of the latter yielded rutamycin B.     

Total synthesis of NW-G01, a cyclic hexapeptide antibiotic, and 34-epi-NW-G01

NW-G01, a cyclic hexapeptide antibiotic, and 34-epi-NW-G01 were synthesized by the highly stereoselective convergent approach for the first time, thereby unambiguously determining the absolute structure of NW-G01.     

Total synthesis of an antitubercular lactone antibiotic, (+)-tubelactomicin A

(+)-Tubelactomicin A (1), an antitubercular lactone, has been synthesized from (S)-citronellol (2) and 2-deoxy-l-ribonolactone (18) through intramolecular Diels-Alder reaction, Suzuki-Miyaura coupling, and Shiina macrolactonization.     

Total Synthesis of 6-Deoxydihydrokalafungin,a Key Biosynthetic Precursor of Actinorhodin,and Its Epimer

In this article, we report the total synthesis of 6-deoxydihydrokalafungin (DDHK), a key biosynthetic intermediate of a dimeric benzoisochromanequinone antibiotic, actinorhodin (ACT), and its epimer, epi-DDHK. Tricyclic hemiacetal with 3-siloxyethyl group was subjected to Et₃SiH reduction to establish the 1,3-cis stereochemistry in the benzoisochromane, and a subsequent oxidation/deprotection sequence then afforded epi-DDHK. A bicyclic acetal was subjected to AlH₃ reduction to deliver the desired 1,3-trans isomer in an approximately 3:1 ratio, which was subjected to a similar sequence to that used for the 1,3-cis isomer that successfully afforded DDHK. A semisynthetic approach from (S)-DNPA, an isolable biosynthetic precursor of ACT, was also examined to afford DDHK and its epimer, which are identical to the synthetic products.     

Total synthesis of the chlorinated marine natural product dysamide B

[Structure: see text] Two approaches to the synthesis of (2S,4S)-5,5-dichloroleucine are compared, and the parent amino acid was used in the first total synthesis of the polychlorinated marine natural product, dysamide B. A key step was the lead tetraacetate-mediated decarboxylation of an alpha,alpha-dichloro acid in the presence of 1,4-cyclohexadiene to generate the dichloromethyl group.     

Total synthesis of an antitumor antibiotic,Fostriecin (CI-920)

The total synthesis of an antitumor antibiotic, fostriecin (CI-920), via a highly convergent route is described. A characteristic feature of the present total synthesis is that the synthesis was achieved via a coupling procedure of three segments A, B, and C. The unsaturated lactone moiety of fostriecin, corresponding to segment A, was constructed from a known Horner-Emmons reagent, and the stereochemistry of the C-5 position was introduced by asymmetric reduction with (R)-BINAl-H. Segment B having a series of stereogenic centers was synthesized from (R)-malic acid and the stereogenic centers at the C-8 and C-9 positions were prepared by a combination of Wittig reaction and Sharpless asymmetric dihydroxylation reaction. The conjugated Z,Z,E-triene moiety of fostriecin, corresponding to segment C, was eventually constructed by Wittig reaction and Stille coupling reaction. The phosphate moiety, which is known to be essentially important for the antitumor activity, was introduced via two routes: (i) direct phosphorylation of the monohydroxyl derivative in which other hydroxyl groups are protected with silyl groups; (ii) cyclic phosphorylation and selective cleavage of the cyclic phosphate derivative. Although the former route is basically the same as those reported by other groups, the latter route is novel and more effective than the former one. The present total synthesis would serve as a versatile synthetic route to not only fostriecin, but also its various analogues including stereoisomers.     

Synthesis of chloroquinocin, a pyranonaphthoquinone antibiotic against Gram-positive bacteria

Chloroquinocin 1 is an antimicrobial agent against Gram-positive bacteria, including MRSA (methicillin-resistant Staphylococcus aureus). A successful synthesis of 1 was attained through a unique chlorination of the corresponding naphthoquinone derivative 12 as a key step.