Merrifield resin-supported chain transfer agents, precursors for RAFT polymerization

The modification of Merrifield resins to form chain transfer agent (CTA) precursors for reversible addition fragmentation chain transfer (RAFT) polymerization is investigated. A series of CTA precursor resins were prepared and characterized by FTIR and elemental analysis (EA). [reaction: see text]     

Cerebrosides and a monoacylmonogalactosylglycerol from Clinacanthus nutans

A mixture of nine cerebrosides and a monoacylmonogalactosylglycerol were separated from the leaves of Clinacanthus nutans. The structures of the cerebrosides were characterized as 1-O-beta-D-glucosides of phytosphingosines, which comprised a common long-chain base, (2S,3S,4R,8Z)-2-amino-8(Z)-octadecene-1,3,4-triol with nine 2-hydroxy fatty acids of varying chain lengths (C(16), C(18), C(20-26)) linked to the amino group. The glycosylglyceride was characterized as (2S)-1-O-linolenoyl-3-O-beta-D-galactopyranosylglycerol. The structures were established on the basis of the spectroscopic data and chemical reactions.     

Sesterterpenes and phenolic alkenes from the Thai sponge Hyrtios erectus

Sesterterpene, erectusolide A (1), six phenolic alkenes, erectuseneols A?F (2–7) and nine known compounds, luffalactone (8), luffariolide E (9), (6E)- and (6Z)-neomanoalide 24,25-diacetates (10 and 11), 6,6-dimethylundecane-2,5,10-trione (12), threo- and erythro-cavernosines (13 and 14), (4E,6E)-dehydromanoalide (15), echinoclerodane A (16), were isolated from the marine sponge Hyrtios erectus. Compound 13 was isolated for the first time from a natural source. The structures of these compounds were elucidated on the basis of spectroscopic analysis. The phenolic alkenes 3 and 7, the sesterterpenes 8–11 and 15, and compounds 12–14 were evaluated for cytotoxic activities against six cancer cell lines, MOLT-3, HepG2, HeLa, HuCCA-1, A549, and MDA-MB-231.     

Mono- versus bis-chelate formation in triazenide and amidinate complexes of magnesium and zinc

Magnesium and zinc complexes of the monoanionic ligands N,N'-bis(2,6-di-isopropylphenyl)triazenide, L1, N,N'-bis(2,6-di-isopropylphenyl)acetamidinate, L2, and N,N'-bis(2,6-di-isopropylphenyl)tert-butylamidinate, L3, have been synthesized, but only L3 possesses sufficient steric bulk to prevent bis-chelation. Hence, the reaction of L1H with excess ZnEt2 leads to the isolation of (L1)2Zn, 1; L1H also reacts with Bu2Mg in Et2O to afford (L1)2Mg(Et2O), 2. Similar reactivity is observed for L2H, leading to the formation of (L2)2Zn, 3, and (L2)2Mg, 4. The reaction of L2H with ZnR2 may also afford the tetranuclear aggregates {(L2)Zn2R2}2O, 5 (R=Me) and 6 (R=Et). By contrast, the tert-butylamidinate ligand was found to exclusively promote mono-chelation, allowing (L3)ZnCl(THF), 7, [(L3)Zn(micro-Cl)]2, 8, (L3)ZnN(SiMe3)2, 9, (L3)MgiPr(Et2O), 10, and (L3)MgiPr(THF), 11, to be isolated. X-ray crystallographic analyses of 1, 2, 3, 4, 5, 6, 8, and 10 indicate that the capacity of L3 to resist bis-chelation is due to greater occupation of the metal coordination sphere by the N-aryl substituents.     

Chromones from the branches of Harrisonia perforata

Four new chromones, perforamone A, B, C, and D have been isolated together with six known compounds, peucenin-7-methyl ether, O-methylalloptaeroxylin, perforatic acid, eugenin, saikochromone A and greveichromenol, from the branches of Harrisonia perforata (Simaroubaceae). The structures were identified by spectroscopic data. The compounds were tested for antimycobacterial and antiplasmodial activities.     

Chemical constituents of the roots of Piper sarmentosum

Sixteen compounds were isolated from the fresh roots of Piper sarmentosum. Seven of these have been previously isolated from the fruits and leaves of this plant: the aromatic alkene (1), 1-allyl-2-methoxy-4,5-methylenedioxybenzene (4), beta-sitosterol, pyrrole amide (6), sarmentine (10), sarmentosine (13) and pellitorine (14). (+)-Sesamin (2), horsfieldin (3), two pyrrolidine amides 11 and 12, guineensine (15) and brachystamide B (16) are new for P. sarmentosum. Sarmentamide A, B, and C (7-9) are new natural products. Compounds 1--4 and 6--16 were tested for antiplasmodial, antimycobacterial and antifungal activities.     

New rearranged clerodane diterpenes from Tinospora baenzigeri.

Baenzigeroside B, a new rearranged clerodane diterpene glucoside, was isolated from the stems of Tinospora baenzigeri. The aglycone of baenzigeroside B, baenzigeride B (isolated as its acetate), was found together with baenzigeride A, baenzigerosides A and B in the leaves of the same plant. Baenzigeride B and baenzigeroside B are the first examples of a new class of rearranged clerodane diterpenes. The possible biogenesis of the compounds is discussed.     

Polymer Architectures via Reversible Addition Fragmentation Chain Transfer (RAFT) Polymerization

Various versatile chain transfer agents (CTAs) have been synthesized for reversible addition fragmentation chain transfer (RAFT) polymerzation. Such CTAs have been used to modify hydroxyl containing materials and produce well-controlled molecular architectures such as amphiphilic copolymer from poly (ethylene glycol), AB block copolymer consisting of a biodegradable segment, poly (l-lactic acid) (PLLA) and grafted copolymers of poly (styrene), poly (methyl methacrylate) and poly (methyl acrylate) from cellulose.     

Pyrazine nucleoside analogs. Synthesis and reactions of some 5-thio-substituted pyrazines

5-Benzylthio-1,2-dihydro-2-oxopyrazine ( 8 ) was prepared from 2-amino-5-bromopyrazine by sequential treatment with sodium thiobenzylate and diazotization. Condensation of the silyl derivative of 8 with a protected 2-deoxyribofuranosyl chloride gave α and β anomers of 5-benzylthiopyrazine nucleosides. Reaction of 2,5-dichloropyrazine 4-oxide with sodium thiobenzylate followed by hydrolysis gave 5-benzylthio-1,2-dihydro-2-oxopyrazine 4-oxide ( 16 ).     

A new dihydrobenzofuran lignan and potential α-glucosidase inhibitory activity of isolated compounds from Mitrephora teysmannii

A new dihydrobenzofuran lignan, (2R,3S)-2-(3′,4′-dimethoxyphenyl)-5-(3-hydroxypropyl)-7-methoxy-2,3-dihydrobenzofuran-3-methyl acetate, named as mitredrusin (1), was isolated from the leaves of Mitrephora teysmannii (Annonaceae) together with 12 known compounds including a related dihydrobenzofuran lignan: (?)-3′,4-di-O-methylcedrusin (2), four polyacetylenic acids: 13(E)-octadecene-9,11-diynoic acid (3), 13(E),17-octadecadiene-9,11-diynoic acid (4), octadeca-9,11,13-triynoic acid (5) and octadeca-17-en-9,11,13-triynoic acid (6), five lignans: (?)-eudesmin (7), (?)-epieudesmin (8), (?)-phillygenin (9), magnone A (10) and forsythialan B (11) and two megastigmans: (3S,5R,6S,7E,9R)-7-megastigmene-3,6,9-triol (12) and annoionol A (13). The chemical structures of these compounds were established on the basis of their 1-D and 2-D NMR spectroscopic data. All compounds were evaluated for their α-glucosidase inhibitory activity. Among these isolates, polyacetylenic acids 3 and 4 showed more than 20-fold much higher activity compared with that of the antidiabetic drug acarbose.