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Dawei Ma

Publications and source records attributed to Dawei Ma.

43 records · Page 3Linked to original sources
PubMed2003

Synthesis of an oxazoline analogue of apratoxin A.

[structure: see text] Michael addition of Me(2)Cu(CN)Li(2) to alpha,beta-unsaturated lactone 7 derived from beta-hydroxyl ketone 5 provides lactone 8, which is converted to alcohol 11 using Oppolzer's methodology as the key step. Connection of 11 with the l-proline moiety and subsequent installation of an oxazoline ring affords 16, which is coupled with tripeptide 21; subsequent macrocyclization then furnishes 4, an oxazoline analogue of apratoxin A.

Antineoplastic Agents↗
PubMed2003

Asymmetric total synthesis of (-)-alkaloid 223A and its 6-epimer.

The enantiopure gamma-amino alcohols 7 and 18 are prepared by using the diastereoselective Michael addition of lithium N-benzyl (R)-alpha-methylbenzylamide to alpha,beta-unsaturated esters as a key step. The Michael addition of 7 or 18 to an alkynone 8 followed by an intramolecular cyclization afford the cyclic enamine 10 or 20, which are subjected to the diastereoselective hydrogenation, and the subsequent transformations provide 6-epi-alkaloid 223A and alkaloid 223A, respectively.

Alkaloids↗
PubMed2003

Aromatic nucleophilic substitution or CuI-catalyzed coupling route to martinellic acid.

Condensation of beta-amino ester 8b with triflate 7 gives N-aryl amino ester 11, which is converted into 2-substituted 4-oxoquinoline 4 using an intramolecular Dieckmann reaction as the key step. CuI-mediated coupling of beta-amino ester 8a with 1,4-diiodobenzene followed by an intramolecular acylation and Pd-catalyzed carbonylation provide another manner to 4. Alkylation of 4 and subsequent reductive amination deliver the cyclic imine 14, which is transformed into triamine 3 by ordinary operations. Guanylation of 3 under mild condition followed by deprotection results in the synthesis of martinellic acid 1.

Alkaloids↗
PubMed2002

Synthesis of 7-substituted benzolactam-V8s and their selectivity for protein kinase C isozymes.

[reaction: see text] Condensation of L-valine benzyl ester toluenesulfonic acid salt with a substituted cyclohexadione followed by aromatization with the assistance of NBS provides an N-aryl L-valine benzyl ester. This intermediate is converted into 7-substituted benzolactam-V8s using an asymmetric Strecker reaction as the key step. The target molecules show a different pattern of isozyme selectivity relative to the 8-substituted benzolactam-V8s.

Enzyme Inhibitors↗
PubMed2002

Structural basis of RasGRP binding to high-affinity PKC ligands.

The Ras guanyl releasing protein RasGRP belongs to the CDC25 class of guanyl nucleotide exchange factors that regulate Ras-related GTPases. These GTPases serve as switches for the propagation and divergence of signaling pathways. One interesting feature of RasGRP is the presence of a C-terminal C1 domain, which has high homology to the PKC C1 domain and binds to diacylglycerol (DAG) and phorbol esters. RasGRP thus represents a novel, non-kinase phorbol ester receptor. In this paper, we investigate the binding of indolactam(V) (ILV), 7-(n-octyl)-ILV, 8-(1-decynyl)benzolactam(V) (benzolactam), and 7-methoxy-8-(1-decynyl)benzolactam(V) (methoxylated benzolactam) to RasGRP through both experimental binding assays and molecular modeling studies. The binding affinities of these lactams to RasGRP are within the nanomolar range. Homology modeling was used to model the structure of the RasGRP C1 domain (C1-RasGRP), which was subsequently used to model the structures of C1-RasGRP in complex with these ligands and phorbol 13-acetate using a computational docking method. The structural model of C1-RasGRP exhibits a folding pattern that is nearly identical to that of C1b-PKCdelta and is comprised of three antiparallel-strand beta-sheets capped against a C-terminal alpha-helix. Two loops A and B comprising residues 8-12 and 21-27 form a binding pocket that has some positive charge character. The ligands phorbol 13-acetate, benzolactam, and ILV are recognized by C1-RasGRP through a number of hydrogen bonds with loops A and B. In the models of C1-RasGRP in complex with phorbol 13-acetate, benzolactam, and ILV, common hydrogen bonds are formed with two residues Thr12 and Leu21, whereas other hydrogen bond interactions are unique for each ligand. Furthermore, our modeling results suggest that the shallower insertion of ligands into the binding pocket of C1-RasGRP compared to C1b-PKCdelta may be due to the presence of Phe rather than Leu at position 20 in C1-RasGRP. Taken together, our experimental and modeling studies provide us with a better understanding of the structural basis of the binding of PKC ligands to the novel phorbol ester receptor RasGRP.

Amino Acid Sequence↗
PubMed1999

Asymmetric Strecker-Type Reaction of alpha-Aryl Ketones. Synthesis of (S)-alphaM4CPG, (S)-MPPG, (S)-AIDA, and (S)-APICA, the Antagonists of Metabotropic Glutamate Receptors.

Heating a mixture of alpha-aryl ketone with (R)-phenylglycinol produces a mixture of imine and 1,3-dioxazolidine. Treatment of this mixture with trimethylsilyl cyanide followed by transformation of nitrile to ester gives Strecker-type reaction products. The diastereoselectivity of the generated alpha-amino esters is from 2/1 to 7/1, and the (R,S)isomer is found as the major product. The (R,S) and (R,R)isomers can be separated by conversion to their N-Cbz or cyclization derivatives. Using this methodology, four antagonists of metabotropic glutamate receptors, (S)-alphaM4CPG, (S)-MPPG, (S)-AIDA, and (S)-APICA, are synthesized.

Journal Article↗