Full details of the synthesis of the fully substituted vancomycin CD and DE ring systems are described and a potential solution to the control of the atropisomer stereochemistry is defined.

Certain classes of neuroactive steroids (NASs) are positive allosteric modulators (PAM) of synaptic and extrasynaptic GABA receptors. Herein, we report new SAR insights in a series of 5β-nor-19-pregnan-20-one analogues bearing substituted pyrazoles and triazoles at C-21, culminating in the discovery of 3α-hydroxy-3β-methyl-21-(4-cyano-1H-pyrazol-1'-yl)-19-nor-5β-pregnan-20-one (SAGE-217, 3), a potent GABA receptor modulator at both synaptic and extrasynaptic receptor subtypes, with excellent oral DMPK properties. Compound 3 has completed a phase 1 single ascending dose (SAD) and multiple ascending dose (MAD) clinical trial and is currently being studied in parallel phase 2 clinical trials for the treatment of postpartum depression (PPD), major depressive disorder (MDD), and essential tremor (ET).

The degradation of vancomycin to a series of aglucovancomycin derivatives containing modifications in key functional groups and a study of their thermal atropisomerism are detailed. In all of the cases, selective isomerism of the DE ring system atropisomers was observed under conditions where the CD and AB stereochemistries were unaffected. Competitive retro aldol ring cleavage of the CD and DE ring systems (CD > DE) was observed but could be minimized by the choice of solvent and thermal conditions (DE ring system) or precluded by alcohol protection (CD ring system). Similarly, competitive main chain succinimide formation through the loss of ammonia from the Asn residue could be minimized by the choice of thermal conditions or prevented by carboxamide protection. Resynthesis of natural aglucovancomycin, (M,M,M)-2, and its unnatural DE atropisomer (P,M,M)-2 from 6 are described. The comparative antimicrobial activity of the key derivatives and their unnatural DE ring system P-diastereomers are disclosed.

Neuroactive steroids (NASs) have been shown to impact central nervous system (CNS) function through positive allosteric modulation of the GABA(A) receptor (GABA(A)-R). Herein we report the effects on the activity and pharmacokinetic properties of a series of nor-19 pregnanolone analogues bearing a heterocyclic substituent at C-21. These efforts resulted in the identification of SGE-516, a balanced synaptic/extrasynaptic GABA(A) receptor modulator, and SGE-872, a selective extrasynaptic GABA(A) receptor modulator. Both molecules possess excellent druglike properties, making them advanced leads for oral delivery of GABA(A) receptor modulators.

Continued studies on the synthesis and atropisomerism of the vancomycin CD and DE ring systems based on aromatic nucleophilic substitution macrocyclization reactions for formation of the biaryl ethers are detailed in efforts that further define substituent effects, explore the impact of protecting groups, and establish the stereochemical integrity of peripheral substituents. These have led to the identification of a previously unrecognized site of epimerization within our original approach to the DE ring system and the introduction of significant improvements in the approach that will find utilization in syntheses of the vancomycin CDE ring system and of the natural product itself. The preparation of a complete set of DE ring system isomers bearing the unnatural stereochemistry at the labile C8, C11, and C14 sites was accomplished for comparison and established that C8 is prone to epimerization to the more stable, unnatural S versus R absolute stereochemistry if it bears an ester, but not a carboxamide, substituent. Additionally, an improved synthesis of the CD ring system, enlisting a C14 carboxamide versus ester substituent, is disclosed and establishes the stereochemical integrity of our prior approach which incorporated a C14 ester. A set of fully functionalized CD and DE ring systems were prepared and include the development of conditions for the final deprotections required for incorporation into efforts on the natural product. The examination of the antimicrobial activity of these key substructures of vancomycin is detailed.