The “prohormone” scene is a volatile one, in which the attempts of the regulatory authorities to regulate an intrinsically innovative market seem futile – every time the DEA bans a compound, the supplement companies respond by bringing out something new to take it’s place.
Most recently, PHF Supplements announced that they’re working on producing 17b-hydroxy-7a,17a-dimethyl-1,4-androstadiene-3-one. Those of you familiar with steroidal nomenclature will recognise that this compound closely resembles the oral steroid “dianabol”; the only difference is that this has the addition of a 7a-methyl group.
Fig 1. Structural diagram of 17b-hydroxy-7a,17a-dimethyl-1,4-androstadiene-3-one
This compound would require no enzymatic conversion in vivo, since it’s already orally active, so it would be generally considered to be a “designer steroid” rather than a “prohormone”.
Like many of the prohormones and designer steroids previously introduced to what is increasingly euphemistically called the supplement market, this compound was previously studied by researchers in the 1960s who were searching for steroids with a high degree of separation between myotrophic (anabolic) and androgenic effects.
A number of different laboratories were undertaking research in this area, concentrating on various different structural modifications to find a way to produce effective anabolics with minimal androgenic activity. The Upjohn company were particularly interested in the 7a-methyl group. This had previously been added to some corticosteroids, and been found to reduce their activity. 
The Upjohn group found that when they added this group to testosterone and other testosterone derivatives, it significantly increased their activity.  They added the substituent to esterified testosterone, methandrostenolone (dianabol), and 17a-methyl testosterone. In all cases they found the 7a-methylated compounds caused significantly more anabolism in their rat subjects than their non-7a-methylated counterparts.
In the case of the 7a-methyl methandrostenolone derivative, they had this to say:
“17b-hydroxy-7a,17-dimethyl-1,4-androstadien-3-one was approximately twice as active as 17b-hydroxy-17-methyl-1,4-androstadien-3-one (methandrostenolone)”.
Fig 2. Oral activity of Methandrostenolone and its 7a-methyl derivative compared to methyltestosterone.
The greatest increase in anabolic activity however was found to be in 7a,17a-dimethyl testosterone, which they refer to in the text as U-19763. Today we are more familiar with this compound by it’s brand name: Bolasterone. Since U-19763 was the strongest compound, and also had the best ratio of anabolic to androgenic effects, the other drugs were discarded and forgotten about – until now.
One of the problems that faced the researchers of the time was the difficulty in producing a pure 7a-methyl compound. The reaction that creates the methyl group attacks from both sides of the steroid, which leads to an epimeric mixture of both 7a-methyl and 7b-methyl compounds which are then difficult to separate, and the 7b-methylated compounds are effectively useless.
The synthesis of Bolasterone for example, the only 7a-methyl testosterone derivative to make it (albeit briefly) to the legitimate medical market, also produces the weakly androgenic 7b-methylated epimer Calusterone (a drug once used clinically for the treatment of breast cancer) as a byproduct.
This is a problem that is also likely to face the Chinese lab that will be producing the raw materials for PHF Supplements. In 1965 the Upjohn team were struggling with yields that ranged from 15 – 50%, though it may be that better yields are possible with today’s scientific knowledge and technology.